Dissertations / Theses: 'Ionospheric physics'

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Dorfman, Seth E. "Intense spreading of radar echoes from ionospheric plasmas." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32897.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.
Includes bibliographical references (leaf 41).
On December 25, 2004, a large-scale ionospheric plasma bubble was observed over Arecibo Observatory in Puerto Rico, inducing significant range spreading on ionograms. This phenomena may be explained by means of the E x B instability and gravitational Rayleigh-Taylor instability. A derivation of the dispersion relations for X and O mode waves transmitted from an ionosonde and an analysis of the collisional Rayleigh-Taylor instability leading to an expression for the growth rate are presented as background information. Ray tracing code developed by Nathan Dalrymple, a previous graduate student of Professor Min-Chang Lee, is extended, first to draw refractive index surfaces to illustrate a key principle in ray tracing and later to simulate range spreading due to depleted ionospheric ducts [1]. Data from Arecibo incoherent scatter radar and Arecibo's CADI digisonde is examined showing strong evidence for the development of a plasma bubble following a rise in the plasma layer and the appearance of a horizontal density gradient. In one portion of the ionosphere, this gradient is found to be at an angle of approximately 70 degrees to the Earth's magnetic field, a favorable condition for the excitation of the Rayleigh-Taylor instability over Arecibo.
by Seth E. Dorfman.
S.B.

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2

Chapagain, Narayan P. "Dynamics of Equatorial Spread F Using Ground-Based Optical and Radar Measurements." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/897.

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The Earth's equatorial ionosphere most often shows the occurrence of large plasma density and velocity fluctuations with a broad range of scale sizes and amplitudes. These night time ionospheric irregularities in the F-region are commonly referred to as equatorial spread F (ESF) or plasma bubbles (EPBs). This dissertation focuses on analysis of ground-based optical and radar measurements to investigate the development and dynamics of ESF, which can significantly disrupt radio communication and GPS navigation systems. OI (630.0 nm) airglow image data were obtained by the Utah State University all-sky CCD camera, primarily during the equinox period, from three different longitudinal sectors under similar solar flux conditions: Christmas Island in the Central Pacific Ocean, Ascension Island in South Atlantic, and Brasilia and Cariri in Brazil. Well-defined magnetic field-aligned depletions were observed from each of these sites enabling detailed measurements of their morphology and dynamics. These data have also been used to investigate day-to-day and longitudinal variations in the evolution and distribution of the plasma bubbles, and their nocturnal zonal drift velocities. In particular, comparative optical measurements at different longitudinal sectors illustrated interesting findings. During the post midnight period, the data from Christmas Island consistently showed nearly constant eastward bubble velocity at a much higher value (~80 m/s) than expected, while data from Ascension Island exhibited a most unusual shear motion of the bubble structure, up to 55 m/s, on one occasion with westward drift at low latitude and eastward at higher latitudes, evident within the field of view of the camera. In addition, long-term radar observations during 1996-2006 from Jicamarca, Peru have been used to study the climatology of post-sunset ESF irregularities. Results showed that the spread F onset times did not change much with solar flux and that their onset heights increased linearly from solar minimum to solar maximum. On average, radar plume onset occurred earlier with increasing solar flux, and plume onset and peak altitudes increased with solar activity. The F-region upward drift velocities that precede spread F onset increased from solar minimum to solar maximum, and were approximately proportional to the maximum prereversal drift peak velocities.

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Jensen, Joseph B. "The Effect of Ionospheric Conductivity on Magnetospheric Dynamics." Thesis, University of New Hampshire, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10839528.

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The connection between ionospheric conductivity and the dynamics of the magnetosphere was investigated, using several methods to change the ionospheric conductivity and then study the resultant changes to the magnetosphere. Computer simulations of the Earth's geospace environment were utilized using OpenGGCM coupled with an ionosphere model CTIM and a ring current model RCM.

Three methods were used to modify ionospheric conductivity. The incoming particle precipitation was modified by several orders of magnitude α = .01, .1, 1, 10, the ionospheric conductivity was increased or decreased by factors β = .25, .5, 1, 2, and 4, and for the last method differing values of F_10.7, 70, 110, 150, 200, and 250 were used. Each of the methods is different because F_10.7 mostly affects the dayside, while precipitation mostly affects the nightside, then using the β changes the conductivity over the whole ionosphere. This gives a good range for studying the effects of ionospheric conductivity on the magnetosphere.

The magnetospheric dynamics studied are: the dayside magnetopause location, the reconnection rate of the Earth's magnetosphere, X-line formation in the magnetotail, and substorm dynamics, both the frequency and magnitude of substorm occurrence.

To understand the effect of particle precipitation on conductivity two events were simulated, a calm period on 4 May 2005 and a strong storm period on 17 March 2013. Scaling the precipitation energy flux by several orders of magnitude, conductivities in the auroral oval were influenced which, in turn, influence the cross polar cap potentials. With the change in conductance, magnetospheric convection is enhanced or reduced, and the location of the subsolar distance of the magnetopause can change by up to one R_E. The investigation of the reconnection rate for the varying precipitation simulations using the Hesse-Forbes-Bern method shows that particle precipitation affects the magnetic reconnection rate in these two events. The most notable differences, up to 40\%, occur on short time scales, that is, hours. A relation for longer time scales (tens of hours) between precipitation and reconnection for these two events is more difficult to ascertain. Differences in cross polar cap potential (CPCP) and reconnection rate (R) can be explained by viscous interactions and polar cap saturation. When precipitation was decreased, polar conductance was decreased, viscous interactions are stronger, and CPCP is higher than R. For high precipitation, high conductance cases the polar cap is in the saturation regime and CPCP is lower than R. Hemispheric asymmetries were found in the cross polar cap potential and in the calculated reconnection rate derived from the Northern and Southern Hemispheres. The majority of this research has already been published in the Journal of Geophysical Research: Space physics, "Particle Precipitation Effects on Convection and the Magnetic Reconnection Rate in Earth's Magnetosphere" https://doi.org/10.1002/2017JA024030.

For the whole ionospheric conductivity study, different values of β = .25, .5, 1, 2, 4 were used to modify the ionospheric conductivity after it had been calculated by the ionosphere model. A moderate storm period, 16 May 2011 was simulated. Many of the same conclusions found in the precipitation study were found in this study as well, such as, CPCP decreasing as conductivity increases, the point at which the polar cap saturates decreases with increasing conductivity, and reconnection rates change on short time scales, but the overall average rate remains very similar. The incoming precipitation was used to identify auroral brightening that is linked with substorms. The criteria for auroral brightenings used in this study is where the maximum precipitation increased by at least 1 mW/m² within 20 minutes. The criteria for substorms is that the maximum precipitation increases by 80\% within 20 minutes. Identifying all the auroral brightenings and substorms showed that as conductivity increased the maximum amount of precipitation decreased, and also the number and frequency of both the substorms and auroral brightenings decreased. The occurrence of extended X-lines in the magnetotail was analyzed, where if an earthward flow of greater than 50 km/s extended for greater than 10 R_e in Y_GSE was classified as an extended X-line. This is not to be confused with a bursty bulk flow or dipolarization front, which happen from reconnection but usually do not have a large extent in Y_GSE. Identifying extended X-lines in this manner showed a similar trend that as conductivity increased the number of extended X-lines decreased, and while there was not much of an indication if the size or location is affected much, the amount of time the simulation had extended X-lines present decreased.

For the F_10.7 study, using values of 70, 110, 150, 200, and 250, the ionospheric conductivity was influenced mostly on the dayside. (Abstract shortened by ProQuest.)

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Scherliess, Ludger. "Empirical Studies of Ionospheric Electric Fields." DigitalCommons@USU, 1997. https://digitalcommons.usu.edu/etd/6823.

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The first comprehensive study of equatorial- to mid-latitude ionospheric electric fields (plasma drifts) is presented, using extensive incoherent scatter radar measurements from Jicamarca, Arecibo, and Millstone Hill, and F-region ion drift meter data from the polar orbiting DE-2 satellite. Seasonal and solar cycle dependent empirical quiet-time electric field models from equatorial to mid latitudes are developed, which improve and extend existing climatological models. The signatures of electric field perturbations during geomagnetically disturbed periods, associated with changes in the high-latitude currents and the characteristics of storm-time dynamo electric fields driven by enhanced energy deposition into the high-latitude ionosphere, are studied. Analytical empirical models that describe these perturbation drifts are presented. The study provided conclusive evidence for the two basic components of ionospheric disturbance electric fields. It is shown that magnetospheric dynamo electric fields can penetrate with significant amplitudes into the equatorial- to mid-latitude ionosphere, but only for periods up to 1 hour, consistent with results from the Rice Convection Model. The storm-time wind-driven electric fields are proportional to the high-latitude energy input, vary with local time and latitude, and have largest magnitudes during nighttime. These perturbations affect differently the zonal and meridional electric field components. It is shown that equatorial zonal electric fields (vertical drifts) can be disturbed up to 30 hours after large enhancements in the high-latitude currents. These perturbation electric fields are associated with enhanced high-latitude energy deposition taking place predominantly between about 1-12 hours earlier and found to be in good agreement with the Blanc-Richmond disturbance dynamo model. A second class of perturbations occurs around midnight and in the dawn-noon sector with delays of about 18-30 hours between the equatorial- and the high-latitude disturbances , and maximizes during locally quiet geomagnetic times. The latitudinal variation of the meridional disturbance electric fields (zonal drifts) is also presented. It is shown that these perturbation electric fields are predominantly downward/equatorward at all latitudes and due to both prompt penetration and disturbance dynamo electric fields. These results are also generally consistent with predictions from global convection and disturbance dynamo models.

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De, Larquier Sebastien. "The mid-latitude ionosphere under quiet geomagnetic conditions: propagation analysis of SuperDARN radar observations from large ionospheric perturbations." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/24770.

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The Earth's ionosphere is a dynamic environment strongly coupled to the neutral atmosphere, magnetosphere and solar activity. In the context of this research, we restrict our interest to the mid-latitude (a.k.a., sub-auroral) ionosphere during quiet geomagnetic conditions. The Super Dual Auroral Radar Network (SuperDARN) is composed of more than 30 low-power High Frequency (HF, from 8-18 MHz) Doppler radars covering the sub-auroral, auroral and polar ionosphere in both hemispheres. SuperDARN radars rely on the dispersive properties of the ionosphere at HF to monitor dynamic features of the ionosphere. Though originally designed to follow auroral expansion during active periods, mid-latitude SuperDARN radars have observed ground and ionospheric scatter revealing several interesting features of the mid-latitude ionosphere during periods of moderate to low geomagnetic activity. The past 7 years' expansion of SuperDARN to mid-latitudes, combined with the recent extended solar minimum, provides large-scale continuous views of the sub-auroral ionosphere for the first time. We have leveraged these circumstances to study prominent and recurring features of the mid-latitude ionosphere under quiet geomagnetic conditions. First, we seek to establish a better model of HF propagation effects on SuperDARN observations. To do so, we developed a ray-tracing model coupled with the International Reference Ionosphere (IRI). This model is tested against another well established ray-tracing model, then optimized to be compared to SuperDARN observations (Chapter 2). The first prominent ionospheric feature studied is an anomaly in the standard ionospheric model of photo-ionization and recombination. This type of event provides an ideal candidate for testing the ray-tracing model and analyzing propagation effects in SuperDARN observations. The anomaly was first observed in ground backscatter occurring around sunset for the Blackstone, VA SuperDARN radar. We established that it is related to an unexpected enhancement in electron densities that leads to increased refraction of the HF signals. Using the ray-tracing, IRI model, and measurements from the Millstone Hill Incoherent Scatter Radar (ISR), we showed that this enhancement is part of a global phenomenon in the Northern Hemisphere, and is possibly related to the Southern Hemisphere's Weddell Sea Anomaly. We also tested a potential mechanism involving thermospheric winds and geomagnetic field configuration which showed promising results and will require further modeling to confirm (Chapter 3). The second ionospheric feature was a type of decameter-scale irregularity associated with very low drift velocities. Previous work had established that these irregularities occur throughout the year, during nighttime, and equatorward of both the auroral regions and the plasmapause boundary. An initial analysis suggested that the Temperature Gradient Instability (TGI) was responsible for the growth of such irregularities. We first used our ray-tracing model to distinguish between HF propagation effects and irregularity occurrence in SuperDARN observations. This revealed the irregularities to be widespread within the mid-latitude ionosphere and located in the bottom-side F-region (Chapter 4). A second study using measurements from the Millstone Hill ISR revealed that TGI driven growth was possible but only in the top-side F-region ionosphere. We found that initial growth may occur primarily at larger wavelengths, with subsequent cascade to decameter-scale with coupling throughout the F-region (Chapter 5). In summary, the research conducted during this PhD program has established a robust method to analyze quiet-time SuperDARN observations. It also furthered our physical understanding of some prominent features of the mid-latitude ionosphere. It leaves behind a flexible ray-tracing model, multiple online tools to browse SuperDARN data, and a thorough and growing Space Science API providing access to multiple datasets, models and visualization tools.
Ph. D.

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Pradipta, Rezy. "Incoherent scatter radar detection of enhanced plasma line in ionospheric E-region over Arecibo." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36122.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.
Includes bibliographical references (p. 45).
A series of incoherent scatter radar (ISR) observation were conducted at the Arecibo Observatory from December 27, 2005 until January 3, 2006. From plasma line measurements that were taken during this radar campaign, we found that plasma line enhancement was quite frequently seen in the ionospheric E-region. We hypothesized that the E-region plasma line enhancement over Arecibo was caused by precipitated electrons from the radiation belts. The precipitated electrons will enhance the population of suprathermal electrons in the E-region. Subsequently, suprathermal electrons will cause excitation of Langmuir waves that could be detected by incoherent scatter radar as plasma lines. In this thesis, we are going to examine and discuss the observed features of E-region plasma line enhancement over Arecibo to test this hypothesis. In addition, a theoretical discussion on Langmuir waves is also presented in a chapter of this thesis. Finally, we also introduce the Spread F Index (SFI) as a convenient bookkeeping method to summarize spread F condition over a certain period of time.
by Rezy Pradipta.
S.B.

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Kane, Mark Vinton. "Transient subsurface features in Mars Express radar data: an explanation based on ionospheric holes." Thesis, University of Iowa, 2012. https://ir.uiowa.edu/etd/3477.

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This study was motivated by the discovery of semi-circular subsurface craters, or basins, at multiple locations on Mars by the MARSIS (Mars Advanced Radar for Subsurface and Ionospheric Sounding) radar sounder on board the Mars Express spacecraft. The nature of these subsurface structures was called into question when it was realized that some of the radar observations were not repeatable on subsequent passes over the same region. If they were true geological structures, such as ancient craters buried by dust, one would expect to always see them when the spacecraft passes over these regions. The transient nature of the observations led to the suggestion that these structures were actually of ionospheric origin. In this paper we will provide evidence, including a proof-of-concept result, that these features are produced by holes in the ionosphere, and not by subsurface structures. We discuss the possibility that the ionospheric holes are caused by an interaction of the ionosphere with local crustal magnetic fields. We introduce the ionospheric model which we used to simulate the MARSIS sounder moving and pulsing radio waves through the Martian ionosphere, and show that the results of ray tracing through this density profile are consistent with data seen in the MARSIS radargrams.

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Nichols, James Warren. "The design of a new far ultraviolet interferometer for ionospheric spectroscopy." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA241767.

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Thesis (M.S. in Physics)--Naval Postgraduate School, December 1990.
Thesis Advisor(s): Cleary, David D. ; Davis, D. Scott. "December 1990." Description based on title screen as viewed on April 2, 2010. DTIC Identifier(s): Ionosphere, Ultraviolet Spectroscopy, Interferometer. Author(s) subject terms: Ionosphere, Ultraviolet Spectroscopy, Interferometer. Includes bibliographical references (p. 64-67). Also available in print.

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Subramanium, Mahesh. "A Study of the Gradient Drift Instability in the High-Latitude Ionosphere Using the Utah State University Time Dependent Ionospheric Model." DigitalCommons@USU, 1996. https://digitalcommons.usu.edu/etd/4869.

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Research over the years has established that the Gradient Drift Instability process causes small-scale irregularities, mostly along the edges of the high-latitude polar cap patches. Studying these irregularities will help in the development of a global Scale Ionospheric model, which is a central part of a global space weather forecast system. Much theoretical work has been done with varying degrees of complexity to study this instability in the high latitude patches. In this work we have used the Utah State University Time Dependent Ionospheric Model to model the high-latitude patches, calculate the growth rate of the instability, and perform a macro-scale study of the phenomenon. This is the first time that real ionospheric values have been used to calculate the growth rate and to provide two-dimensional maps identifying Gradient Drift Instability-caused irregularity regions in the polar cap. Our research shows that regions of intense instability occur along the edges of the tongue of ionization and its throat regions with strong rates along the borders of the cusp region.

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Löfås, Henrik. "Ionospheric modification by powerful HF-waves : Underdense F-region heating by X-Mode." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121898.

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Observations of modifications of the electron temperature in the F-region produced by powerful high-frequency waves transmitted in X-mode are presented. The experiments were performed during quiet nighttime conditions with low ionospheric densities so no reflections occurred. Nevertheless temperature enhancements of the order of 300-400K were obtained. The modifications found can be well described by the theory of Ohmic heating by the pump wave and both temporal and spatial changes are reproduced. A brief overview of several different experimental campaigns at EISCAT facilities in the period from October 2006 to February 2008 are also given pointing out some interesting features from the different experiments. The main focus is then on the campaign during October 2006 and modifications of the electron temperature in the F-region.

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Praveen, Vikram. "Event Driven GPS Data Collection System for Studying Ionospheric Scintillation." Miami University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=miami1323894410.

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Rathod, Chirag. "Examining Plasma Instabilities as Ionospheric Turbulence Generation Mechanisms Using Pseudo-Spectral Methods." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/102892.

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Turbulence in the ionosphere is important to understand because it can negatively affect communication signals. This work examines different scenarios in the ionosphere in which turbulence may develop. The two main causes of turbulence considered in this work are the gradient drift instability (GDI) and the Kelvin-Helmholtz instability (KHI). The likelihood of the development of the GDI during the August 17, 2017 total solar eclipse is studied numerically. This analysis uses the ``Sami3 is Also a Model of the Ionosphere" (SAMI3) model to study the effect of the eclipse on the plasma density. The calculated GDI growth rates are small compared to how quickly the eclipse moves over the Earth. Therefore, the GDI is not expected to occur during the solar eclipse. A novel 2D electrostatic pseudo-spectral fluid model is developed to study the growth of these two instabilities and the problem of ionospheric turbulence in general. To focus on the ionospheric turbulence, a set of perturbed governing equations are derived. The model accurately captures the GDI growth rate in different limits; it is also benchmarked to the evolution of instability development in different collisional regimes of a plasma cloud. The newly developed model is used to study if the GDI is the cause of density irregularities observed in subauroral polarization streams (SAPS). Data from Global Positioning System (GPS) scintillations and the Super Dual Auroral Radar Network (SuperDARN) are used to examine the latitudinal density and velocity profiles of SAPS. It is found that the GDI is stabilized by velocity shear and therefore will only generate density irregularities in regions of low velocity shear. Furthermore, the density irregularities cannot extend through regions of large velocity shear. In certain cases, the turbulence cascade power laws match observation and theory. The transition between the KHI and the GDI is studied by understanding the effect of collisions. In low collisionality regimes, the KHI is the dominant instability. In high collisionality regimes, the GDI is the dominant instability. Using nominal ionospheric parameters, a prediction is provided that suggests that there exists an altitude in the upper textit{F} region ionosphere above which the turbulence is dominated by the KHI.
Doctor of Philosophy
In the modern day, all wireless communication signals use electromagnetic waves that propagate through the atmosphere. In the upper atmosphere, there exists a region called the ionosphere, which consists of plasma (a mixture of ions, electrons, and neutral particles). Because ions and electrons are charged particles, they interact with the electromagnetic communication signals. A better understanding of ionospheric turbulence will allow for aid in forecasting space weather as well as improve future communication equipment. Communication signals become distorted as they pass through turbulent regions of the ionosphere, which negatively affects the signal quality at the receiving end. For a tangible example, when Global Positioning System (GPS) signals pass through turbulent regions of the ionosphere, the resulting position estimate becomes worse. This work looks at two specific causes of ionospheric turbulence: the gradient drift instability (GDI) and the Kelvin-Helmholtz instability (KHI). Under the correct background conditions, these instabilities have the ability to generate ionospheric turbulence. To learn more about the GDI and the KHI, a novel simulation model is developed. The model uses a method of splitting the equations such that the focus is on just the development of the turbulence while considering spatially constant realistic background conditions. The model is shown to accurately represent results from previously studied problems in the ionosphere. This model is applied to an ionospheric phenomenon known as subauroral polarization streams (SAPS) to study the development of the GDI and the KHI. SAPS are regions of the ionosphere with large westward velocity that changes with latitude. The shape of the latitudinal velocity profile depends on many other factors in the ionosphere such as the geomagnetic conditions. It is found that for certain profiles, the GDI will form in SAPS with some of these examples matching observational data. At higher altitudes, the model predicts that the KHI will form instead. While the model is applied to just the development of the GDI and the KHI in this work, it is written in a general manner such that other causes of ionospheric turbulence can be easily studied in the future.

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Jenniges, Janelle V. "A Study of the Dayside High-Lattitude Ionospheric Electrodynamics During Extended Solar Minimum." DigitalCommons@USU, 2015. https://digitalcommons.usu.edu/etd/4481.

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The high-latitude electric eld fall-o region connects convection in the polar cap to the region where ring currents modify the penetration electric field equatorward of the polar cap boundary. This region is often overlooked because it falls between the limits of low latitude and high-latitude ionospheric models. However, penetrating electric fields cause large changes in ion composition; and therefore, correctly modeling the electric fields and plasma drift in this region aids in correctly specifying the ionosphere. Many ionospheric models use the Kp index as a physical driver, and so the latitude dependence of the plasma drift in the fall-o region was investigated as a function of Kp using Defense Meteorological Satellite Program ion drift data from the 2007{2010 solar minimum. Both the dusk and dawn sectors were analyzed and t to analytical functions describing the fall-o with decreasing latitude. The latitude dependencies were found to dier in the dusk and dawn sectors with a factor of two increase in the expansion of the duskside polar cap radius and auroral region over the dawnside. Additionally, the low-Kp polar cap radius was found to be five degrees smaller than the radius currently used in simple ionospheric models.

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Lomidze, Levan. "The Role of Thermospheric Neutral Winds in the Mid-latitude Ionospheric Evening Anomalies." DigitalCommons@USU, 2015. https://digitalcommons.usu.edu/etd/4238.

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One of the intriguing features of the F-region ionosphere are anomalous evening enhancements of the electron density over certain mid-latitude sites. The most prominent example of this enhancement is the Weddell Sea Anomaly. Although the evening anomalies have been known for several decades, their generation mechanisms are still under debate and their accurate modeling remains a challenge. In this dissertation, the role of thermospheric neutral winds in the generation of these anomalies is investigated. Thermospheric winds play an important role in the dynamics of the F-region ionosphere, and, as it will be shown, in the generation of the evening anomalies. However, to date, their reliable estimation remains a challenge. To mitigate this shortcoming, data assimilation models were employed. First, seasonal global maps of F-region peak parameters (NmF2 and hmF2) from COSMIC radio occultation measurements were assimilated into the Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) model. The model estimates magnetic meridional winds at low and mid-latitudes. GAIM-FP estimated winds were shown to be in good agreement with independent ground-based wind observations. Next, in order to address the role of neutral wind components in the generation of anomalies, a separate, 3-D physics-based Thermosphere Wind Assimilation Model (TWAM) was developed. TWAM is based on an implicit Kalman filter technique, and combines GAIM-FP magnetic meridional wind data with the equation of motion of the neutral gas to provide the climatology of the thermospheric wind components. The neutral wind components estimated by TWAM were also found to be in close quantitative agreement with independent ground-based wind observations, and were shown to accurately reproduce NmF2 and hmF2 over the anomalies. To understand the physical mechanism behind the anomalies, the plasma production, loss, and transport processes were analyzed. It was found that, due to the action of the equatorward wind, the evening density maximum forms at altitudes where the recombination rate is relatively small. It was revealed that at this time and altitude, plasma loss due to transport also weakens. As a consequence, the relative role of solar production increases over the net loss process and the electron density enhancement occurs.

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Santana, Julio III. "Investigating Ionospheric Parameters Using the Plasma Line Measurements From Incoherent Scatter Radar." Miami University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=miami1344024880.

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Negale, Michael. "Investigating the Climatology of Mesospheric and Thermospheric Gravity Waves at High Northern Latitudes." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/6937.

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An important property of the Earth's atmosphere is its ability to support wave motions, and indeed, waves exist throughout the Earth's atmosphere at all times and all locations. What is the importance of these waves? Imagine standing on the beach as water waves come crashing into you. In this case, the waves transport energy and momentum to you, knocking you off balance. Similarly, waves in the atmosphere crash, known as breaking, but what do they crash into? They crash into the atmosphere knocking the atmosphere off balance in terms of the winds and temperatures. Although the Earth's atmosphere is full of waves, they cannot be observed directly; however, their effects on the atmosphere can be observed. Waves can be detected in the winds and temperatures, as mentioned above, but also in pressure and density. In this dissertation, three different studies of waves, known as gravity waves, were performed at three different locations. For these studies, we investigate the size of the waves and in which direction they move. Using specialized cameras, gravity waves were observed in the middle atmosphere (50-70 miles up) over Alaska (for three winter times) and Norway (for one winter time). A third study investigated gravity waves at a much higher altitude (70 miles on up) using radar data from Alaska (for three years). These studies have provided important new information on these waves and how they move through the atmosphere. This in turn helps to understand in which direction these waves are crashing into the atmosphere and therefore, which direction the energy and momentum are going. Studies such as these help to better forecast weather and climate.

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Tshisaphungo, Mpho. "Validation of high frequency propagation prediction models over Africa." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1015239.

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The ionosphere is an important factor in high frequency (HF) radio propagation providing an opportunity to study ionospheric variability as well as the space weather conditions under which HF communication can take place. This thesis presents the validation of HF propagation conditions for the Ionospheric Communication Enhanced Profile Analysis and Circuit (ICEPAC) and Advanced Stand Alone Prediction System (ASAPS) models over Africa by comparing predictions with the measured data obtained from the International Beacon Project (IBP). Since these models were not developed using information on the African region, a more accurate HF propagation prediction tool is required. Two IBP transmitter stations are considered, Ruaraka, Kenya (1.24°S, 36.88°E) and Pretoria, South Africa (25.45°S, 28.10°E) with one beacon receiver station located in Hermanus, South Africa (34.27°S, 19.l2°E). The potential of these models in terms of HF propagation conditions is illustrated. An attempt to draw conclusions for future improvement of the models is also presented. Results show a low prediction accuracy for both ICEPAC and ASAPS models, although ICEPAC provided more accurate predictions for daily HF propagation conditions. This thesis suggests that the development of a new HF propagation prediction tool for the African region or the modification of one of the existing models to accommodate the African region, taking into account the importance of the African ionospheric region, should be considered as an option to ensure more accurate HF Propagation predictions over this region.

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Shim, JA Soon. "Analysis of Total Electron Content (TEC) Variations in the Low- and Middle-Latitude Ionosphere." DigitalCommons@USU, 2009. https://digitalcommons.usu.edu/etd/403.

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Detailed study of the spatial correlations of day-to-day ionospheric TEC variations on a global scale was performed for four 30-day-long periods in 2004 (January, March/April, June/July, September/October) using observations from more than 1000 ground-based GPS receivers. In order to obtain the spatial correlations, initially, the day-to-day variability was calculated by first mapping the observed slant TEC values for each 5-minute GPS ground receiver-satellite pair to the vertical and then differencing it with its corresponding value from the previous day. This resulted in more than 150 million values of day-to-day change in TEC (delta TEC). Next, statistics were performed on the delta TEC values. The study indicates strong correlationsbetween geomagnetic conjugate points, and these correlations are larger at low latitudes than at middle latitudes. Typical correlation lengths, defined as the angular separation at which the correlation coefficient drops to 0.7, were found to be larger at middle latitudes than at low latitudes. The correlation lengths are larger during daytime than during nighttime. The results indicate that the spatial correlation is largely independent of season. These spatial correlations are important for understanding the physical mechanisms that cause ionospheric weather variability and are also relevant to data assimilation. In an effort to better understand the effects of neutral wind and electric field on the TEC variability, a physics-based numerical Ionosphere/Plasmasphere Model (IPM) was used. The model solves the transport equations for the six ions, O+, NO+, O2+, N2+, H+, and He+, on convecting flux tubes that realistically follow the geomagnetic field. Two of the inputs required by the IPM are the thermospheric neutral wind and the low-latitude electric field, which can be given by existing empirical model or externally specified by the user. To study the relative importance of the neutral wind and the electric field for the TEC variations, these two model inputs were externally modified and the resulting variations in TEC were compared. Neutral wind and electric field modifications were introduced at three different local times in order to investigate the effect of different start times of the imposed perturbations on TEC. This study focused on modeled low- and middlelatitude TEC variations in the afternoon and post-sunset at three different longitude sectors for medium solar activity and low geomagnetic activity. The largest changes in TEC were found predominantly in the equatorial anomaly, and a significant longitudinal dependence was observed. The results indicate that the perturbation effect on the TEC at 2100 LT varied nonlinearly with the elapsed time after the imposed neutral wind and electric field perturbations. An important outcome of this study is that daytime neutral wind and/or electric field modifications will lead to essentially identical TEC changes in the 2100 local time sector.

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Norin, Lars. "Secondary Electromagnetic Radiation Generated by HF Pumping of the Ionosphere." Doctoral thesis, Uppsala universitet, Astronomi och rymdfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9393.

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Electromagnetic waves can be used to transmit information over long distances and are therefore often employed for communication purposes. The electromagnetic waves are reflected off material objects on their paths and interact with the medium through which they propagate. For instance, the plasma in the ionosphere can refract and even reflect radio waves propagating through it. By increasing the power of radio waves injected into the ionosphere, the waves start to modify the plasma, resulting in the generation of a wide range of nonlinear processes, including turbulence, in particular near the reflection region. By systematically varying the injected radio waves in terms of frequency, power, polarisation, duty cycle, inclination, etc. the ionosphere can be used as an outdoor laboratory for investigating fundamental properties of the near-Earth space environment as well as of plasma turbulence. In such ionospheric modification experiments, it has been discovered that the irradiation of the ionosphere by powerful radio waves leads to the formation of plasma density structures and to the emission of secondary electromagnetic radiation, a phenomenon known as stimulated electromagnetic emission. These processes are highly repeatable and have enabled systematic investigations of the nonlinear properties of the ionospheric plasma. In this thesis we investigate features of the plasma density structures and the secondary electromagnetic radiation. In a theoretical study we analyse a certain aspect of the formation of the plasma structures. The transient dynamics of the secondary radiation is investigated experimentally in a series of papers, focussing on the initial stage as well as on the decay. In one of the papers we use the transient dynamics of the secondary radiation to reveal the intimate relation between certain features of the radiation and structures of certain scales. Further, we present measurements of unprecedentedly strong secondary radiation, attributed to stimulated Brillouin scattering, and report measurements of the secondary radiation using a novel technique imposed on the transmitted radio waves.

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Tracy, Brian David. "Lunar Tidal Effects in the Electrodynamics of the Low-Latitude Ionosphere." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/1968.

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We used extensive measurements made by the Jicamarca Unattended Long-Term Investigations of the Ionosphere and Atmosphere (JULIA) and Incoherent Scatter Radar (ISR) systems at Jicamarca, Peru during geomagnetic quiet conditions to determine the climatologies of lunar tidal effects on equatorial vertical plasma drifts. We use, for the first time, the expectation maximization (EM) algorithm to derive the amplitudes and phases of the semimonthly and monthly lunar tidal perturbations. Our results indicate, as expected, lunar tidal effects can significantly modulate the equatorial plasma drifts. The local time and seasonal dependent phase progression has been studied in much more detail than previously and has shown to have significant variations from the average value. The semimonthly drift amplitudes are largest during December solstice and smallest during June solstice during the day, and almost season independent at night. The monthly lunar tidal amplitudes are season independent during the day, while nighttime monthly amplitudes are largest and smallest in December solstice and autumnal equinox, respectively. The monthly and semimonthly amplitudes decrease from early morning to afternoon and evening to morning with moderate to large increases near dusk and dawn. We also examined these perturbation drifts during periods of sudden stratospheric warmings (SSWs). Our results show, for the first time, the enhancements of the lunar semimonthly tidal effects associated with SSWs to occur at night, as well as during the day. Our results also indicate during SSWs, monthly tidal effects are not enhanced as strongly as the semimonthly effects.

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21

Fu, Haiyang. "Modeling of Plasma Irregularities Associated with Artificially Created Dusty Plasmas in the Near-Earth Space Environment." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19248.

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Plasma turbulence associated with the creation of an artificial dust layer in the earth's ionosphere is investigated. The Charged Aerosol Release Experiment (CARE) aims to understand the mechanisms for enhanced radar scatter from plasma irregularities embedded in dusty plasmas in space. Plasma irregularities embedded in a artificial dusty plasma in space may shed light on understanding the mechanism for enhanced radar scatter in Noctilucent Clouds (NLCs) and Polar Mesospheric Summer Echoes (PMSEs) in the earth's mesosphere. Artificially created, charged-particulate layers also have strong impact on radar scatter as well as radio signal propagation in communication and surveillance systems. The sounding rocket experiment was designed to develop theories of radar scatter from artificially created plasma turbulence in charged dust particle environment. Understanding plasma irregularities embedded in a artificial dusty plasma in space will also contribute to addressing possible effects of combustion products in rocket/space shuttle exhaust in the ionosphere. In dusty space plasmas, plasma irregularities and instabilities can be generated during active dust aerosol release experiments. Small scale irregularities (several tens of centimeter to meters) and low frequency waves (in the ion/dust scale time in the order of second) are studied in this work, which can be measured by High Frequency (HF), Very High Frequency (VHF) and Ultra High Frequency (UHF) radars. The existence of dust aerosol particles makes computational modeling of plasma irregularities extremely challenging not only because of multiple spatial and temporal scale issue but also due to complexity of dust aerosol particles. This work will provide theoretical and computational models to study plasma irregularities driven by dust aerosol release for the purpose of designing future experiments with combined ground radar, optical and in-situ measurement. In accordance with linear analysis, feasible hybrid computational models are developed to study nonlinear evolution of plasma instabilities in artificially created dusty space plasmas. First of all, the ion acoustic (IA) instability and dust acoustic (DA) instability in homogenous unmagnetized plasmas are investigated by a computational model using a Boltzmann electron assumption. Such acoustic-type instabilities are attributed to the charged dust and ion streaming along the geomagnetic field. Secondly, in a homogenous magnetized dusty plasma, lower-hybrid (LH) streaming instability will be generated by dust streaming perpendicular to the background geomagnetic field. The magnetic field effect on lower-hybrid streaming instabilities is investigated by including the ratio of electron plasma frequency and electron gyro frequency in this model. The instability in weakly magnetized circumstances agree well with that for the ion acoustic (IA) instability by a Boltzmann model. Finally, in an inhomogeneous unmagnetized/magnetized dust boundary layer, possible instabilities will be addressed, including dust acoustic (DA) wave due to flow along the boundary and lower-hybrid (LH) sheared instability due to flow cross the boundary. With applications to active rocket experiments, plasma irregularity features in a linear/nonlinear saturated stage are characterized and predicted. Important parameters of the dust aerosol clouds that impact the evolution of waves will be also discussed for upcoming dust payload generator design. These computational models, with the advantage of following nonlinear wave-particle interaction, could be used for space dusty plasmas as well as laboratory dusty plasmas.
Ph. D.

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Barabash, Victoria. "Investigation of Polar Mesosphere Summer Echoes in Northern Scandinavia." Doctoral thesis, Umeå University, Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-176.

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This PhD thesis deals with phenomena which are closely related to the unique thermal structure of the polar summer mesosphere, namely Polar Mesosphere Summer Echoes (PMSE). PMSE are strong radar echoes commonly observed by VHF MST radars from thin layers in the 80-90 km altitude interval at high latitudes during summer. They follow a seasonal pattern of abrupt appearance in late May and a gradual disappearance in mid-August. This period corresponds roughly to the time between the completion of the summer time cooling of the polar mesopause to the time of reversal of the mesospheric circulation to autumn condition. In this connection, PMSE are associated with the extremely low temperatures, i.e. below 140 K, which are unique to the polar summer mesopause. Traditional theories of radar (partial) reflection and scattering have been unable to explain the PMSE and the exact mechanism for their occurrence remains unclear despite the steadily increasing interest in them over the past 20 years. Currently accepted theories regarding the mechanism giving rise to PMSE agree that one of the conditions needed for enhanced radar echoes is the presence of low-mobility charge carries such as large cluster ions and ice aerosols which capture the ambient electrons. It has been established that the PMSE are in some way associated with noctilucent clouds (NLC), layers of ice crystals, which constitute the highest observed clouds in the earth’s atmosphere. PMSE occurrence and dynamics are also found to be closely connected with the planetary and gravity waves.

Observations of PMSE presented in this thesis have been carried out by the Esrange MST radar (ESRAD) located at Esrange (67°56’N, 21°04’E) just outside Kiruna in northernmost Sweden. The radar operates at 52 MHz with 72 kW peak power and a maximum duty cycle of 5%. The antenna consists of 12x12 array of 5-element Yagis with a 0.7l spacing. During the PMSE measurements the radar used a 16-bit complementary code having a baud length of 1mS. This corresponds to height resolution of 150 m. The sampling frequency was set at 1450 Hz. The covered height range was 80-90 km. The presence of PMSE was determined on the basis of the radar SNR (signal-to-noise ratio). The PMSE measurements have been made during May-August each year since 1997.

PMSE seasonal and diurnal occurrence rates as well as dynamics have been studied in connection with tidal winds, planetary waves, temperature and water vapor content in the mesosphere (Papers I, IV and VI). Simultaneous and common-volume observations of PMSE and noctilucent clouds have been performed by radar, lidar and CCD camera (Paper V). Correlation between variations in PMSE and variations in extra ionization added by precipitating energetic electrons or high-energy particles from the Sun has been examined (Papers II and III). Possible influence of transport effects due to the electric field on PMSE appearance has been studied during a solar proton event (Paper III).

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Habarulema, John Bosco. "A contribution to TEC modelling over Southern Africa using GPS data." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005241.

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Modelling ionospheric total electron content (TEC) is an important area of interest for radio wave propagation, geodesy, surveying, the understanding of space weather dynamics and error correction in relation to Global Navigation Satellite Systems (GNNS) applications. With the utilisation of improved ionosonde technology coupled with the use of GNSS, the response of technological systems due to changes in the ionosphere during both quiet and disturbed conditions can be historically inferred. TEC values are usually derived from GNSS measurements using mathematically intensive algorithms. However, the techniques used to estimate these TEC values depend heavily on the availability of near-real time GNSS data, and therefore, are sometimes unable to generate complete datasets. This thesis investigated possibilities for the modelling of TEC values derived from the South African Global Positioning System (GPS)receiver network using linear regression methods and artificial neural networks (NNs). GPS TEC values were derived using the Adjusted Spherical Harmonic Analysis (ASHA) algorithm. Considering TEC and the factors that influence its variability as “dependent and independent variables” respectively, the capabilities of linear regression methods and NNs for TEC modelling were first investigated using a small dataset from two GPS receiver stations. NN and regression models were separately developed and used to reproduce TEC fluctuations at different stations not included in the models’ development. For this purpose, TEC was modelled as a function of diurnal variation, seasonal variation, solar and magnetic activities. Comparative analysis showed that NN models provide predictions of GPS TEC that were an improvement on those predicted by the regression models developed. A separate study to empirically investigate the effects of solar wind on GPS TEC was carried out. Quantitative results indicated that solar wind does not have a significant influence on TEC variability. The final TEC simulation model developed makes use of the NN technique to find the relationship between historical TEC data variations and factors that are known to influence TEC variability (such as solar and magnetic activities, diurnal and seasonal variations and the geographical locations of the respective GPS stations) for the purposes of regional TEC modelling and mapping. The NN technique in conjunction with interpolation and extrapolation methods makes it possible to construct ionospheric TEC maps and to analyse the spatial and temporal TEC behaviour over Southern Africa. For independent validation, modelled TEC values were compared to ionosonde TEC and the International Reference Ionosphere (IRI) generated TEC values during both quiet and disturbed conditions. This thesis provides a comprehensive guide on the development of TEC models for predicting ionospheric variability over the South African region, and forms a significant contribution to ionospheric modelling efforts in Africa.

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24

Hall, Jan-Ove. "Interaction between Electromagnetic Waves and Localized Plasma Oscillations." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4282.

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25

Jorba, Ferro Oriol. "Étude de l'influence de la propreté électrostatique du satellite sur les mesures du champ électrique basse fréquence de TARANIS." Thesis, Toulouse, ISAE, 2018. http://www.theses.fr/2018ESAE0042/document.

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Les satellites en orbite terrestre se déplacent dans le plasma ionosphérique, un mélange de particules chargées, et éventuellement de particules neutres. Des électrons et des ions issus de ce plasma, ainsi que les émissions Ultra-Violets(UV) en provenance du soleil, interagissent avec les surfaces du satellite et modifient sa charge électrostatique. Cette chargement peut induire elle-même des décharges électrostatiques aux conséquences allant de perturbations électromagnétiques (fausses commandes par exemple) à la perte du satellite. En orbites de basse altitude (LEO) l'énergie cinétique et thermique du plasma est généralement faible et donc, les satellites vont rarement présenter des décharges importantes. Néanmoins, les missions scientifiques qui embarquent des instruments très performants et précis peuvent être affectées par cette interaction satellite-plasma-émissions UV. Cette thèse s'intéresse particulièrement à ces phénomènes de charge des structures externes du satellite et à l'impact de ce chargement sur les mesures scientifiques effectuées à bord, i.e. mesures du champ électrique et de la densité du plasma thermique
Earth-orbiting satellites travel in ionospheric plasma, a mixture of charged particles, and possibly neutral particles. Electrons and ions from this plasma, as well as Ultra-Violet (UV) emissions from the sun, interact with the surfaces of the satellite and modify its electrostatic charge. This loading can itself induce electrostatic discharges to the consequences ranging from electromagnetic disturbances (false commands for example) to the loss of the satellite. In low-Earth orbits (LEO), the kinetic and thermal energy of the plasma is generally low and therefore satellites rarely exhibit large discharges. Nevertheless, scientific missions that carry high-performance and accurate instruments can be affected by this satellite-plasma-UV-emissions interaction. This thesis is particularly interested in these phenomena of charge of the external structures of the satellite and the impact of this load on the scientific measurements carried out on board, i.e. measures of the electric field and the density of the thermal plasma

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26

Liperovskaya, E. V., Claudia-Veronika Meister, M. Parrot, V. V. Bogdanov, and N. E. Vasil‘eva. "On Es-spread effects in the ionosphere connected to earthquakes." Universität Potsdam, 2006. http://opus.kobv.de/ubp/volltexte/2007/1500/.

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In the present work, phenomena in the ionosphere are studied, which are connected with earthquakes (16 events) having a depth of less than 50 km and a magnitude M larger than 4. Analysed are night-time Es-spread effects using data of the vertical sounding station Petropavlovsk- Kanchatsky (φ=53.0°, λ=158.7°) from May 2004 until August 2004 registered every 15 minutes. It is found that the maximum distance of the earthquake from the sounding station, where pre-seismic phenomena are yet observable, depends on the magnitude of the earthquake. Further it is shown that 1-2 days before the earthquakes, in the premidnight hours, the appearance of Es-spread increases. The reliability of this increase amounts to 0.95.

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27

Talaee, Omid. "Distribution of Electron Temperatures in Titan's Lower Ionosphere." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-194685.

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The report contained herein is a statistical analysis of electron temperatures withinTitan’s lower ionosphere. Electron temperatures in this altitudinal range are of greatimport for researchers. The main contributing factors are investigated to see whatphysical processes are the sources of variability in electron temperatures. Oneimportant result from this analysis lends itself to determining recombinationcoefficients thus determining organic process rates occurring within Titan’satmosphere. To accomplish this analysis, data from the Langmuir probe aboard the Cassini craft isutilized. The Langmuir probe is an instrument which can be used to measure currentdifferences in a plasma environment. From this, plasma properties such astemperature, density, and velocity can be calculated. It was named after IrvingLangmuir, whose theories became the basis for Orbit Motion Limited theory. Of the possible factors that determine the variation in electron temperatures, altitudewas the most evident and largest contributor. Once the data had been reduced toremove the effect of altitude on the temperature, other factors such as latitude, solarzenith angle, and ram angle were investigated to ascertain which, if any, wasresponsible for variations in temperature. Upon completion of the analysis, it waslearned that ram angle also had an identifiable effect upon electron temperatures. This effect was further investigated to ensure confidence in the results. Thecompletion of this part of the analysis showed that the effect shown with respect toram angle was indeed reproducible and that no other investigated factor had a majoreffect on electron temperatures. After the confidence procedure was completed,several previous studies findings were confirmed. These confirmed results include therelation of solar zenith angle with respect to both electron temperature distributionand density distribution, as well as a possible confirmation relating temperature anddensity for electrons.n/

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Rosenqvist, Lisa. "Energy Transfer and Conversion in the Magnetosphere-Ionosphere System." Doctoral thesis, Uppsala University, Department of Astronomy and Space Physics, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8716.

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Magnetized planets, such as Earth, are strongly influenced by the solar wind. The Sun is very dynamic, releasing varying amounts of energy, resulting in a fluctuating energy and momentum exchange between the solar wind and planetary magnetospheres. The efficiency of this coupling is thought to be controlled by magnetic reconnection occurring at the boundary between solar wind and planetary magnetic fields. One of the main tasks in space physics research is to increase the understanding of this coupling between the Sun and other solar system bodies. Perhaps the most important aspect regards the transfer of energy from the solar wind to the terrestrial magnetosphere as this is the main source for driving plasma processes in the magnetosphere-ionosphere system. This may also have a direct practical influence on our life here on Earth as it is responsible for Space Weather effects. In this thesis I investigate both the global scale of the varying solar-terrestrial coupling and local phenomena in more detail. I use mainly the European Space Agency Cluster mission which provide unprecedented three-dimensional observations via its formation of four identical spacecraft. The Cluster data are complimented with observations from a broad range of instruments both onboard spacecraft and from groundbased magnetometers and radars.

A period of very strong solar driving in late October 2003 is investigated. We show that some of the strongest substorms in the history of magnetic recordings were triggered by pressure pulses impacting a quasi-stable magnetosphere. We make for the first time direct estimates of the local energy flow into the magnetotail using Cluster measurements. Observational estimates suggest a good energy balance between the magnetosphere-ionosphere system while empirical proxies seem to suffer from over/under estimations during such extreme conditions.

Another period of extreme interplanetary conditions give rise to accelerated flows along the magnetopause which could account for an enhanced energy coupling between the solar wind and the magnetosphere. We discuss whether such conditions could explain the simultaneous observation of a large auroral spiral across the polar cap.

Contrary to extreme conditions the energy conversion across the dayside magnetopause has been estimated during an extended period of steady interplanetary conditions. A new method to determine the rate at which reconnection occurs is described that utilizes the magnitude of the local energy conversion from Cluster. The observations show a varying reconnection rate which support the previous interpretation that reconnection is continuous but its rate is modulated.

Finally, we compare local energy estimates from Cluster with a global magnetohydrodynamic simulation. The results show that the observations are reliably reproduced by the model and may be used to validate and scale global magnetohydrodynamic models.

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Wilder, Frederick Durand. "Reverse Convection Potential Saturation in the Polar Ionosphere." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/31847.

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The results of an investigation of the reverse convection potentials in the day side high latitude ionosphere during periods of steady northward interplanetary magnetic field (IMF) are reported. While it has been shown that the polar cap potential in the ionosphere exhibits non-linear saturation behavior when the IMF becomes increasingly southward, it has yet to be shown whether the high latitude reverse convection cells in response to increasingly northward IMF exhibit similar behavior. Solar wind data from the ACE satellite from 1998 to 2005 was used to search for events in the solar wind when the IMF is northward and the interplanetary electric field is stable for more than 40 minutes. Bin-averaged SuperDARN convection data was used with a spherical harmonic fit applied to calculate the average potential pattern for each northward IMF bin. Results show that the reverse convection cells do, in fact, exhibit non-linear saturation behavior. The saturation potential is approximately 20 kV and is achieved when the electric coupling function reaches between 18 and 30 kV/RE.
Master of Science

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30

Liperovskaya, E. V., M. Parrot, V. V. Bogdanov, Claudia-Veronika Meister, M. V. Rodkin, and V. A. Liperovsky. "On long-term variations of foF2 in the mid-latitude ionosphere before strong earthquakes." Universität Potsdam, 2006. http://opus.kobv.de/ubp/volltexte/2007/1501/.

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The statistical analysis of the variations of the dayly-mean frequency of the maximum ionospheric electron density foF2 is performed in connection with the occurrence of (more than 60) earthquakes with magnitudes M > 6.0, depths h < 80 km and distances from the vertical sounding station R < 1000 km. For the study, data of the Tokyo sounding station are used, which were registered every hour in the years 1957-1990. It is shown that, on the average, foF2 decreases before the earthquakes. One day before the shock the decrease amounts to about 5 %. The statistical reliability of this phenomenon is obtained to be better than 0.95. Further, the variations of the occurrence probability of the turbulization of the F-layer (F spread) are investigated for (more than 260) earthquakes with M > 5.5, h < 80 km, R < 1000 km. For the analysis, data of the Japanese station Akita from 1969-1990 are used, which were obtained every hour. It is found that before the earthquakes the occurrence probability of F spread decreases. In the week before the event, the decrease has values of more than 10 %. The statistical reliability of this phenomenon is also larger than 0.95. Examining the seismo-ionospheric effects, here periods of time with weak heliogeomagnetic disturbances are considered, the Wolf number is less than 100 and the index ∑ Kp is smaller than 30.

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Hatch, Spencer Mark. "Stormtime and Interplanetary Magnetic Field Drivers of Wave and Particle Acceleration Processes in the Magnetosphere-Ionosphere Transition Region." Thesis, Dartmouth College, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10603779.

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The magnetosphere-ionosphere (M-I) transition region is the several thousand--kilometer stretch between the cold, dense and variably resistive region of ionized atmospheric gases beginning tens of kilometers above the terrestrial surface, and the hot, tenuous, and conductive plasmas that interface with the solar wind at higher altitudes. The M-I transition region is therefore the site through which magnetospheric conditions, which are strongly susceptible to solar wind dynamics, are communicated to ionospheric plasmas, and vice versa. We systematically study the influence of geomagnetic storms on energy input, electron precipitation, and ion outflow in the M-I transition region, emphasizing the role of inertial Alfven waves both as a preferred mechanism for dynamic (instead of static) energy transfer and particle acceleration, and as a low-altitude manifestation of high-altitude interaction between the solar wind and the magnetosphere, as observed by the FAST satellite. Via superposed epoch analysis and high-latitude distributions derived as a function of storm phase, we show that storm main and recovery phase correspond to strong modulations of measures of Alfvenic activity in the vicinity of the cusp as well as premidnight. We demonstrate that storm main and recovery phases occur during ~30% of the four-year period studied, but together account for more than 65% of global Alfvenic energy deposition and electron precipitation, and more than 70% of the coincident ion outflow. We compare observed interplanetary magnetic field (IMF) control of inertial Alfven wave activity with Lyon-Fedder-Mobarry global MHD simulations predicting that southward IMF conditions lead to generation of Alfvenic power in the magnetotail, and that duskward IMF conditions lead to enhanced prenoon Alfvenic power in the Northern Hemisphere. Observed and predicted prenoon Alfvenic power enhancements contrast with direct-entry precipitation, which is instead enhanced postnoon. This situation reverses under dawnward IMF. Despite clear observational and simulated signatures of dayside Alfvenic power, the generation mechanism remains unclear. Last, we present premidnight FAST observations of accelerated precipitation that is best described by a kappa distribution, signaling a nonthermal source population. We examine the implications for the commonly used Knight Relation.

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Liperovsky, V. A., Claudia-Veronika Meister, L. N. Doda, E. V. Liperovskaya, V. F. Davidov, and V. V. Bogdanov. "On the possible influence of radon and aerosol injection on the atmosphere and ionosphere before earthquakes." Universität Potsdam, 2005. http://opus.kobv.de/ubp/volltexte/2007/1499/.

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A model of the generation of pulses of local electric fields with characteristic time scales of 1–10 minutes is considered for atmospheric conditions above fracture regions of earthquakes. In the model, it is proposed that aerosols, increased ionization velocity and upstreaming air flows occur at night-time conditions. The pulses of local electric fields cause respective pulses of infrared emissions. But infrared emissions with time scales of 1–10 minutes were not observed up to now experimentally. The authors think, that the considered non-stationary field and radiation effects might be a new-type of applicable earthquake indicators and ask to perform special earth-based and satellite observations of the night-time atmosphere in seismoactive fracture regions.

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Kaeppler, Stephen Roland. "A rocket-borne investigation of auroral electrodynamics within the auroral-ionosphere." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/2535.

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This dissertation focuses on data analyzed from the Auroral Current and Electrodynamics Structure (ACES) sounding rocket mission. ACES consisted of two payloads launched nearly simultaneously in 2009 into a dynamic multiple-arc aurora. The mission was designed to observe the three-dimensional current system of an auroral arc system. To constrain the spatial-temporal ambiguity, the payloads were flown along nearly conjugate magnetic field footpoints, at various altitudes with small temporal separation. The high altitude payload took in situ measurements of the plasma parameters above the current closure region to measure the input signature into the lower ionosphere. The low-altitude payload took similar observations within the current closure region, where perpendicular cross-field currents can flow. A detailed description of the experimental configuration is presented, including operational details of the fields and plasma instruments flown on both payloads. The methods used to process data from the electrostatic particle detectors and the fluxgate magnetometer on both payloads are presented. Data from the all-sky imager details the auroral configuration at the time of launch. In situ data are presented detailing observations of the electric fields, magnetic fields, and the electron differential energy flux, as the payloads crossed nearly conjugate magnetic field lines. Field-aligned currents were calculated from magnetometer observations on the high altitude payload. These data were combined with electron flux data to show that the high altitude payload traversed regions of upward and downward field-aligned current. The low altitude payload observed signatures in the residual magnetic field components consistent with perpendicular closure current. Ionospheric collisionality is investigated to determine if it is a significant mechanism to explain observed differences in the low energy electron flux between the high altitude and low altitude payload. As a result of increased ionospheric collisionality, the ionospheric conductivity is investigated to interpret the in situ electric field observations. A model of auroral electrodynamics, that is under development, is discussed in the context of interpreting magnetometer data from the low altitude payload. The evolution of precipitating electron flux into the ionosphere and the effect this precipitation has on generating ionization is presented. The electron spectrum produced by the model were fit to the electron flux data observed by the low altitude payload. The height ionization profile, equilibrium electron density, and Hall and Pedersen conductivities were determined from the model electron spectrum incident to the ionosphere. It was shown that the low altitude payload flew just above the peak Hall and Pedersen conductivities, suggesting that the low altitude payload flew directly in the region where perpendicular closure currents were most significant.

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Borälv, Eva. "Substorm Features in the High-Latitude Ionosphere and Magnetosphere : Multi-Instrument Observations." Doctoral thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3478.

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The space around Earth, confined in the terrestrial magnetosphere, is to some extent shielded from the Sun's solar wind plasma and magnetic field. During certain conditions, however, strong interaction can occur between the solar wind and the magnetosphere, resulting in magnetospheric activity of several forms, among which substorms and storms are the most prominent. A general framework for how these processes work have been outlayed through the history of research, however, there still remain questions to be answered. The most striking example regards the onset of substorms, where both the onset cause and location in the magnetosphere/ionosphere are still debated. These are clearly not easily solved problems, since a substorm is a global process, ideally requiring simultaneous measurements in the magnetotail and ionosphere. Investigated in this work are temporal and spatial scales for substorm and convection processes in the Earth's magnetosphere and ionosphere. This is performed by combining observations from a number of both ground-based and spacecraft-borne instruments. The observations indicate that the magnetotail's cross-section is involved to a larger spatial extent than previously considered in the substorm process. Furthermore, convection changes result in topological changes of the magnetosphere on a fast time scale. The results show that the magnetosphere is, on a global magnetospheric scale, highly dynamic during convection changes and ensuing substorms.

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Wohlwend, Christian Stephen. "Modeling the Electrodynamics of the Low-Latitude Ionosphere." DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/11.

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The electrodynamics of the Earth's low-latitude ionosphere is dependent on the ionospheric conductivity and the thermospheric neutral density, temperature, and winds present. This two-part study focused on the gravity wave seeding mechanism of equatorial plasma depletions in the ionosphere and the associated equatorial spread F, as well as the differences between a two-dimensional flux tube integrated electrodynamics model and a three-dimensional model for the same time period. The gravity wave seeding study was based on a parameterization of a gravity wave perturbation using a background empirical thermosphere and a physics-based ionosphere for the case of 12 UT on 26 September 2002. The electrodynamics study utilized a two-dimensional flux tube integrated model in center dipole coordinates, which is derived in this work. This case study examined the relative influence of the zonal wind, meridional wind, vertical wind, temperature, and density perturbations of the gravity wave. It further looked at the angle of the wave front to the field line flux tube, the most influential height of the perturbation, and the difference between planar and thunderstorm source gravity waves with cylindrical symmetry. The results indicate that, of the five perturbation components studied, the zonal wind is the most important mechanism to seed the Rayleigh-Taylor instability needed to develop plasma plumes. It also shows that the bottomside of the F-region is the most important region to perturb, but a substantial E-region influence is also seen. Furthermore, a wave front with a small angle from the field line is necessary, but the shape of the wave front is not critical in the gravity wave is well developed before nightfall. Preliminary results from the three-dimensional model indicate that the equipotential field line assumption of the two-dimensional model is not valid below 100 km and possibly higher. Future work with this model should attempt to examine more of the differences with the two-dimensional model in the electric fields and currents produced as well as with the plasma drifts that lead to plume development.

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Sazykin, Stanislav. "Theoretical Studies of Penetration of Magnetospheric Electric Fields to the Ionosphere." DigitalCommons@USU, 2000. https://digitalcommons.usu.edu/etd/7152.

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Ionospheric disturbance electric fields of magnetospheric origin play an important role in determining the global morphology and dynamics of the ionosphere of the Earth. In this work, we present a number of numerical simulations of the transient electric fields in the middle and inner magnetosphere and the ionosphere equatorward of the auroral zone caused by idealized changes in the magnetospheric driving parameters. For these studies, we u se the Rice Convection Model (RCM), a large computer code of the magnetosphere-ionosphere coupling which consistently computes the electric fields, currents, and plasma densities in the magnetosphere and the electric field and currents in the ionosphere in the quasi-static slow-flow approximation. We made substantial upgrades to the code, which include a module computing realistic solar EDY-produced ionospheric conductances and a new potential solver. Our upgraded version of the RCM also includes a time - varying magnetospheric magnetic field and a self-consistently estimated auroral zone. We first discuss numerical problems encountered in modeling electrodynamics of convection with a time-varying magnetic field, realistic ionospheric conductances, and a self-consistent auroral zone, and our solutions to those difficulties. We then present a number of "computer experiments" with the new version of the RCM with idealized changes in the magnetospheric parameters such as sudden changes in the cross polar cap potential drop, magnetic field reconfiguration corresponding to the overall changes in the high-latitude convection, as well as rotations of the electric field on the polar cap boundary. Prompt penetration ionospheric electric fields simulated with the upgraded RCM are shown to be consistent with the previous simulations. The new simulations and their results are discussed in the context of (1) possible contribution to the variability of the ionospheric electric fields, and (2) role of time-varying magnetic field on the characteristic lifetimes of prompt penetration electric fields at subauroral, middle, and low latitudes.

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Wilder, Frederick Durand. "The Non-Linear Electrodynamic Coupling Between the Solar Wind, Magnetosphere and Ionosphere." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/26586.

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The polar electric potential imposed on the ionosphere by coupling between the earthâ s magnetosphere and the solar wind has been shown to have a non-linear response to the interplanetary electric field (IEF). This dissertation presents an empirical study of this polar cap potential saturation phenomenon. First, the saturation of the reverse convection potential under northward is demonstrated using bin-averaged SuperDARN data. Then, the saturation reverse convection potential is shown to saturate at a higher value at higher solar wind plasma beta. The reverse convection flow velocity is then compared with cross-polar cap flows under southward IMF under summer, winter and equinox conditions. It is demonstrated that the reverse convection flow exhibits the opposite seasonal behavior to cross polar cap flow under southward IMF. Then, an interhemispheric case study is performed to provide an explanation for the seasonal behavior of the reverse convection potential. It is found using DMSP particle precipitation data that the reverse convection cells in the winter circulate at least partially on closed field lines. Finally, SuperDARN and DMSP data are merged to provide polar cap potential measurements for a statistical study of polar cap potential saturation under southward IMF. It is found that the extent of polar cap potential saturation increases with increasing Alfvenic Mach number, and has no significant relation to Alfven wing transmission coefficient or solar wind dynamic pressure.
Ph. D.

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Fathi, Pantea. "Ion-neutral reactions of C2H2N+ with hydrocarbons : relevant to Titan’s ionosphere." Licentiate thesis, Stockholms universitet, Fysikum, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-122952.

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To provide some insights on the formation of long-chain carbon-nitrogen bearing ions in Titan’s atmosphere, laboratory measurements of ion-neutral reactions were conducted and results are presented in the following licentiate thesis. The product ions of the C2H2N+ reaction with saturated and unsaturated neutral hydrocarbons have been studied using guided ion beam mass spectrometer (GIB-MS). The data have been used to infer the product ion signal intensity dependences on pressure and collision energies to obtain information on the reactions contributing to these signals. Theoretical calculations have been carried out to interpret these measurements and to elucidate the reaction pathways leading to the observed product ions. This study provides understanding on the formation of long-chain carbon-nitrogen bearing ions through exothermic and barrierless ion-neutral reactions which are of interest as possible formation routes to heavy positive ions detected in Titan’s atmosphere by Cassini’s ion neutral mass spectrometer (INMS).

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Hui, Debrup. "Altitudinal Variability of Quiet-time Plasma Drifts in the Equatorial Ionosphere." DigitalCommons@USU, 2015. https://digitalcommons.usu.edu/etd/4536.

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The plasma drifts or electric fields and their structures in the ionosphere affect the accuracy of the present-day space-based systems. For the first time, we have used ionospheric plasma drift data from Jicamarca radar measurements to study the climatology of altitudinal variations of vertical and zonal plasma drifts in low latitudes during daytime. We used data from 1998 to 2014 to derive these climatological values in bimonthly bins from 150 km to 600 km. For the vertical plasma drifts, we observed the drifts increasing with altitudes in the morning and slowly changing to drifts decreasing with altitude in the afternoon hours. The drifts change mostly linearly from E- to F-region altitudes except in the morning hours of May-June when the gradients are very small. The zonal drifts show a highly nonlinear increase in the westward drifts at the lower altitudes and then increase slowly at the higher altitudes. We see a break in the slopes at lower altitudes during the morning hours of March-April and May-June. The E-region zonal drifts, unlike vertical drifts, show a very large variability compared to F-region drifts. We also explored the altitudinal profiles of vertical drifts during late afternoon and evening hours when the electrodynamic properties in the ionosphere change rapidly. For the first time using drifts up to 2000 km, we have shown the drifts increase and decrease below and above the F-region peak before becoming height independent. These structures arise to satisfy the curl-free condition of electric fields in low latitudes. The altitudinal gradients of vertical drifts are balanced by a time derivative of the zonal drifts to satisfy the curl-free condition of electric fields. We have shown how these structures evolve with local time around the dusk sector and change with solar flux. During solar minimum, the peak region can go well below 200 km. The present-day electric field models do not incorporate these gradients, particularly in the evening sectors when they change very rapidly. Very often their results do not match with the observations. Including these gradients along with proper magnetic field models will improve the model results and accuracy of our navigation, communication, and positioning systems.

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Davila, Ricardo Cruz. "A Study of Magnetic Activity Effects on the Thermospheric Winds in the Low Latitude Ionosphere." DigitalCommons@USU, 1994. https://digitalcommons.usu.edu/etd/6808.

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The purpose of this thesis is to examine the effects of magnetic activity on the low latitude F-region thermospheric winds. The F-region (120-1600 km) is a partially ionized medium where O+ and O are the major ion and neutral species, respectively. The thermospheric winds at these altitudes are driven primarily by pressure gradient forces resulting from the solar heating during the day and cooling at night. For this study, we use measured Fabry-Perot Interferometer (FPD winds at Arequipa (16.5°S, 71.5°W) and measured FPI and Incoherent Scatter Radar (ISR) winds at Arecibo (18.6°N, 66.8°W). Previous wind studies at Arequipa and Arecibo concentrated on the climatological wind patterns highlighting solar cycle effects and seasonal variations; however, these studies did not address the effects of magnetically disturbed conditions on the seasonal averaged winds. To properly investigate storm time effects on the neutral winds, we must first investigate solar cycle effects on the seasonal averages during magnetically quiet (Kp < 3) conditions. This study will include a detailed analysis of solar cycle effects on the seasonally averaged winds for Arequipa and Arecibo. In addition to the wind averages, we used cubic splines to fit the average wind profiles and to provide better comparisons with modeled results. We also performed a study on the airglow emission heights using both Jicamarca and Arecibo electron density profiles. This established the height which we will use to compare our experimental data with the model winds. To investigate magnetic activity effects on the FPI and ISR winds, we used three magnetic activity cases which cover all storm time scenarios. These magnetic activity cases are the extended quiet, short-term disturbed, and extended disturbed conditions. The first case, the extended quiet, is the condition where the previous and short term magnetic activity is quiet (12 hour Kp ≤ 3 and the Kp ≤ 3). The short-term disturbed case is defined for the condition where the previous magnetic activity is quiet (12 hour Kp ≤ 3) and then becomes disturbed (Kp ≤ 3). Last, we considered the case where previous and short-term magnetic activity are disturbed (12 hour Kp ≤ 3 and the Kp ≤ 3). Our last objective is to use our data to validate the predictions from the Thermosphere/Ionosphere General Circulation model (TIGCM93) and the Horizontal Wind Model (HWM93). This study should further our understanding of the physical processes which produce the low latitude quiet and disturbed winds. The TIGCM93 is a first principal model and the HWM93 is an empirical model based on ground-based and satellite measurements. The main advantage of using the TIGCM93 is the ease of studying the dynamics of ionospheric phenomena by simply changing various model inputs, while the HWM93 allows us a comparison between our experimental wind data sets with the established climatology of the winds over Arequipa and Arecibo.

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Lannér, Viktor. "Incoherent Scattering of Twisted Radar Beams from the Ionosphere." Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-325768.

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In the search for natural orbital angular momentum (OAM) effects, some of the first incoherent scatter experiments with twisted radar beams during aurora were conducted at Poker Flat Incoherent Scatter Radar (PFISR), Alaska, USA, in October 2012. Experimental data of scatter from beam configurations with opposite twists were investigated. By the use of hypothesis tests in combination with Monte Carlo simulations together with traditional estimations of the mean and confidence interval, asymmetries between scatter of radar beams with opposite twists were identified for an integration time of at least 30 minutes. Asymmetries were detected in the internal radar noise too, but not necessarily with the same signs as for the asymmetries from the ionospheric signals. The asymmetries identified could be due to amplified noise for signals coming from intense aurora or perhaps the rectangular-shaped antenna array used at PFISR. These two possible causes need to be ruled out before suggesting that the asymmetries identified are an outcome of OAM effects present in the ionosphere.

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Mannix, Christopher Robert. "Measuring and modelling the impact of the ionosphere on space based synthetic aperture radars." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6869/.

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Synthetic aperture radar (SAR) is a technique widely used in applications that require all-weather imaging. The ionosphere affects the operation of these radars, with those operating at L-band (1-2 GHz) and below at risk of being seriously compromised by the ionosphere. A method of using Global Positioning System (GPS) data to synthesize the impact of the ionosphere on SAR systems has been presented. The technique was used to assess the viability of using a signal phase correction derived from a reference location in a SAR image to correct ionospheric effects across the image. A dataset of SAR images and GPS measurements collected simultaneously on Ascension Island were used to test two techniques for deriving ionospheric strength of turbulence (C\(_k\)L) from SAR images – one using measurements of trihedral corner reflectors (CR) and the other measurements of natural clutter. The CR C\(_k\)L values showed a correlation of 0.69 with GPS estimates of C\(_k\)L, whilst the clutter measurements showed a correlation of up to 0.91 with the CR values. Finally, a study of using the effects of intensity scintillation on SAR images to measure the S\(_4\) index was performed. The study was not able to reproduce previous results, but produced significant practical conclusions.

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Matalqah, Mohammed [Verfasser], Wolfgang [Gutachter] Stahl, and Erwin [Gutachter] Sedlmayr. "Development and experiments with the Ionospektroskop and a comparison with selected ionospheric parameters / Mohammed Matalqah ; Gutachter: Wolfgang Stahl, Erwin Sedlmayr." Berlin : Technische Universität Berlin, 2015. http://d-nb.info/1156274834/34.

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Ågren, Karin. "On the Formation and Structure of the Ionosphere of Titan." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-172148.

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We present results on the ionospheric structure around Titan observed during numerous deep (<1000 km) flybys by the Cassini spacecraft. Our results are based on measurements by the radio and plasma wave science instrument, in particular the Langmuir probe. In addition, data from the magnetometer and electron spectrometer have contributed. The ionosphere of Titan is created when the atmosphere of the moon becomes ionised. There are several mechanisms that contribute to this, the most important of which are considered to be photoionisation by EUV from the Sun with associated photoelectron ionisation, and particle impact ionisation by electrons and ions from Saturn’s corotating magnetosphere. We investigate the influence of the solar zenith angle on the electron number density at the ionospheric peak. The results show on average four times more plasma on the dayside compared to the nightside, with typical densities of 2500 – 3500 cm-3 and 400 – 1000 cm-3, respectively. In a complementary study, we make a case study of a nightside flyby and show that the altitude structure of the deep ionosphere is reproducible by a simple electron impact ionisation model. Taken together, this leads to the conclusion that solar photons are the main ionisation source of the dayside ionosphere. However, magnetospheric particle precipitation also contributes and can explain the electron densities seen on the nightside. As Titan does not exhibit any large intrinsic magnetic field, the fact that it is embedded in the magnetosphere of Saturn means that the Kronian field drapes around the moon and gives rise to an induced magnetosphere. We show that there are currents of the order of 10 – 100 nA m-2 flowing in the ionosphere of the moon. Associated with the currents are perpendicular electric fields ranging from 0.5 to 3 µV m-1. Finally, we investigate measurements obtained during T70, the deepest Titan flyby performed to date. We show that there is a substantial amount of negative ions present below an altitude of 900 km. This confirms previous result by the electron spectrometer, showing negative ions at higher altitudes in Titan’s ionosphere.

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Shebanits, Oleg. "Determination of Ion Number Density from Langmuir Probe Measurements in the Ionosphere of Titan." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132567.

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Saturn’s largest moon, Titan, presents a very interesting subject for study because of its atmosphere’s complex organic chemistry. Processes taking place there might shed some light on the origins of organic compounds on Earth in its early days. The international spacecraft Cassini-Huygens was launched to Saturn in 1997 for a detailed study of the gas giant and its moons, specifically Titan. The Swedish Institute of Space Physics in Uppsala has manufactured the Langmuir probe instrument for the Cassini spacecraft now orbiting Saturn, and is responsible for its operation and data analysis. This project concerns the analysis of Titan’s ionosphere measurements from this instrument, from all “deep” flybys of the moon (<1400km altitude) in the period October 2004 - April 2010. Using the Langmuir Probe analysis tools, the ion flux is derived by compensating for the atmospheric EUV extinction (that varies with the photoelectron current from the probe). The photoelectron current emitted from the probe also gives an artifact in the data that for this project needs to be deducted before analysis. This factor has already been modeled, while the extinction of Titan’s atmosphere has only been taken into account on event basis (not systematically). The EUV corrected ion flux data is then used to derive the ion number density in Titan’s atmosphere, by setting up an average ion mass altitude distribution (using the Ion Neutral Mass Spectrometer results for comparison) and deriving the spacecraft speed along the Cassini spacecraft trajectory through Titan’s ionosphere. The ion number density results proved to correlate very well with the theoretical ionospheric profiles on the day side of Titan (see graphical representation in the Results section). On the night side, a perturbation of the ion flux data was discovered by comparison with Ion Neutral Mass Spectrometer data, supporting earlier measurements of negative ions reported by Coates et al 2009. The project was carried out at the Swedish Institute of Space Physics (Institutet för Rymdfysik, IRF) in Uppsala.
Saturnus största måne Titan är ett väldigt intressant forskningsobjekt på grund av dess atmosfärs komplexa organiska kemi. Processer som pågår i Titans täta atmosfär kan hjälpa oss att förstå ursprunget till organiska föreningar på Jorden i dess unga ålder. Den internationella rymdsonden Cassini-Huygens blev uppskjuten mot Saturnus 1997, för att i detalj undersöka gasjätten och dess månar, speciellt Titan. Institutet för Rymdfysik (IRF) i Uppsala är ansvariga för operation och dataanalys av Langmuirsonden ombord Cassini som ligger i omloppsbanan kring Saturnus sedan 2004. Detta projekt omfattar analys av Langmuirsondens mätningar av Titans jonosfär från alla ”djupa” förbiflygningar av månen under perioden oktober 2004 – april 2010. Med hjälp av analysverktygen för Langmuirsonden, tas jonflödet fram efter kompensation för den atmosfäriska EUV extinktionen som ger upphov till fotoelektronströmmen från sonden. Fotoelektronströmmen som utsänds från proben ger en artefakt i data och måste (för detta projekt) korrigeras före analysen. Denna faktor är redan bestämd, men extinktionen av Titans atmosfär har endast korrigerats för i enstaka fall. Det korrigerade datat används för att få fram jondensiteten i Titans atmosfär genom att en genomsnittlig jonmass/höjd fördelning antas (jämförs med resultat från INMS-instrumentet) och kombineras med den beräknade hastighet som Cassini håller i banan genom jonosfären. Projektet utfördes vid Institutet för Rymdfysik, Uppsala.

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Hammarsten, Michael. "A statistical study of incoherent scatter plasma line enhancements during the International Polar Year ’07-’08 in Svalbard." Thesis, Luleå tekniska universitet, Rymdteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60158.

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There was a large radar campaign during 2007 and 2008, the International Polar Year (IPY),and at that time the EISCAT Svalbard Radar was operated and measured the ionosphere continuouslyat most times. This report presents statistical results from an electron enhancementpoint of view. Until now there has been some research into the field and results based on theions in the ionosphere, and the enhancements we refer to as Naturally enhanced ion acousticlines (NEIALs). Plasma line data from May 2007 to February 2008 has been analysed inorder to find and classify enhancements as NEIALs have been classified but with respect tothe electron distribution instead of the ion distribution. A method of detection was developedin order to differentiate the enhancements from the background with a relation between theminimum and maximum power of each measured dump. Results show that there is a largedifference between the downshifted plasma lines and the upshifted plasma lines, both has arange distribution peak at 180 km and the upshifted plasma line has another peak at 230 kmwhich the downshifted plasma line does not. The occurrence rate of the enhancements was1.64 % for the downshifted plasma line and 4.69 % for the upshifted plasma line. Threedifferent types of enhancements are classified using the variance distribution for the peakfrequency of that detected dump, Single, Profile, and Diffuse. The Single enhancements havea bit different spectral, range, and time of day distributions than of the Profile and Diffusedistributions. The Diffuse classifications are mostly wrong classifications and aliasing and itis very similar to Profile enhancements as seen by its distribution.

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Sullivan, Joanna Mary. "Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/65694/.

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Optical measurements of small-scale auroral structures are here combined with spectrographic data in order to study the relationship between auroral morphology and the energy characteristics of the precipitating population. It is shown that rayed auroral structures are associated with precipitating electrons with a broad range in energy, including a significant population at energies of around 100 eV. In comparison, observations of fast-moving auroral arc elements are shown to result from precipitation energy distributions peaking at several keV with a very small low-energy component. This spectrographic information feeds directly into the study of naturally enhanced ion-acoustic lines, or NEIALs, which have been observed by incoherent-scatter radars at high-latitudes. It has been proposed that these radar enhancements result from natural plasma instability, causing the generation of ion-acoustic waves through the decay of unstable Langmuir waves, themselves driven by low-energy electron streams. Using multi-spectral imaging in combination with radar observations, a direct link is shown between ion-acoustic wave enhancements and precipitating electrons at 100 eV energies. Wave enhancements at the radar wavevector which are three orders of magnitude above the thermal level, are successfully modelled using the Langmuir decay interpretation for the time of observation. Electron populations with a broad energy range are thought to result from Alfv´enic acceleration mechanisms, which play an important role in the generation of smallscale auroral structure. With the recent advancements in multi-spectral imaging, it is now possible to resolve auroral filaments of a few hundred meters width. An interferometric imaging capability is under development for the EISCAT Svalbard Radar system, in order to resolve scattering wave structures on similar spatial scales within the radar beam. A technique is demonstrated by which to calibrate the position of coherent echoes detected by the interferometer. This will be of great use in clarifying the role of precipitating electron beams in turbulent plasma processes on small scales.

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Krämer, Eva. "Bow shock current closure to Earth's polar ionosphere - A statistical study using AMPERE and OMNI data." Thesis, Umeå universitet, Institutionen för fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-184853.

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The bow shock current is hypothesized to connect to the Earth's magnetosphere on open field lines and to contribute as a field aligned current to the polar ionospheric currents. In order to investigate this, two years of AMPERE data are used to compute the average region 1 currents, and average currents within the polar cap boundary, under different interplanetary magnetic field (IMF) clock angles and IMF magnitudes. The average currents are studied for stable IMF conditions. Therefore data is selected if the IMF By and Bz components do not change sign in a 30 minutes time interval to ensure sufficiently stable conditions. In addition, the AMPERE current maps are renormalized and recentered such that the region 1 currents have a fixed extent. These averaged current maps are then used to discuss the sources of the currents in the polar cap and their possible connection to the bow shock current. The currents in the polar ionosphere are found to generally agree with the statistical convection pattern. For a strong east-west IMF there are some discrepancies for the region 0 currents which indicates a possible bow shock current closure. Furthermore there are currents in the polar cap of the northern hemisphere for a strong southward IMF, which however do not have the expected polarity for bow shock current closure. Therefore they must have another, but unknown, origin. In addition, SuperDARN data is used to confirm that currents on the dayside of the polar cap and polwards of the Region 1 currents are on open field lines for a strong eastward or westward IMF. Further investigations are needed to confirm the bow shock closure in the ionosphere. Additional investigations are needed to identify the source of the polar cap currents for a strong southward IMF.

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Shebanits, Oleg. "Titan’s ionosphere and dust : – as seen by a space weather station." Doctoral thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-329490.

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Titan, the largest moon of Saturn, is the only known moon with a fully developed nitrogen-rich atmosphere, its ionosphere is detectable as high as 2200 km above its surface and hosts complex organic chemistry. Titan’s atmosphere and ionosphere has striking similarities to current theories of these regions around Earth 3.5 billion years ago. The Cassini spacecraft has been in orbit around Saturn since 2004 and carries a wide range of instruments for investigating Titan’s ionosphere, among them the Langmuir probe, a “space weather station”, manufactured and operated by the Swedish Institute of Space Physics, Uppsala. This thesis presents studies of positive ions, negative ions and negatively charged dust grains (also called aerosols) in Titan’s ionosphere using the in-situ measurements by the Cassini Langmuir probe, supplemented by the data from particle mass spectrometers. One of the main results is the detection of significant (up to about 4000 cm-3) charge densities of heavy (up to about 13800 amu/charge) negative ions and dust grains in Titan’s ionosphere below 1400 km altitude. The dust is found to be the main negative charge carrier below about 1100 km on the nightside/terminator ionosphere, forming a dusty plasma (also called “ion-ion” plasma). A new analysis method is developed using a combination of simultaneous observations by multiple instruments for a case study of four flybys of Titan’s ionosphere, further constraining the ionospheric plasma charge densities. This allows to predict a dusty plasma in the dayside ionosphere below 900 km altitude (thus declaring it a global phenomenon), as well as to empirically estimate the average charge of the negative ions and dust grains to between -2.5 and -1.5 elementary charges. The complete Cassini dataset spans just above 13 years, allowing to study effects of the solar activity on Titan’s ionosphere. From solar minimum to maximum, the increase in the solar EUV flux increases the densities by a factor of ~2 in the dayside ionosphere and, surprisingly, decreases by a factor of ~3-4 in the nightside ionosphere. The latter is proposed to be an effect of the ionospheric photochemistry modified by higher solar EUV flux. Modelling photoionization also reveals an EUV trend (as well as solar zenith angle and corotational plasma ram dependencies) in the loss rate coefficient.

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De, Pascuale Sebastian. "The plasmasphere extension of Earth's atmosphere: a perspective from the Van Allen probes." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6405.

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Earth's plasmasphere persists as an extension of the ionosphere into space. The toroidal region of plasma is shaped by electric and magnetic forces in the terrestrial magnetosphere. As a dense population of cold plasma, the plasmasphere interacts with particles in the hot ring current and energetic radiation belts. Evolution of plasmaspheric density under the driving influence of the solar wind crosses many physical scales. Convective erosion during geomagnetic storms occurs on the order of hours, reducing the size of the plasmasphere by forming an abrupt plasmapause density gradient that varies in radial and diurnal location. The history of geomagntic activity determines the presence of morphological structures as small as notches and as large as plumes. Plasma of atmospheric origin is carried sunward by convection through drainage plumes towards the magnetopause where it can diminish the effectiveness of magnetic reconnection. Long-lived plumes are sustained by a higher rate of refilling than typically observed during plasmasphere recovery from geomagnetic disturbances. The response of the plasmasphere, then, is an integral part of the feedback cycle between the magnetosphere and ionosphere in the exchange of energy and particles. This thesis aims to address three questions concerning the nature of the plasmasphere through the development of empirical and physics-based models under recent observations provided by the Van Allen Probes (RBSP-A & -B). First, what is the distribution of density content in the plasmasphere? For a two year period with full MLT coverage by RBSP, the upper-hybrid resonance frequency in plasma wave spectra is used to identify sudden changes consistent with the plasmapause feature and to calculate the magnetic equatorial electron density. Plasmapause encounter radial locations for both spacecraft are correlated with a geomagnetic activity index showing significant scatter around a linear fit. On average, the predicted plasmapause location does account for the separation between the saturated plasmasphere and the depleted plasmatrough. A density threshold corresponding to the plasmapause boundary is used to sort RBSP measurements into these two classified plasma regions. Model profiles are developed for each region and compared to the results from previous missions. The importance of solar wind properties in regulating the severity of plasmasphere erosion is demonstrated. Second, how does the plasmapause form and vary with geomagnetic activity? The two-dimensional plasmasphere density model, RAM-CPL, is employed to simulate two geomagnetic storms observed by the RBSP spacecraft. Inner-magnetospheric convection is parameterized by the Kp-index and solar wind properties. The performance of RAM-CPL is evaluated by the correspondence between virtual and actual plasmapause encounters. Overall, RAM-CPL achieved good agreement with RBSP observations of the plasmapause to within 0.5 L and measurements of electron density to within one order of magnetude inside the plasmasphere. An empirical model of ring current-ionosphere feedback was included to account for asymmetric erosion, but did not contribute significantly in the MLT sectors of interest when compared to electric field measurements. The difference in background activity level during quiet conditions between the two convection parameterizations was found to lead to 1 L difference in plasmapause location for each simulation trial. Solar wind driven simulations produce sharper and deeper erosion of the plasmapause at the onset of a geomagnetic storm, but also allow for larger recovery of the plasmasphere when compared to Kp-index driven simulations. Third, what is the role of the ionosphere in sustaining the plasmasphere? Four geomagnetic events are observed by RBSP in opposing MLT sectors to exhibit undisturbed plasmasphere refilling following significant erosion of the plasmapause. RAM-CPL simulations of the strongest storm parameterized by solar wind properties shows the full evolution of plasmasphere density from the narrowing of a sunward plume at the onset of erosion, that begins to corotate into a duskside bulge as activity diminishes, to the outward recovery of the plasmapause over several days. A piecewise empirical model of plasmasphere refilling is composed from profiles of equatorial electron density and the observed correlation between the Kp-index and plasmapause location. The RAM-CPL timescale of refilling mediates the increase in density from plasmatrough to plasmasphere levels matching RBSP measurements during the quiet period after the storm. Density observations of the other geomagnetic events are consistent with reports of a two-stage refilling process.

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Dissertations / Theses on the topic 'Ionospheric physics'

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