Swarm Satellites Research Articles

Spatial Development of Strong Storm-Induced Ionospheric Perturbations during 25–27 August 2018

The 25–27 August 2018 geomagnetic storm was the third largest storm in the 24th solar cycle. It was a surprising space event that originated from low-level solar activity. This study provides an overview of the temporal–spatial behaviors of plasma irregularities as functions of geographic longitude, latitude, and altitude using ground-based (GNSS receivers and ionosonde) instruments and space-borne Swarm satellites. The results not only reveal enhanced equatorial ionization anomaly (EIA) and hemispheric asymmetry over the Asian–Australian and American sectors at a particular time but also hemispheric asymmetric features of global ROT in the main and recovery phases. Additionally, this storm triggered positive plasma irregularities in altitudes of 100 to 150 km near the Auroral zone, and the changed ratio of bottom-side plasma irregularities exceeded 250%. This finding has been cross-validated by other instruments and models. Furthermore, the storm significantly affected the thermospheric O/N2 density ratio, equatorial electrojet, and vertical E×B drifts. The equatorial and mid-latitude plasma irregularities may be a combined action of thermospheric composition change, equatorial electrojet, and vertical E×B drifts. Finally, the storm induced positive Joule heating irregularities in the Auroral ionosphere in altitudes of 100 to 400 km with a maximum changed ratio of over 200%, as well as enhanced cross-Polar voltage to ~90 kv. The Polar ionospheric irregularities may be associated with additional energy input through particle precipitation, Joule heating, and ionospheric current intensification.

Preliminary study of topside ionospheric variations using SWARM satellites over the Malaysia Region

The European Space Agency (ESA) launched a satellite constellation mission called Swarm in 2013. The Swarm satellites named A, B and C are equipped with Global Positioning System (GPS) receivers which can be used to study the topside of the ionosphere. In Malaysia, the use of ionospheric data from the Swarm satellites is still new as most researchers previously used GPS receivers on the Earth. This paper presents the preliminary result of topside-ionosphere parameter, Total Electron Content (TEC) over Malaysia using the Swarm satellite data. TEC from the Swarm data were analyzed during quiet and disturbed geomagnetic days. The results showed that the Swarm satellites passed through Malaysia twice in 24 hours and the variations of TEC over Malaysia ranged from 2 to 20 TECU. Analysis of the topside ionosphere during a geomagnetic storm showed a sudden decreased of TEC compared to the quiet days. The findings indicate that the variations of topside TEC using Swarm are in agreement with those found in previous studies.

Modeling the Climatology of Low‐ and Mid‐Latitude F‐Region Ionospheric Currents Using the Swarm Constellation

AbstractWe present a new empirical model of quiet‐time F‐region ionospheric currents and associated magnetic fields. This model is designed to accurately represent these currents and fields at low and mid latitudes. For each individual Swarm satellite, the preprocessed data is represented as a non‐potential toroidal magnetic field using the Mie representation in a thin‐shell and spherical harmonic expansions. This approach allows to fully separate spatial and climatological variations as well as to assess the robustness of the model with respect to both measurement errors and data sampling with local time. The obtained model describes the toroidal magnetic fields and the associated radial poloidal electric currents at two distinct altitudes in the ionosphere F region. Clear signatures of low‐ and mid‐latitude interhemispheric field‐aligned currents (IHFACs) are identified. The model reproduces well‐known characteristics of the climatology of IHFACs and provides new insights, for example, on the average daily variations of IHFACs during winter in the Northern Hemisphere. It also well recovers the variations of IHFACs with longitude. The potential driving mechanisms of these variations, such as longitudinal variations of the main field and modulation by upward propagating atmospheric tides, are discussed. The new model can be used to analyze the relationship between atmospheric tides and IHFACs. It can also be used to investigate the connection between the magnetic fields and electric currents from the ionospheric E and F regions in order to improve the separation of these fields as well as our understanding of the overall ionospheric electric current system.

Transpolar Pc1 Wave Ducting: Swarm, DMSP, and Ground Observations

AbstractAlfvén mode Pc1 waves undergo mode conversion to the fast mode due to induced Hall current in the ionosphere. The fast mode Pc1 waves are trapped and propagate across the magnetic field through the ionospheric waveguide. This process is called Pc1 wave ducting (PWD). Ducting is expected to be in any direction, but most of the existing literature investigated only PWDs toward the equator. In this paper, we report the rare observations of PWD propagating from sub‐auroral latitudes and pervading the polar cap using Swarm satellites, ground magnetometers, and Defense Meteorological Satellite Program (DMSP) satellites. We first identify the injection region of Pc1 wave where localized broadband transverse waves, isolated aurora, and energetic proton precipitations are concurrently observed. Then, we compare ducting characteristics in the ionosphere between the two hemispheres. For the three events investigated here, PWDs in the Southern Hemisphere (SH) pervaded the polar cap while Pc1 waves in the Northern Hemisphere (NH) did not. This hemispheric asymmetry is attributed to the plasma density in the SH sufficient to form the Pc1 waveguide. However, a sharp plasma density gradient on the propagation path still interrupts the ducting even in higher plasma density () regions. The observation of two intersecting Swarm satellites indicates the PWD is not only elongated meridionally, but also can have a significant zonal extent beyond that of the injection region.

Validation of Swarm Langmuir Probes by Incoherent Scatter Radars at High Latitudes

Electron density measured at high latitudes by the Swarm satellites was compared with measurements by the incoherent scatter radars at Resolute Bay and Poker Flat. Overall, the ratio of Swarm-based electron density to that measured by the radars was about 0.5–0.6. Smaller ratios were observed at larger electron densities, usually during the daytime. At low electron densities less than 3 × 1010 m−3, the ratios were typically above 1, indicating an overestimation effect. The overestimation effect was stronger at night and for Swarm B. It was more evident at lower solar activity when the electron densities in the topside ionosphere were lower.

Колебания геомагнитного поля в диапазоне 2.5–12 Гц в F-слое ионосферы по данным спутников SWARM

We have analyzed geomagnetic variations in the 2.5–12 Hz frequency range in the ionospheric F layer above the electron density maximum, using data from two SWARM satellites. The analysis is based on the data obtained under weak and moderate magnetic activity for 12 days in September and December 2016. To separate spatial inhomogeneities from time variations of the magnetic field, we analyzed signal waveforms and cross-spectra in a 2.56 s sliding window. A maximum in the occurrence and power spectral density of the variations was found at latitudes above the polar boundary of the auroral oval, which correspond to the magnetospheric input layers and dayside polar cusp/cleft. Typical waveforms of the high-latitude variations are the wave packets lasting for 5–10 periods, recorded with a short time delay by two satellites spaced by 40–100 km. These variations might be the ionospheric manifestation of the electromagnetic ion-cyclotron waves generated at the non-equatorial magnetosphere near the polar cusp. The waveforms and cross-spectra of the variations are examined in more details for two cases with different spatial distributions of the magnetic field in the ionosphere. For the ionospheric conditions corresponding to event 1 (September 17, 80° geomagnetic latitude, afternoon sector), spatial distributions of wave magnetic field in the ionosphere and on Earth are estimated using a model of Alfvén beam with a finite radius incident on the ionosphere [Fedorov et al., 2018].

Колебания геомагнитного поля в диапазоне 2.5–12 Гц в F-слое ионосферы по данным спутников SWARM

We have analyzed geomagnetic variations in the 2.5–12 Hz frequency range in the ionospheric F layer above the electron density maximum, using data from two SWARM satellites. The analysis is based on the data obtained under weak and moderate magnetic activity for 12 days in September and December 2016. To separate spatial inhomogeneities from time variations of the magnetic field, we analyzed signal waveforms and cross-spectra in a 2.56 s sliding window. A maximum in the occurrence and power spectral density of the variations was found at latitudes above the polar boundary of the auroral oval, which correspond to the magnetospheric input layers and dayside polar cusp/cleft. Typical waveforms of the high-latitude variations are the wave packets lasting for 5–10 periods, recorded with a short time delay by two satellites spaced by 40–100 km. These variations might be the ionospheric manifestation of the electromagnetic ion-cyclotron waves generated at the non-equatorial magnetosphere near the polar cusp. The waveforms and cross-spectra of the variations are examined in more details for two cases with different spatial distributions of the magnetic field in the ionosphere. For the ionospheric conditions corresponding to event 1 (September 17, 80° geomagnetic latitude, afternoon sector), spatial distributions of wave magnetic field in the ionosphere and on Earth are estimated using a model of Alfvén beam with a finite radius incident on the ionosphere [Fedorov et al., 2018].

Influence of Solar Activity on Precise Orbit Prediction of LEO Satellites

The perturbations of low earth orbit (LEO) satellites operating in the orbit of 300 ∼ 2000 km are complicated. In particular, the atmospheric drag force and solar radiation pressure force change rapidly over a short period of time due to solar activities. Using spaceborne global positioning system (GPS) data of the CHAMP, GRACE and SWARM satellites from 2002 to 2020, this paper studies in depth the influence of solar activity on LEO satellites’ precise orbit prediction by performing a series of orbit prediction experiments. The quality of GPS data is more susceptible to being influenced by solar activity during years when this activity is high and the changes in dynamic parameters are consistent with those of solar activity. The effects of solar activity on LEO orbit prediction accuracy are analyzed by comparing the predicted orbits with the precise ones. During years of high solar activity, the average root-mean-squares prediction errors at 10, 20, and 30 minutes are 0.15, 0.20, and 0.26 m, respectively, which are larger than the corresponding values in low-solar-activity years by 59%, 63%, and 68%, respectively. These results demonstrate that solar activity has a great influence on the orbit prediction accuracy, especially during high-solar-activity years. We should strengthen the real-time monitoring of solar activity and geomagnetic activity, and formulate corresponding orbit prediction strategies for the active solar period.

SwarmFACE: A Python package for field-aligned currents exploration with Swarm

The SwarmFACE package utilizes magnetic field measurements by the Swarm satellites to study systems of field-aligned currents (FACs). Improvements of well-established techniques as well as novel single- and multi-satellite methods or satellite configurations are implemented to extend the characterization of FAC systems beyond the Swarm official Level-2 FAC product. Specifically, the included single-satellite algorithm allows to consider the FAC sheet inclination with respect to the satellite orbit and can work with low- or high-resolution data. For dual-satellite FAC estimation the package provides three algorithms, based on the least-squares, on the singular value decomposition, and on the Cartesian boundary-integral methods. These algorithms offer advantages over the corresponding Level-2 algorithm by providing more stable solutions for ‘extreme’ configurations, e.g. close to the orbital cross-point, and by allowing for a more general geometry of the spacecraft configuration. In addition, the singular value decomposition algorithm adapts itself to the spacecraft configuration, allowing for continuous, dual-satellite based FAC solutions over the entire polar region. Similarly, when Swarm forms a close configuration, the package offers the possibility to estimate the FAC density with a three-satellite method, obtaining additional information, associated to a different (larger) scale. All these algorithms are incorporating a robust framework for FAC error assessment. The SwarmFACE package further provides useful utilities to automatically estimate the auroral oval location or the intervals when Swarm forms a close configuration above the auroral oval. In addition, for each auroral oval crossing, a series of FAC quality indicators, related to the FAC methods’ underlying assumptions, can be estimated, like the current sheet inclination and planarity or the degree of current sheet stationarity.

Extracting Spatial–Temporal Coherent Patterns in Geomagnetic Secular Variation Using Dynamic Mode Decomposition

AbstractRapid growth of magnetic‐field observations through SWARM and other satellite missions motivate new approaches to analyze it. Dynamic mode decomposition (DMD) is a method to recover spatially coherent motion with a periodic time dependence. We use this method to simultaneously analyze the geomagnetic radial field and its secular variation from CHAOS‐7 at high latitudes. A total of five modes are permitted by noise levels in the observations. One mode represents a slowly evolving background state, whereas the other four modes describe a pair of waves; each wave is comprised of a complex DMD mode and its complex conjugate. The waves have periods of T1 = 19.1 and T2 = 58.4 years and quality factors of Q1 = 11.0 and Q2 = 4.6, respectively. A 60‐year wave is consistent with previous predictions for zonal waves in a stratified fluid. The 20‐year wave is also consistent with previous reports at high latitudes, although its nature is less clear.

A‐CHAIM: Near‐Real‐Time Data Assimilation of the High Latitude Ionosphere With a Particle Filter

AbstractThe Assimilative Canadian High Arctic Ionospheric Model (A‐CHAIM) is an operational ionospheric data assimilation model that provides a 3D representation of the high latitude ionosphere in Near‐Real‐Time (NRT). A‐CHAIM uses low‐latency observations of slant Total Electron Content (sTEC) from ground‐based Global Navigation Satellite System (GNSS) receivers, ionosondes, and vertical TEC from the JASON‐3 altimeter satellite to produce an updated electron density model above 45° geomagnetic latitude. A‐CHAIM is the first operational use of a particle filter data assimilation for space environment modeling, to account for the nonlinear nature of sTEC observations. The large number (>104) of simultaneous observations creates significant problems with particle weight degeneracy, which is addressed by combining measurements to form new composite observables. The performance of A‐CHAIM is assessed by comparing the model outputs to unassimilated ionosonde observations, as well as to in‐situ electron density observations from the SWARM and DMSP satellites. During moderately disturbed conditions from 21 September 2021 through 29 September 2021, A‐CHAIM demonstrates a 40%–50% reduction in error relative to the background model in the F2‐layer critical frequency (foF2) at midlatitude and auroral reference stations, and little change at higher latitudes. The height of the F2‐layer (hmF2) shows a small 5%–15% improvement at all latitudes. In the topside, A‐CHAIM demonstrates a 15%–20% reduction in error for the Swarm satellites, and a 23%–28% reduction in error for the DMSP satellites. The reduction in error is distributed evenly over the assimilation region, including in data‐sparse regions.

Investigation of the Topside Ionosphere over Cyprus and Russia Using Swarm Data

Using the topside electron density (Ne) measurements recorded over Cyprus and Russia, we investigate the latitudinal variation in the topside electron density during the interval 2014–2020, encompassing a period of high-to-low solar activity. The selected topside electron density dataset employed in this study is based on the in situ Langmuir probe data on board the European Space Agency (ESA) Swarm satellites, in the vicinity of the three Digisonde stations in Nicosia (35.14°N, 33.2°E), Moscow (55.5°N, 37.3°E) and Saint Petersburg (60.0°N, 30.7°E). Our investigation demonstrates that the ratio Ne_Swarm/NmF2 between the coincident Ne_Swarm and the Digisonde NmF2 observations is higher than one on various occasions over Nicosia during the nighttime, which is not the case over Moscow and Saint Petersburg, signifying a discrepancy feature of the electron density at Swarm altitudes which depends not only on the solar activity and time of day but also on the latitude.

Integrated Analysis of Lithosphere-Atmosphere-Ionospheric Coupling Associated with the 2021 Mw 7.2 Haiti Earthquake

The search for Earthquake (EQ) precursors in the ionosphere and atmosphere from satellite data has provided significant information about the upcoming main shock. This study presents the abnormal atmospheric and ionospheric perturbations associated with the Mw 7.2 Haiti EQ on 14 August 2021 at geographical coordinates (18° N, 73° W) and shallow hypocentral depth of 10 km from the data of permanent Global Navigation Satellite System (GNSS) stations near the epicenter, followed by Swarm satellites data. The total vertical electron (VTEC) anomalies occur within a 5-day window before the main shock in the analysis of nearby operation stations, followed by Swarm (A and C satellites) ionospheric anomalies in the same 5-day window before the main shock. Moreover, the geomagnetic activities are completely quiet within 10 days before and 10 days after the main shock. Similarly, the atmospheric parameters endorse the EQ anomalies within 5 days before the main shock day. The evolution of gases from the lithosphere at the epicentral region possessed significant atmospheric and ionospheric perturbations within the EQ preparation period of 5-day before the main shock under the hypothesis of Lithosphere-Atmosphere-Ionosphere Coupling (LAIC).

Quick Report on the ML = 3.3 on 1 January 2023 Guidonia (Rome, Italy) Earthquake: Evidence of a Seismic Acceleration

This paper investigates possible anomalies on the occasion of the ML = 3.3 earthquake, which occurred on 1st January 2023 close to Guidonia Montecelio (Rome, Italy). This earthquake followed another very close event recorded on 23 December 2022 with a magnitude ML = 3.1 (epicentral distance of less than 1 km). Seismological investigations clearly show an acceleration of seismicity in the preceding six months in a circular area of about a 60 km radius. Two conclusions coming from the time-to-failure power law fitting to the cumulative Benioff strain curve are the most probable: the ML3.3 of 1 January 2023 is the mainshock of the seismic sequence, or an incoming earthquake of a magnitude of about 4.1 provides a slightly better fit (higher determination coefficient) of the seismic data. Further investigations are necessary to assess whether the accumulated stress has been totally released. No atmospheric anomalies related to this seismic activity have been identified, even if some SO2 emissions seem to be induced by the tectonic and volcanic sources in the south Tyrrhenian Sea. Swarm satellite magnetic data show about 20 anomalous tracks six months before the Guidonia earthquake. In particular, on 16 December 2022, anomalous oscillations of the east component of the geomagnetic field are temporally compatible with the seismic acceleration, but other sources are also possible. Other anomalous magnetic signals are more likely to be associated with the ongoing seismic activity offshore of the Marche region in Italy (the strongest event up to now is Mw = 5.5 on 9 November 2022 close to Pesaro Urbino).

Anomalous Disturbance of the Ionosphere in the East Asia Region During the Geomagnetically Quiet Day on 1 November 2016

AbstractIn this study, multiple data sets from Beidou geosynchronous Earth orbit (GEO) satellite, ionosonde, magnetometer, Swarm satellite, and meteor radar were used to investigate an anomalous disturbance of the ionosphere in East Asia on 1 November 2016. During 03:00–08:00 universal time (UT), the total electron content (TEC) observed by the Beidou GEO satellite decreased by up to 8.17% at low latitudes and increased by up to 140.19% at middle to low latitudes in East Asia compared to the average TEC on the reference days. The F2 peak electron density (NmF2) measured by ionosondes decreased by 16.00% at Sanya (109.4°E, 18.3°N) and increased by 51.96% and 53.97% at Wuhan (114.4°E, 30.5°N) and Shaoyang (111.3°E, 27.1°N), respectively. The equatorial electric field (EEF) observed by the Swarm satellite at 06:59 UT on 1 November was approximately 77.57% higher than on 4 November. The variations of equatorial electrojet near 100°E and 120°E on 1 November presented an east‐west asymmetry in which there was a significant enhancement in the east while there was no obvious increase in the west. The TEC enhancement derived by the Center for Orbit Determination in Europe also showed the same east‐west asymmetry in the two longitudes. Based on the comprehensive analysis of multiple observational data, the increase in EEF caused the ionospheric TEC and NmF2 to decrease at low latitudes and increase at middle to low latitudes in East Asia during 03:00–08:00 UT on 1 November 2016. The lower atmospheric tidal forcing could contribute to the enhancement of the EEF.

Global Characteristics of Improved Interhemispheric Field‐Aligned Currents and of F‐Region Meridional Currents Observed by the Swarm Dual‐Spacecraft

AbstractThe Swarm satellite constellation provides an excellent opportunity to explore ionospheric current systems. In this study, we have reanalyzed the ionospheric currents derived by the Swarm dual‐satellite approach, to investigate the characteristic of inter‐hemispheric field‐aligned currents (IHFAC). One major improvement is that the influence of the ambient magnetic field on the IHFAC intensity has been taken into account, and the derived IHFAC densities are normalized to their ionospheric E‐region footprints. In addition, we have extended the analysis to the middle latitudes within ±60° MLat, which show IHFAC features different from those at low latitudes. For the first time the tidal features at mid‐latitudes are studied. They are dominated by longitudinal wave‐1 and wave‐2 patterns. A superposition of these tidal components reflects a confinement of the IHFAC tidal modulation to daytime in the western hemisphere. The tidal signatures at middle latitudes are better organized in universal time than in local time. The strongest IHFACs are appearing around 18–19 UT, near noon in the American sector. This is related to the overlap with the South Atlantic Anomaly. For the first time we define and analyze the F‐region meridional currents (FMC), interpreting the remaining part of the ionospheric radial current (IRC), which is not covered by IHFAC. The mean FMCs are found to be highly symmetric with respect to the magnetic equator and only amounts to one‐third or half of the IHFAC density, however, they show neither typical longitudinal, diurnal variations, or tidal signatures.

Investigation of the effects of geomagnetic storms on ionospheric irregularities using the combination of ground-based GNSS and SWARM satellites data

Investigation of the effects of geomagnetic storms on ionospheric irregularities using the combination of ground-based GNSS and SWARM satellites data

Thermal stability analysis of a satellite-borne optical bench based on quasi-kinematic support

Macau Science Satellite-1 (known as MSS-1) is a low-inclination mission that will be launched at the beginning of 2023. An optical bench is used for accessing high-precision strength and direction measurements of the magnetic field. In this paper, we present a thermal stability design for the optical bench based on quasi-kinematic support by kinematic hinges on the MSS-1. The change in angles with the finite element method (FEM) model modified by thermal deformation test data is analyzed. The robustness of the structure is also investigated via the Monte Carlo method. Two main results are obtained. First, the peak-to-peak value (<italic>V</italic>p-p) of the inter-boresight angle is at most 1.24″, and the <italic>V</italic>p-p of the inter-boresight angle modification and analysis is no more than 3.13″, both of which are better than those on the Swarm satellites in orbit. Second, the 90° fibers of the carbon-reinforced arm need to be strictly controlled during the technological process.

Spacecraft potential variations of the Swarm satellites at low Earth orbital altitudes

Spacecraft potential variations of the Swarm satellites at low Earth orbital altitudes

Mid‐Latitude Ionospheric Response to a Weak Geomagnetic Activity Event During Solar Minimum

AbstractSalient depletions (30%–40% of the reference values) were observed in the vertical total electron content (VTEC) from the Global Navigation Satellite System (GNSS) network and the topside ionosphere electron density from Swarm satellites measurements over the Western Atlantic and Northeast American regions during a weak geomagnetic activity event (maximum Kp = 2.3) between Day‐of‐Year (DOY) 155 and 156 in 2019. These depletions coincided with thermospheric Oxygen (O) to Nitrogen (N2) column density ratio (∑O/N2) depletions observed by the Global‐scale Observations of the Limb and Disk (GOLD) mission. The National Center for Atmospheric Research (NCAR) Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIEGCM) reproduces VTEC depletions qualitatively, which is used to investigate the underlying mechanisms. Term analysis of the TIEGCM oxygen ion (O+) continuity equation showed that the VTEC depletion was dominated by chemical processes and neutral wind transport effects, which were partially offset by the transport due to E × B drifts and ambipolar diffusion. On the dayside, the contribution from the neutral wind transport was induced by a weak poleward meridional wind during the geomagnetic activity. With the decrease of electron density, the loss rate in the chemical term was reduced, which led to a large reduction of the contribution from chemical processes to electron density and TEC changes during the event, and the contribution of the neutral wind to VTEC depletion even exceeded that of chemical processes after 14:10 UT.