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The nature of the variability of the Total Electron Content (TEC) over Europe is investigated during 2009 and 2019 Northern Hemisphere (NH) SSW events in this study by using a combination of Global Navigation Satellite System (GNSS) based TEC observations and Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM) simulations. To simulate the SSW effects in TIE-GCM, the dynamical fields from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X) simulations of 2009 and 2019 SSWs are specified at the TIE-GCM lower boundary. The observed and simulated TEC are in overall good agreement and therefore the simulations are used to understand the sources of mid-latitude TEC variability during both SSWs. Through comparison of TIE-GCM simulations with and without geomagnetic forcing, we find that the TEC variability during the 2019 SSW event, was predominantly geomagnetically forced, while for the 2009 SSW, the major variability in TEC was accounted for by the changes in vertically propagating migrating semidiurnal solar (SW2) and lunar (M2) tides. By comparing the TIE-GCM simulations with and without the SW2 and M2 tides, we find that these semidiurnal tides contribute to urn:x-wiley:21699380:media:jgra56728:jgra56728-math-000120%–25% increase in the quiet background TEC.

The Kp index is a measure of the midlatitude global geomagnetic activity and represents short-term magnetic variations driven by solar wind plasma and interplanetary magnetic field. The Kp index is one of the most widely used indicators for space weather alerts and serves as input to various models, such as for the thermosphere and the radiation belts. It is therefore crucial to predict the Kp index accurately. Previous work in this area has mostly employed artificial neural networks to nowcast Kp, based their inferences on the recent history of Kp and on solar wind measurements at L1. In this study, we systematically test how different machine learning techniques perform on the task of nowcasting and forecasting Kp for prediction horizons of up to 12 hr. Additionally, we investigate different methods of machine learning and information theory for selecting the optimal inputs to a predictive model. We illustrate how these methods can be applied to select the most important inputs to a predictive model of Kp and to significantly reduce input dimensionality. We compare our best performing models based on a reduced set of optimal inputs with the existing models of Kp, using different test intervals, and show how this selection can affect model performance.

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., Key Points: Production and distribution of nowcast and definitive Kp index and derived products. Kp is estimated to have decreased from 1932 to 2020 by one third of a unit due to geomagnetic secular variation. Improved agreement between nowcast and definitive Kp since August 2020.

In this study, we investigated the scale sizes of equatorial plasma irregularities (EPIs) using measurements from the Swarm satellites during its early mission and final constellation phases. We found that with longitudinal separation between Swarm satellites larger than 0.4°, no significant correlation was found any more. This result suggests that EPI structures include plasma density scale sizes less than 44 km in the zonal direction. During the Swarm earlier mission phase, clearly better EPI correlations are obtained in the northern hemisphere, implying more fragmented irregularities in the southern hemisphere where the ambient magnetic field is low. The previously reported inverted-C shell structure of EPIs is generally confirmed by the Swarm observations in the northern hemisphere, but with various tilt angles. From the Swarm spacecrafts with zonal separations of about 150 km, we conclude that larger zonal scale sizes of irregularities exist during the early evening hours (around 1900 LT)., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1112

Earth, Planets and Space, 73 (1), ISSN:1343-8832, ISSN:1880-5981

ZusammenfassungDas Virus SARS-CoV‑2 und die damit einhergehende Erkrankung COVID-19 stellen die Gesundheitssysteme weltweit vor große Herausforderungen. Besonders die vulnerable Gruppe pflegebedürftiger Menschen in der Langzeitpflege ist gefährdet, schwere Krankheitsverläufe zu erleiden oder an der Infektion zu versterben.In einer bundesweiten Querschnittsstudie wurden mittels einer Onlinebefragung die Situation und die Bedarfe stationärer und ambulanter Langzeitpflegeeinrichtungen während der SARS-CoV-2-Pandemie erfasst und analysiert.Konkret forderten Teilnehmende aus 531 Einrichtungen einheitliche Handlungsempfehlungen zu SARS-CoV‑2, ausreichende und finanzierbare Schutz- und Hygienematerialien, Reihentestungen in den Einrichtungen, fundierte Beratung bei der Umsetzung von Maßnahmen, einen konkreten Pandemieplan und unterstützende Öffentlichkeitsarbeit in den Medien. Dazu wurden eine höhere Vergütung der Pflegenden, eine bessere Personalausstattung und stärkere Wertschätzung der pflegerischen Profession gefordert.Um die vulnerable Gruppe pflegebedürftiger Menschen vor einer SARS-CoV-2-Infektion zu schützen, muss die Langzeitpflege stärker in den Fokus der gesundheitspolitischen Maßnahmen während der Pandemie gerückt werden.

The magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long‐term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day‐to‐day variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet‐time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day‐to‐day variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long‐term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation.

In December 2019, the 13th revision of the International Geomagnetic Reference Field (IGRF) was released by the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD. This revision comprises two new spherical harmonic main field models for epochs 2015.0 (DGRF-2015) and 2020.0 (IGRF-2020) and a model of the predicted secular variation for the interval 2020.0 to 2025.0 (SV-2020-2025). The models were produced from candidates submitted by fifteen international teams. These teams were led by the British Geological Survey (UK), China Earthquake Administration (China), Universidad Complutense de Madrid (Spain), University of Colorado Boulder (USA), Technical University of Denmark (Denmark), GFZ German Research Centre for Geosciences (Germany), Institut de physique du globe de Paris (France), Institut des Sciences de la Terre (France), Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (Russia), Kyoto University (Japan), University of Leeds (UK), Max Planck Institute for Solar System Research (Germany), NASA Goddard Space Flight Center (USA), University of Potsdam (Germany), and Universit\'e de Strasbourg (France). The candidate models were evaluated individually and compared to all other candidates as well to the mean, median and a robust Huber-weighted model of all candidates. These analyses were used to identify, for example, the variation between the Gauss coefficients or the geographical regions where the candidate models strongly differed. The majority of candidates were sufficiently close that the differences can be explained primarily by individual modeling methodologies and data selection strategies. None of the candidates were so different as to warrant their exclusion from the final IGRF-13. The IAGA V-MOD task force thus voted for two approaches: the median of the Gauss coefficients of the candidates for the DGRF-2015 and IGRF-2020 models and the robust Huber-weighted model for the predictive SV-2020-2025. In this paper, we document the evaluation of the candidate models and provide details of the approach used to derive the final IGRF-13 products. We also perform a retrospective analysis of the IGRF-12 SV candidates over their performance period (2015-2020). Our findings suggest that forecasting secular variation can benefit from combining physics-based core modeling with satellite observations.

Transient signal loss of the global positioning system (GPS) has been frequently observed by receivers on board the European Space Agency's Swarm mission when the satellites encounter ionospheric plasma irregularities. In this study we provided the first comparison of the GPS signal amplitude degradations from receivers on board low Earth orbiting satellites at different altitudes. Intense carrier phase variations but almost no amplitude fades (less than 2 dB Hz) are observed when the spaceborne receiver lies right inside the ionospheric plasma irregularities, like the case for the Swarm and CHAMP satellites flying at about 400–500 km. This indicates that the strong phase variation, but not the amplitude fades, causes the receivers to stop tracking the GPS signals. When the receiver is located 100–200 km below the slab of plasma irregularities, like the case for the GOCE satellite flying at about 250 km, signal amplitude fades exceeding 10 dB Hz are observed, in addition to strong phase variation. Our results suggest that a considerable distance of the receiver to the plasma irregularity slab is needed to affect the Fresnel diffractive process and further causes GPS signal amplitude fades.

An exceptionally strong stationary planetary wave with Zonal Wavenumber 1 led to a sudden stratospheric warming (SSW) in the Southern Hemisphere in September 2019. Ionospheric data from European Space Agency's Swarm satellite constellation mission show prominent 6-day variations in the dayside low-latitude region at this time, which can be attributed to forcing from the middle atmosphere by the Rossby normal mode “quasi-6-day wave” (Q6DW). Geopotential height measurements by the Microwave Limb Sounder aboard National Aeronautics and Space Administration's Aura satellite reveal a burst of global Q6DW activity in the mesosphere and lower thermosphere during the SSW, which is one of the strongest in the record. The Q6DW is apparently generated in the polar stratosphere at 30–40 km, where the atmosphere is unstable due to strong vertical wind shear connected with planetary wave breaking. These results suggest that an Antarctic SSW can lead to ionospheric variability through wave forcing from the middle atmosphere.

Space weather driven atmospheric density variations affect low Earth orbit (LEO) satellites during all phases of their operational lifetime. Rocket launches, re-entry events and space debris are also similarly affected. A better understanding of space weather processes and their impact on atmospheric density is thus critical for satellite operations as well as for safety issues. The Horizon 2020 project Space Weather Atmosphere Model and Indices (SWAMI) project, which started in January 2018, aims to enhance this understanding by:Developing improved neutral atmosphere and thermosphere models, and combining these models to produce a new whole atmosphere model.Developing new geomagnetic activity indices with higher time cadence to enable better representation of thermospheric variability in the models, and improving the forecast of these indices.The project stands out by providing an integrated approach to the satellite neutral environment, in which the main space weather drivers are addressed together with model improvement. The outcomes of SWAMI will provide a pathway to improved space weather services as the project will not only address the science issues, but also the transition of models into operational services.The project aims to develop a unique new whole atmosphere model, by extending and blending the Unified Model (UM), which is the Met Office weather and climate model, and the Drag Temperature Model (DTM), which is a semi-empirical model which covers the 120–1500 km altitude range. A user-focused operational tool for satellite applications shall be developed based on this. In addition, improved geomagnetic indices shall be developed and shall be used in the UM and DTM for enhanced nowcast and forecast capability.In this paper, we report on progress with SWAMI to date. The UM has been extended from its original upper boundary of 85 km to run stably and accurately with a 135 km lid. Developments to the UM radiation scheme to enable accurate performance in the mesosphere and lower thermosphere are described. These include addition of non-local thermodynamic equilibrium effects and extension to include the far ultraviolet and extreme ultraviolet. DTM has been re-developed using a more accurate neutral density observation database than has been used in the past. In addition, we describe an algorithm to develop a new version of DTM driven by geomagnetic indices with a 60 minute cadence (denoted Hp60) rather than 3-hourlyKpindices (and corresponding ap indices). The development of the Hp60 index, and the Hp30 and Hp90 indices, which are similar to Hp60 but with 30 minute and 90 minute cadences, respectively, is described, as is the development and testing of neural network and other machine learning methods applied to the forecast of geomagnetic indices.

This paper examines the response of the upper atmosphere to equatorial Kelvin waves with a period of ∼3 days, also known as ultrafast Kelvin waves (UFKWs). The whole atmosphere model Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) is used to simulate the UFKW events in the late summer of 2010 and 2011 as well as in the boreal winter of 2012/2013. When the lower layers of the model below 30‐km altitude are constrained with meteorological data, GAIA is able to reproduce salient features of the UFKW in the mesosphere and lower thermosphere as observed by the Aura Microwave Limb Sounder. The model also reproduces ionospheric response, as validated through comparisons with total electron content data from the Gravity field and steady‐state Ocean Circulation Explorer satellite as well as with earlier observations. Model results suggest that the UFKW produces eastward‐propagating ∼3‐day variations with zonal wavenumber 1 in the equatorial zonal electric field and F region plasma density. Model results also suggest that for a ground observer, identifying ionospheric signatures of the UFKW is a challenge because of ∼3‐day variations due to other sources. This issue can be overcome by combining ground‐based measurements from different longitudes. As a demonstration, we analyze ground‐based magnetometer data from equatorial stations during the 2011 event. It is shown that wavelet spectra of the magnetic data at different longitudes are only in partial agreement, with or without a ∼3‐day peak, but a spectrum analysis based on multipoint observations reveals the presence of the UFKW.

The equatorial electrojet (EEJ) is an electric current that flows eastwards in the ionospheric E-region, along themagnetic equator. Occasionally, it reverses during morning and afternoon hours, leading to periods of westwardcurrent that are known as counter electrojet (CEJ) events. The EEJ/CEJ magnetic signal can be isolated fromother large-scale variations by using a pair of stations from the same longitude sector, one equatorial and other oflow-latitude, and taking the difference between their H components.Here, we present the first analysis of CEJ climatology and CEJ dependence on solar flux and lunar phasefor the Brazilian sector, based on an extensive ground-based data set for the years 2008 to 2017 from thegeomagnetic observatory Tatuoca (1.2◦S, 48.5◦W), and we compare it to the results found for Huancayoobservatory(12.0◦S, 75.3◦W) in the Peruvian sector.We found a predominance of morning CEJ events for both sectors. The afternoon CEJ occurrence rate inthe Brazilian sector is twice as high as in the Peruvian sector. The afternoon CEJ occurrence rate strongly dependson season, with maximum rates occurring during the northern-hemisphere summer for the Brazilian sector andduring the northern-hemisphere winter for the Peruvian sector. Significant discrepancies between the two sectorsare also found for morning CEJ rates during the northern-hemisphere summer. These longitudinal differences arein agreement with a CEJ climatology derived from contemporary Swarm satellite data and can be attributed in partto the well-known longitudinal wave-4 structure in the background EEJ strength that results from nonmigratingsolar tides and stationary planetary waves. Simulations with the Thermosphere-Ionosphere-ElectrodynamicsGeneral Circulation Model show that the remaining longitudinal variability of CEJ rates during northern summercan be explained by the effect of migrating tides in the presence of the varying geomagnetic field in the SouthAtlantic Anomaly.

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.

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.

The effects of coupling between different layers of the atmosphere during Stratospheric Sudden Warming (SSW) events have been studied quite extensively in the past fewyears, and in this context large lunitidal enhancements in the equatorial ionosphere have also been widely discussed. In this study we report about the longitudinal variabilities in lunitidal enhancement in the equatorial electrojet (EEJ) during SSWs through ground and space observations in the Peruvian and Indian sectors. We observe that the amplification of lunitidal oscillations in EEJ is significantly larger over the Peruvian sector in comparison to the Indian sector. We further compare the lunitidal oscillations in both the sectors during the 2005-2006 and 2008-2009 major SSW events and during a non-SSW winter of 2006-2007. It is found that the lunitidal amplitude in EEJ over the Peruvian sector showed similar enhancements during both the major SSWs, but the enhancements were notably different in the Indian sector. Independent from SSW events, we have also performed a climatological analysis of the lunar modulation of the EEJ during December solstice over both the sectors by using 10years of CHAMP magnetic measurements and found larger lunitidal amplitudes over the Peruvian sector confirming the results from ground magnetometer observations. We have also analyzed the semidiurnal lunar tidal amplitude in neutral temperature measurements from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) at 110km and found lesser longitudinal variability than the lunitidal amplitude in EEJ. Our results suggest that the longitudinal variabilities in lunitidal modulation of the EEJ during SSWs could be related to electrodynamics in the E region dynamo.

Earth’s magnetic field results from various internal and external sources. The electric currents in the ionosphere are major external sources of the magnetic field in the daytime. High-resolution magnetometers onboard low-Earth-orbit satellites such as CHAMP and Swarm can detect small-scale currents in the nighttime ionosphere, where plasma density gradients often become unstable and form irregular density structures. The magnetic field variations caused by the ionospheric irregularities are comparable to that of the lithospheric contribution. Two phenomena in the nighttime ionosphere that contribute to the magnetic field variation are presented: equatorial plasma bubble (EPB) and medium-scale traveling ionospheric disturbance (MSTID). EPB is formed by the generalized Rayleigh–Taylor instability over the dip equator and grows nonlinearly to as high as 2000 km apex altitude. It is characterized by deep plasma density depletions along magnetic flux tubes, where the diamagnetic effect produced by a pressure-gradient-driven current enhances the main field intensity. MSTID is a few hundred kilometer-scale disturbance in the midlatitude ionosphere generated by the coupled electrodynamics between the ionospheric $E$ and $F$ regions. The field-aligned currents associated with EPBs and MSTIDs also have significant signatures in the magnetic field perpendicular to the main field direction. The empirical discovery of the variations in the magnetic field due to plasma irregularities has motivated the inclusion of electrodynamics in the physical modeling of these irregularities. Through an effective comparison between the model results and observations, the physical process involved has been largely understood. The prediction of magnetic signatures due to plasma irregularities has been advanced by modeling studies, and will be helpful in interpreting magnetic field observations from satellites.

High-precision magnetic measurements taken by LEO satellites (flying at altitudes between 300 and 800 km) allow for studying the ionosphericand magnetospheric processes and electric currents that causes only weak magnetic signature of a few nanotesla during geomagnetic quiet conditions. Of particular importance for this endeavour are multipoint observationsin space, such as provided by the Swarm satellite constellation mission, inorder to better characterize the space-time-structure of the current systems. Focusing on geomagnetic quiet conditions, we provide an overview of ionospheric and magnetospheric sources and illustrate their magnetic signatureswith Swarm satellite observations.

In this study we investigated conditions for loss of GPS signals observed by the Swarm satellites during a 2 year period, from December 2013 to November 2015. Our result shows that the Swarm satellites encountered most of the total loss of GPS signal at the ionization anomaly crests, between ±5° and ±20° magnetic latitude, forming two bands along the magnetic equator, and these low-latitude events mainly appear around postsunset hours from 19:00 to 22:00 local time. By further checking the in situ electron density measurements of Swarm, we found that practically, all the total loss of GPS signal events at low latitudes are related to equatorial plasma irregularities (EPIs) that show absolute density depletions larger than 10 × 1011 m−3; then, the Swarm satellites encountered for up to 95% loss of GPS signal for at least one channel and up to 45% tracked less than four GPS satellites (making precise orbit determination impossible). For those EPIs with density depletions less than 10 × 1011 m−3, the chance of tracked GPS signals less than four reduces to only 1.0%. Swarm also observed total loss of all GPS signal at high latitudes, mainly around local noon, and these events are related to large spatial density gradients due to polar patches or increased geomagnetic/auroral activities. We further found that the loss of GPS signals were less frequent after appropriate settings of the Swarm GPS receivers had been updated. However, the more recent period of the mission, e.g., after the GPS receiver settings have been updated, also coincides with less severe electron density depletions due to the declining solar cycle, making GPS loss events less likely. We conclude that both lower electron density gradients and appropriate GPS receiver settings reduce the probability for Swarm satellites loss of GPS signals.

The Swarm constellation has been used to estimate zonal currents in the topside F-region ionosphere at about 500 km. Near-simultaneous magnetic field measurements from two altitudes but the same meridian are used for the current density calculations. We consider the period 15 February to 23 June 2014 for deriving a full 24-hour local time coverage of the latitudinal distribution over ±50° in magnetic latitude. Intervals with close orbital phasing at the two heights are considered, which repeat every 6 days. From such days seven successive orbits are used where the epochs of equator crossings differ by less than 2 minutes. Deduced current densities are predominantly eastward (about 20 nA/m2) on the dayside and westward (about 10 nA/m2) on the nightside. A number of different drivers contribute to the observed total current. We identified the gravity-driven eastward current as the most prominent at low latitudes. Eastward currents in the northern hemisphere are clearly stronger than in the south. This is attributed to the proximity of our study period to June solstice, when the solar radiation is stronger in the north. In addition, inter-hemispheric winds from the northern (summer) to the southern (winter) hemisphere contribute. They cause eastward currents in the north and westward in the south. We find a relatively large variability of the zonal currents both in space and time. The standard deviation is at least twice as large as the mean value of current density. This large variability is suggested to be related to gravity wave forcing from below.

Open Access. Text © 2018. The authors. CC BY 3.0 Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited., Ideas for this article were developed during international team meetings supported by the International Space Science Institute (ISSI; Bern, Switzerland). The National Center for Atmospheric Research is supported by the U.S. National Science Foundation. J.L.C., C.S., and T.A.S. are partly supported by the German Research Foundation’s Priority Program 1788 “DynamicEarth.” L.P.G. is supported by NASA through LWS grant NNX13AI62G and by U.S. NSF grant AGS-1343056. H.S. is partly supported by the German Research Foundation (DFG) under FOR 1898 (MS-GWaves), project SCHM 2158/5-1 (GWING). V.L.H. is supported by U.S. NSF AGS-1343031, NASA LWS NNX14AH54G, and NASA HGI NNX17AB80G. B.F. is supported by the Spanish MCINN under grant ESP2014-54362-P and EC FEDER funds.

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 ΔH 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 ΔH 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.

Magnetic and electric field observations from the European Space Agency Swarm mission are used to report the direction of electromagnetic energy flux associated with equatorial plasma depletions. Contrary to expectations, the observations suggest a general interhemispheric Poynting flux rather than concurrent flows at both hemispheres toward or away from the equator. Of high interest is a particular behavior noticed over the region with the largest variation in the magnetic declination. This is a Poynting flux flowing mainly into the southern magnetic hemisphere about between 60 degrees W and 30 degrees E and into the northern magnetic hemisphere between 110 degrees W and 60 degrees W. The abrupt change in the flow direction at 60 degrees W is suggested to be caused by an asymmetry between the hemispheres on the ionospheric conductivity, likely due to the influence of thermospheric winds and the presence of the South Atlantic Anomaly.

We report on simultaneous observations of electromagnetic ion cyclotron (EMIC) waves associated with traveling convection vortex (TCV) events caused by transient solar wind dynamic pressure (P-d) impulse events. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft located near the magnetopause observed radial fluctuations of the magnetopause, and the GOES spacecraft measured sudden compressions of the magnetosphere in response to sudden increases in Pd. During the transient events, EMIC waves were observed by interhemispheric conjugate ground-based magnetometer arrays as well as the GOES spacecraft. The spectral structures of the waves appear to be well correlated with the fluctuating motion of the magnetopause, showing compression-associated wave generation. In addition, the wave features are remarkably similar in conjugate hemispheres in terms of bandwidth, quasiperiodic wave power modulation, and polarization. Proton precipitation was also observed by the DMSP spacecraft during the wave events, from which the wave source region is estimated to be 72 degrees-74 degrees in magnetic latitude, consistent with the TCV center. The confluence of space-borne and ground instruments including the interhemispheric, high-latitude, fluxgate/induction coil magnetometer array allows us to constrain the EMIC source region while also confirming the relationship between EMIC waves and the TCV current system. National Science Foundation (NSF) [AGS-1547252]; NSF [PLR-1543364, PLR-1247975, PLR-1443507, PLR-1341677, PLR-1341493] The work at New Jersey Institute of Technology was supported by National Science Foundation (NSF) grant AGS-1547252. The work at Virginia Tech was supported by NSF grant PLR-1543364. The fluxgate magnetometer projects at SPA and AGOs are supported by NSF grants PLR-1247975 and PLR-1443507, respectively, to New Jersey Institute of Technology. The induction coil magnetometer projects at STF, IQA, SPA, and AGOs are supported by NSF grants PLR-1341677 to the University of New Hampshire and PLR-1341493 to Augsburg College. The authors would like to thank the following persons/institutes for providing data: the THEMIS team for fluxgate magnetometer and electrostatic analyzer data; the NOAA GOES team for fluxgate magnetometer data; the DMSP team for SSJ particle data; Lorne McKee at Natural Resources Canada (NRCan) and INTERMAGNET for fluxgate magnetometer data from IQA, which is operated by NRCan; the Technical University of Denmark National Space Institute (DTU Space) for the fluxgate magnetometer data (STF); the British Antarctic Survey (BAS) team for fluxgate data (HBA); and the AGO project team for operations of the magnetometer stations. All data used in this study can be obtained from the following data repositories and tools: OMNI, ACE, and THEMIS data from the NASA Coordinated Data Analysis Web (CDAWeb) at http://cdaweb.sci.gsfc.nasa.gov and Space Physics Environment Data Analysis Software (SPEDAS); GOES magnetometer data from the data archive at National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information (NCEI, previously known as NGDC) (http://satdat.ngdc.noaa.gov/sem/goes/data/new_full/); DMSP particle data from the DMSP Online Spectrogram Viewer Tool at http://sd-www.jhuapl.edu/Aurora/spectrogram/index.html; IQA fluxgate data from the Intermagnet (www.intermagnet.org); STF fluxgate magnetometer data from the DTU database (https://ftp.space.dtu.dk/data/Ground_magnetometers/Adjusted/); HBA fluxgate data from the BAS Data Access System (http://psddb.nerc-bas.ac.uk); and SPA and AGO fluxgate and induction coil magnetometer data from the New Jersey Institute of Technology database (www.antarcticgeospace.org).

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.

The Earth’s magnetic field results from different sources in the Earth’s interior and in near Earth space. Commonly, when investigating solar-terrestrial interactions where the Earth’s internal field plays a major role, scientists concentrate on strong (tens to thousands of nanotesla) and rapid (seconds to days) magnetic field variations that are caused by currents in the ionosphere and magnetosphere when solar activity, and correspondingly the electric currents in Earth’s environment, are enhanced. However, for studying the internal sources of the geomagnetic field, originating in the core and crust, scientists use observations from so called “geomagnetic quiet” times, when external field variations are expected to be weak. However, even these weak variations impact internal field modelling, and incomplete knowledge of them hinders their separation. Difficulties arise in particular in characterizing the long term behaviour of external sources, e.g., seasonal and solar cycle variations of the magnetospheric ring current, polar convection currents or ionospheric dynamo currents driven by atmospheric tides, since they have amplitudes and spatial scales similar to those of the core field’s secular variation or the lithospheric field. Since such external currents are also present during geomagnetic quiet conditions they may result in biased core and crustal field models. An additional complexity arises from magnetic observations taken by satellites because of the movement of the platform, leading to a possible space-time ambiguity.

Low Earth orbiting geomagnetic satellite missions, such as the Swarm satellite mission, are the only means to monitor and investigate ionospheric currents on a global scale and to make in situ measurements of F region currents. High-precision geomagnetic satellite missions are also able to detect ionospheric currents during quiet-time geomagnetic conditions that only have few nanotesla amplitudes in the magnetic field. An efficient method to isolate the ionospheric signals from satellite magnetic field measurements has been the use of residuals between the observations and predictions from empirical geomagnetic models for other geomagnetic sources, such as the core and lithospheric field or signals from the quiet-time magnetospheric currents. This study aims at highlighting the importance of high-resolution magnetic field models that are able to predict the lithospheric field and that consider the quiet-time magnetosphere for reliably isolating signatures from ionospheric currents during geomagnetically quiet times. The effects on the detection of ionospheric currents arising from neglecting the lithospheric and magnetospheric sources are discussed on the example of four Swarm orbits during very quiet times. The respective orbits show a broad range of typical scenarios, such as strong and weak ionospheric signal (during day- and nighttime, respectively) superimposed over strong and weak lithospheric signals. If predictions from the lithosphere or magnetosphere are not properly considered, the amplitude of the ionospheric currents, such as the midlatitude Sq currents or the equatorial electrojet (EEJ), is modulated by 10–15 % in the examples shown. An analysis from several orbits above the African sector, where the lithospheric field is significant, showed that the peak value of the signatures of the EEJ is in error by 5 % in average when lithospheric contributions are not considered, which is in the range of uncertainties of present empirical models of the EEJ., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 887

We present multimission observations of field-aligned currents, auroral oval, and magnetopause crossings during the 17 March 2015 magnetic storm. Dayside reconnection is expected to transport magnetic flux, strengthen field-aligned currents, lead to polar cap expansion and magnetopause erosion. Our multimission observations assemble evidence for all these manifestations. After a prolonged period of strongly southward interplanetary magnetic field, Swarm and AMPERE observe significant intensification of field-aligned currents .The dayside auroral oval, as seen by DMSP, appears as a thin arc associated with ongoing dayside reconnection. Both the field-aligned currents and the auroral arc move equatorward reaching as low as approx. 60 deg. magnetic latitude. Strong magnetopause erosion is evident in the in situ measurements of the magnetopause crossings by GOES 13/15 and MMS. The coordinated Swarm, AMPERE, DMSP, MMS and GOES observations, with both global and in situ coverage of the key regions, provide a clear demonstration of the effects of dayside reconnection on the entire magnetosphere.

Swarm is a three-satellite constellation mission launched by the European Space Agency (ESA) on 22 November2013. It consists of three identical spacecraft, two of which (Swarm Alpha and Swarm Charlie) are flying almost side-by-side in polar orbits at lower altitude (about 470 km in September 2016) with an East-West separation of 1.4º in longitude corresponding to 155 km at the equator. The third satellite (Swarm Bravo) is in a slightly higher orbit (about 520 km altitude in September2016). Each of the three satellites carry a magnetometry package (consisting of absolute scalar magnetometer,fluxgate vector magnetometer, and star imager) for measuring the direction and strength of the magnetic field,and instruments to measure plasma and electric field parameters as well as gravitational acceleration. Time and position are provided by on-board GPS. The configuration of the various instruments on each of the three Swarm spacecraft is shown in Fig. 1. More information about the mission can be found at http://earth.esa.int/swarm.

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.

The atmospheric lunar tide is one known source of ionospheric variability. The subject received renewed attention as recent studies found a link between stratospheric sudden warmings and amplified lunar tidal perturbations in the equatorial ionosphere. There is increasing evidence from ground observations that the lunar tidal influence on the ionosphere depends on longitude. We use magnetic field measurements from the CHAMP satellite during July 2000–September 2010 and from the two Swarm satellites during November 2013–February 2017 to determine, for the first time, the complete seasonal-longitudinal climatology of the semidiurnal lunar tidal variation in the equatorial electrojet intensity. Significant longitudinal variability is found in the amplitude of the lunar tidal variation, while the longitudinal variability in the phase is small. The amplitude peaks in the Peruvian sector (∼285∘E) during the Northern-Hemisphere winter and equinoxes, and in the Brazilian sector (∼325∘E) during the Northern-Hemisphere summer. There are also local amplitude maxima at ∼55∘E and ∼120∘E. The longitudinal variation is partly due to the modulation of ionospheric conductivities by the inhomogeneous geomagnetic field. Another possible cause of the longitudinal variability is neutral wind forcing by nonmigrating lunar tides. A tidal spectrum analysis of the semidiurnal lunar tidal variation in the equatorial electrojet reveals the dominance of the westward-propagating mode with zonal wavenumber 2 (SW2), with secondary contributions by westward-propagating modes with zonal wavenumber 3 (SW3) and 4 (SW4). Eastward-propagating waves are largely absent from the tidal spectrum. Further study will be required for the relative importance of ionopsheric conductivities and nonmigrating lunar tides.

The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere toward dawn and out of the ionosphere toward dusk, linked by a westward electrojet. We use multispacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal substructure on scales of 100 km at altitudes of 4000–7000 km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120–240 s after Cluster 4 at 1300–2000 km higher altitude. Both spacecraft observed large-scale regions of net upward and downward field-aligned current, consistent with the large-scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north-south direction, in contrast to the expected east-west orientation of the preonset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs), we conclude that significant questions remain for the explanation of SCW structuring by BBF-driven “wedgelets.” Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the SCW. Key Points The substorm current wedge (SCW) has significant azimuthal structure Current sheets within the SCW are north-south aligned The substructure of the SCW raises questions for the proposed wedgelet scenario

Swarm a three satellite constellation to study the dynamics of the Earth's magnetic field and its interactions with the Earth system is expected to be launched in late 2013. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution in order to gain new insights into the Earth system by improving our understanding of the Earth's interior and environment. In order to derive advanced models of the geomagnetic field (and other higher level data products) it is necessary to take explicit advantage of the constellation aspect of Swarm. The Swarm SCARF (Satellite Constellation Application and Research Facility) has been established with the goal of deriving Level 2 products by combination of data from the three satellites and of the various instruments. The present paper describes the Swarm input data products (Level lb and auxiliary data) used by SCARF the various processing chains of SCARF and the Level 2 output data products determined by SCARF. Copyright © The Society of Geomagnelism and Earth Planetary and Space Sciences (SGEPSS).

Equivalent ionospheric currents obtained with the spherical elementary current systems (SECS) method and derived from nearly 100 ground magnetometers spread over North America and Greenland are compared with ionospheric flow vectors measured by the SuperDARN radars during both the summer and winter seasons. This comparison is done over a range of spatial separations, magnetic latitudes, magnetic local times, and auroral electrojet activity to investigate under what conditions the vectors are anti-parallel to one another. Our results show that in general the equivalent ionospheric currents are anti-parallel to the flows and the best results are achieved within the auroral oval during active geomagnetic conditions in the dawn, dusk and noon sectors in the northern hemisphere summer. These results indicate the best anti-parallel alignment occurs when the currents and flows are large and well defined. Factors that may influence the alignment include ionospheric conductivity gradients and quiet time backgrounds. Our results can be used to approximate the macroscopic (∼1000 km) ionospheric convection patterns. The SECS maps represent a value-added product from the raw magnetometer database and can be used for contextual interpretation; they can help with our understanding of magnetosphere-ionosphere coupling mechanisms using ground arrays and the magnetospheric spacecraft data, and they can be used as input for other techniques.

The evening of 30October 2003 was subject to a major storm main phase. For this time, we combine large-scale electron content maps from GPS imaging with time series of electron density and temperature of two EISCAT radars in Tromsø and Svalbard and the Sondrestrom radar, for observing the north polar ionosphere. The GPS assimilations resulted in the image of the electron content trace of an anti-sunward polar Tongue Of Ionisation (TOI) consecutively to 20:00UT. In combination with the radar observations we concluded that the TOI persisted during the whole period of continuous southward IMF Bz until about 22:40UT while its largest extension toward the nightside auroral region was found between 21:00-22:00UT. A typical Fregion electron temperature of ~2000 K and the plasma velocity of ~800 ms-1 support its convective origin from the dayside mid-latitudes. Due to the structured appearance of the electron content distribution and the radar electron density time series we believe that discrete plasma patches formed inside the anti-sunward drift pattern. After two large oscillations of the IMF Bz the nightside plasma density was observed to re-enhance after 23:00UT along a longitudinal band below 70 N. Coinciding electron temperatures of ~2000 K suggest again the convective nature of the plasma, while a modified convection pattern is expected.