TY - JOUR A1 - Park, Jaeheung A1 - Stolle, Claudia A1 - Xiong, Chao A1 - Lühr, Hermann A1 - Pfaff, Robert F. A1 - Buchert, Stephan A1 - Martinis, Carlos R. T1 - A dayside plasma depletion observed at midlatitudes during quiet geomagnetic conditions JF - Geophysical research letters N2 - In this study we investigate a dayside, midlatitude plasma depletion (DMLPD) encountered on 22 May 2014 by the Swarm and GRACE satellites, as well as ground-based instruments. The DMLPD was observed near Puerto Rico by Swarm near 10 LT under quiet geomagnetic conditions at altitudes of 475-520 km and magnetic latitudes of similar to 25 degrees-30 degrees. The DMLPD was also revealed in total electron content observations by the Saint Croix station and by the GRACE satellites (430 km) near 16 LT and near the same geographic location. The unique Swarm constellation enables the horizontal tilt of the DMLPD to be measured (35 degrees clockwise from the geomagnetic east-west direction). Ground-based airglow images at Arecibo showed no evidence for plasma density depletions during the night prior to this dayside event. The C/NOFS equatorial satellite showed evidence for very modest plasma density depletions that had rotated into the morningside from nightside. However, the equatorial depletions do not appear related to the DMLPD, for which the magnetic apex height is about 2500 km. The origins of the DMLPD are unknown, but may be related to gravity waves. Y1 - 2015 U6 - https://doi.org/10.1002/2014GL062655 SN - 0094-8276 SN - 1944-8007 VL - 42 IS - 4 SP - 967 EP - 974 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Rodríguez Zuluaga, Juan A1 - Stolle, Claudia A1 - Yamazaki, Yosuke A1 - Xiong, Chao A1 - England, Scott L. T1 - A synoptic-scale wavelike structure in the nighttime equatorial ionization anomaly JF - Earth and Space Science : ESS N2 - Both ground- and satellite-based airglow imaging have significantly contributed to understanding the low-latitude ionosphere, especially the morphology and dynamics of the equatorial ionization anomaly (EIA). The NASA Global-scale Observations of the Limb and Disk (GOLD) mission focuses on far-ultraviolet airglow images from a geostationary orbit at 47.5 degrees W. This region is of particular interest at low magnetic latitudes because of the high magnetic declination (i.e., about -20 degrees) and proximity of the South Atlantic magnetic anomaly. In this study, we characterize an exciting feature of the nighttime EIA using GOLD observations from October 5, 2018 to June 30, 2020. It consists of a wavelike structure of a few thousand kilometers seen as poleward and equatorward displacements of the EIA-crests. Initial analyses show that the synoptic-scale structure is symmetric about the dip equator and appears nearly stationary with time over the night. In quasi-dipole coordinates, maxima poleward displacements of the EIA-crests are seen at about +/- 12 degrees latitude and around 20 and 60 degrees longitude (i.e., in geographic longitude at the dip equator, about 53 degrees W and 14 degrees W). The wavelike structure presents typical zonal wavelengths of about 6.7 x 10(3) km and 3.3 x 10(3) km. The structure's occurrence and wavelength are highly variable on a day-to-day basis with no apparent dependence on geomagnetic activity. In addition, a cluster or quasi-periodic wave train of equatorial plasma depletions (EPDs) is often detected within the synoptic-scale structure. We further outline the difference in observing these EPDs from FUV images and in situ measurements during a GOLD and Swarm mission conjunction. KW - equatorial ionization anomaly KW - equatorial ionosphere KW - equatorial plasma bubbles KW - wave structure KW - forcing from below Y1 - 2021 U6 - https://doi.org/10.1029/2020EA001529 SN - 2333-5084 VL - 8 IS - 2 PB - American Geophysical Union CY - Malden, Mass. 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 - 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 - 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 - 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 - Park, Jaeheung A1 - Stolle, Claudia A1 - Yamazaki, Yosuke A1 - Rauberg, Jan A1 - Michaelis, Ingo A1 - Olsen, Nils T1 - Diagnosing low-/mid-latitude ionospheric currents using platform magnetometers BT - CryoSat-2 and GRACE-FO JF - Earth, planets and space N2 - Electric currents flowing in the terrestrial ionosphere have conventionally been diagnosed by low-earth-orbit (LEO) satellites equipped with science-grade magnetometers and long booms on magnetically clean satellites. In recent years, there are a variety of endeavors to incorporate platform magnetometers, which are initially designed for navigation purposes, to study ionospheric currents. Because of the suboptimal resolution and significant noise of the platform magnetometers, however, most of the studies were confined to high-latitude auroral regions, where magnetic field deflections from ionospheric currents easily exceed 100 nT. This study aims to demonstrate the possibility of diagnosing weak low-/mid-latitude ionospheric currents based on platform magnetometers. We use navigation magnetometer data from two satellites, CryoSat-2 and the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), both of which have been intensively calibrated based on housekeeping data and a high-precision geomagnetic field model. Analyses based on 8 years of CryoSat-2 data as well as similar to 1.5 years of GRACE-FO data reproduce well-known climatology of inter-hemispheric field-aligned currents (IHFACs), as reported by previous satellite missions dedicated to precise magnetic observations. Also, our results show that C-shaped structures appearing in noontime IHFAC distributions conform to the shape of the South Atlantic Anomaly. The F-region dynamo currents are only partially identified in the platform magnetometer data, possibly because the currents are weaker than IHFACs in general and depend significantly on altitude and solar activity. Still, this study evidences noontime F-region dynamo currents at the highest altitude (717 km) ever reported. We expect that further data accumulation from continuously operating missions may reveal the dynamo currents more clearly during the next solar maximum. KW - Platform magnetometers KW - CryoSat-2 KW - GRACE-FO KW - Inter-hemispheric KW - field-aligned currents KW - F-region dynamo currents Y1 - 2020 U6 - https://doi.org/10.1186/s40623-020-01274-3 SN - 1343-8832 SN - 1880-5981 VL - 72 IS - 1 PB - Springer CY - New York ER - 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 - GEN A1 - Park, J. A1 - Lühr, H. A1 - Stolle, Claudia A1 - Malhotra, G. A1 - Baker, J. B. H. A1 - Buchert, Stephan A1 - Gill, R. T1 - Estimating along-track plasma drift speed from electron density measurements by the three Swarm satellites T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Plasma convection in the high-latitude ionosphere provides important information about magnetosphere-ionosphere-thermosphere coupling. In this study we estimate the along-track component of plasma convection within and around the polar cap, using electron density profiles measured by the three Swarm satellites. The velocity values estimated from the two different satellite pairs agree with each other. In both hemispheres the estimated velocity is generally anti-sunward, especially for higher speeds. The obtained velocity is in qualitative agreement with Super Dual Auroral Radar Network data. Our method can supplement currently available instruments for ionospheric plasma velocity measurements, especially in cases where these traditional instruments suffer from their inherent limitations. Also, the method can be generalized to other satellite constellations carrying electron density probes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 503 KW - ionosphere KW - plasma convection Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-408417 SN - 1866-8372 IS - 503 ER - TY - JOUR A1 - Park, J. A1 - Luehr, H. A1 - Stolle, Claudia A1 - Malhotra, G. A1 - Baker, J. B. H. A1 - Buchert, Stephan A1 - Gill, R. T1 - Estimating along-track plasma drift speed from electron density measurements by the three Swarm satellites JF - Annales geophysicae N2 - Plasma convection in the high-latitude ionosphere provides important information about magnetosphere-ionosphere-thermosphere coupling. In this study we estimate the along-track component of plasma convection within and around the polar cap, using electron density profiles measured by the three Swarm satellites. The velocity values estimated from the two different satellite pairs agree with each other. In both hemispheres the estimated velocity is generally anti-sunward, especially for higher speeds. The obtained velocity is in qualitative agreement with Super Dual Auroral Radar Network data. Our method can supplement currently available instruments for ionospheric plasma velocity measurements, especially in cases where these traditional instruments suffer from their inherent limitations. Also, the method can be generalized to other satellite constellations carrying electron density probes. KW - Ionosphere KW - Plasma convection Y1 - 2015 U6 - https://doi.org/10.5194/angeo-33-829-2015 SN - 0992-7689 SN - 1432-0576 VL - 33 IS - 7 SP - 829 EP - 835 PB - Copernicus CY - Göttingen ER -