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1
De, Deuge Maria. "Optical observations of gravity waves in the high-latitude thermosphere /." Title page, abstract and contents only, 1990. http://web4.library.adelaide.edu.au/theses/09SM/09smd485.pdf.
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2
Negale, Michael. "Investigating the Climatology of Mesospheric and Thermospheric Gravity Waves at High Northern Latitudes." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/6937.
Повний текст джерелаАнотація:
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.
3
Beldon, Charlotte. "VHF radar studies of mesosphere and thermosphere." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.512294.
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4
Halliday, Oliver John. "Atmospheric convection and gravity waves." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/22414/.
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5
Eckermann, Stephen D. "Atmospheric gravity waves : obsevations and theory /." Title page, table of contents and abstract only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09phe1862.pdf.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1990.Copies of author's previously published articles inserted. Includes bibliographical references (leaves 261-288).
6
Gibson-Wilde, Dorothy E. "Atmospheric gravity waves in constituent distributions /." Title page, abstract and contents only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phg4516.pdf.
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7
Yan, Xiuping. "Satellite observations of atmospheric gravity waves." Thesis, University of Leicester, 2010. http://hdl.handle.net/2381/7979.
Повний текст джерелаАнотація:
A new methodology of gravity wave observations has been developed for the HIgh Resolution Dynamics Limb Sounder (HIRDLS). Individual vertical profiles of gravity-wave temperature perturbations that were determined by subtraction of a dynamic 31 day background field and a 1000 km along-track temperature filter were Fourier transformed to estimate the gravity-wave temperature amplitudes and vertical wavelengths (~2 – 16 km) in the stratosphere. Gravity wave activity is highly variable with season and can be highly orographically dependent, especially in the winter extratropics. Investigations of episodes of enhanced gravity waves over the southern Andes, the Cascade Range and the Rockies in the winter months of 2006 indicate that orographic gravity waves propagate downwind from the mountains. By way of contrast, observations of gravity waves around the Himalayas show a strong relationship with the cyclones in that region. HIRDLS observations over the southern Andes during July-September 2006 were compared to the orographic gravity-wave parameterization scheme in the UK Met Office Unified Model®. The results indicate that the observed waves are likely to be orographically excited. The observed wave activity extends large distances (a few thousand kilometres) downwind of the mountains and over the ocean. This downstream wave activity is not represented by the parameterization scheme similar to many schemes, which assume that the waves propagate vertically above the mountains only. Gravity waves over the tropics and tropical South America were compared with the AVHRR Outgoing Longwave Radiation (OLR), TRMM convective rainfall and ECMWF winds for convective sources. The comparisons show that the peak gravity wave temperature amplitudes correspond closely to the OLR ≤ 200 W/m ², in good agreement with the mesoscale cyclones and are above the updrifts, which indicate deep convective generation of the gravity waves. These waves show vertical propagation with higher-frequency and ~ 7.5 km vertical wavelengths in the lower stratosphere.
8
Watkins, Christopher Lloyd. "Atmospheric gravity waves on giant planets." Thesis, Queen Mary, University of London, 2012. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8683.
Повний текст джерелаАнотація:
Internal gravity waves are a common feature of stratified fluids. They facilitate transport of momentum and energy – thus influencing the evolution of the fluid. There is a large body of research addressing the behaviour of gravity waves in the terrestrial atmosphere. This thesis builds and extends the research to giant planets – in particular to close-in extrasolar giant planets and the solar system giant planet, Jupiter. Because the atmospheres of close-in giant planets are expected to be strongly stratified, knowledge of the behaviour of gravity waves in such atmospheres is especially important. Close-in giant planets are thought to have their rotations and orbital period 1:1 synchronised, i.e., they are “tidally locked”. Such planets do not exist in the Solar System. However, many are known from observations of extrasolar systems. Their synchronisation means that they have a permanent day-side and night-side leading to interesting atmospheric dynamics. Modelling these circulations with global circulation models (GCMs) and comparing these models with observations is an active research area. However, many GCMs filter some or all gravity waves removing their effects. This thesis addresses this by explicitly looking at the effects gravity waves can have on the circulation. It is shown that gravity waves provide a mechanism for accelerating, decelerating, and heating the flow. Further, horizontally propagating gravity waves are shown to provide a possible means for coupling the day- and night-sides of tidally locked planets. As well as affecting the dynamics of the atmosphere, gravity wave behaviour is affected by the dynamics of the atmosphere. Therefore, gravity waves can be used to explore atmospheric properties. In this thesis gravity waves observed in Jupiter’s atmosphere, by the Galileo probe, are used to identify features of Jupiter’s atmosphere such as the altitude of the turbopause and the vertical profile of zonal winds at the probe entry site.
9
Powell, Jonathan. "Stochastic modelling of atmospheric gravity waves." Thesis, University of Edinburgh, 2004. http://hdl.handle.net/1842/15652.
Повний текст джерелаАнотація:
Internal gravity waves have an important effect on the large-scale circulation of the middle atmosphere, which is conditioned by the deposition of momentum due to their breaking. The propagation of gravity waves is influenced by the properties of the background wind. This thesis examines this influence: it uses stochastic techniques to study gravity wave propagation through a randomly fluctuating background wind. It begins by describing general features of the atmosphere and gravity wave propagation. The basic equations of fluid flow within the atmosphere are derived. These lead via the WKB approximation to a dispersion relation and to ray equations for gravity wave propagation. Propagation equations, such as the ray equations and dispersion relation, are derived in a general context. The notion of a Wigner matrix is introduced, and this is used to derive transport equations for a general Hamiltonian system that may contain random components. These results generalise earlier works by Ryzhik and Guo and Wang. Atmospheric gravity waves are described as an application and the equations derived via the WKB approximation are recovered. The major factor influencing the distribution of gravity waves is the spread of their wavenumber as they propagate through a wind. This is described by the Doppler spreading model. A one-dimensional system with a randomly fluctuating background wind, dependent on altitude only, is considered. The model revisits that of Souprayen by using an Ornstein-Uhlenbeck process to describe the wind. Simple equations for the energy spectrum induced by gravity waves are derived. Analytic forms of the energy spectrum are given and features of the spectrum such as the m-3 spectral tail (where m is the vertical wavenumber), central wavenumber and scaling with the Brunt-Väisälä frequently are found to be consistent with observations. An equation for the force on the background, induced by gravity wave breaking is also derived.
10
Jacobi, Christoph, Friederike Liilienthal, T. Schmidt, and la Torre A. de. "Modeling the Southern Hemisphere winter circulation using realistic zonal mean gravity wave information in the lower atmosphere." Universität Leipzig, 2016. https://ul.qucosa.de/id/qucosa%3A16703.
Повний текст джерелаАнотація:
A mechanistic global circulation model is used to simulate the mesospheric and lower thermospheric circulation during austral winter. The model includes a gravity wave (GW) parameterization that is initiated by prescribed GW parameters in the troposphere. In standard configuration, these waves are described by a simple distribution with large amplitudes in the winter hemisphere and small ones in summer. Here we replace this distribution by a more realistic one, which is based on observations of potential GW energy using GPS radio occultations, but which is normalized to the same global mean amplitude. The model experiment shows that this new gravity wave distribution leads to weaker zonal winds in the mesosphere, a downward shift of the meridional poleward mesospheric wind jet, enhanced downwelling in the mid-to-high-latitude winter mesosphere and warming of the polar stratopause.Ein globales mechanistisches Zirkulationsmodell wird verwendet um die Dynamik der Mesosphäre und unteren Thermosphäre im Südwinter zu simulieren. Das Modell beinhaltet eine Schwerewellenparametrisierung die durch eine vorgeschriebene Schwerewellenverteilung in der oberen Troposphäre angetrieben wird. In der Standardkonfiguration besteht diese aus einer einfachen zonal gemittelten Verteilung mit größeren Amplituden im Winter als im Sommer. Wir ersetzen diese Verteilung durch eine realistischere, die auf der beobachteten globalen Verteilung der potentiellen Energie von Schwerewellen basiert und auf die gleiche global gemittelte Amplitude normiert wird. Das Modellexperiment zeigt, dass die neue Schwerewellenverteilung zu schwächeren zonalen Winden in der Mesosphäre, einer Verschiebung des meridionalen Jets nach unten, verstärkten Abwinden in der Mesosphäre mittlerer und höherer Breiten im Winter, und einer Erwärmung der polaren Winterstratopause führt.
11
Abu, Samah Azizan B. Hj. "Observations of gravity waves at atmospheric fronts." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276732.
Повний текст джерела
12
Zink, Florian. "Gravity waves and turbulence in the lower atmosphere /." Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09phz778.pdf.
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13
Krishnamurthy, Venkataramanaiah. "The slow manifold and the persisting gravity waves." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/54304.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985.Microfiche copy available in Archives and Science.
Bibliography: leaves 144-146.
by Venkataramanaiah Krishnamurthy.
Ph.D.
14
Wang, Shuguang. "Gravity waves from vortex dipoles and jets." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2875.
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15
黃元華 and Yuen-wah Wong. "A study of atomospheric gravity waves in East Asia by investigation oftheir effects upon the ionosphere." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1991. http://hub.hku.hk/bib/B31232875.
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16
Wong, Yuen-wah. "A study of atomospheric gravity waves in East Asia by investigation of their effects upon the ionosphere /." [Hong Kong : University of Hong Kong], 1991. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13148424.
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17
Jacobi, Christoph, and Manfred Ern. "Gravity waves and vertical shear of zonal wind in the summer mesosphere-lower thermosphere." Universität Leipzig, 2013. https://ul.qucosa.de/id/qucosa%3A16408.
Повний текст джерелаАнотація:
Gravity wave amplitudes and momentum fluxes derived from SABER temperature measurements are analysed together with Collm meteor radar zonal winds. The momentum flux (MF) divergence derived from the SABER temperatures shows a maximum that is found at greater altitudes during solar minimum than during solar maximum. Therefore, the zonal mean wind and wind shear profiles are shifted upwards
then, leading to a modulation of the otherwise negative correlation between solar cycle and mesosphere/lower thermosphere winds.Amplituden von Schwerewellen und zugehörigen Impulsflüsse werden zusammen mit Windmessungen des Meteorradars Collm analysiert. Die Impulsflussdivergenz, abgeleitet aus SABER-Temperaturprofilen, hat ein Maximum welches im solaren Minimum nach oben verschoben ist. Dadurch werden auch die Vertikalprofile des Zonalwindes und der Windscherung nach oben verschoben, wodurch die ansonsten negative Sonnenfleckenzyklusabhängigkeit des zonalen Windes in der Mesosphäre/unteren Thermosphäre im solaren Minimum umgekehrt wird.
18
Wu, Lichuan. "Introducing Surface Gravity Waves into Earth System Models." Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-314760.
Повний текст джерелаАнотація:
Surface gravity waves alter the turbulence of the bottom atmosphere and the upper ocean. Accordingly, they can affect momentum flux, heat fluxes, gas exchange and atmospheric mixing. However, in most state-of-the-art Earth System Models (ESMs), surface wave influences are not fully considered or even included. Here, applying surface wave influences into ESMs is investigated from different aspects. Tuning parameterisations for including instantaneous wave influences has difficulties to capture wave influences. Increasing the horizontal resolution of models intensifies storm simulations for both atmosphere-wave coupled (considering the influence of instantaneous wave-induced stress) and stand-alone atmospheric models. However, coupled models are more sensitive to the horizontal resolution than stand-alone atmospheric models. Under high winds, wave states have a big impact on the sea spray generation. Introducing a wave-state-dependent sea spray generation function and Charnock coefficient into a wind stress parameterisation improves the model performance concerning wind speed (intensifies storms). Adding sea spray impact on heat fluxes improves the simulation results of air temperature. Adding sea spray impact both on the wind stress and heat fluxes results in better model performance on wind speed and air temperature while compared to adding only one wave influence. Swell impact on atmospheric turbulence closure schemes should be taken into account through three terms: the atmospheric mixing length scale, the swell-induced momentum flux at the surface, and the profile of swell-induced momentum flux. Introducing the swell impact on the three terms into turbulence closure schemes shows a better performance than introducing only one of the influences. Considering all surface wave impacts on the upper-ocean turbulence (wave breaking, Stokes drift interaction with the Coriolis force, Langmuir circulation, and stirring by non-breaking waves), rather than just one effect, significantly improves model performance. The non-breaking-wave-induced mixing and Langmuir circulation are the most important terms when considering the impact of waves on upper-ocean mixing. Accurate climate simulations from ESMs are very important references for social and biological systems to adapt the climate change. Comparing simulation results with measurements shows that adding surface wave influences improves model performance. Thus, an accurate description of all important wave impact processes should be correctly represented in ESMs, which are important tools to describe climate and weather. Reducing the uncertainties of simulation results from ESMs through introducing surface gravity wave influences is necessary.
19
Phillips, A. "Dynamics of the Antarctic mesosphere and lower thermosphere /." Title page, contents and abstract only, 1989. http://web4.library.adelaide.edu.au/theses/09PH/09php5583.pdf.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of Adelaide, Mawson Institute for Antarctic Research, 1990.Copies of author's previously published articles inserted. Includes bibliographical references (leaves 219-226).
20
Lange, Martin, and Christoph Jacobi. "Analysis of gravity waves from radio occultation measurements." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-217072.
Повний текст джерелаАнотація:
In the height range 10–30 km atmospheric gravity waves lead to periodic perturbations of the background temperature field in the order of 2-3 K, that are resolved in temperature profiles derived from radio occultation measurements. Due to the spherical symmetry assumption in the retrieval algorithm and the low horizontal resolution of the measurement damping in the amplitude and phase shift of the waves occurs leading to remarkable errors in the retrieved temperatures. The influence of the geometric wave parameters and the measurement geometry on plane gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investigated with a 2D model ranging ±1000 km around the tangent point and 10-50 km in height. The investigation shows, that with radio occultation measurements more than 90 % of the simulated waves can be resolved and more than 50% with amplitudes above 90%. But the geometrical parameters cannot be identified, since one signal can be attributed to different combinations of wave parameters and view angle. Even short waves with horizontal wavelengths below 200 km can be derived correctly in amplitude and phase if the vertical tilt is small or the view angle of the receiver satellite is in direction of the wave crestsAtmosphärische Schwerewellen führen im Höhenbereich 10-30 km zu periodischen Störungendes Hintergrundtemperaturfeldes in der Größenordnung von 2-3 K, die in Temperaturprofilen aus Radiookkultationsmessungen aufgelöst werden. Aufgrund der sphärischen Symmetrieannahme im Retrievalverfahren und durch die niedrige horizontale Auflösung des Messverfahrens werden Phasenverschiebungen und Dämpfung der Amplitude verursacht, die zu beachtlichen Fehlern bei den abgeleiteten Temperaturen führen. Der Einfluss der geometrischen Wellenparameter und der Messgeometrie auf ebene Schwerewellen im Bereich 100-1000 km horizontale und 1-10 km vertikale Wellenlänge wird untersucht mit einem 2D-Modell, dass sich auf ein Gebiet von ±1000 km um den Tangentenpunkt und von 10-50 km in der Höhe erstreckt. Die Untersuchung zeigt, dass mit Radiookkultationsmessungen mehr als 90% der simulierten Wellen aufgelöst werden und mehr als 50% mit Amplituden oberhalb von 90% der ursprünglichen. Die geometrischen Parameter können jedoch nicht aus Einzelmessungen abgeleitet werden, da ein Signal zu verschiedenen Kombinationen von Wellenparametern und Sichtwinkel zugeordnet werden kann. Auch relativ kurze Wellen mit horizontalen Wellenlängen unterhalb von 200 km können korrekt in der Amplitude und Phase aufgelöst werden, falls die Neigung des Wellenvektors gegen die vertikale gering ist oder der Sichtwinkel des Empfängersatelliten in Richtung der Wellenberge ist
21
Wright, Corwin. "Detection of stratospheric gravity waves using HIRDLS data." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:ef4aa65d-67c1-43ac-90de-1b5bda6c8230.
Повний текст джерелаАнотація:
Temperature measurements from the HIRDLS instrument on NASA's Aura satellite are analysed for the purposes of detecting and studying internal gravity waves in the terrestrial stratosphere. A detailed description of the methodology used to obtain these data is given, including details of the instrument correction processes used to compensate for errors introduced by a blockage in the instrument optics. A short precis of the relevant theoretical considerations related to atmospheric gravity waves is then outlined. The thesis then discusses the use of the Stockwell (time-frequency) Transform for the detection of gravity waves in HIRDLS data, together with a detailed analysis of the limitations of this method, and the results obtained from this analysis are analysed by comparison to other instruments and climatology. It is concluded that the Stockwell Transform is an appropriate method for the analysis of the HIRDLS dataset, and that the results obtained are robust. We apply these results to analyse stratospheric gravity wave activity during the 2005/06 Arctic sudden stratospheric warming. By comparing the magnitude and form of the gravity wave results to local wind data obtained from ECMWF operational analyses, we conclude that a heavily deformed stratopause observed during this period by other instruments was most probably due to wind-based filtering of the gravity wave spectrum during this period.
22
Ménard, Richard. "Saturation d'ondes de gravité et balance non-linéaire." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65947.
Повний текст джерела
23
Jacob, P. G. "Manifestations of atmospheric gravity waves in the airglow at 95 km /." Title page, contents and abstract only, 1985. http://web4.library.adelaide.edu.au/theses/09PH/09phj15.pdf.
Повний текст джерела
24
Medvedev, Alexander S., Hiromu Nakagawa, Chris Mockel, Erdal Yiğit, Takeshi Kuroda, Paul Hartogh, Kaori Terada, et al. "Comparison of the Martian thermospheric density and temperature from IUVS/MAVEN data and general circulation modeling." AMER GEOPHYSICAL UNION, 2016. http://hdl.handle.net/10150/614739.
Повний текст джерелаАнотація:
Newly released Imaging Ultraviolet Spectrograph/Mars Atmosphere and Volatile EvolutioN (IUVS/MAVEN) measurements of CO2 density in the Martian thermosphere have been used for comparison with the predictions of the Max Planck Institute Martian General Circulation Model (MPI-MGCM). The simulations reproduced (within one standard deviation) the available zonal mean density and derived temperature above 130 km. The MGCM replicated the observed dominant zonal wave number 3 nonmigrating tide and demonstrated that it represents a nonmoving imprint of the topography in the thermosphere. The comparison shows a great dependence of the simulated density and temperature to the prescribed solar flux, atomic oxygen abundances and gravity wave effects, with the former two being especially important in the thermosphere above 130 km and the latter playing a significant role both in the mesosphere and thermosphere.
25
Lange, Martin, and Christoph Jacobi. "Analysis of gravity waves from radio occultation measurements." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 26 = Meteorologische Arbeiten aus Leipzig ; 7 (2002), S. 101-108, 2002. https://ul.qucosa.de/id/qucosa%3A15225.
Повний текст джерелаАнотація:
In the height range 10–30 km atmospheric gravity waves lead to periodic perturbations of the background temperature field in the order of 2-3 K, that are resolved in temperature profiles derived from radio occultation measurements. Due to the spherical symmetry assumption in
the retrieval algorithm and the low horizontal resolution of the measurement damping in the amplitude and phase shift of the waves occurs leading to remarkable errors in the retrieved temperatures. The influence of the geometric wave parameters and the measurement geometry on plane gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investigated with a 2D model ranging ±1000 km around the tangent point and 10-50 km in height. The investigation shows, that with radio occultation measurements more than 90 % of the simulated waves can be resolved and more than 50% with amplitudes above 90%. But the geometrical parameters cannot be identified, since one signal can be attributed to different combinations of wave parameters and view angle. Even short waves with horizontal wavelengths below 200 km can be derived correctly in amplitude and phase if the vertical tilt is small or the view angle of the receiver satellite is in direction of the wave crests.Atmosphärische Schwerewellen führen im Höhenbereich 10-30 km zu periodischen Störungendes Hintergrundtemperaturfeldes in der Größenordnung von 2-3 K, die in Temperaturprofilen aus Radiookkultationsmessungen aufgelöst werden. Aufgrund der sphärischen Symmetrieannahme im Retrievalverfahren und durch die niedrige horizontale Auflösung des Messverfahrens werden Phasenverschiebungen und Dämpfung der Amplitude verursacht, die zu beachtlichen Fehlern bei den abgeleiteten Temperaturen führen. Der Einfluss der geometrischen Wellenparameter und der Messgeometrie auf ebene Schwerewellen im Bereich 100-1000 km horizontale und 1-10 km vertikale Wellenlänge wird untersucht mit einem 2D-Modell, dass sich auf ein Gebiet von ±1000 km um den Tangentenpunkt und von 10-50 km in der Höhe erstreckt. Die Untersuchung zeigt, dass mit Radiookkultationsmessungen mehr als 90% der simulierten Wellen aufgelöst werden und mehr als 50% mit Amplituden oberhalb von 90% der ursprünglichen. Die geometrischen Parameter können jedoch nicht aus Einzelmessungen abgeleitet werden, da ein Signal zu verschiedenen Kombinationen von Wellenparametern und Sichtwinkel zugeordnet werden kann. Auch relativ kurze Wellen mit horizontalen Wellenlängen unterhalb von 200 km können korrekt in der Amplitude und Phase aufgelöst werden, falls die Neigung des Wellenvektors gegen die vertikale gering ist oder der Sichtwinkel des Empfängersatelliten in Richtung der Wellenberge ist.
26
Rabbitt, Michael John. "The effect of internal gravity waves on large scale atmospheric flows." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328943.
Повний текст джерела
27
Dasananda, Songkot. "Capability of MLS instruments in the observations of atmospheric gravity waves." Thesis, University of Edinburgh, 2001. http://hdl.handle.net/1842/13569.
Повний текст джерелаАнотація:
We found that the temperature response functions of both UARS MLS and EOS MLS instrument for waves with typical vertical wavelength of 1-20 km are sharply peaked at certain horizontal wavelengths but their amplitudes are always less than ~60% in case of UARS MLS and 80% for EOS MLS. The responses at vertical wavelength of 10-20 km, in particular, are considerably high to waves with horizontal wavelength of scales ~200-500 km which are propagating away from the satellite position with respect to the line-of-sight direction. These are waves that should be most detectable with both of the MLS instruments in the real observations in terms of the amplitude response. The variance response functions in the 32-measurement limb-tracking mode of UARS MLS and 150-measurment limb-tracking mode of EOS MLS have also peaked at some certain horizontal wavelengths for waves of vertical wavelength 1-20 km but their amplitudes never exceeds ~20% for UARS MLS and 30% for EOS MLS. Like the temperature response, the variance responses at vertical wavelengths of 10-20 km are maximum to waves with horizontal wavelength of scales ~200-500 km which are propagating away from the satellite position with respect to the LOS. In the contrary, gravity waves with vertical wavelength of few kilometers are unlikely to be much visible to the MLS instruments due to the very low response regardless of their horizontal wavelength scales or directions of propagation.
28
Geldenhuis, Andre. "The Atmospheric Gravity Wave Transfer Function above Scott Base." Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/3698.
Повний текст джерелаАнотація:
Gravity waves have a significant dynamic effect in the mesosphere. In particular, they drive the mesospheric circulation and are the reason that the summer polar mesosphere is cooler than the winter polar mesosphere. This thesis examines whether the effects of gravity waves are largely determined by filtering effects which allow only gravity waves with certain properties to propagate into the atmosphere. The filtering of gravity waves above Scott Base, Antarctica is examined using a radiosonde derived gravity wave source function, an MF-radar derived mesospheric gravity wave climatology, and a model derived filtering function. Least squares fitting of the source function and filtering function to the observed mesospheric gravity wave climatology allows us to determine which gravity wave phase velocities and propagation direction are likely to be present in the mesosphere and the relative importance of filtering and sources in this region. It is concluded the blocking of eastward gravity waves is important in winter and westward waves in summer.
29
Khanyile, Bhekumuzi Sfundo. "An investigation of the atmospheric wave dynamics in the polar region using ground based instruments." Thesis, University of Fort Hare, 2011. http://hdl.handle.net/10353/447.
Повний текст джерелаАнотація:
Abstract This study presents the characteristics of small-scale gravity waves in the mesosphere region as derived from the imaging riometer data at high altitude (~90 km) over SANAE (72˚S, 3˚W). Wavelet analysis and FFT (Fast Fourier transform) have been applied to extract short period gravity wave parameters for the year 2000. The horizontal wavelength, phase speed and observed period of gravity waves are typically 10-100 km, 5-60 m.s-1 and 3-60 minutes, respectively. The horizontal propagation direction is north-eastward throughout the year. This could probably be due to selective filtering by the zonal wind. Zonal and meridional winds in the region of the MLT (mesosphere and lower thermosphere) have been measured using HF radars at high latitudes in the southern hemisphere. Data from January 2000 to December 2003 have been used with the aim of investigating the characteristics of planetary wave activity at ~90 km. For SANAE and Halley stations, 2-, 5-, 10-, 16- and 20-day planetary waves are dominant in summer and winter. The results show the seasonal variations of the mean winds, which are caused by the internal variability of the quasi stationary planetary waves. Planetary wave coupling processes between UKMO assimilated and mesospheric data have also been investigated. The cross wavelet results show a strong coupling during winter months. The results suggest that planetary waves are generated at lower atmospheric heights and propagate upwards into mesospheric heights. However, not all observed disturbances in mesospheric heights can be explained by the propagation of planetary waves from lower atmospheric heights.
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Woithe, Jonathan Mark. "Optical studies of the mesospheric region." Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09phw847.pdf.
Повний текст джерелаАнотація:
Includes copies of articles co-authored by the author during the preparation of this thesis. Includes bibliographical references (leaves 233-245). A three-field photometer was employed at the University of Adelaide's Buckland Park field site to collect optical observations of the 557.7nm OI and 730nm OH airglow emissions on an almost continuous basis since May 1995 to May 2000, with observations made whenever the moon was not up.
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Pugmire, Jonathan Rich. "Mesospheric Gravity Wave Climatology and Variances Over the Andes Mountains." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/7387.
Повний текст джерелаАнотація:
Look up! Travelling over your head in the air are waves. They are present all the time in the atmosphere all over the Earth. Now imagine throwing a small rock in a pond and watching the ripples spread out around it. The same thing happens in the atmosphere except the rock is a thunderstorm, the wind blowing over a mountain, or another disturbance. As the wave (known as a gravity wave) travels upwards the thinning air allows the wave to grow larger and larger. Eventually the gravity wave gets too large – and like waves on the beach – it crashes causing whitewater or turbulence. If you are in the shallow water when the ocean wave crashes or breaks, you would feel the energy and momentum from the wave as it pushes or even knocks you over. In the atmosphere, when waves break they transfer their energy and momentum to the background wind changing its speed and even direction. This affects the circulation of the atmosphere.
These atmospheric waves are not generally visible to the naked eye but by using special instruments we can observe their effects on the wind, temperature, density, and pressure of the atmosphere. This dissertation discusses the use of a specialized camera to study gravity waves as they travel through layers of the atmosphere 50 miles above the Andes Mountains and change the temperature. First, we introduce the layers of the atmosphere, the techniques used for observing these waves, and the mathematical theory and properties of these gravity waves. We then discuss the camera, its properties, and its unique feature of acquiring temperatures in the middle layer of the atmosphere. We introduce the observatory high in the Andes Mountains and why it was selected. We will look at the nightly fluctuations (or willy-nillyness) and long-term trends from August 2009 until December 2017. We compare measurements from the camera with similar measurements obtained from a satellite taken at the same altitude and measurements from the same camera when it was used at a different location, over Hawaii. Next, we measure the amount of change in the temperature and compare it to a nearby location on the other side of the Andes Mountains. Finally, we look for a specific type of gravity wave caused by wind blowing over the mountains called a mountain wave and perform statistics of those observed events over a period of six years.
By understanding the changes in atmospheric properties caused by gravity waves we can learn more about their possible sources. By knowing their sources, we can better understand how much energy is being transported in the atmosphere, which in turn helps with better weather and climate models.
Even now –all of this is going on over your head!
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Matsumura, Mitsuru. "Numerical Studies on Acoustic Resonance between the Ground and the Lower Thermosphere and the Associated Gravity Waves." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157788.
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Cai, Xuguang. "The Investigation of Gravity Waves in the Mesosphere / Lower Thermosphere and Their Effect on Sporadic Sodium Layer." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/6891.
Повний текст джерелаАнотація:
Gravity waves in the atmosphere are the waves with gravity and buoyancy force as the restoring forces. Gravity waves will significantly impact the Mesosphere Lower / Thermosphere (MLT), and the breaking of gravity waves is the key factor to cause the cool summer and warm winter in the Mesopause region. Therefore, it is important for us to investigate gravity waves. In this dissertation, we mainly use USU Na lidar data to explore gravity waves in the MLT. The exploration is made up of two projects. One is the investigation of gravity wave breaking and the associated dynamic instability by USU Na Lidar and Advanced Mesosphere Temperature Mapper (AMTM). Another is the calculation of gravity wave temperature perturbations and potential energy density by least-squares fitting based on the data from the full-diurnal cycle observation of Na lidar. The sporadic sodium layer is the sharp increase of Na density in a small vertical range (several kilometers) above the Na main layer in the MLT. The formation of the sporadic sodium layer above 100 km remains unknown until now. Here we will investigate the mechanism of the generation of sporadic sodium layer using numeric modeling, including the effect of tide and gravity wave on the variation of Na density.
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Rønning, Snorre Stavik. "Optimizing an Infrared Camera for Observing Atmospheric Gravity Waves from a CubeSat Platform." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-20915.
Повний текст джерелаАнотація:
The NTNU Test Satellite (NUTS) is a double CubeSat deigned by master students at NTNU. The goal of the project is to image atmospheric gravity waves in the OH airglow layer. This thesis explores the theory behind gravity waves and discuss the design of an infrared camera as a payload onboard. Different requirement based on scientific and mechanical limitations are presented. Based on this a suitable infrared camera is presented.
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Karabanov, Oleksandr G. "Seasonal and spatial structure of the gravity waves and vertical winds over the central USA derived from the NOAA Profiler Network data." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-06262006-145120/.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2007.Dr. Paul Steffes, Committee Member ; Dr. Irina Sokolik, Committee Member ; Dr. Robert Black, Committee Member ; Dr. Robert G. Roper, Committee Chair ; Dr. Derek Cunnold, Committee Member.
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Beres, Jadwiga H. "Gravity waves generated by tropical convection : generation mechanisms and implications for global circulation models /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/10048.
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Wilford, Graeme W. "The numerical solution of atmospheric models describing the interactions of inertio-gravity and Rossby waves." Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/843580/.
Повний текст джерелаАнотація:
This thesis documents three years of work involved in the numerical solution of atmospheric wave models. Derivation of these models is established whilst introducing the basic physical laws governing fluid motion. Numerical techniques axe investigated with particular reference to the solution of parabolic and elliptic partial differential equations. Parallel computer systems are discussed and basic concepts introduced with the emphasis placed on distributed virtual parallelism. The role of inertio-gravity waves under the influence of cyclonic Rossby waves is investigated with respect to the production of atmospheric turbulence. Results from evolving numerical systems bound by various conditions are presented. It is discovered that the wave interaction is not the sole cause of atmospheric blocking as was previously thought. The use of a loosely coupled parallel environment is discussed in relation to potential increases in speed or size of the numerical model. A solution technique is modified to enable such an implementation. The full nonlinear Barre de Saint-Venant model of fluid motion is solved using a combination of finite difference and spectral methods. Preliminary results are presented and further avenues of investigation are discussed.
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Norton, Andrew David. "Analysis of Ionospheric Data Sets to Identify Periodic Signatures Matching Atmospheric Planetary Waves." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/101791.
Повний текст джерелаАнотація:
Atmospheric planetary waves play a role in introducing variability to the low-latitude ionosphere. To better understand this coupling, this study investigates times when oscillations seen in both atmospheric planetary waves and ionospheric data-sets have similar periodicity. The planetary wave data-set used are temperature observations made by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). These highlight periods during which 2-Day westward propagating wave-number 3 waves are evident in the mesosphere and lower thermosphere. The ionospheric data-set is Total Electron Content (TEC), which is used to identify periods during which the ionosphere appears to respond to the planetary waves. Data from KP and F10.7 indices are used to determine events that may be of external origin. A 17-year time-span from 2002 to 2018 is used for this analysis so that both times of solar minimum and maximum can be studied. To extract the periods of this collection of data a Morlet Wavelet analysis is used, along with thresholding to indicate events when similar periods are seen in each data-set. Trends are then determined, which can lead to verification of previous assumptions and new discoveries.Master of Science
The thermosphere and ionosphere are impacted by many sources. The sun and the magnetosphere externally impact this system. Planetary waves, which originate in the lower atmosphere, internally impact this system. This interaction leads to periodic signatures in the ionosphere that reflect periodic signatures seen in the lower atmosphere, the sun and the magnetosphere. This study identifies these times of similar oscillations in the neutral atmosphere, the ionosphere, and the sun, in order to characterize these interactions. Events are cataloged through wavelet analysis and thresholding techniques. Using a time-span of 17 years, trends are identified using histograms and percentages. From these trends, the characteristics of this coupling can be concluded. This study is meant to confirm the theory and provide new insights that will hopefully lead to further investigation through modeling. The goal of this study is to gain a better understanding of the role that planetary waves have on the interaction of the atmosphere and the ionosphere.
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Samtleben, Nadja, and Ch Jacobi. "Impact of intermittent gravity wave activity on the middle atmospheric circulation during boreal winter." Universität Leipzig, 2018. https://ul.qucosa.de/id/qucosa%3A31793.
Повний текст джерелаАнотація:
Simulations of the circulation in the middle atmosphere during northern winter performed with a nonlinear, mechanistic, global circulation model show that the upper mesospheric jet is greatly overestimated and also the position with respect to latitude and height does not correspond to observations. Apart from that also the winter wind reversal in the mesopause region, evoked by breaking gravity waves (GWs), is located too low around 80km, but is observed to be usually around 100 km. These discrepancies are planned to be eliminated by modifying the distribution of GW amplitudes driving the GW parameterization. This distribution is currently based on potential GW energy data derived from GPS radio occultation measurements and has to be replaced by a distribution based on momentum flux estimates applying
midfrequency approximation. The results show a weaker mesospheric jet more realistically tilted towards lower latitudes with height. Also the meridional circulation extending from the summer to the winter pole decelerates and less GWs are propagating into the mesosphere. By additionally varying the GW amplitudes in magnitude and time, the wind reversal is shifted upwards and the mesospheric jet is slowed down.Simulationen der Zirkulation der mittleren Atmosphäre während des nordhemisphärischen Winters unter Verwendung eines nicht-linearen mechanistischen globalen Zirkulationsmodells ergaben beim Vergleich mit Messungen, dass der simulierte, mesosphärische Jet stark überschätzt wird und dessen Position von den Beobachtungen abweicht. Die in der Mesopausenregion einsetzende Windumkehr, hervorgerufen durch brechende Schwerewellen, befindet sich in etwa 80 km anstatt in 100 km. Diese Diskrepanzen sollen eliminiert werden. Hierfür wird die Verteilung der Schwerewellenamplituden, die die Schwerewellenparametrisierung innerhalb des Modells antreibt, am oberen Rand der Troposphäre modifiziert. Diese basiert derzeit auf global beobachteten, zonal gemittelten Daten der potentiellen Energie von Schwerewellen abgeleitet aus GPS Radiookkultationsmessungen und soll durch eine auf Impulsflüssen basierende Verteilung ersetzt werden. Das Modellexperiment zeigt, dass der mesosphärische Jet mit der Höhe in Richtung niedriger Breiten geneigt ist und abgebremst wird. Zudem schwächt die Meridionalzirkulation vom Sommer- zum Winterpol leicht ab und weniger Schwerewellen dringen bis in die Mesosphäre vor. Zusätzlich wird durch zeitliche und unterschiedlich starke Variation der Schwerewellenamplitude die Windumkehr verlagert und der mesosphärische Jet abgebremst.
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Wu, Lichuan. "Impact of surface gravity waves on air-sea fluxes and upper-ocean mixing." Licentiate thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-276466.
Повний текст джерелаАнотація:
Surface gravity waves play a vital role in the air-sea interaction. They can alter the turbulence ofthe bottom atmospheric layer as well as the upper-ocean layer. Accordingly, they can affect themomentum flux, heat fluxes, as well as the upper-ocean mixing. In most numerical models, waveinfluences are not considered or not fully considered. The wave influences on the atmosphereand the ocean are important for weather forecasts and climate studies. Here, different aspects ofwave impact on the atmosphere and the ocean are introduced into numerical models.In the first study, a wave-state-dependent sea spray generation function and Charnock co-efficient were applied to a wind stress parameterization under high wind speeds. The newlyproposed wind stress parameterization and a sea spray influenced heat flux parameterizationwere applied to an atmosphere-wave coupled model to study their influence on the simulationof mid-latitude storms. The new wind stress parameterization reduces wind speed simulationerror during high wind speed ranges and intensifies the storms. Adding the sea spray impacton heat fluxes improves the model performance concerning the air temperature. Adding the seaspray impact both on the wind stress and heat fluxes results in best model performance in allexperiments for wind speed, and air temperature.In the second study, the influence of surface waves on upper-ocean mixing was parameter-ized into a 1D k − ε ocean turbulence model though four processes (wave breaking, Stokes driftinteraction with the Coriolis force, Langmuir circulation, and stirring by non-breaking waves)based mainly on existing investigations. Considering all the effects of surface gravity waves,rather than just one effect, significantly improves model performance. The non-breaking-wave-induced mixing and Langmuir turbulence are the most important terms when considering theimpact of waves on upper-ocean mixing. Sensitivity experiments demonstrate that vertical pro-files of the Stokes drift calculated from 2D wave spectrum improve the model performancesignificantly compared with other methods of calculating the vertical profiles of the Stokes drift.Introducing the wave influences in modelling systems, the results verified against measure-ments. Concluding from these studies for the further model development, the wave influencesshould be taken into account to improve the model performance.
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Heckl, Mareike [Verfasser], and Markus [Akademischer Betreuer] Rapp. "Using MTP measurements to characterise atmospheric gravity waves in the tropopause region / Mareike Kenntner ; Betreuer: Markus Rapp." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2018. http://d-nb.info/1161341846/34.
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Yu, Yonghui. "MODEL STUDIES OF TIME-DEPENDENT DUCTING FOR HIGH-FREQUENCY GRAVITY WAVES AND ASSOCIATED AIRGLOW RESPONSES IN THE UPPER ATMOSPHER." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3623.
Повний текст джерелаАнотація:
This doctoral dissertation has mainly concentrated on modeling studies of shorter period acoustic-gravity waves propagating in the upper atmosphere. Several cases have been investigated in the literature, which are focusing on the propagation characteristics of high-frequency gravity wave packets. The dissertation consists of five main divisions of which each has its own significance to be addressed, and these five chapters are also bridged in order with each other to present a theme about gravity wave ducting dynamics, energetics, and airglows. The first chapter is served as an introduction of the general topic about atmospheric acoustic-gravity waves. Some of the historical backgrounds are provided as an interesting refreshment and also as a motivation reasoning this scientific research for decades. A new 2-D, time-dependent, and nonlinear model is introduced in the second chapter (the AGE-TIP model, acronymically named atmospheric gravity waves for the Earth plus tides and planetary waves). The model is developed during this entire doctoral study and has carried out almost all research results in this dissertation. The third chapter is a model application for shorter period gravity waves ducted in a thermally stratified atmosphere. In spite of mean winds the thermal ducting occurs because ducted waves are fairly common occurrences in airglow observations. One-dimensional Fourier analysis is applied to identify the ducted wave modes that reside within multiple thermal ducts. Besides, the vertical energy flux and the wave kinetic energy density are derived as wave diagnostic variables to better understand the time-resolved vertical transport of wave energy in the presence of multiple thermal ductings. The fourth chapter is also a model application for shorter period gravity waves, but it instead addresses the propagation of high-frequency gravity waves in the presence of mean background wind shears. The wind structure acts as a significant directional filter to the wave spectra and hence causes noticeable azimuthal variations at higher altitudes. In addition to the spectral analysis applied previously the wave action has been used to interpret the energy coupling between the waves and the mean flow among some atmospheric regions, where the waves are suspected to extract energy from the mean flow at some altitudes and release it to other altitudes. The fifth chapter is a concrete and substantial step connecting theoretical studies and realistic observations through nonlinearly coupling wave dynamic model with airglow chemical reactions. Simulated O (1S) (557.7 nm) airglow images are provided so that they can be compared with observational airglow images. These simulated airglow brightness variations response accordingly with minor species density fluctuations, which are due to propagating and ducting nonlinear gravity waves within related airglow layers. The thermal and wind structures plus the seasonal and geographical variabilities could significantly influence the observed airglow images. By control modeling studies the simulations can be used to collate with concurrent observed data, so that the incoherencies among them could be very useful to discover unknown physical processes behind the observed wave scenes.Ph.D.
Department of Physics
Sciences
Physics PhD
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Frissell, Nathaniel A. "Ionospheric Disturbances: Midlatitude Pi2 Magnetospheric ULF Pulsations and Medium Scale Traveling Ionospheric Disturbances." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/74976.
Повний текст джерелаАнотація:
The ionosphere is an electrically charged atmospheric region which is coupled to the sun, the magnetosphere, and the neutral atmosphere. The ionospheric state can significantly impact technological systems, especially those which utilize radio frequency energy. By studying ionospheric disturbances, it is possible to gain a deeper understanding of not only the ionosphere itself, but also the natural and technological systems it is coupled to. This dissertation research utilizes high frequency (HF) radio remote sensing techniques to study three distinct types of ionospheric disturbances. First, ground magnetometers and a new mid latitude SuperDARN HF radar at Blackstone, Virginia are used to observe magnetospheric Pi2 ultra low frequency (ULF) pulsations in the vicinity of the plasmapause. Prior to these pulsations, two Earthward moving fast plasma flows were detected by spacecraft in the magnetotail. Signatures of inner magnetospheric compression observed by the Blackstone radar provide conclusive evidence that the plasma flow bursts directly generated the ground Pi2 signature via a compressional wave. This mechanism had previously been hypothesized, but never confirmed. Next, ten SuperDARN radars in the North American Sector are used to investigate the sources and characteristics of atmospheric gravity waves (AGW) associated medium scale traveling ionospheric disturbances (MSTIDs) at both midlatitudes and high latitudes. Consistent with prior studies, the climatological MSTID population in both latitudinal regions was found to peak in the fall and winter and have a dominant equatorward propagation direction. Prior studies suggested these MSTIDs were caused by mechanisms associated with auroral and space weather activity; however, it is shown here that the AE and Sym-H indices are poorly correlated with MSTID observations. A new, multi-week timescale of MSTID activity is reported. This leads to the finding that MSTID occurrence is highly correlated with an index representative of polar vortex activity, possibly controlled by a filtering mechanism that is a function of stratospheric neutral wind direction. Finally, a case study of a radio blackout of transionospheric HF communications caused by an X2.9 class solar flare is presented. This study demonstrates the potential of a novel technique employing signals of opportunity and automated receiving networks voluntarily created by an international community of amateur radio operators.Ph. D.
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Noersomadi. "Characteristics of tropical tropopause and stratospheric gravity waves analyzed using high resolution temperature profiles from GNSS radio occultation." Kyoto University, 2019. http://hdl.handle.net/2433/242617.
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Kafle, Durga N. "Rayleigh-Lidar Observations of Mesospheric Gravity Wave Activity above Logan, Utah." DigitalCommons@USU, 2009. https://digitalcommons.usu.edu/etd/466.
Повний текст джерелаАнотація:
A Rayleigh-scatter lidar operated from Utah State University (41.7°N, 111.8°W) for a period spanning 11 years ― 1993 through 2004. Of the 900 nights observed, data on 150 extended to 90 km or above. They were the ones used in these studies related to atmospheric gravity waves (AGWs) between 45 and 90 km. This is the first study of AGWs with an extensive data set that spans the whole mesosphere. Using the temperature and temperature gradient profiles, we produced a climatology of the Brunt-Väisälä (buoyancy) angular frequency squared, N2 (rad/s)2. The minimum and maximum values of N2 vary between 2.2×10-4 (rad/s)2 and 9.0×10-4 (rad/s)2. The corresponding buoyancy periods vary between 7.0 and 3.5 minutes. While for long averages the atmosphere above Logan, Utah, is convectively stable, all-night and hourly profiles showed periods of convective instability (i.e., negative N2). The N2 values were often significantly different from values derived from the NRL-MSISe00 model atmosphere because of the effects of inversion layers and semiannual variability in the lidar data.
Relative density fluctuation profiles with 3-km altitude resolution and 1-hour temporal resolution showed the presence of monochromatic gravity waves on almost every night throughout the mesosphere. The prevalent values of vertical wavelength and vertical phase velocity were 12-16 km and 0.5-0.6 m/s, respectively. However, the latter has the significant seasonal variation. Using these two observed parameters, buoyancy periods, and the AGW dispersion relation, we derived the ranges of horizontal wavelength, phase velocity, and source distance. The prevalent values were 550-950 km, 32-35 m/s, and 2500-3500 km, respectively.
The potential energy per unit mass Ep showed great night-to-night variability, up to a factor of 20, at all heights. Ep grew at approximately the adiabatic rate below 55-65 km and above 75-80 km. Step function decreases in Ep imply that the AGWs in between gave up considerable energy to the background atmosphere. In addition, Ep varies seasonally. Below 70 km, it has a semiannual variation with a maximum in winter and minima in the equinoxes. At the highest altitudes it has an annual variation with a maximum in winter and a minimum in summer.
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Mohr, Matthias. "Mesoscale Simulations of Atmospheric Flow in Complex Terrain." Doctoral thesis, Uppsala University, Department of Earth Sciences, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3461.
Повний текст джерелаАнотація:
The MIUU mesoscale model was further developed, in order to include information on large-scale atmospheric fields from global or regional atmospheric climate- and weather-prediction models. For this purpose, a new lateral boundary condition was developed and implemented into the model. The new lateral boundary condition is a combination of two existing conditions, namely the flow relaxation scheme and the tendency modification scheme.
Tests indicated that an optimum lateral boundary configuration would be obtained with moderate to strong flow relaxation at higher levels, small flow relaxation at lower levels (within the atmospheric boundary layer), upstream advection at the outermost 4 grid points, and 6% horizontal grid stretching starting at a substantial distance from the lateral boundaries. The flow relaxation coefficients should be specified carefully, in order to minimize the reflection of all kinds of waves at the lateral boundaries.
The summer thermal low in the mean-sea-level pressure field over North America is traditionally analyzed over the northern end of the Gulf of California. The position of this low is influenced by the application of the so-called plateau correction in obtaining mean-sea-level pressure values from highly elevated stations in North America. A model study indicated that the low should be located approximately 450 km to the north and somewhat to the east of the above location.
A statistical comparison of model results from two mesoscale models against upper-air and surface measurements from several sites was carried out. Statistical methods, however, give only an insufficient picture of overall model performance. A comparison between predicted and measured tracer concentrations could be used to better evaluate the overall performance of different models.
Sound propagation in the atmosphere was predicted in a mountain valley using a mesoscale atmospheric model together with a sound propagation model. This suggests that forecasts of sound propagation should be possible in future.
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Mauritsen, Thorsten. "On the Arctic Boundary Layer : From Turbulence to Climate." Doctoral thesis, Stockholm : Department of Meteorology, Stockholm University, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-6585.
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Moss, Andrew. "Wave dynamics of the stratosphere and mesosphere." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707571.
Повний текст джерелаАнотація:
Gravity waves play a fundamental role in driving the large-scale circulation of the atmosphere. They are influenced both by the variation in their sources and the filtering effects of the winds they encounter as they ascend through the atmosphere. In this thesis we present new evidence that gravity waves play a key role in coupling the troposphere, stratosphere and mesosphere. In particular, we examine the connection of gravity waves to two important large-scale oscillations that occur in the atmosphere, namely the Madden-Julian Oscillation (MJO) in the troposphere and the Mesospheric Semi-Annual Oscillation (MSAO). We present the first ever demonstration that the MJO acts to modulate the global field of gravity waves ascending into the tropical stratosphere. We discover a significant correlation with the MJO zonal-wind anomalies and so suggest that the MJO modulates the stratospheric gravity-wave field through a critical-level wave-filtering mechanism. Strong evidence for this mechanism is provided by consideration of the winds encountered by ascending waves. The Ascension Island meteor radar is used for the first time to measure momentum fluxes over the Island. These measurements are then used to investigate the role of gravity-wave in driving a dramatic and anomalous wind event that was observed to occur during the first westward phase of the MSAO in 2002. Gravity waves are shown to play an important role in driving this event, but the observations presented here also suggest that the current theory of the mechanism describing these anomalous mesospheric wind events is not valid. Both of these studies highlight the critical importance of gravity waves to the dynamics of the atmosphere and highlight the need for further work to truly understand these waves, their processes and their variability.
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Emmoth, Frej-Eric. "Investigating UV nightglow within the framework of the JEM-EUSO Experiments." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-81340.
Повний текст джерелаАнотація:
The main mission of the JEM-EUSO (Extreme Universe Space Observatory) Collaborationis to observe Cosmic Rays. These high energy particles come from a variety of sources and bombard the Earth all the time. However, the higher the energy, the lower the flux, and particles with an energy above 1018eV (called Ultra High Energy Cosmic Rays or UHECRs) are so sparse that just a few might hit the atmosphere in a year. When CRs, and UHECRs, hit the atmosphere they cause what is called Extensive Air Showers, EAS, a cascade of secondary particles. This limits the effectiveness of ground based observatories, and that is where theJEM-EUSO Collaboration comes in. The goal is to measure UHECRs, by observing the fluorescence of the EAS from space. This way huge areas of the atmosphere can be covered and both galactic hemispheres can be studied. Since the JEM-EUSO instruments are telescopes measuring in the near UV range, a lot of other phenomena can be observed. One of these applications is UV nightglow. Airglow in general are lights in the sky which are emitted from the atmosphere itself, while nightglow is simply the nighttime airglow. There are many uses of airglow, and one of these is as a medium to observe atmospheric gravity waves. The aim of this thesis is to investigate how a space-based photon counting telescope, such as those of the JEM-EUSO Collaboration, can be used to measure disturbances in the terrestrial nightglow, to identify atmospheric gravity waves. To accomplish this, a theoretical basis for these interactions was explored and a simple scenario was built to explore the plausibility of measuring UV nightglow modulations. The aim was to see what variables would affect a measurement, and how important they were. Along side this, a calibration was conducted on one of the JEM-EUSO Collaborations instruments, the EUSO-TA (EUSO-Telescope Array). The goal in the end was to try and measurethe night sky, to complement the calculations. The investigation showed that the conditions during the measurement are very important to the measurement. This includes things like background intensity, nightglow activity, and magnitude/shape of the modulations. Of more importance though are the parameters which can be actively changed to improve the measurement, the most important of which is measurement time. It was concluded that a measurement of the nightglow modulation should be, under the right conditions, possible to do with a currently operating instrument, the Mini-EUSO, or similar instrument. The calibration of the EUSO-TA involved a series of repairs and tests, which highlighted some strengths and weaknesses of the instrument. However, the calibration itself produced few workable results that in the best case scenario reduced the focal surface to an unevenly biased 2-by-2 Elementary Cell square. Unfortunately this would not be sufficient to do proper measurements with, but the process did point out shortcomings with the then involved sensors, as well as some problematic aspects of the software operating the instrument.
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Lefèvre, Maxence. "Modélisation petite échelle de l'atmosphère de Vénus : convection et onde de gravité." Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS475.
Повний текст джерелаАнотація:
Les observations par les missions Venus Express et Akatsuki ont apporté une vision sans précédent de la turbulence de l’atmosphère de Vénus. L’extension verticale de la couche convective présente au coeur des nuages ainsi que sa variabilité avec la latitude et l’heure locale ont été étudiées, des ondes de gravité de petite échelle ont été observées au-dessus et en dessous de la convection. Les mesures par radio-occultation au sommet des nuages, vers 70 km d’altitude, ont rapporté une atmosphère stable, cependant des cellules ont été observées à ces altitudes aux basses latitudes à midi. Récemment, des ondes stationnaires de grande échelle en forme d’arc de cercle ont été observées au-dessus des plus grands reliefs dans les tropiques. Malgré toutes ces observations des questions demeurent. Pour répondre à ces questions nous avons décidé d’utiliser le modèle WRF pour pouvoir résoudre la turbulence de petite échelle. Le transfert radiatif du modèle de circulation générale (GCM) de Vénus du LMD a été couplé à ce modèle pour être le plus réaliste possible. Avec les simulations aux grands tourbillons, l’activité convective dans l’atmosphère de Vénus a pu être étudiée. Avec le mode mesoscale, les ondes de montagnes ont été étudiées et les plus grands reliefs des tropiques engendrent des ondes de montagnes de grande échelle similaires en amplitude et en extension latitudinale avec les observationsThe observations made by the mission Venus Express and Akatsuki gave unprecedented insight of the turbulence of the atmosphere of Venus. The vertical extension of the cloud convective layer as well as the variability with latitude and local time has been studied, small-scale gravity waves have been observed both above and below this convection layer. Despite a stable atmosphere, cellular features have been observed at the top of the cloud at low latitude at noon. Recently large stationnary bow-shape waves have been measured above the main topographic features at low latitude. Despite these observations, some questions remain. In order to address these questions we used the WRF dynamical core to be able to resolve smallscale turbulence. With Large-Eddy Simulations (LES), simulations were performed to resolve the convective activity of the could layer and the induced gravity waves. With the mesoscale mode, high-resolution topography produces stationary bow-shape waves with amplitude and latitudinal extension consistent with observations