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The Space Weather (SWE) Service Network of the European Space Agency’s (ESA’s) Space Safety Programme provides timely and reliable space weather information to end users allowing the mitigation and prevention of the impact of hazards from space on the communication and navigation systems, power grids, and aviation, etc. The SWE Service Network consists of 5 Expert Service Centres (ESCs), Solar Weather, Space Radiation, Ionospheric Weather, Geomagnetic Conditions, and Heliospheric Weather, which are distributed and established across Europe providing coverage of space weather phenomena and impacts on ground and space-based infrastructure. Note that a free registration at the ESA's SWE portal is necessary to get access to the protected applications or products.Here, we give an overview of 18 products that currently are provided by GFZ in the Ionospheric Weather ESC (I-ESC) and Geomagnetic Conditions ESC (G-ESC). These products are derived from the Low Earth Orbiting (LEO) satellite and ground-based observations. In I-ESC, the following Swarm mission products are provided: Rate Of the change of TEC (ROT), Total Electron Content (TEC), in-situ electron density (Ne), Ionospheric Bubble Index (IBI), Rate Of the change of TEC Index (ROTI). And in G-ESC: the location and intensity level of the Polar Electrojet (PEJ), Field-Aligned Currents (FACs), and Vector Magnetic Field (MAG) components. The following global geomagnetic indices are provided in G-ESC, nowcast Kp (three-hourly), Hp60 (one-hourly and open-ended), Hp30 (half-hourly and open-ended) indices, most recent definitive Kp index, Kp, Ap, Hp60, ap60, Hp30, ap30 indices on tabular form, Kp and Ap (since 1932), Hp60, ap60, Hp30 and ap30 (since 1995) indices archive.

The Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission GRACE-FO are gravity satellites jointly developed by the National Aeronautics and Space Administration (NASA) and German Aerospace Center (DLR), which are composed of two satellites. Such tandem satellite missions provide us with a good opportunity to evaluate the ionospheric total electron content (TEC) derived from their onboard global positioning system (GPS) receivers. In addition, the K-band ranging system (KBR) between two satellites provides also the in-situ electron density (Ne) at the satellite orbits, which can help further to evaluate the reliability of TEC. By combing the observations from GRACE and GRACE-FO, 20 years of data (from 2002 to 2022) have been accumulated to analyze the solar cycle dependence of TEC and Ne at the topside ionosphere. Our results show that the TEC from the tandem satellites is generally the same, but slight differences can still be found, showing solar cycle and local time dependences. In addition, we found that the TEC differences between the tandem satellites of GRACE are somehow smaller than that of GRACE-FO, and the consistency between the TEC and inter-satellite electron density results of GRACE is also better.

In this study we performed a detailed analysis on the scale-size of field-aligned currents (FACs) at auroral latitudes, using the well-calibrated magnetic data from the non-dedicated magnetic field mission, Gravity Recovery and Climate Experiment Follow-On (GRACE-FO). With two spacecraft following each other, the GRACE-FO provides a good opportunity to identify the variation of FACs with different scale lengths. The results show that the auroral FACs can be classified into two groups: the small-scale ones, shorter than some tens of kilometers, dominated by kinetic Alfvén waves, are quite dynamic; and the large-scale ones, typically larger than 150 km, can be considered as quasi-static and persist longer than 1 min. The GRACE-FO observations also reveal that the small-scale FACs at the same location sometimes can persist over 25 s, e.g., around dusk and dawn hours, which is longer than the typical persistent period (10 s) of kinetic Alfvén waves as earlier reported. The FAC structures show clear magnetic local time dependence, with higher correlations between the spacecraft around dusk and dawn hours; lower correlations are found around midnight and lowest correlations around noon, implying that the small-scale FACs most frequently appear at the noon cusp region. Slightly better correlations of FACs between two spacecraft are found during local summer, and such seasonal dependence is dominated by the correlations of small-scale FACs at noon. However, further analysis shows that the small-scale FACs at noon have largest occurrence and intensity during local summer, which reveals that when interpreting the cross-correlation analysis the intensity of FACs needs to be taken into account. Graphical Abstract

Topside Ionosphere Radio Observations from multiple Low Earth Orbiting (LEO)-missions (TIRO) is a project in ESA’s Swarm Data, Innovation, and Science Cluster (DISC) framework. TIRO provides high accuracy Total Electron Content (TEC) from dual-frequency GPS receivers onboard CHAMP (2000-2010), GRACE (2002-2017), and GRACE Follow-On (since 2018) missions. Special emphasis is put to ensure maximum consistency between the previously and operationally derived data sets from GOCE and Swarm to investigate conjunctions and thus ensure the consistency of the entire timeline from as early as CHAMP up to GRACE-FO. The primary science instrument onboard GRACE and GRACE-FO is a K-Band inter-satellite ranging system, which in this study is used to derive an estimate of the in-situ electron density. The derived electron density will be validated using both, the International Reference Ionosphere (IRI) model and radar observations taken at Millstone Hill, Arecibo, EISCAT, Resolute Bay, and Jicamarca. In combination, these products form long-term series and almost cover two full solar cycles by the continuous TEC data set and electron density either taken by CHAMP, GRACE, Swarm, or GRACE-FO. We will present climatological studies as well as case studies of selected events, such as equatorial plasma depletions, simultaneously observed by GPS and K-Band.

Global geomagnetic indices are widely used not only to characterize the geomagnetic disturbance level but also for the parameterization of physical and empirical models of the near-Earth space environment and in data (re)analysis. One of the most utilized index families is the three-hourly Kp and the ap, Ap, Cp, C9 indices derived and disseminated by the GFZ German Research Centre for Geosciences.The new global geomagnetic open-ended, high-cadence, Kp-like Hpo index family (consisting of the half-hourly Hp30, ap30 and hourly Hp60, ap60) was developed within the Space Weather Atmosphere Models and Indices (SWAMI) project of the H2020 EU research activity. These open-ended Hpo indices are based on the data of the same 13 geomagnetic observatory and similar algorithms as the three-hourly Kp index. The open-ended indices are designed such that 15 Hp60 and 32 Hp60 values exceeding 9 (maximum amplitude for the Kp index) have been assigned since 1995.Near real-time indices and archive indices back to 1995 are available for download under the CC BY 4.0 license and include the linear versions of the Hp30 and Hp60 indices, the ap30 and ap60 indices. Near real-time plots of the Hp30 and Hp60 indices for the current day and the previous six days are also provided. Here, the operational capabilities and examples of these indices will be presented.

The relation between the plasmapause (PP) and various ionospheric phenomena, such as the midlatitude ionospheric trough (MIT) has been studied for decades. More recently, it was found that the equatorward boundary of small-scale field-aligned currents (SSB) and the PP are also closely coupled. In spite of prolonged efforts many details of these relationships, as well as the mechanisms responsible for them remain poorly understood. ESA's Swarm mission in conjunction with magnetospheric missions (RBSP, Arase, and THEMIS) provides an unprecedented opportunity to study these relationships on a global scale and over an extended period. Swarm delivers observations of MIT, the associated sub-auroral electron temperature enhancement (SETE), as well as SSB, while PP crossings can be inferred from in-situ magnetospheric electron density measurements. In this study, we use 7 years of Swarm observations and PP positions from 2014 to 2017 to address some of the open questions. We confirm that MIT/SETE and PP are directly coupled, however only in the nighttime. Their correlation remains high after post-dawn, however, with an increasing, MLT-dependent time lag. Afternoon MIT observations were found conjugated with a plasmaspheric plume. The correlation between SSB and PP is also high and they intersect each other near MLT midnight. Our results confirm the scenario that the PP is formed on the night side, and propagates to the dayside by co-rotating with the Earth and suggest that the plasma is transported from the depleted ionospheric/dense plasmaspheric stagnation region also westward/sunward forming the afternoon MIT/narrow plumes, respectively.

Ionospheric plasma irregularities can be successfully studied with the Swarm satellites. Parameters derived from the in-situ plasma measurements and from the topside ionosphere total electron content provide a comprehensive dataset for characterizing plasma structuring along the orbits of the Swarm satellites. The Ionospheric Plasma IRregularities (IPIR) data product summarizes these parameters and allows for systematic studies of ionospheric irregularities. IPIR has already been used in investigations of structuring and variability of ionospheric plasma. This report provides a detailed description of algorithms behind the IPIR data product and demonstrates its use for ionospheric studies.

Based on magnetic field data from the Swarm satellite constellation advanced estimates of field‐aligned and radial currents at middle and low latitudes can be derived. Detailed results have been obtained for low‐latitude (14°–35° magnetic latitude) interhemispheric field‐aligned currents related to the solar quiet (Sq) current system. The continuous data set of five years allows resolving the dependences on local time, season, and longitude. We confirm the known current flow from the southern to the northern hemisphere around June solstice. Unexpected results are obtained for the months following December. Stratospheric sudden warming events are suggested as a reason for that. These phenomena are known to amplify lunar tides and atmospheric planetary waves. Furthermore, we investigated the mean characteristic of the meridional current systems connected to the wind‐driven F region dynamo above the magnetic equator. Typical features of radially downward currents around noon and upward currents in the evening sector could be confirmed. From a detailed analysis of the connected field‐aligned current distribution we deduced that the mean altitude of the dynamo region is higher in the evening than around noon. And it appears also at greater heights in the western hemisphere than in the eastern. Special current configurations are encountered in the longitude range containing the South Atlantic Anomaly. Here summer‐like conditions are prevailing through all seasons. This infers that the ionospheric conductivity is significantly enhanced in this region of weak magnetic field strength.

Field‐aligned currents play a major role in magnetized plasmas. They are the main agents for coupling the dynamics between magnetosphere and ionosphere. Perturbations of magnetic field distribution, plasma pressure or flow on one end are communicated by field‐aligned currents along the whole flux tube. Furthermore, they transport energy, practically lossless, from dynamo regions in the magnetosphere into the upper atmosphere. The knowledge of field‐aligned current distribution is therefore of great interest for understanding the magnetosphere‐ionosphere system. In this chapter we describe the expressions that illustrate the relationship between plasma motion in the magnetosphere and electric currents flowing along the background magnetic field. These currents can only be sensed above the ionospheric E‐layer, e.g. by low‐Earth orbiting satellites. However, to obtain reliable current density estimates is quite challenging. In a climatological sense, field‐aligned currents appear along two concentric rings in the high‐latitude ionosphere with opposite flow directions. Details of these patterns are controlled by the orientation of the interplanetary magnetic field. The transverse scale sizes determine important characteristics of field‐aligned currents.

In the past decades researchers have revealed links between a series of sub-auroral ionospheric phenomena and the plasmapause (PP) dynamics, such as the mid-latitude ionospheric trough (MIT) and the associated sub-auroral temperature enhancement (SETE), the light-ion trough (LIT), the sub-auroral ion drift (SAID) or the more intense sub-auroral polarisation stream (SAPS), and most recently, the inner boundary of small-scale field-aligned currents (SSFACs). Most of these phenomena can be directly observed by the Swarm constellation of ESA at LEO. Thus, Swarm presents a unique opportunity to study the relations between them and also their relation to the PP dynamics.In a recent Swarm DISC project, PRISM (Plasmapause Related boundaries in the topside Ionosphere as derived from Swarm Measurements), three new products have been developed. Two products characterise the MIT (and the associated SETE). The MITx_LP utilises the Langmuir probe measurements of electron density and temperature, while the MITxTEC product derives the MIT properties from GPS TEC observations. The third product, PPIxFAC provides information on the location and the main characteristics of the equatorial boundary of SSFACs, and it also includes a proxy for the location of the PP at MLT midnight.In this presentation we introduce the above Swarm L2 products, present the results of a comparative study aiming at revealing their mutual relations and also their dynamic coupling to the PP. Then we demonstrate how the observations of all these ionospheric phenomena combined can be used to develop an improved proxy for monitoring the PP dynamics at LEO as one of the goals of our new ESA-funded project PLASMA.

The new planetary open-ended Hpo index family (consisting of the half-hourly Hp30 and hourly Hp60) has been developed within the Space Weather Atmosphere Models and Indices (SWAMI) project (see http://swami-h2020.eu/) of the H2020 European Union research activity. These new indices resemble the Kp index by having a similar derivation scheme and a nearly identical frequency distribution of index values for events with values < 9. However, they have provided a better temporal resolution than the 3-hourly Kp index. Additionally, the events with values > 9- are further subdivided using an open-ended scale (9o, 9+, 10-, 10o, 10+, 11-, ...) to better represent different levels of strong geomagnetic activity. In this study, the advantages and integrity of Hp30 and Hp60 indices are analysed and discussed. The comparison of these indices with the 3-hourly Kp index in terms of frequency distribution and correlation and with other geophysical parameters are also presented.Near real-time indices and archive indices back to 1995 are available from GFZ under the CC BY 4.0 license including linear versions of the Hp30 and Hp60 indices, the ap30 and ap60 indices (see https://www.gfz-potsdam.de/en/section/geomagnetism/data-products-services/hpo-index/). Near real-time plots of the Hp30, Hp60 and Kp indices for the current day and the previous six days are also provided.

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

A sudden stratospheric warming (SSW) is an extreme wintertime meteorological phenomenon occurring mostly over the Arctic region. Studies have shown that an Arctic SSW can influence the whole atmosphere including the ionosphere. In September 2019, a rare SSW event occurred in the Antarctic region, following strong wave-1 planetary wave activity. The event provides an opportunity to investigate its broader impact on the upper atmosphere, which has been largely unexplored in previous studies. Ionospheric data from ESA's Swarm satellite constellation mission show prominent 6-day variations in the dayside low-latitude region during the SSW, including 20-70% variations in the equatorial zonal electric field, 20-40% variations in the electron density, and 5-10% variations in the top-side total electron content. These ionospheric variations have characteristics of a westward-propagating wave with zonal wavenumber 1, and 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 NASA's Aura satellite reveal a burst of global Q6DW activity in the mesosphere and lower thermosphere at this time, which is one of the strongest in the record. These results suggest that an Antarctic SSW can lead to ionospheric variability by altering middle atmosphere dynamics and propagation characteristics of large-scale waves from the middle atmosphere to the upper atmosphere.

An open-ended, high cadence, Kp-like geomagnetic index, called Hp index, is developed within the H2020 project SWAMI (Space Weather Atmosphere Models and Indices). The traditional Kp index is an excellent measure for energy input by the solar wind and is widely used in space weather science and applications. The new planetary index Hp resembles the Kp index by having a similar derivation scheme and a nearly identical frequency distribution of index values. Hp is available from 1995 onward with different time resolutions, e.g., 30 minutes and 60 minutes, and thus provides a higher temporal resolution than the 3-hourly Kp index. Additionally, events with Hp > 9- were further subdivided using an open-ended scale (9o, 9+, 10-, 10o, 10+, 11-, ...) to represent the highest levels of geomagnetic activity with higher resolution.

The Swarm three-satellite constellation mission provides high resolution and high-quality observations of the Earth’s magnetic field and of multiple parameters of the ionosphere, which lead to new knowledge on the Earth’s interior and space environment and help to investigate space weather effects on space technology. Several findings would otherwise not have been possible and demonstrate that missions like Swarm are indispensable for Earth and space exploration. In addition, aspects of longterm variations or enhanced understanding in temporal and spatial resolution on regional scales could be gained in combination with other missions. This presentation focuses on recent achievements on the low latitude ionosphere. Examples include an empirical model of the occurrence of post-sunset equatorial plasma irregularities derived in combination with ten years of CHAMP geomagnetic data, an enhanced description of the Swarm irregularity observations together with regional maps of the South Atlantic ionosphere from GOLD, and the identification of differing GPS scintillation characteristics evoked by the irregularities in comparison with the lower orbit GOCE data. Equatorial electrojet and plasma data from Swarm also helped to empirically prove that Antarctic sudden stratospheric warming events, such as in September 2019, couple to the low latitude ionosphere through modified planetary waves.

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.

The Disturbance storm time (Dst) index is derived using the H-component perturbation on magnetometers from four observatories (Hermanus, Kakioka, Honolulu, and San Juan) near the Sq focus. The Dst index is a quantitative measure of geomagnetic activity (major disturbances are negative) that monitors the intensity of the magnetospheric ring current and it is derived and maintained by WDC Kyoto. The local nowcast index presented here is a geomagnetic index that is derived similarily to the Dst index for the each of the following low and mid-latitude observatories: Tristan da Cunha (South Atlantic, TDC), St. Helena (South Atlantic, SHE), Keetmanshoop (Namibia, KMH), Vassouras (Brazilian, VSS), Gan (Maldives, GAN) and Panagjurishte (Bulgaria, PAG). This local index is developed within the ESA’s SSA SWE G-ESC activity. Here, we assess the influence of the quiet-time Sq estimation on the local ring current index and the correlation of the index with other solar and geophysical parameters.

In this study, we present global climatological distributions of ionospheric plasma irregularities based on measurements by the Swarm satellites. These first global statistics obtained by direct, in situ measurements of plasma variations with Swarm confirm the presence of three main regions of strong ionospheric irregularities: the magnetic equator extending from postsunset to early morning, in the auroral ovals (from dayside cusp to nightside), and inside the polar caps. At equatorial latitudes, ionospheric irregularities form two bands of enhanced plasma fluctuations centered around ±10° magnetic latitude. Due to different plasma processes, ionospheric irregularities at high and low latitudes show different distributions. Though the averaged intensity of plasma irregularities is weaker at equatorial latitudes than at high latitudes, the occurrence rate of significant plasma fluctuations (corresponding to extreme events) is much higher at the equator than that at high latitudes. Equatorial irregularities display clear seasonal and longitudinal variations; that is, they are most prominent over South America during the December solstice and are located over Africa during the June solstice. The magnitude of ionospheric irregularities at all latitudes is strongly controlled by the solar activity. Ionospheric irregularities become significantly weaker after 2016 during the current declining phase of solar activity. The interplanetary magnetic field Bz modulates the occurrence of ionospheric irregularities at both high and low latitudes.

Various ESA projects and several proposals to first Swarm DISC Call for Ideas (May 2016) suggested possible evolution for the current Swarm Level 2 FAC products, and the implementation of quality flags for the FAC products. The Field-Aligned Currents—Methodology Inter-Comparison Exercise (FAC-MICE) consisted in comparison of the various methods to determine the FAC from Swarm data, with a test dataset of 28 Swarm auroral crossings delivered to participants last June. Eight groups performed the FAC-MICE analysis. The results of this exercise, discussed in the dedicated ‘Swarm Ionospheric Currents Products workshop’ in ESTEC on September 2017, highlighted the strengths of the various methods/approaches. Following discussion with the participants to this workshop, we are now working to develop an open source platform for user-definable FAC calculation.

One of the Swarm prime mission goals is the estimation of ionospheric currents. Of particular interest in this context are field-aligned currents (FACs). In order to improve our ability of determining FACs, two of the Swarm spacecraft are orbiting side-by-side separated only by 1.4° in longitude. This close-formation flight enables the application of Ampere’s integral law to magnetic field measurements for estimating radial currents. From experience gained in space we can state that most reliable results are obtained in the auroral region. Here the spacing of the measurement quad and the size of current structures match best. In the vicinity of the poles, close to the orbital crossovers, spacecraft separations become too small for reliable gradient measurements. At low latitudes the separation becomes largest (~150 km). Here certain FAC features, e.g. associated with plasma instabilities and disturbances exist, which cannot be analysed reliably with the dual-SC approach. However, mid-latitude large-scale currents like the inter-hemispheric FACs can be recorded reliably by the Swarm mission. Besides presenting some measurement examples special emphasis is put on the discussion of underlying assumptions and on the limitations of the approach.

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.

As part of its attitude and orbit control system, the GRACE-FO satellites carry vector magnetometers. After appropriate calibration and characterisation of artificial magnetic disturbances, the mean residual to the high precision magnetic models is below 1 nT during times of geomagnetic quiet conditions. Furthermore, navigational GPS observations are used to derived data of the total electron content integrated over the upper ionosphere and KBR data are used to derive in situ electron density. These observations are valuable assets to characterize the natural variability of Earth's magnetic field and its space environment. The performance of GRACE-FO magnetic and plasma data is discussed on selected scientific examples. E.g., during magnetic storm events, GRACE-FO, in a constellation with other satellites, reveals the local time dependence of the magnetospheric ring current signature, and monitors significant plasma density enhancements at low and high latitudes. It is further demonstrated that the dual-satellite constellation of GRACE-FO is most suitable to derive the persistence of auroral field-aligned currents with scale lengths of 180 km or longer. The data derived from non-dedicated observations extends the scientific application areas of the GRACE-FO to space weather and monitoring. Together with similar data sets such as from CHAMP, GRACE, GOCE, and Swarm among others, magnetic and ionospheric monitoring over nearly two solar cycles is available at LEO for different local times or altitudes.

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.

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 Daedalus mission has been proposed to the European Space Agency (ESA) in response to the call for ideas for the Earth Observation programme's 10th Earth Explorer. It was selected in 2018 as one of three candidates for a Phase-0 feasibility study. The goal of the mission is to quantify the key electrodynamic processes that determine the structure and composition of the upper atmosphere, the gateway between the Earth’s atmosphere and space. An innovative preliminary mission design allows Daedalus to access electrodynamics processes down to altitudes of 150 km and below. Daedalus will perform in-situ measurements of plasma density and temperature, ion drift, neutral density and wind, ion and neutral composition, electric and magnetic fields and precipitating particles. These measurements will unambiguously quantify the amount of energy deposited in the upper atmosphere during active and quiet geomagnetic times via Joule heating and energetic particle precipitation, estimates of which currently vary by orders of magnitude between models. An innovation of the Daedalus preliminary mission concept is that it includes the release of sub-satellites at low altitudes: combined with the main spacecraft, these sub-satellites will provide multi-point measurements throughout the Lower Thermosphere-Ionosphere region, down to altitudes below 120 km, in the heart of the most under-explored region in the Earth's atmosphere. This paper describes Daedalus as originally proposed to ESA.

The polar ionosphere is often characterized by irregularities and fluctuations in the plasma density. We present a statistical study of ionospheric plasma irregularities based on the observations from the European Space Agency's Swarm mission. The in situ electron density obtained with the Langmuir probe and the total electron content from the onboard global positioning system receiver are used to detect ionospheric plasma irregularities. We derive the irregularity parameters from the electron density in terms of the rate of change of density index and electron density gradients. We also use the rate of change of total electron content index as the irregularity parameter based on the global positioning system data. The background electron density and plasma irregularities are closely controlled by the Earth's magnetic field, with averaged enhancements close to the magnetic poles. The climatological maps in magnetic latitude/magnetic local time coordinates show predominant plasma irregularities near the dayside cusp, polar cap, and nightside auroral oval. These irregularities may be associated with large‐scale plasma structures such as polar cap patches, auroral blobs, auroral particle precipitation, and the equatorward wall of the ionospheric trough. The spatial distributions of irregularities depend on the interplanetary magnetic field (IMF). By filtering the irregularity parameters according to IMF By, we find a clear asymmetry of the spatial distribution in the cusp and polar cap between the Northern (NH) and Southern Hemispheres (SH). For negative IMF By, irregularities are stronger in the dusk (dawn) sector in the NH (SH) and vice versa. This feature is in agreement with the high‐latitude ionospheric convection pattern that is regulated by the IMF By component. The plasma irregularities are also controlled by the solar activity within the current declining solar cycle. The irregularities in the SH polar cap show a seasonal variation with higher values from September to April, while the seasonal variation in the NH is only obvious around solar maximum during 2014–2015.

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.

To study and characterise the ionospheric plasma irregularities at all latitudes, one can employ in-situ measurements by satellites in polar orbits, such as the European Space Agency’s Swarm mission. Based on the Swarm data, we have developed the Ionospheric Plasma IRregularities (IPIR) product for a global characterisation of ionospheric irregularities along the satellite track at all latitudes. This new Level-2 data product combines complementary datasets from the Swarm satellites: the electron density from the electric field instrument, the GPS data from the onboard GPS receiver, and the magnetic field data from the onboard magnetometers. This can be used as a new tool for global studies of ionospheric irregularities and turbulence.

At polar regions a continuous outflow occurs of terrestrial atmosphere into space. Thermodynamic forces are not strong enough to allow air parcels escaping the Earth’s gravity field. But due to the partial ionization of the upper atmosphere by the sun’s short-wavelength radiation electrodynamic forces can move the charged particles upward along open field lines. Already in the early space age it was recognized that considerable amounts of ionospheric ions populate the magnetosphere. In this chapter, the acceleration mechanisms of the upwelling ions at altitudes of source regions are investigated. For the first time the role of the neutral particles in the thermosphere is also included in the considerations. In our studies we make use of data from the satellites CHAMP (400 km), GRACE (500 km), and DMSP (830 km). Detailed studies are performed to analyze the conditions accompanying the upwelling of neutral and ionized particles. Here we consider average properties of field-aligned currents, thermospheric wind, and electron temperature. Also, the dependences on environmental conditions are tested. Hardly any dependence on seasons emerges either for air upwelling or for ion upflow. An important driver for the processes seems to be magnetic field reconnection between the terrestrial and interplanetary magnetic field (IMF) and with that the orientation of the IMF. Intense flows of precipitating electrons, which are caused by the merging process, play a central role for both kinds of upflow. But further drivers, different for the two species, are needed to facilitate the observed ion and neutral upwelling.

Based on magnetic field data sampled by the Swarm satellite constellation it is possible for the first time to determine uniquely F region currents at low latitudes. Initial results are presented from the first 200 days of formation flight (17 April to 5 November 2014). Detailed results have been obtained for interhemispheric field-aligned currents connecting the solar quiet day magnetic variation (Sq) current systems in the two hemispheres. We obtain prominent currents from the Southern (winter) Hemisphere to the Northern around noon. Weaker currents in opposite direction are observed during morning and evening hours. Furthermore, we could confirm the existence of vertical currents above the dip equator, downward around noon and upward around sunset. For both current systems we present and discuss longitudinal variations.

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 present work has investigated the configuration of field-aligned currents (FACs) during a long period of radial interplanetary magnetic field (IMF) on 19 May 2002 by using high-resolution and precise vector magnetic field measurements of the CHAMP satellite. During the interest period IMF By and Bz are weakly positive and Bx keeps pointing to the Earth for almost 10 hours. The geomagnetic indices Dst is about -40 nT and AE about 100 nT on average. The cross polar cap potential calculated from Assimilative Mapping of Ionospheric Electrodynamics and derived from DMSP observations have average values of 10-20 kV. Obvious hemispheric differences are shown in the configurations of FACs on the day and nightside. At the south pole FACs diminish in intensity to magnitudes of about 0.1 μA/m2, the plasma convection maintains two cell flow pattern, and the thermospheric density is quiet low. However, there are obvious activities in the northern cusp region. One pair of FACs with a downward leg toward the pole and upward leg on the equatorward side emerge in the northern cusp region, exhibiting opposite polarity to FACs typical for duskward IMF orientation. An obvious sunward plasma flow channel persists during the whole period. These ionospheric features might be manifestations of an efficient magnetic reconnection process occurring in the northern magnetospheric flanks at high latitude. The enhanced ionospheric current systems might deposit large amount of Joule heating into the thermosphere. The air densities in the cusp region get enhanced and subsequently propagate equatorward on the dayside. Although geomagnetic indices during the radial IMF indicate low level activity, the present study demonstrates that there are prevailing energy inputs from the magnetosphere to both the ionosphere and thermosphere in the northern polar cusp region.

Numerical simulation results of weakly-developed drift-wave turbulence using the gyro-fluid code GEM3 [B. D. Scott, Plasma Phys. Controlled Fusion, 45, A385 (2003)] is analyzed. The formation of turbulent structures in the maximum density gradient region is observed, which is causally connected with the primary drift-wave instability. Turbulent structures peel-off quasi-coherent drift modes and propagate radially outwards into the plasma edge where they appear as intermittent density bursts. It is demonstrated that the radial propagation of the turbulent structures is due to convection in the self-consistent potential perturbation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Drift-wave turbulence in the linear VINETA [1] device was studied using the adapted version [2] of the threedimensional gyrofluid code GEM3 [3]. The density and parallel velocity gyrofluid equations of electrons and ions for the cylindrical annulus are solved. It is shown that the code is able to reproduce the main experimental signatures of intermittency. The influence of the interaction of the plasma with neutrals – the so-called ‘neutral wind’ – on the intermittent turbulence in VINETA is discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

The two-moment version of the three-dimensional gyrofluid code GEM3 has been adapted for the simulation of drift-wave turbulence in the linear device VINETA [1]. In the modified GEM3 code gyrofluid equations for the density and parallel velocity of electrons and ions are solved for the cylindrical annulus. Computations are done for the electrostatic case using an exponential background density profile observed experimentally.

The diocotron instability influence on the value of average electron density in a discharge with crossed electric and magnetic fields has been studied in magnetron and inverted magnetron geometries. The obtained results is in agreement with experimental data. It is found that in magnetron with a thin cathode the mode l=1 is unstable in a narrow interval of electron densities. The width of this interval vanishes when the cathode radius tends to zero.

[1] Based on two years of Subauroral Polarization Streams (SAPS) events detected by DMSP satellites in the dusk-premidnight sector, we have studied the temporal and spatial effects of SAPS on thermospheric quantities. The events are divided into two different MLT (magnetic local time) groups covered by F13 and F14/15. Concurrent CHAMP observations taken between −30° and +60° in longitude (−2 h and +4 h MLT) with respect to the SAPS detection location and within a time window of 1.5 h before and 3 h after the SAPS detection time are used for comparison. For the first time the spatial and temporal effects of SAPS are shown. SAPS have great influences on the zonal wind in all MLT bins (17–21 MLT) around the F13 MLT sector, with the largest effect appearing around 19 MLT, about 0–2 hours MLT after SAPS onset. SAPS have relatively little effect around 23–24 MLT, as deduced from F14/15 SAPS. For most cases the zonal wind peaks in the first orbit, concurrent with the SAPS onset. But around 19 MLT the zonal wind attains peak velocities about 1.5 h after the SAPS detection. This is claimed to be related to the longer persistence of SAPS events in this MLT sector than in other sectors. The background air density gets enhanced by SAPS with the most prominent variation occurring around 19 MLT. There are density bulges appearing around the SAPS latitude. The electron density trough gets deepened and attains the minimum in the first orbit after the SAPS onset. The largest depletion can also be found around 19 MLT. Both the eastward and westward Hall currents (electrojets) get strengthened right after SAPS onset. The zonal wind peaks 2°–3° in latitudes equatorward of the eastward electrojet.

Based on two years of Subauroral Polarization Streams (SAPS) events detected by DMSP satellites in the dusk-premidnight sector, we have studied the temporal and spatial effects of SAPS on thermospheric quantities. The events are divided into two different MLT (magnetic local time) groups covered by F13 and F14/15. Concurrent CHAMP observations taken between −30° and +60° in longitude (−2 h and +4 h MLT) with respect to the SAPS detection location and within a time window of 1.5 h before and 3 h after the SAPS detection time are used for comparison. For the first time the spatial and temporal effects of SAPS are shown. SAPS have great influences on the zonal wind in all MLT bins (17–21 MLT) around the F13 MLT sector, with the largest effect appearing around 19 MLT, about 0–2 hours MLT after SAPS onset. SAPS have relatively little effect around 23–24 MLT, as deduced from F14/15 SAPS. For most cases the zonal wind peaks in the first orbit, concurrent with the SAPS onset. But around 19 MLT the zonal wind attains peak velocities about 1.5 h after the SAPS detection. This is claimed to be related to the longer persistence of SAPS events in this MLT sector than in other sectors. The background air density gets enhanced by SAPS with the most prominent variation occurring around 19 MLT. There are density bulges appearing around the SAPS latitude. The electron density trough gets deepened and attains the minimum in the first orbit after the SAPS onset. The largest depletion can also be found around 19 MLT. Both the eastward and westward Hall currents (electrojets) get strengthened right after SAPS onset. The zonal wind peaks 2°–3° in latitudes equatorward of the eastward electrojet.

The nonlinear evolution of a nonneutral electron gas-discharge plasma density in crossed E ⊥ B fields taking into account nonelastic electron-neutral collisions and a low electron temperature has been considered. It is shown that the temperature effect depends on the sign of the initial density gradient and accelerates or decelerates the process of relaxation and flattening of the electron density equilibrium profile.