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Artykuły w czasopismach na temat „Geomagnetically quiet”

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Data publikacji: 6 września 2023

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1

Unnikrishnan, K. "A comparative study on chaoticity of equatorial/low latitude ionosphere over Indian subcontinent during geomagnetically quiet and disturbed periods." Nonlinear Processes in Geophysics 17, no. 6 (2010): 765–76. http://dx.doi.org/10.5194/npg-17-765-2010.

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Abstract. In the present study, the latitudinal aspect of chaotic behaviour of ionosphere during quiet and storm periods are analyzed and compared by using GPS TEC time series measured at equatorial trough, crest and outside crest stations over Indian subcontinent, by employing the chaotic quantifiers like Lyapunov exponent (LE), correlation dimension (CD), entropy and nonlinear prediction error (NPE). It is observed that the values of LE are low for storm periods compared to those of quiet periods for all the stations considered here. The lowest value of LE is observed at the trough station, Agatti (2.38° N, Geomagnetically), and highest at crest station, Mumbai (10.09° N, Geomagnetically) for both quiet and storm periods. The values of correlation dimension computed for TEC time series are in the range 2.23–2.74 for quiet period, which indicate that equatorial ionosphere may be described with three variables during quiet period. But the crest station Mumbai shows a higher value of CD (3.373) during storm time, which asserts that four variables are necessary to describe the system during storm period. The values of non linear prediction error (NPE) are lower for Agatti (2.38° N, Geomagnetically) and Jodhpur (18.3° N, Geomagnetically), during storm period, compared to those of quiet period, mainly because of the predominance of non linear aspects during storm periods The surrogate data test is carried out and on the basis of the significance of difference of the original data and surrogates for various aspects, the surrogate data test rejects the null hypothesis that the time series of TEC during storm and quiet times represent a linear stochastic process. It is also observed that using state space model, detrended TEC can be predicted, which reasonably reproduces the observed data. Based on the values of the above quantifiers, the features of chaotic behaviour of equatorial trough crest and outside the crest regions of ionosphere during geomagnetically quiet and disturbed periods are briefly discussed.
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2

SHEN, Changshou, Minyun ZI, Jingsong WANG, and Jiyao XU. "Structure Distribution ofNmF2 during a Geomagnetically Quiet Period." Chinese Journal of Geophysics 46, no. 6 (2003): 1050–57. http://dx.doi.org/10.1002/cjg2.425.

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3

Kane, T. A., R. A. Makarevich, and J. C. Devlin. "HF radar observations of ionospheric backscatter during geomagnetically quiet periods." Annales Geophysicae 30, no. 1 (2012): 221–33. http://dx.doi.org/10.5194/angeo-30-221-2012.

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Abstract. The quiet-time coherent backscatter from the F-region observed by the Tasman International Geospace Environment Radar (TIGER) Bruny Island HF radar is analysed statistically in order to determine typical trends and controlling factors in the ionospheric echo occurrence. A comparison of the F-region peak density values from the IRI-2007 model and ionosonde measurements in the vicinity of the radar's footprint shows a very good agreement, particularly at subauroral and auroral latitudes, and model densities within the radar's footprint are used in the following analyses. The occurrence of F-region backscatter is shown to exhibit distinct diurnal, seasonal and solar cycle variations and these are compared with model trends in the F-region peak electron density and Pedersen conductance of the underlying ionosphere. The solar cycle effects in occurrence are demonstrated to be strong and more complex than a simple proportionality on a year-to-year basis. The diurnal and seasonal effects are strongly coupled to each other, with diurnal trends exhibiting a systematic gradual variation from month to month that can be explained when both electron density and conductance trends are considered. During the night, the echo occurrence is suggested to be controlled directly by the density conditions, with a direct proportionality observed between the occurrence and peak electron density. During the day, the echo occurrence appears to be controlled by both conductance and propagation conditions. It is shown that the range of echo occurrence values is smaller for larger conductances and that the electron density determines what value the echo occurrence takes in that range. These results suggest that the irregularity production rates are significantly reduced by the highly conducting E layer during the day while F-region density effects dominate during the night.
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4

Kitamura, N., K. Seki, Y. Nishimura, et al. "Photoelectron flows in the polar wind during geomagnetically quiet periods." Journal of Geophysical Research: Space Physics 117, A7 (2012): n/a. http://dx.doi.org/10.1029/2011ja017459.

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5

Maeda, Sawako, Hitoshi Fujiwara, and Satonori Nozawa. "Momentum balance of daysideEregion neutral winds during geomagnetically quiet summer days." Journal of Geophysical Research: Space Physics 104, A9 (1999): 19871–79. http://dx.doi.org/10.1029/1999ja900224.

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6

Liu, Z. ‐Y, Q. ‐G Zong, H. Zou, Y. F. Wang, and B. Wang. "Drifting Electron Holes Occurring During Geomagnetically Quiet Times: BD‐IES Observations." Journal of Geophysical Research: Space Physics 124, no. 11 (2019): 8695–706. http://dx.doi.org/10.1029/2019ja027194.

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7

Edward, Uluma, Ndinya Boniface, and Omondi George. "SCINDA-GPS derived TEC depletions and amplitude scintillations over Kisumu, Kenya during selected quiet and storm days of 2013 and 2014." International Journal of Advanced Astronomy 8, no. 1 (2020): 1. http://dx.doi.org/10.14419/ijaa.v8i1.30232.

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Total Electron Content (TEC) depletion and amplitude scintillation (S4) can be derived from, SCINDA-GPS receivers situated in various parts of the equatorial region. In this paper we present results of characterization of TEC depletions and amplitude scintillations over Kisumu, Kenya (Geomagnetic coordinates: 9.64o S, 108.59o E; Geographic coordinates: 0.02o S, 34.6o E) for both selected geomagnetically quiet and geomagnetically disturbed conditions between 1st January 2013 and 31st December 2014 using data derived from the Kisumu NovAtel GSV4004B SCINDA-GPS receiver situated at Maseno University. TEC depletions and amplitude scintillations affect Global Positioning System (GPS) signals in the ionosphere as they propagate from the satellite to the receiver. This study aims to investigate day to day variability of TEC depletions and amplitude scintillations over Kisumu, Kenya during both geomagnetically quiet and geomagnetically disturbed days of 2013 and 2014 which was a high solar activity period for Solar Cycle 24. Seasonal variability of TEC depletions and S4 index is also presented. The Receiver Independent Exchange (RINEX) data for the years 2013 and 2014 was retrieved from the Kisumu SCINDA-GPS receiver, processed to obtain Vertical Total Electron Content (VTEC), S4 and Universal Time (UT) and fed into MATLAB to generate VTEC and S4 plots against UT for each selected quiet and storm day within the 2013 and 2014 period. The obtained results showed a diurnal variation of TEC where TEC was minimum at pre-sunrise, maximum during daytime and minimum during nighttime. The minimum TEC during pre-sunrise and nighttime was attributed to reduced solar intensity while maximum TEC during daytime is attributed to increased solar intensity. Most of the selected quiet and storm days of the years 2013 and 2014 showed TEC depletions and TEC enhancements corresponding with enhanced amplitude scintillations between 1800UT and 20:00UT. This might be attributed to the rapid rise of the F-layer and the increase in the vertical E x B plasma drift due to the Pre-reversal Enhancement (PRE) of the eastward electric field. Post-midnight TEC depletions and amplitude scintillations were observed for some days and this was attributed to the effect of zonal winds which brought post-midnight enhancement of the E x B drift. The percentage occurrence of amplitude scintillations for the selected quiet and storm days exhibited a seasonal dependence with equinoctial months having higher occurrences than the solstitial months. The higher average S4 index during equinoctial months might be attributed to increased solar intensity resulting from the close alignment of the solar terminator and the geomagnetic meridian.
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8

Bounhir, Aziza, Zouhair Benkhaldoun, Jonathan J. Makela, et al. "Thermospheric Dynamics in Quiet and Disturbed Conditions." Proceedings of the International Astronomical Union 13, S335 (2017): 151–58. http://dx.doi.org/10.1017/s174392131700919x.

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AbstractThis paper presents the thermospheric winds and temperature properties measured with a Fabry-Pérot interferometer (FPI) over Oukaimeden observatory (31.2°N, 7.8°W, 22.8°N magnetic) in Morocco. After Three years of successful functioning from 2014 to 2017, we can address the seasonal behavior of the temperature and the winds (vertical, zonal and meridional). The dependence of the thermospheric winds and temperature on the solar cycle is also presented. The day-to-day variations of the quiet time wind pattern exhibits the importance of other type of waves superposed to the main diurnal tides. The storm time wind and temperature exhibits also a variety of ways to react to the storm. However, there is seasonal effect to the storm that will be illustrated in this paper. The signature of the MTM phenomenon is also present in the winds and temperature in geomagnetically quiet and disturbed nights. The occurrence of this phenomenon over the studied area is also addressed.
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9

Mendes, Odim, Margarete Oliveira Domingues, Ezequiel Echer, Rajkumar Hajra, and Varlei Everton Menconi. "Characterization of high-intensity, long-duration continuous auroral activity (HILDCAA) events using recurrence quantification analysis." Nonlinear Processes in Geophysics 24, no. 3 (2017): 407–17. http://dx.doi.org/10.5194/npg-24-407-2017.

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Abstract. Considering the magnetic reconnection and the viscous interaction as the fundamental mechanisms for transfer particles and energy into the magnetosphere, we study the dynamical characteristics of auroral electrojet (AE) index during high-intensity, long-duration continuous auroral activity (HILDCAA) events, using a long-term geomagnetic database (1975–2012), and other distinct interplanetary conditions (geomagnetically quiet intervals, co-rotating interaction regions (CIRs)/high-speed streams (HSSs) not followed by HILDCAAs, and events of AE comprised in global intense geomagnetic disturbances). It is worth noting that we also study active but non-HILDCAA intervals. Examining the geomagnetic AE index, we apply a dynamics analysis composed of the phase space, the recurrence plot (RP), and the recurrence quantification analysis (RQA) methods. As a result, the quantification finds two distinct clusterings of the dynamical behaviours occurring in the interplanetary medium: one regarding a geomagnetically quiet condition regime and the other regarding an interplanetary activity regime. Furthermore, the HILDCAAs seem unique events regarding a visible, intense manifestations of interplanetary Alfvénic waves; however, they are similar to the other kinds of conditions regarding a dynamical signature (based on RQA), because it is involved in the same complex mechanism of generating geomagnetic disturbances. Also, by characterizing the proper conditions of transitions from quiescent conditions to weaker geomagnetic disturbances inside the magnetosphere and ionosphere system, the RQA method indicates clearly the two fundamental dynamics (geomagnetically quiet intervals and HILDCAA events) to be evaluated with magneto-hydrodynamics simulations to understand better the critical processes related to energy and particle transfer into the magnetosphere–ionosphere system. Finally, with this work, we have also reinforced the potential applicability of the RQA method for characterizing nonlinear geomagnetic processes related to the magnetic reconnection and the viscous interaction affecting the magnetosphere.
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10

Mendoza, B., and J. Ramírez. "A straightforward estimation of the maximum sunspot number for cycle 23." Annales Geophysicae 17, no. 5 (1999): 639–41. http://dx.doi.org/10.1007/s00585-999-0639-7.

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Abstract. Using the annual number of geomagnetically quiet days (aa < 20 γ) for the year after the solar minimum, this precursor method predicts that the maximum sunspot number for cycle 23 will be 140 ± 32, indicating that cycle 23 will be similar to cycles 21 and 22.Key words. Solar physics · astrophysics and astronomy (magnetic fields; general)
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11

Jonah, Olusegun F., Shunrong Zhang, Anthea J. Coster, et al. "Understanding Inter-Hemispheric Traveling Ionospheric Disturbances and Their Mechanisms." Remote Sensing 12, no. 2 (2020): 228. http://dx.doi.org/10.3390/rs12020228.

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Traveling ionospheric disturbances (TIDs) are wave-like disturbances in ionospheric plasma density. They are often observed during both quiet (medium-scale TID) and geomagnetically disturbed (large-scale TID) conditions. Their amplitudes can reach double-digit percentages of the background plasma density, and their existence presents a challenge for accurate ionosphere specification. In this study, we examine TID properties using observations obtained during two geomagnetically disturbed periods using multiple ground and space-borne instruments, such as magnetometers, Global Navigation Satellite System (GNSS) receivers, and the SWARM satellite. Reference quiet time observations are also provided for both storms. We use a thermosphere–ionosphere–electrodynamics general circulation model (TIEGCM) results to properly interpret TID features and their drivers. This combination of observations and modeling allows the investigation of variations of TID generation mechanisms and subsequent wave propagation, particularly as a function of different plasma background densities during various geophysical conditions. The trans-equatorial coupling of TIDs in the northern and southern hemispheres is also investigated with respect to attenuation and propagation characteristics. We show that TID properties during trans-equatorial events may be substantially affected by storm time background neutral wind perturbation.
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12

Morozova, Anna L., Teresa Barata, and Tatiana Barlyaeva. "PCA-MRM Model to Forecast TEC at Middle Latitudes." Atmosphere 13, no. 2 (2022): 323. http://dx.doi.org/10.3390/atmos13020323.

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The total electron content (TEC) over the Iberian Peninsula was modelled using PCA-MRM models based on decomposition of the observed TEC series using the principal component analysis (PCA) and reconstruction of the daily modes’ amplitudes by a multiple linear regression model (MRM) using space weather parameters as regressors. The following space weather parameters are used: proxies for the solar UV and XR fluxes, number of the solar flares of different classes, parameters of the solar wind and of the interplanetary magnetic field, and geomagnetic indices. Time lags of 1 and 2 days between the TEC and space weather parameters are used. The performance of the PCA-MRM model is tested using data for 2015, both geomagnetically quiet and disturbed periods. The model performs well for quiet days and days with solar flares but without geomagnetic disturbances. The MAE and RMSE metrics are of the order of 3–5 TECu for daytime and ~2 TECu for night-time. During geomagnetically disturbed periods, the performance of the model deteriorates but only for daytime: MAE and RMSE are of the order of 4–6 TECu and can rise to ~13 TECu for the strongest geomagnetic storms.
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13

Pavlov, A. V., and N. M. Pavlova. "Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study." Annales Geophysicae 27, no. 4 (2009): 1363–75. http://dx.doi.org/10.5194/angeo-27-1363-2009.

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Abstract. We present a statistical study of variations in the F2-layer peak electron density, NmF2, and altitude, hmF2, over the Argentine Islands ionosonde. The critical frequencies, foF2, and, foE, of the F2 and E-layers, and the propagation factor, M(3000)F2, measured by the ionosonde during the 1957–1959 and 1962–1995 time periods were used in the statistical analysis to determine the values of NmF2 and hmF2. The probabilities to observe maximum and minimum values of NmF2 and hmF2 in a diurnal variation of the electron density are calculated. Our study shows that the main part of the maximum diurnal values of NmF2 is observed in a time sector close to midnight in November, December, January, and February exhibiting the anomalous diurnal variations of NmF2. Another anomalous feature of the diurnal variations of NmF2 exhibited during November, December, and January when the minimum diurnal value of NmF2 is mainly located close to the noon sector. These anomalous diurnal variations of NmF2 are found to be during both geomagnetically quiet and disturbed conditions. Anomalous features are not found in the diurnal variations of hmF2. The statistical study of the NmF2 winter anomaly phenomena over the Argentine Islands ionosonde was carried out. The variations in a maximum daytime value, R, of a ratio of a geomagnetically quiet daytime winter NmF2 to a geomagnetically quiet daytime summer NmF2 taken at a given UT and for approximately the same level of solar activity were studied. The conditional probability of the occurrence of R in an interval of R, the most frequent value of R, the mean expected value of R, and the conditional probability to observe the F2-region winter anomaly during a daytime period were calculated for low, moderate, and high solar activity. The calculations show that the mean expected value of R and the occurrence frequency of the F2-region winter anomaly increase with increasing solar activity.
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14

Nishida, A., T. Mukai, T. Yamamoto, S. Kokubun, and K. Maezawa. "A unified model of the magnetotail convection in geomagnetically quiet and active times." Journal of Geophysical Research: Space Physics 103, A3 (1998): 4409–18. http://dx.doi.org/10.1029/97ja01617.

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15

Chisham, G. "Giant pulsations: An explanation for their rarity and occurrence during geomagnetically quiet times." Journal of Geophysical Research: Space Physics 101, A11 (1996): 24755–63. http://dx.doi.org/10.1029/96ja02540.

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16

Pezzopane, M., P. R. Fagundes, L. Ciraolo, E. Correia, M. A. Cabrera, and R. G. Ezquer. "Unusual nighttime impulsivefoF2 enhancement below the southern anomaly crest under geomagnetically quiet conditions." Journal of Geophysical Research: Space Physics 116, A12 (2011): n/a. http://dx.doi.org/10.1029/2011ja016593.

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17

Khazanov, G. V., E. N. Krivorutsky, and D. G. Sibeck. "Formation of the Potential Jump Over the Geomagnetically Quiet Sunlit Polar Cap Region." Journal of Geophysical Research: Space Physics 124, no. 6 (2019): 4384–401. http://dx.doi.org/10.1029/2019ja026576.

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18

Oko, S. O., C. A. Onwumechili, and P. O. Ezema. "Geomagnetically quiet day ionospheric currents over the Indian sector—II. Equatorial electrojet currents." Journal of Atmospheric and Terrestrial Physics 58, no. 5 (1996): 555–64. http://dx.doi.org/10.1016/0021-9169(95)00056-9.

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19

Singh, Ashutosh K., K. K. Singh, A. K. Singh, and Lalmani. "Simultaneous observation of whistlers and emissions during a geomagnetically quiet period at low latitude." Astrophysics and Space Science 331, no. 2 (2010): 459–68. http://dx.doi.org/10.1007/s10509-010-0465-0.

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20

Rodriguez, J. V., H. C. Carlson, and R. A. Heelis. "Auroral forms that extend equatorward from the persistent midday aurora during geomagnetically quiet periods." Journal of Atmospheric and Solar-Terrestrial Physics 86 (September 2012): 6–24. http://dx.doi.org/10.1016/j.jastp.2012.06.001.

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21

Crowley, G., T. B. Jones, and J. R. Dudeney. "Comparison of short period TID morphologies in Antarctica during geomagnetically quiet and active intervals." Journal of Atmospheric and Terrestrial Physics 49, no. 11-12 (1987): 1155–62. http://dx.doi.org/10.1016/0021-9169(87)90098-5.

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22

Ezema, P. O., C. A. Onwumechili, and S. O. Oko. "Geomagnetically quiet day ionospheric currents over the Indian sector—III. Counter equatorial electrojet currents." Journal of Atmospheric and Terrestrial Physics 58, no. 5 (1996): 565–77. http://dx.doi.org/10.1016/0021-9169(95)00057-7.

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23

Liu, Libo, Yuyan Yang, Huijun Le, et al. "Unexpected Regional Zonal Structures in Low Latitude Ionosphere Call for a High Longitudinal Resolution of the Global Ionospheric Maps." Remote Sensing 14, no. 10 (2022): 2315. http://dx.doi.org/10.3390/rs14102315.

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This study reports unexpected strong longitudinal structures from Global Navigation Satellite System (GNSS) derived total electron content (TEC) observations in the low-latitude ionosphere over Asia. The observations during 2019–2020 show diverse patterns in the zonal difference of regional TEC, even under geomagnetically quiet conditions. The TEC in the northern hemisphere occasionally exhibits drastic zonal gradients. The intense regional gradients in TEC span a longitudinal extent of about 20°. The higher values may appear on the east or the west side. Strong zonal gradients may appear in all seasons, regardless of geomagnetically quiet or active conditions. The 15 December 2019 and 16 March 2020 cases depict an intense zonal differences cluster in the narrow latitudinal band of 16°N to 28°N, spanning a regional scale smaller than the normal longitudinal structures. In contrast, the Global Ionospheric Maps (GIMs) with a longitudinal resolution of 5° show a much flatter zonal picture. Such intense and regional-scale zonal structures in the low-latitude ionosphere call for a high zonal resolution of GIMs in terms of better geographically distributed observations. Notably, no counterpart regional structures are found at the conjugated points in the southern hemisphere during the two cases. Although the physical drivers are not certain, the appearance only in the northern hemisphere possibly excludes the dominant contribution to forming the regional structures from the equatorial electric field.
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24

Klausner, Virginia, Andrés Reinaldo Rodriguez Papa, Cláudia Maria Nicole Cândido, Margarete Oliveira Domingues, and Odim Mendes. "An alternative way to identify local geomagnetically quiet days: a case study using wavelet analysis." Annales Geophysicae 34, no. 4 (2016): 451–62. http://dx.doi.org/10.5194/angeo-34-451-2016.

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Abstract. This paper proposes a new method to evaluate geomagnetic activity based on wavelet analysis during the solar minimum activity (2007). In order to accomplish this task, a newly developed algorithm called effectiveness wavelet coefficient (EWC) was applied. Furthermore, a comparison between the 5 geomagnetically quiet days determined by the Kp-based method and by wavelet-based method was performed. This paper provides a new insight since the geomagnetic activity indexes are mostly designed to quantify the extent of disturbance rather than the quietness. The results suggest that the EWC can be used as an alternative tool to accurately detect quiet days, and consequently, it can also be used as an alternative to determine the Sq baseline to the current Kp-based 5 quietest days method. Another important aspect of this paper is that most of the quietest local wavelet candidate days occurred in an interval 2 days prior to the high-speed-stream-driven storm events. In other words, the EWC algorithm may potentially be used to detect the quietest magnetic activity that tends to occur just before the arrival of high-speed-stream-driven storms.
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Song, Seok-Min, and Kyungguk Min. "Analysis of the Tsyganenko Magnetic Field Model Accuracy during Geomagnetic Storm Times Using the GOES Data." Journal of Astronomy and Space Sciences 39, no. 4 (2022): 159–67. http://dx.doi.org/10.5140/jass.2022.39.4.159.

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Because of the small number of spacecraft available in the Earth’s magnetosphere at any given time, it is not possible to obtain direct measurements of the fundamental quantities, such as the magnetic field and plasma density, with a spatial coverage necessary for studying, global magnetospheric phenomena. In such cases, empirical as well as physics-based models are proven to be extremely valuable. This requires not only having high fidelity and high accuracy models, but also knowing the weakness and strength of such models. In this study, we assess the accuracy of the widely used Tsyganenko magnetic field models, T96, T01, and T04, by comparing the calculated magnetic field with the ones measured in-situ by the GOES satellites during geomagnetically disturbed times. We first set the baseline accuracy of the models from a data-model comparison during the intervals of geomagnetically quiet times. During quiet times, we find that all three models exhibit a systematic error of about 10% in the magnetic field magnitude, while the error in the field vector direction is on average less than 1%. We then assess the model accuracy by a data-model comparison during twelve geomagnetic storm events. We find that the errors in both the magnitude and the direction are well maintained at the quiet-time level throughout the storm phase, except during the main phase of the storms in which the largest error can reach 15% on average, and exceed well over 70% in the worst case. Interestingly, the largest error occurs not at the Dst minimum but 2–3 hours before the minimum. Finally, the T96 model has consistently underperformed compared to the other models, likely due to the lack of computation for the effects of ring current. However, the T96 and T01 models are accurate enough for most of the time except for highly disturbed periods.
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Onwumechili, C. A., S. O. Oko, and P. O. Ezema. "Geomagnetically quiet day ionospheric currents over the Indian sector—I. Worldwide part of Sq currents." Journal of Atmospheric and Terrestrial Physics 58, no. 5 (1996): 541–53. http://dx.doi.org/10.1016/0021-9169(95)00055-0.

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Liu, L., W. Wan, M. L. Zhang, B. Ning, S. R. Zhang, and J. M. Holt. "Variations of topside ionospheric scale heights over Millstone Hill during the 30-day incoherent scatter radar experiment." Annales Geophysicae 25, no. 9 (2007): 2019–27. http://dx.doi.org/10.5194/angeo-25-2019-2007.

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Abstract. A 30-day incoherent scatter radar (ISR) experiment was conducted at Millstone Hill (288.5° E, 42.6° N) from 4 October to 4 November 2002. The altitude profiles of electron density Ne, ion and electron temperature (Ti and Te), and line-of-sight velocity during this experiment were processed to deduce the topside plasma scale height Hp, vertical scale height VSH, Chapman scale height Hm, ion velocity, and the relative altitude gradient of plasma temperature (dTp/dh)/Tp, as well as the F2 layer electron density (NmF2) and height (hmF2). These data are analyzed to explore the variations of the ionosphere over Millstone Hill under geomagnetically quiet and disturbed conditions. Results show that ionospheric parameters generally follow their median behavior under geomagnetically quiet conditions, while the main feature of the scale heights, as well as other parameters, deviated significantly from their median behaviors under disturbed conditions. The enhanced variability of ionospheric scale heights during the storm-times suggests that the geomagnetic activity has a major impact on the behavior of ionospheric scale heights, as well as the shape of the topside electron density profiles. Over Millstone Hill, the diurnal behaviors of the median VSH and Hm are very similar to each other and are not so tightly correlated with that of the plasma scale height Hp or the plasma temperature. The present study confirms the sensitivity of the ionospheric scale heights over Millstone Hill to thermal structure and dynamics. The values of VSH/Hp tend to decrease as (dTp/dh)/Tp becomes larger or the dynamic processes become enhanced.
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28

Buresova, D., Lj R. Cander, A. Vernon, and B. Zolesi. "Real-time ionospheric N(h) profile updating over Europe using IRI-2000 model." Advances in Radio Science 2 (May 27, 2005): 299–303. http://dx.doi.org/10.5194/ars-2-299-2004.

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Abstract. In this paper a method for real-time updating of ionospheric electron density profile, N(h), over Europe using an ionospheric model and real-time measurements at ionosonde locations is presented. The N(h) profile update over European area has been simulated with the IRI-2000 ionospheric model and real-time N(h) profiles obtained from the EU COST271 Action Space Weather Database. Preliminary findings are shown for the geomagnetically quiet day on 4 May 2003 and disturbed day on 24 May 2002. Results are discussed in the context of real-time N(h) profile updating capabilities and effectiveness.
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29

Witasse, O., J. Lilensten, C. Lathuillere, and B. Pibaret. "Meridional thermospheric neutral wind at high latitude over a full solar cycle." Annales Geophysicae 16, no. 10 (1998): 1400–1409. http://dx.doi.org/10.1007/s00585-998-1400-3.

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Abstract. EISCAT radar experiments over a full solar cycle between January 1984 and March 1995 have been used to construct meridional neutral wind patterns in the ionospheric F region. For locally geomagnetically quiet periods the neutral winds have been binned according to season, solar activity, and universal time. The diurnal and seasonal behaviors and the effect of the solar flux are described. An empirical model of the meridional neutral wind for the high latitudes at eight altitudes in the ionospheric F region over a full solar cycle is presented. Results are compared with other recent empirical models.Key words. Auroral ionosphere · Thermospheric dynamics · EISCAT
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30

Aladjev, G. A., O. V. Evstafiev, V. S. Mingalev, G. I. Mingaleva, E. D. Tereshchenko, and B. Z. Khudukon. "Interpretation of ionospheric F-region structures in the vicinity of ionisation troughs observed by satellite radio tomography." Annales Geophysicae 19, no. 1 (2001): 25–36. http://dx.doi.org/10.5194/angeo-19-25-2001.

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Abstract. Tomographic images of the spatial distribution of electron density in the ionospheric F-region are presented from the Russian-American Tomography Experiment (RATE) in November 1993 as well as from campaigns carried out in northern Scandinavia in November 1995 and in Russia in April 1990. The reconstructions selected display the ionisation troughs above the tomographic chains of receivers during geomagnetically quiet and disturbed periods. Two mathematical models of the high-latitude ionosphere developed in the Polar Geophysical Institute have been applied for interpretation of the observed tomographic images.Key words. Ionosphere (electric fields and currents; ion chemistry and composition; plasma convection)
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31

Elmunim, Nouf Abd, Mardina Abdullah, and Siti Aminah Bahari. "Evaluating the Performance of IRI-2016 Using GPS-TEC Measurements over the Equatorial Region." Atmosphere 12, no. 10 (2021): 1243. http://dx.doi.org/10.3390/atmos12101243.

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Total electron content (TEC) is an important parameter in the ionosphere that is extensively used to study the variability of the ionosphere as it significantly affects radio wave propagations, causing delays on GPS signals. Therefore, evaluating the performance of ionospheric models is crucial to reveal the variety of ionospheric behaviour in different solar activity periods during geomagnetically quiet and disturbed periods for further improvements of the IRI model performance over the equatorial region. This research aimed to investigate the variations of ionospheric VTEC and observe the improvement in the performance of the IRI-2016 (IRI-2001, IRI01-corr, and NeQuick). The IRI-2016 was evaluated with the IRI-2012 using NeQuick, IRI-2001, and IRI01-corr topside electron density options. The data were obtained using a dual-frequency GPS receiver installed at the Universiti Utara Malaysia Kedah (UUMK) (geographic coordinates 4.62° N–103.21° E, geomagnetic coordinates 5.64° N–174.98° E), Mukhtafibillah (MUKH) (geographic coordinates 6.46° N–100.50° E, geomagnetic coordinates 3.32° S–172.99° E), and Tanjung Pengerang (TGPG) (geographic coordinates 1.36° N–104.10°E, geomagnetic coordinates 8.43° S–176.53° E) stations, during ascending to high solar activity at the geomagnetically quiet and disturbed periods in October 2011, March 2012, and March 2013. The maximum hourly ionospheric VTEC was observed during the post-noon time, while the minimum was during the early morning time. The ionospheric VTEC modelled by IRI-2016 had a slight improvement from the IRI-2012. However, the differences were observed during the post-noon and night-time, while the modelled VTEC from both IRI models were almost similar during the early morning time. Regarding the daily quiet and disturbed period’s prediction capability of the IRI-2016 and IRI-2012, IRI-2016 gave better agreement with the measured VTEC. The overall results showed that the model’s prediction performance during the high solar activity period in 2013 was better than the one during the ascending solar activity period. The results of the comparison between IRI-2016 and IRI-2012 in high solar activity exhibited that during quiet periods, all the IRI models showed better agreement with the measured VTEC compared to the disturbed periods.
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32

Chen, Junjie, and Jiuhou Lei. "A Simulation Study on the Latitudinal Variations of Ionospheric Zonal Electric Fields Under Geomagnetically Quiet Conditions." Journal of Geophysical Research: Space Physics 124, no. 2 (2019): 1444–53. http://dx.doi.org/10.1029/2018ja026174.

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33

Zhao, B., W. Wan, L. Liu, et al. "Anomalous enhancement of ionospheric electron content in the Asian-Australian region during a geomagnetically quiet day." Journal of Geophysical Research: Space Physics 113, A11 (2008): n/a. http://dx.doi.org/10.1029/2007ja012987.

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34

Nishida, A., T. Yamamoto, K. Tsuruda, et al. "Structure of the neutral sheet in the distant tail (x=−210 Re) in geomagnetically quiet times." Geophysical Research Letters 21, no. 25 (1994): 2951–54. http://dx.doi.org/10.1029/94gl01422.

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35

Sindelarova, T., Z. Mosna, D. Buresova, J. Chum, L. A. McKinnell, and R. Athieno. "Observations of wave activity in the ionosphere over South Africa in geomagnetically quiet and disturbed periods." Advances in Space Research 50, no. 2 (2012): 182–95. http://dx.doi.org/10.1016/j.asr.2012.04.016.

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36

Pavlo, A. V., and M. J. Buonsanto. "Anomalous electron density events in the quiet summer ionosphere at solar minimum over Millstone Hill." Annales Geophysicae 16, no. 4 (1998): 460–69. http://dx.doi.org/10.1007/s00585-998-0460-8.

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Abstract. This study compares the observed behavior of the F region ionosphere over Millstone Hill with calculations from the IZMIRAN model for solar minimum for the geomagnetically quiet period 23-25 June 1986, when anomalously low values of hmF2(&lt;200 km) were observed. We found that these low values of hmF2 (seen as a G condition on ionograms) exist in the ionosphere due to a decrease of production rates of oxygen ions resulting from low values of atomic oxygen density. Results show that determination of a G condition using incoherent scatter radar data is sensitive both to the true concentration of O+ relative to the molecular ions, and to the ion composition model assumed in the data reduction process. The increase in the O++ N 2 loss rate due to vibrationally excited N2 produces a reduction in NmF2 of typically 5-10% , but as large as 15% , bringing the model and data into better agreement. The effect of vibrationally excited NO+ ions on electron densities is negligible.Key words. Ionosphere (Ion chemistry and composition; Ionosphere-atmosphere interactions; Mid-latitude ionosphere).
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37

Jensen, J. W., and B. G. Fejer. "Longitudinal dependence of middle and low latitude zonal plasma drifts measured by DE-2." Annales Geophysicae 25, no. 12 (2007): 2551–59. http://dx.doi.org/10.5194/angeo-25-2551-2007.

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Abstract. We used ion drift observations from the DE-2 satellite to study for the first time the longitudinal variations of middle and low latitude F region zonal plasma drifts during quiet and disturbed conditions. The quiet-time middle latitude drifts are predominantly westward; the low latitude drifts are westward during the day and eastward at night. The daytime quiet-time drifts do not change much with longitude; the nighttime drifts have strong season dependent longitudinal variations. In the dusk-premidnight period, the equinoctial middle latitude westward drifts are smallest in the European sector and the low latitude eastward drifts are largest in the American-Pacific sector. The longitudinal variations of the late night-early morning drifts during June and December solstice are anti-correlated. During geomagnetically active times, there are large westward perturbation drifts in the late afternoon-early night sector at upper middle latitudes, and in the midnight sector at low latitudes. The largest westward disturbed drifts during equinox occur in European sector, and the smallest in the Pacific region. These results suggest that during equinox SAPS events occur most often at European longitudes. The low latitude perturbation drifts do not show significant longitudinal
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38

McCormac, F. G., T. L. Killeen, J. P. Thayer, et al. "Circulation of the polar thermosphere during geomagnetically quiet and active times as observed by Dynamics Explorer 2." Journal of Geophysical Research 92, A9 (1987): 10133. http://dx.doi.org/10.1029/ja092ia09p10133.

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39

Amabayo, Emirant B., Edward Jurua, and Pierre J. Cilliers. "Assessment of scintillation proxy maps for a scintillation study during geomagnetically quiet and disturbed conditions over Uganda." Journal of Atmospheric and Solar-Terrestrial Physics 154 (February 2017): 47–54. http://dx.doi.org/10.1016/j.jastp.2016.12.009.

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40

Kitamura, N., A. Shinbori, Y. Nishimura, T. Ono, M. Iizima, and A. Kumamoto. "Seasonal variations of the electron density distribution in the polar region during geomagnetically quiet periods near solar maximum." Journal of Geophysical Research: Space Physics 114, A1 (2009): n/a. http://dx.doi.org/10.1029/2008ja013288.

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41

Giang, T. T., M. Hamrin, M. Yamauchi, et al. "Outflowing protons and heavy ions as a source for the sub-keV ring current." Annales Geophysicae 27, no. 2 (2009): 839–49. http://dx.doi.org/10.5194/angeo-27-839-2009.

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Abstract. Data from the Cluster CIS instrument have been used for studying proton and heavy ion (O+ and He+) characteristics of the sub-keV ring current. Thirteen events with dispersed heavy ions (O+ and He+) were identified out of two years (2001 and 2002) of Cluster data. All events took place during rather geomagnetically quiet periods. Three of those events have been investigated in detail: 21 August 2001, 26 November 2001 and 20 February 2002. These events were chosen from varying magnetic local times (MLT), and they showed different characteristics. In this article, we discuss the potential source for sub-keV ring current ions. We show that: (1) outflows of terrestrial sub-keV ions are supplied to the ring current also during quiet geomagnetic conditions; (2) the composition of the outflow implies an origin that covers an altitude interval from the low-altitude ionosphere to the plasmasphere, and (3) terrestrial ions are moving upward along magnetic field lines, at times forming narrow collimated beams, but frequently also as broad beams. Over time, the ion beams are expected to gradually become isotropised as a result of wave-particle interaction, eventually taking the form of isotropic drifting sub-keV ion signatures. We argue that the sub-keV energy-time dispersed signatures originate from field-aligned terrestrial ion energising and outflow, which may occur at all local times and persist also during quiet times.
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42

Sahai, Y., F. Becker-Guedes, P. R. Fagundes, et al. "Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 "Halloween Storms"." Annales Geophysicae 27, no. 12 (2009): 4463–77. http://dx.doi.org/10.5194/angeo-27-4463-2009.

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Abstract. The response of the ionospheric F-region in the South American sector during the super geomagnetic storms on 29 and 30 October 2003 is studied in the present investigation. In this paper, we present ionospheric sounding observations during the period 29–31 October 2003 obtained at Palmas (a near equatorial location) and Sao Jose dos Campos (a location under the southern crest of the equatorial ionospheric anomaly), Brazil, along with observations during the period 27–31 October 2003 from a chain of GPS stations covering the South American sector from Imperatriz, Brazil, to Rio Grande, Argentina. Also, complementary observations that include sequences of all-sky images of the OI 777.4 and 630.0 nm emissions observed at El Leoncito, Argentina, on the nights of 28–29 (geomagnetically quiet night) and 29–30 (geomagnetically disturbed night) October 2003, and ion densities observed in the South American sector by the DMSP F13, F14 and F15 satellites orbiting at about 800 km on 29 and 30 October 2003 are presented. In addition, global TEC maps derived from GPS observations collected from the global GPS network of International GPS Service (IGS) are presented, showing widespread and drastic TEC changes during the different phases of the geomagnetic disturbances. The observations indicate that the equatorial ionospheric irregularities or plasma bubbles extend to the Argentinean station Rawson (geom. Lat. 33.1° S) and map at the magnetic equator at an altitude of about 2500 km.
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43

Zhang, Yixin, Yang Liu, Junlei Mei, Chunxi Zhang, and Jinling Wang. "A Study on the Characteristics of the Ionospheric Gradient under Geomagnetic Perturbations." Sensors 20, no. 7 (2020): 1805. http://dx.doi.org/10.3390/s20071805.

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The Earth’s ionosphere is greatly influenced by geomagnetic activities, especially geomagnetic storms. During a geomagnetic storm, the ionosphere suffers many perturbations, leading to a spatial gradient that are neglected during geomagnetically quiet periods. An ionospheric gradient generates potential hazards for a ground-based argumentation system (GBAS) by enlarging the errors in the delay corrections between ground monitor stations and users. To address this problem, this work investigates the characteristics of the ionospheric gradient under geomagnetic storms. Global Navigation Satellite System (GNSS) observations from the continuously operating reference station (CORS) network were used to analyze the ionospheric gradients during the geomagnetic storm on 8 September 2017. The statistical behavior of the ionospheric gradient was further discussed. Experiments show that strong geomagnetic perturbations lead to large ionospheric gradients, and the gradients also vary with the geomagnetic location.
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44

Mannucci, A. J., C. O. Ao, X. Pi, and B. A. Iijima. "The impact of large scale ionospheric structure on radio occultation retrievals." Atmospheric Measurement Techniques Discussions 4, no. 3 (2011): 2525–65. http://dx.doi.org/10.5194/amtd-4-2525-2011.

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Abstract. We study the impact of large-scale ionospheric structure on the accuracy of radio occultation (RO) retrievals of atmospheric parameters such as refractivity and temperature. We use a climatological model of the ionosphere as well as an ionospheric data assimilation model to compare quiet and geomagnetically disturbed conditions. The largest contributor to ionospheric bias is physical separation of the two GPS frequencies as the GPS signal traverses the ionosphere and atmosphere. We analyze this effect in detail using ray-tracing and a full geophysical retrieval system. During quiet conditions, our results are similar to previously published studies. The impact of a major ionospheric storm is analyzed using data from the 30 October 2003 "Halloween" superstorm period. The temperature retrieval bias under disturbed conditions varies from 1 K to 2 K between 20 and 32 km altitude, compared to 0.2–0.3 K during quiet conditions. These results suggest the need for ionospheric monitoring as part of an RO-based climate observation strategy. We find that even during quiet conditions, the magnitude of retrieval bias depends critically on ionospheric conditions, which may explain variations in previously published bias estimates that use a variety of assumptions regarding large scale ionospheric structure. We quantify the impact of spacecraft orbit altitude on the magnitude of bending angle error. Satellites in higher altitude orbits (≧700 km) tend to have lower biases due to the tendency of the residual bending to cancel between the top and bottomside ionosphere. We conclude with remarks on the implications of this study for long-term climate monitoring using RO.
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45

Bailey, Rachel L., Thomas S. Halbedl, Ingrid Schattauer, et al. "Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach." Annales Geophysicae 35, no. 3 (2017): 751–61. http://dx.doi.org/10.5194/angeo-35-751-2017.

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Abstract. Geomagnetically induced currents (GICs) in power systems, which can lead to transformer damage over the short and the long term, are a result of space weather events and geomagnetic variations. For a long time, only high-latitude areas were considered to be at risk from these currents, but recent studies show that considerable GICs also appear in midlatitude and equatorial countries. In this paper, we present initial results from a GIC model using a thin-sheet approach with detailed surface and subsurface conductivity models to compute the induced geoelectric field. The results are compared to measurements of direct currents in a transformer neutral and show very good agreement for short-period variations such as geomagnetic storms. Long-period signals such as quiet-day diurnal variations are not represented accurately, and we examine the cause of this misfit. The modelling of GICs from regionally varying geoelectric fields is discussed and shown to be an important factor contributing to overall model accuracy. We demonstrate that the Austrian power grid is susceptible to large GICs in the range of tens of amperes, particularly from strong geomagnetic variations in the east–west direction.
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46

Chi, P. J., and G. Le. "Observations of magnetospheric high‐ m poloidal waves by ST‐5 satellites in low Earth orbit during geomagnetically quiet times." Journal of Geophysical Research: Space Physics 120, no. 6 (2015): 4776–83. http://dx.doi.org/10.1002/2015ja021145.

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47

J. E., Thomas,, George, N. J., Ekanem, A.M, and Akpan, A. E. "IONOSPHERIC PLASMA VARIATIONS AFORE THE EAST OF KURIL ISLANDS EARTHQUAKE OF 13th JANUARY, 2007." Geological Behavior 4, no. 1 (2020): 42–46. http://dx.doi.org/10.26480/gbr.01.2020.42.46.

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Plasma Analyzer (IAP) and Langmuir Probe (ISL) experiments of the DEMETER microsatellite were used to check the state of the ionosphere in the region of the M8.1 East of Kuril Islands earthquake of 13th January, 2007,30 days afore and 10 days after the event using statistical approach. The study strongly revealed that all three investigated ionospheric parameters of electron density, total ion density and electron temperature displayed unfamiliar ionospheric variations eight days before the earthquake in the daytime time half orbit measurement. To this, the electron density, total ion density and electron temperature recorded a variation of 4.09, 5.73 and -2.03 respectively. These irregularities were vetted for untrue signals using the geomagnetic indices of Kp and Dst. It was however realized that the state of the ionosphere was geomagnetically quiet during this day, hence the observed variations were seismogenic.
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48

Jenner, Luke A., Alan G. Wood, Gareth D. Dorrian, et al. "Plasma density gradients at the edge of polar ionospheric holes: the absence of phase scintillation." Annales Geophysicae 38, no. 2 (2020): 575–90. http://dx.doi.org/10.5194/angeo-38-575-2020.

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Abstract. Polar holes were observed in the high-latitude ionosphere during a series of multi-instrument case studies close to the Northern Hemisphere winter solstice in 2014 and 2015. These holes were observed during geomagnetically quiet conditions and under a range of solar activities using the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR) and measurements from Global Navigation Satellite System (GNSS) receivers. Steep electron density gradients have been associated with phase scintillation in previous studies; however, no enhanced scintillation was detected within the electron density gradients at these boundaries. It is suggested that the lack of phase scintillation may be due to low plasma density levels and a lack of intense particle precipitation. It is concluded that both significant electron density gradients and plasma density levels above a certain threshold are required for scintillation to occur.
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49

Sumod, S. G., T. K. Pant, C. Vineeth, and M. M. Hossain. "A new insight into the vertical neutral-ion coupling between the mesopause and equatorial ionosphere F-region." Annales Geophysicae 29, no. 2 (2011): 421–26. http://dx.doi.org/10.5194/angeo-29-421-2011.

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Abstract. This letter reports unique observations, illustrating the vertical coupling between the daytime mesopause and F-region of the ionosphere over the magnetic dip equatorial station Trivandrum (8.5° N, 76.5° E, 0.5° N dip lat.) in India. For the "first time", it has been shown that the temporal variations in the mean daytime mesopause temperatures (MPT), during geomagnetically quiet days corroborate well with that of the base height changes (h'F) of the ionospheric F-region. However, there exist some characteristic time delays between these two, which vary from 0 to 90 min. The MPTs are measured using the unique Multi-Wavelength Dayglow Photometer while the h'Fs are derived using a co-located digital Ionosonde. The observed time delays are attributed to the intercompeting roles between the diffusion and wave-dynamical processes in modulating the transport of atomic oxygen at these altitudes.
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50

Feshchenko, E. Y., and Y. P. Maltsev. "Erosion of the inner magnetosphere during geomagnetic storms." Annales Geophysicae 15, no. 12 (1997): 1532–36. http://dx.doi.org/10.1007/s00585-997-1532-x.

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Abstract. Using the empirical magnetic field model dependent on the Dst index and solar wind dynamic pressure, we calculated the behaviour of the contour B = Bs in the equatorial plane of the magnetosphere where Bs is the magnetic field in the subsolar point at the magnetopause. The inner domain of the magnetosphere outlined by this contour contains the bulk of geomagnetically trapped particles. During quiet time the boundary of the inner magnetosphere passes at the distance ~10 RE at noon and at ~7 RE at midnight. During very intense storms this distance can be reduced to 4–5 RE for all MLT. The calculation results agree well with the satellite measurements of the magnetopause location during storms. The ionospheric projection of the B = Bs contour calculated with the Euler potential technique is close to the equatorward edge of the auroral oval.
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