TY - JOUR A1 - Cervantes Villa, Juan Sebastian A1 - Shprits, Yuri A1 - Aseev, Nikita A1 - Drozdov, Alexander A1 - Castillo Tibocha, Angelica Maria A1 - Stolle, Claudia T1 - Identifying radiation belt electron source and loss processes by assimilating spacecraft data in a three-dimensional diffusion model JF - Journal of geophysical research : Space physics N2 - Data assimilation aims to blend incomplete and inaccurate data with physics-based dynamical models. In the Earth's radiation belts, it is used to reconstruct electron phase space density, and it has become an increasingly important tool in validating our current understanding of radiation belt dynamics, identifying new physical processes, and predicting the near-Earth hazardous radiation environment. In this study, we perform reanalysis of the sparse measurements from four spacecraft using the three-dimensional Versatile Electron Radiation Belt diffusion model and a split-operator Kalman filter over a 6-month period from 1 October 2012 to 1 April 2013. In comparison to previous works, our 3-D model accounts for more physical processes, namely, mixed pitch angle-energy diffusion, scattering by Electromagnetic Ion Cyclotron waves, and magnetopause shadowing. We describe how data assimilation, by means of the innovation vector, can be used to account for missing physics in the model. We use this method to identify the radial distances from the Earth and the geomagnetic conditions where our model is inconsistent with the measured phase space density for different values of the invariants mu and K. As a result, the Kalman filter adjusts the predictions in order to match the observations, and we interpret this as evidence of where and when additional source or loss processes are active. The current work demonstrates that 3-D data assimilation provides a comprehensive picture of the radiation belt electrons and is a crucial step toward performing reanalysis using measurements from ongoing and future missions. KW - acceleration KW - code KW - density KW - emic waves KW - energetic particle KW - mechanisms KW - reanalysis KW - ultrarelativistic electrons KW - weather Y1 - 2019 U6 - https://doi.org/10.1029/2019JA027514 SN - 2169-9380 SN - 2169-9402 VL - 125 IS - 1 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Luo, Xiaomin A1 - Xiong, Chao A1 - Gu, Shengfeng A1 - Lou, Yidong A1 - Stolle, Claudia A1 - Wan, Xin A1 - Liu, Kangkang A1 - Song, Weiwei T1 - Geomagnetically conjugate observations of equatorial plasma irregularities from swarm constellation and ground-based GPS stations JF - Journal of geophysical research: Space physics N2 - The near-polar orbit satellites of Swarm mission provide a good opportunity to investigate the conjugacy of equatorial plasma irregularities (EPIs) since their trajectories at low latitudes are basically aligned with fixed geographical longitude. However, the Swarm in situ electron density occasionally shows EPIs at only one hemisphere at this longitude. In this study, we provide detailed analysis of such EPI events from the in situ electron densities and onboard global positioning system (GPS) measurements of Swarm low pair satellites, and simultaneous GPS data from two geomagnetically conjugate ground stations at the Africa longitudes. The result indicates that when Swam in situ electron density sometime shows EPIs at only one hemisphere, the GPS scintillations are still observed from the Swarm onboard receiver and by the two conjugate ground stations. It implies that the EPIs should generally elongate along the geomagnetic flux tube. More than two-year statistic results show that the onset time of scintillation in the northern station is on average 16 and 18 min earlier than that in the southern station for September equinox and December solstice in 2015, while for March equinox in 2016 the onset time of scintillation of northern station is about 11 min later than that of southern station, which indicates the asymmetry features of EPIs along the flux tube. Further analysis of nearly three-year GPS data from two conjugate stations at the Asia longitudes, we find that during solar maximum years the local sunset time plays an important role for causing the difference of onset time of scintillation between two conjugate stations. Y1 - 2019 U6 - https://doi.org/10.1029/2019JA026515 SN - 2169-9380 SN - 2169-9402 VL - 124 IS - 5 SP - 3650 EP - 3665 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Matzka, Jürgen A1 - Siddiqui, Tarique Adnan A1 - Lilienkamp, Henning A1 - Stolle, Claudia A1 - Veliz, Oscar T1 - Quantifying solar flux and geomagnetic main field influence on the equatorial ionospheric current system at the geomagnetic observatory Huancayo JF - Journal of Atmospheric and Solar-Terrestrial Physics N2 - In order to analyse the sensitivity of the equatorial ionospheric current system, i.e. the solar quiet current system and the equatorial electrojet, to solar cycle variations and to the secular variation of the geomagnetic main field, we have analysed 51 years (1935-1985) of geomagnetic observatory data from Huancayo, Peru. This period is ideal to analyse the influence of the main field strength on the amplitude of the quiet daily variation, since the main field decreases significantly from 1935 to 1985, while the distance of the magnetic equator to the observatory remains stable. To this end, we digitised some 19 years of hourly mean values of the horizontal component (H), which have not been available digitally at the World Data Centres. Then, the sensitivity of the amplitude Ali of the quiet daily variation to both solar cycle variations (in terms of sunspot numbers and solar flux F10.7) and changes of the geomagnetic main field strength (due to secular variation) was determined. We confirm an increase of Delta H for the decreasing main field in this period, as expected from physics based models (Cnossen, 2016), but with a somewhat smaller rate of 4.4% (5.8% considering one standard error) compared with 6.9% predicted by the physics based model. KW - Magnetic field KW - Equatorial ionosphere KW - Geomagnetic secular variation KW - Solar cycle Y1 - 2017 U6 - https://doi.org/10.1016/j.jastp.2017.04.014 SN - 1364-6826 SN - 1879-1824 VL - 163 SP - 120 EP - 125 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Matzka, Jürgen A1 - Stolle, Claudia A1 - Yamazaki, Yosuke A1 - Bronkalla, Oliver A1 - Morschhauser, Achim T1 - The geomagnetic Kp index and derived indices of geomagnetic activity JF - Space weather : the international journal of research and applications N2 - The geomagnetic Kp index is one of the most extensively used indices of geomagnetic activity, both for scientific and operational purposes. This article reviews the properties of the Kp index and provides a reference for users of the Kp index and associated data products as derived and distributed by the GFZ German Research Centre for Geosciences. The near real-time production of the nowcast Kp index is of particular interest for space weather services and here we describe and evaluate its current setup. Y1 - 2021 U6 - https://doi.org/10.1029/2020SW002641 SN - 1542-7390 VL - 19 IS - 5 PB - Wiley CY - New York 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 - 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, Jaeheung A1 - Lühr, Hermann A1 - Kervalishvili, Guram N. A1 - Rauberg, Jan A1 - Michaelis, Ingo A1 - Stolle, Claudia A1 - Kwak, Young-Sil T1 - Nighttime magnetic field fluctuations in the topside ionosphere at midlatitudes and their relation to medium-scale traveling ionospheric disturbances: The spatial structure and scale sizes JF - Journal of geophysical research : Space physics N2 - Previous studies suggested that electric and/or magnetic field fluctuations observed in the nighttime topside ionosphere at midlatitudes generally originate from quiet time nocturnal medium-scale traveling ionospheric disturbances (MSTIDs). However, decisive evidences for the connection between the two have been missing. In this study we make use of the multispacecraft observations of midlatitude magnetic fluctuations (MMFs) in the nighttime topside ionosphere by the Swarm constellation. The analysis results show that the area hosting MMFs is elongated in the NW-SE (NE-SW) direction in the Northern (Southern) Hemisphere. The elongation direction and the magnetic field polarization support that the area hosting MMFs is nearly field aligned. All these properties of MMFs suggest that they have close relationship with MSTIDs. Expectation values of root-mean-square field-aligned currents associated with MMFs are up to about 4nA/m(2). MMF coherency significantly drops for longitudinal distances of 1 degrees. KW - midlatitude nighttime magnetic fluctuation KW - nighttime MSTID KW - Swarm constellation Y1 - 2015 U6 - https://doi.org/10.1002/2015JA021315 SN - 2169-9380 SN - 2169-9402 VL - 120 IS - 8 SP - 6818 EP - 6830 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Park, Jaeheung A1 - Lühr, Hermann A1 - Kervalishvili, Guram A1 - Rauberg, Jan A1 - Stolle, Claudia A1 - Kwak, Young-Sil A1 - Lee, Woo Kyoung T1 - Morphology of high-latitude plasma density perturbations as deduced from the total electron content measurements onboard the Swarm constellation JF - Journal of geophysical research : A, Space physics N2 - In this study, we investigate the climatology of high-latitude total electron content (TEC) variations as observed by the dual-frequency Global Navigation Satellite Systems (GNSS) receivers onboard the Swarm satellite constellation. The distribution of TEC perturbations as a function of geographic/magnetic coordinates and seasons reasonably agrees with that of the Challenging Minisatellite Payload observations published earlier. Categorizing the high-latitude TEC perturbations according to line-of-sight directions between Swarm and GNSS satellites, we can deduce their morphology with respect to the geomagnetic field lines. In the Northern Hemisphere, the perturbation shapes are mostly aligned with the L shell surface, and this anisotropy is strongest in the nightside auroral (substorm) and subauroral regions and weakest in the central polar cap. The results are consistent with the well-known two-cell plasma convection pattern of the high-latitude ionosphere, which is approximately aligned with L shells at auroral regions and crossing different L shells for a significant part of the polar cap. In the Southern Hemisphere, the perturbation structures exhibit noticeable misalignment to the local L shells. Here the direction toward the Sun has an additional influence on the plasma structure, which we attribute to photoionization effects. The larger offset between geographic and geomagnetic poles in the south than in the north is responsible for the hemispheric difference. Y1 - 2017 U6 - https://doi.org/10.1002/2016JA023086 SN - 2169-9380 SN - 2169-9402 VL - 122 IS - 1 SP - 1338 EP - 1359 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Park, Jaeheung A1 - Lühr, Hermann A1 - Stolle, Claudia A1 - Rodriguez-Zuluaga, Juan A1 - Knudsen, David J. A1 - Burchill, Johnathan K. A1 - Kwak, Young-Sil T1 - Statistical survey of nighttime midlatitude magnetic fluctuations: Their source location and Poynting flux as derived from the Swarm constellation JF - Journal of geophysical research : Space physics N2 - This is the first statistical survey of field fluctuations related with medium-scale traveling ionospheric disturbances (MSTIDs), which considers magnetic field, electric field, and plasma density variations at the same time. Midlatitude electric fluctuations (MEFs) and midlatitude magnetic fluctuations (MMFs) observed in the nighttime topside ionosphere have generally been attributed to MSTIDs. Although the topic has been studied for several decades, statistical studies of the Poynting flux related with MEF/MMF/MSTID have not yet been conducted. In this study we make use of electric/magnetic field and plasma density observations by the European Space Agency's Swarm constellation to address the statistical behavior of the Poynting flux. We have found that (1) the Poynting flux is directed mainly from the summer to winter hemisphere, (2) its magnitude is larger before midnight than thereafter, and (3) the magnitude is not well correlated with fluctuation level of in situ plasma density. These results are discussed in the context of previous studies. Y1 - 2016 U6 - https://doi.org/10.1002/2016JA023408 SN - 2169-9380 SN - 2169-9402 VL - 121 SP - 11235 EP - 11248 PB - American Geophysical Union CY - Washington ER - 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 -