TY - JOUR A1 - Soares, Gabriel A1 - Yamazaki, Yosuke A1 - Matzka, Jürgen A1 - Pinheiro, Katia A1 - Morschhauser, Achim A1 - Stolle, Claudia A1 - Alken, Patrick T1 - Equatorial counter electrojet longitudinal and seasonal variablity in the American sector JF - Journal of geophysical research : Space physics N2 - The equatorial electrojet occasionally reverses during morning and afternoon hours, leading to periods of westward current in the ionospheric E region that are known as counter electrojet (CEJ) events. We present the first analysis of CEJ climatology and CEJ dependence on solar flux and lunar phase for the Brazilian sector, based on an extensive ground-based data set for the years 2008 to 2017 from the geomagnetic observatory Tatuoca (1.2 degrees S, 48.5 degrees W), and we compare it to the results found for Huancayo (12.0 degrees S, 75.3 degrees W) observatory in the Peruvian sector. We found a predominance of morning CEJ events for both sectors. The afternoon CEJ occurrence rate in the Brazilian sector is twice as high as in the Peruvian sector. The afternoon CEJ occurrence rate strongly depends on season, with maximum rates occurring during the northern-hemisphere summer for the Brazilian sector and during the northern-hemisphere winter for the Peruvian sector. Significant discrepancies between the two sectors are also found for morning CEJ rates during the northern-hemisphere summer. These longitudinal differences are in agreement with a CEJ climatology derived from contemporary Swarm satellite data and can be attributed in part to the well-known longitudinal wave-4 structure in the background equatorial electrojet strength that results from nonmigrating solar tides and stationary planetary waves. Simulations with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model show that the remaining longitudinal variability in CEJ during northern summer can be explained by the effect of migrating tides in the presence of the varying geomagnetic field in the South Atlantic Anomaly. Y1 - 2018 U6 - https://doi.org/10.1029/2018JA025968 SN - 2169-9380 SN - 2169-9402 VL - 123 IS - 11 SP - 9906 EP - 9920 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Siddiqui, Tarique Adnan A1 - Maute, Astrid A1 - Pedatella, Nick A1 - Yamazaki, Yosuke A1 - Lühr, Hermann A1 - Stolle, Claudia T1 - On the variability of the semidiurnal solar and lunar tides of the equatorial electrojet during sudden stratospheric warmings JF - Annales geophysicae N2 - The variabilities of the semidiurnal solar and lunar tides of the equatorial electrojet (EEJ) are investigated during the 2003, 2006, 2009 and 2013 major sudden stratospheric warming (SSW) events in this study. For this purpose, ground-magnetometer recordings at the equatorial observatories in Huancayo and Fuquene are utilized. Results show a major enhancement in the amplitude of the EEJ semidiurnal lunar tide in each of the four warming events. The EEJ semidiurnal solar tidal amplitude shows an amplification prior to the onset of warmings, a reduction during the deceleration of the zonal mean zonal wind at 60 degrees N and 10 hPa, and a second enhancement a few days after the peak reversal of the zonal mean zonal wind during all four SSWs. Results also reveal that the amplitude of the EEJ semidiurnal lunar tide becomes comparable or even greater than the amplitude of the EEJ semidiurnal solar tide during all these warming events. The present study also compares the EEJ semidiurnal solar and lunar tidal changes with the variability of the migrating semidiurnal solar (SW2) and lunar (M2) tides in neutral temperature and zonal wind obtained from numerical simulations at E-region heights. A better agreement between the enhancements of the EEJ semidiurnal lunar tide and the M2 tide is found in comparison with the enhancements of the EEJ semidiurnal solar tide and the SW2 tide in both the neutral temperature and zonal wind at the E-region altitudes. Y1 - 2018 U6 - https://doi.org/10.5194/angeo-36-1545-2018 SN - 0992-7689 SN - 1432-0576 VL - 36 IS - 6 SP - 1545 EP - 1562 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Xiong, Chao A1 - Stolle, Claudia A1 - Park, Jaeheung T1 - Climatology of GPS signal loss observed by Swarm satellites JF - Annales geophysicae N2 - By using 3-year global positioning system (GPS) measurements from December 2013 to November 2016, we provide in this study a detailed survey on the climatology of the GPS signal loss of Swarm onboard receivers. Our results show that the GPS signal losses prefer to occur at both low latitudes between +/- 5 and +/- 20 degrees magnetic latitude (MLAT) and high latitudes above 60 degrees MLAT in both hemispheres. These events at all latitudes are observed mainly during equinoxes and December solstice months, while totally absent during June solstice months. At low latitudes the GPS signal losses are caused by the equatorial plasma irregularities shortly after sunset, and at high latitude they are also highly related to the large density gradients associated with ionospheric irregularities. Additionally, the high-latitude events are more often observed in the Southern Hemisphere, occurring mainly at the cusp region and along nightside auroral latitudes. The signal losses mainly happen for those GPS rays with elevation angles less than 20 degrees, and more commonly occur when the line of sight between GPS and Swarm satellites is aligned with the shell structure of plasma irregularities. Our results also confirm that the capability of the Swarm receiver has been improved after the bandwidth of the phase-locked loop (PLL) widened, but the updates cannot radically avoid the interruption in tracking GPS satellites caused by the ionospheric plasma irregularities. Additionally, after the PLL bandwidth increased larger than 0.5 Hz, some unexpected signal losses are observed even at middle latitudes, which are not related to the ionospheric plasma irregularities. Our results suggest that rather than 1.0 Hz, a PLL bandwidth of 0.5 Hz is a more suitable value for the Swarm receiver. KW - Ionosphere KW - equatorial ionosphere KW - ionospheric irregularities KW - radio science KW - radio wave propagation Y1 - 2018 U6 - https://doi.org/10.5194/angeo-36-679-2018 SN - 0992-7689 SN - 1432-0576 VL - 36 IS - 2 SP - 679 EP - 693 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Yamazaki, Yosuke A1 - Stolle, Claudia A1 - Matzka, Jürgen A1 - Alken, Patrick T1 - Quasi-6-Day Wave Modulation of the Equatorial Electrojet JF - Journal of geophysical research : Space physics N2 - The equatorial electrojet is an enhanced eastward current in the dayside E region ionosphere flowing along the magnetic equator. The equatorial electrojet is highly variable as it is subject to various forcing mechanisms including atmospheric waves from the lower layers of the atmosphere. There are occasionally times when the intensity of the equatorial electrojet at a fixed longitude shows an oscillatory variation with a period of approximately 6days. We present case studies of such events based on the equatorial electrojet measurements from the CHAMP and Swarm satellites. The spatial and temporal variability of the equatorial electrojet intensity during these events reveals characteristics of a westward propagating wave with zonal wavenumber 1, consistent with the effect of the quasi-6-day planetary wave. Analyses of the geopotential height data from the Aura satellite confirm the presence of the quasi-6-day planetary wave in the lower thermosphere during the events. The amplitude of the quasi-6-day variation in the equatorial electrojet intensity depends on longitude, but no systematic longitudinal dependence is found for different events. During the event of August 2010, quasi-6-day variations are also observed by ground-based magnetometers and a radar in the Peruvian sector. The effect of the quasi-6-day wave accounts for up to +/- 5.9m/s in the equatorial vertical plasma velocity at noon, which is much larger than previously predicted by a numerical model. These results suggest that the quasi-6-day planetary wave is an important source of short-term variability in the equatorial ionosphere. Y1 - 2018 U6 - https://doi.org/10.1029/2018JA025365 SN - 2169-9380 SN - 2169-9402 VL - 123 IS - 5 SP - 4094 EP - 4109 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Wan, Xin A1 - Xiong, Chao A1 - Rodriguez-Zuluaga, Juan A1 - Kervalishvili, Guram N. A1 - Stolle, Claudia A1 - Wang, Hui T1 - Climatology of the Occurrence Rate and Amplitudes of Local Time Distinguished Equatorial Plasma Depletions Observed by Swarm Satellite JF - Journal of geophysical research : Space physics N2 - In this study, we developed an autodetection technique for the equatorial plasma depletions (EPDs) and their occurrence and depletion amplitudes based on in situ electron density measurements gathered by Swarm A satellite. For the first time, comparisons are made among the detected EPDs and their amplitudes with the loss of Global Positioning System (GPS) signal of receivers onboard Swarm A, and the Swarm Level-2 product, Ionospheric Bubble Index (IBI). It has been found that the highest rate of EPD occurrence takes place generally between 2200 and 0000 magnetic local time (MLT), in agreement with the IBI. However, the largest amplitudes of EPD are detected earlier at about 1900-2100 MLT. This coincides with the moment of higher background electron density and the largest occurrence of GPS signal loss. From a longitudinal perspective, the higher depletion amplitude is always witnessed in spatial bins with higher background electron density. At most longitudes, the occurrence rate of postmidnight EPDs is reduced compared to premidnight ones; while more postmidnight EPDs are observed at African longitudes. CHAMP observations confirm this point regardless of high or low solar activity condition. Further by comparing with previous studies and the plasma vertical drift velocity from ROCSAT-1, we suggest that while the F region vertical plasma drift plays a key role in dominating the occurrence of EPDs during premidnight hours, the postmidnight EPDs are the combined results from the continuing of former EPDs and newborn EPDs, especially during June solstice. And these newborn EPDs during postmidnight hours seem to be less related to the plasma vertical drift. KW - equatorial plasma depletion KW - swarm LP KW - depletion amplitude KW - climatology KW - postmidnight Y1 - 2018 U6 - https://doi.org/10.1002/2017JA025072 SN - 2169-9380 SN - 2169-9402 VL - 123 IS - 4 SP - 3014 EP - 3026 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Yamazaki, Yosuke A1 - Stolle, Claudia A1 - Matzka, Jürgen A1 - Liu, Huixin A1 - Tao, Chihiro T1 - Interannual variability of the daytime equatorial ionospheric electric field JF - Journal of geophysical research : Space physics N2 - Understanding the variability of the ionosphere is important for the prediction of space weather and climate. Recent studies have shown that forcing from the lower atmosphere plays a significant role for the short-term (day-to-day) variability of the low-latitude ionosphere. The present study aims to assess the importance of atmospheric forcing for the variability of the daytime equatorial ionospheric electric field on the interannual (year-to-year) time scale. Magnetic field measurements from Huancayo (12.05 degrees S, 75.33 degrees W) are used to augment the equatorial vertical plasma drift velocity (V-Z) measurements from the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere radar during 2001-2016. V-Z can be regarded as a measure of the zonal electric field. After removing the seasonal variation of similar to 10m/s, midday values of V-Z show an interannual variation of similar to 2m/s with an oscillation period of 2-3years. No evidence of solar cycle influence is found. The Ground-to-topside Atmosphere-Ionosphere model for Aeronomy, which takes into account realistic atmospheric variability below 30km, reproduces the pattern of the observed interannual variation without having to include variable forcing from the magnetosphere. The results indicate that lower atmospheric forcing plays a dominant role for the observed interannual variability of V-Z at 1200 local time. KW - interannual variability KW - plasma drifts KW - equatorial electrojet (EEJ) KW - vertical coupling KW - JULIA KW - GAIA Y1 - 2018 U6 - https://doi.org/10.1029/2017JA025165 SN - 2169-9380 SN - 2169-9402 VL - 123 IS - 5 SP - 4241 EP - 4256 PB - American Geophysical Union CY - Washington ER - TY - GEN A1 - Siddiqui, Tarique Adnan A1 - Maute, Astrid A1 - Pedatella, Nick A1 - Yamazaki, Yosuke A1 - Lühr, Hermann A1 - Stolle, Claudia T1 - On the variability of the semidiurnal solar and lunar tides of the equatorial electrojet during sudden stratospheric warmings T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The variabilities of the semidiurnal solar and lunar tides of the equatorial electrojet (EEJ) are investigated during the 2003, 2006, 2009 and 2013 major sudden stratospheric warming (SSW) events in this study. For this purpose, ground-magnetometer recordings at the equatorial observatories in Huancayo and Fúquene are utilized. Results show a major enhancement in the amplitude of the EEJ semidiurnal lunar tide in each of the four warming events. The EEJ semidiurnal solar tidal amplitude shows an amplification prior to the onset of warmings, a reduction during the deceleration of the zonal mean zonal wind at 60∘ N and 10 hPa, and a second enhancement a few days after the peak reversal of the zonal mean zonal wind during all four SSWs. Results also reveal that the amplitude of the EEJ semidiurnal lunar tide becomes comparable or even greater than the amplitude of the EEJ semidiurnal solar tide during all these warming events. The present study also compares the EEJ semidiurnal solar and lunar tidal changes with the variability of the migrating semidiurnal solar (SW2) and lunar (M2) tides in neutral temperature and zonal wind obtained from numerical simulations at E-region heights. A better agreement between the enhancements of the EEJ semidiurnal lunar tide and the M2 tide is found in comparison with the enhancements of the EEJ semidiurnal solar tide and the SW2 tide in both the neutral temperature and zonal wind at the E-region altitudes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1075 KW - middle atmosphere KW - latitude ionosphere KW - temperature changes KW - lower thermosphere KW - magnetic field KW - TIME-GCM KW - winds KW - circulation KW - events KW - winter Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-468389 SN - 1866-8372 IS - 1075 SP - 1545 EP - 1562 ER - TY - JOUR A1 - Siddiqui, Tarique Adnan A1 - Yamazaki, Yosuke A1 - Stolle, Claudia A1 - Lühr, Hermann A1 - Matzka, Jürgen A1 - Maute, Astrid A1 - Pedatella, Nicholas T1 - Dependence of Lunar Tide of the Equatorial Electrojet on the Wintertime Polar Vortex, Solar Flux, and QBO JF - Geophysical research letters N2 - The lower atmospheric forcing effects on the ionosphere are particularly evident during extreme meteorological events known as sudden stratospheric warmings (SSWs). During SSWs, the polar stratosphere and ionosphere, two distant atmospheric regions, are coupled through the SSW-induced modulation of atmospheric migrating and nonmigrating tides. The changes in the migrating semidiurnal solar and lunar tides are the major source of ionospheric variabilities during SSWs. In this study, we use 55 years of ground-magnetometer observations to investigate the composite characteristics of the lunar tide of the equatorial electrojet (EEJ) during SSWs. These long-term observations allow us to capture the EEJ lunar tidal response to the SSWs in a statistical sense. Further, we examine the influence of solar flux conditions and the phases of quasi-biennial oscillation (QBO) on the lunar tide and find that the QBO phases and solar flux conditions modulate the EEJ lunar tidal response during SSWs in a similar way as they modulate the wintertime Arctic polar vortex. This work provides first evidence of modulation of the EEJ lunar tide due to QBO. Plain Language Summary This study focuses on the vertical coupling between the polar stratosphere and equatorial ionosphere during sudden stratospheric warmings (SSWs). Extreme meteorological events such as SSWs induce variabilities in the ionosphere by modulating the atmospheric migrating and nonmigrating tides, and these variabilities can be comparable to a moderate geomagnetic storm. Observations and modeling studies have found that the changes in the migrating semidiurnal solar and lunar tides are a major source of ionospheric variabilities during SSWs. The equatorial electrojet (EEJ) is a narrow ribbon of current flowing over the dip equator in the ionosphere and is particularly sensitive to tidal changes. Long-term ground-magnetometer recordings have been used in this study to estimate the variations induced in EEJ during SSWs due to the lunar semidiurnal tide in a statistical sense. The wintertime Arctic polar vortex and the occurrence of SSWs are modulated by solar flux conditions and the phases of quasi-biennial oscillation. In this work, we find the first evidence of lunar tidal modulation of EEJ due to quasi-biennial oscillation during SSWs. Our findings will be useful in providing improved predictions of ionospheric variations due to SSWs. The aeronomy community will be the most impacted by this paper. KW - lunar tide KW - equatorial electrojet KW - vertical coupling KW - SSW KW - QBO KW - planetary waves Y1 - 2018 U6 - https://doi.org/10.1029/2018GL077510 SN - 0094-8276 SN - 1944-8007 VL - 45 IS - 9 SP - 3801 EP - 3810 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Prokhorov, Boris E. A1 - Förster, Matthias A1 - Lesur, Vincent A1 - Namgaladze, Alexander A. A1 - Holschneider, Matthias A1 - Stolle, Claudia T1 - Modeling of the ionospheric current system and calculating its JF - Magnetic Fields in the Solar System: Planets, Moons and Solar Wind Interactions N2 - The additional magnetic field produced by the ionospheric current system is a part of the Earth’s magnetic field. This current system is a highly variable part of a global electric circuit. The solar wind and interplanetary magnetic field (IMF) interaction with the Earth’s magnetosphere is the external driver for the global electric circuit in the ionosphere. The energy is transferred via the field-aligned currents (FACs) to the Earth’s ionosphere. The interactions between the neutral and charged particles in the ionosphere lead to the so-called thermospheric neutral wind dynamo which represents the second important driver for the global current system. Both processes are components of the magnetosphere–ionosphere–thermosphere (MIT) system, which depends on solar and geomagnetic conditions, and have significant seasonal and UT variations. The modeling of the global dynamic Earth’s ionospheric current system is the first aim of this investigation. For our study, we use the Potsdam version of the Upper Atmosphere Model (UAM-P). The UAM is a first-principle, time-dependent, and fully self-consistent numerical global model. The model includes the thermosphere, ionosphere, plasmasphere, and inner magnetosphere as well as the electrodynamics of the coupled MIT system for the altitudinal range from 80 (60) km up to the 15 Earth radii. The UAM-P differs from the UAM by a new electric field block. For this study, the lower latitudinal and equatorial electrodynamics of the UAM-P model was improved. The calculation of the ionospheric current system’s contribution to the Earth’s magnetic field is the second aim of this study. We present the method, which allows computing the additional magnetic field inside and outside the current layer as generated by the space current density distribution using the Biot-Savart law. Additionally, we perform a comparison of the additional magnetic field calculation using 2D (equivalent currents) and 3D current distribution. Y1 - 2018 SN - 978-3-319-64292-5 SN - 978-3-319-64291-8 U6 - https://doi.org/10.1007/978-3-319-64292-5_10 SN - 0067-0057 SN - 2214-7985 VL - 448 SP - 263 EP - 292 PB - Springer CY - Dordrecht ER - TY - GEN A1 - Xiong, Chao A1 - Stolle, Claudia A1 - Park, Jaeheung T1 - Climatology of GPS signal loss observed by Swarm satellites T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - By using 3-year global positioning system (GPS)measurements from December 2013 to November 2016, we provide in this study a detailed survey on the climatology of the GPS signal loss of Swarm onboard receivers. Our results show that the GPS signal losses prefer to occur at both low latitudes between ±5 and ±20 ◦ magnetic latitude (MLAT) and high latitudes above 60 ◦ MLAT in both hemispheres. These events at all latitudes are observed mainly during equinoxes and December solstice months, while totally absent during June solstice months. At low latitudes the GPS signal losses are caused by the equatorial plasma irregularities shortly after sunset, and at high latitude they are also highly related to the large density gradients associated with ionospheric irregularities. Additionally, the high-latitude events are more often observed in the Southern Hemisphere, occurring mainly at the cusp region and along nightside auroral latitudes. The signal losses mainly happen for those GPS rays with elevation angles less than 20 ◦ , and more commonly occur when the line of sight between GPS and Swarm satellites is aligned with the shell structure of plasma irregularities. Our results also confirm that the capability of the Swarm receiver has been improved after the bandwidth of the phase-locked loop (PLL) widened, but the updates cannot radically avoid the interruption in tracking GPS satellites caused by the ionospheric plasma irregularities. Additionally, after the PLL bandwidth increased larger than 0.5 Hz, some unexpected signal losses are observed even at middle latitudes, which are not related to the ionospheric plasma irregularities. Our results suggest that rather than 1.0 Hz, a PLL bandwidth of 0.5 Hz is a more suitable value for the Swarm receiver. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 712 KW - Ionosphere (equatorial ionosphere; ionospheric irregularities) KW - radio science (radio wave propagation) Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-427391 SN - 1866-8372 IS - 712 ER -