The Earth’s magnetic field is continuously monitored by a large number of geomagnetic observatories and satellites in low Earth orbit. The use of these measurements can play a significant role in the space weather era. They can be used to monitor space weather events, such as magnetic storms, substorms and geomagnetically induced currents, and furthermore they facilitate studies of dynamic solar-terrestrial events and of their interactions. These measurements can also be used to model the magnetic field of external origin which poses presently the largest problem for progress in geomagnetic field modeling.
The aim of this session is to collect new ideas and results on how magnetic field measurements (from geomagnetic observatories and satellites such as CHAMP, Swarm, CSES, ePOP and so on) can improve our knowledge in the space weather domain.

Co-organized by ST4
Convener: Paola De Michelis | Co-conveners: Ioannis A. Daglis, Mioara Mandea
vPICO presentations
| Tue, 27 Apr, 11:00–12:30 (CEST)

vPICO presentations: Tue, 27 Apr

Chairperson: Paola De Michelis
Mirjam Kellinsalmi, Ari Viljanen, Liisa Juusola, and Sebastian Käki

Geomagnetic variations are mainly produced by external currents in the ionosphere and magnetosphere, and secondarily by induced (internal/telluric) currents in the conducting Earth. Large geomagnetically induced currents (GIC) are associated with large time derivatives of the horizontal magnetic field. Recent results show that the time derivative is typically dominated by the contribution from the telluric currents. Our study aims to find measures to quantify the behaviour of external and internal currents and their time derivatives during large GIC events. Results of this study show that strong external currents have quite narrow directional distributions. Angular variation is larger for internal currents, and especially for their time derivatives. For external currents angular variation is larger at higher latitudes. Similar behaviour is not seen with internal currents.

How to cite: Kellinsalmi, M., Viljanen, A., Juusola, L., and Käki, S.: Dynamics of ionospheric and telluric currents during large events of geomagnetically induced currents, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-812, https://doi.org/10.5194/egusphere-egu21-812, 2021.

Xueling Shi, Michael Hartinger, Joseph Baker, Paul Bedrosian, Benjamin Murphy, Anna Kelbert, Joshua Rigler, and Michael Ruohoniemi

Geomagnetic perturbations related to various phenomena in the near-Earth space environment can induce electric fields within the electrically conducting Earth. The geoelectric field is an important link between magnetospheric/ionospheric phenomena and geomagnetically induced currents in grounded electricity transmission networks. In evaluations of contiguous United Sates hazards, most previous studies have been focused on either 1-minute resolution geoelectric field measurements or geoelectric field time series derived from convoluting 1-minute geomagnetic field data with surface impedance tensors. To investigate sources of hazardous geoelectric fields during magnetic storms, including geoelectric fields induced by ultra-low frequency (ULF: 1 mHz to 1 Hz) waves, we use directly measured 1-second geoelectric field data from magnetotelluric survey stations that are distributed across the contiguous United States. Temporally-localized perturbations in measured geoelectric fields with a prominence of at least 0.5 V/km are detected during magnetic storms with a Dst minimum of at least -100 nT from 2008 to 2019. Most of these perturbations cannot have been resolved with 1-minute data since they correspond to phenomena that vary on smaller timescales and higher frequencies. The sources of geomagnetic perturbations inducing these extreme geoelectric fields can be categorized as interplanetary shocks, substorms, and ULF waves. We compare the geoelectric fields associated with the three sources and characterize their features. Extreme geoelectric fields related to these sources can have amplitudes of 1-2 V/km, comparable to the thresholds commonly used to identify hazardous events.

How to cite: Shi, X., Hartinger, M., Baker, J., Bedrosian, P., Murphy, B., Kelbert, A., Rigler, J., and Ruohoniemi, M.: Sources of hazardous geoelectric fields in the United States during magnetic storms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6934, https://doi.org/10.5194/egusphere-egu21-6934, 2021.

Adamantia Zoe Boutsi, Georgios Balasis, Ioannis A. Daglis, Kanaris Tsinganos, and Omiros Giannakis

Geomagnetically Induced Currents (GIC) constitute an integral part of the space weather research and a subject of ever-growing attention for countries located in the low and middle latitudes. A series of recent studies highlights the importance of considering GIC risks for the Mediterranean region. Here, we exploit data from the HellENIc GeoMagnetic Array (ENIGMA), which is located in Greece, complemented by magnetic observatories in Italy, to calculate corresponding values of the GIC index, i.e., a proxy of the geoelectric field calculated entirely from geomagnetic field variations. We perform our analysis for the most intense magnetic storms (Dst<-150 nT) of solar cycle 24. Our results show a good correlation between the storm sudden commencement (SSC) and an increase of the GIC index value. These investigations indicate that despite the elevated amplitude of the GIC index the associated risk remains at low level for the power networks in Greece and Italy during the considered storm events.

How to cite: Boutsi, A. Z., Balasis, G., Daglis, I. A., Tsinganos, K., and Giannakis, O.: Investigation of the possibility of GIC development in Greece during the strongest magnetic storms of solar cycle 24 , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8410, https://doi.org/10.5194/egusphere-egu21-8410, 2021.

Sebastian Käki, Ari Viljanen, Liisa Juusola, and Kirsti Kauristie

The electric currents flowing in the ionosphere change rapidly and a large amount of energy is dissipated in the auroral ionosphere during auroral substorms. An important part of the auroral current system are the auroral electrojets whose profiles can be estimated from magnetic field measurements from low Earth orbit satellites. We have combined electrojet data derived from the Swarm satellite mission of ESA with the substorm database derived from the SuperMAG ground network data. We organize the electrojet data in relation to the location of the onset and obtain statistics for the development of the integrated current and latitudinal location for the auroral electrojets relative to the onset. Especially we show that just after the onset the latitudinal location of the maximum of the westward electrojet determined from Swarm satellite data is mostly located close to the onset latitude in the local time sector of the onset regardless of where the onset happens.

How to cite: Käki, S., Viljanen, A., Juusola, L., and Kauristie, K.: Spatio-temporal development of large scale auroral electrojet currents relative to substorm onsets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1083, https://doi.org/10.5194/egusphere-egu21-1083, 2021.

Leonie Pick, Joachim Vogt, Adrian Blagau, and Nele Stachlys

The investigation of auroral field-aligned current (FAC) sheets is crucial in the context of space weather research since they serve as main transmitters of energy and momentum across geospace domains. Different magnetosphere-ionosphere coupling modes are reflected by the FACs’ multiscale nature with spatial scales, i.e., latitudinal extensions, ranging from below 1 km to hundreds of kilometers. The multiscale property can be addressed conveniently using ESA’s three-spacecraft mission Swarm. According to common practice a linear correlation analysis is performed on lagged and band-pass filtered scalar FAC density estimates from two nearby spacecraft.

We introduce the framework VALOR (Vectorial Association of Linearly Oriented Residua) which generalizes the common approach in two ways. First, VALOR utilizes the full magnetic field vector primarily observed at both spacecraft without filtering. Second, VALOR allows to test statistical association measures other than linear correlation in dependence of both time and along-track spacecraft lag. The method is further refined by considering the current sheet’s polarization, i.e., the directional preference of the associated magnetic field perturbation, which additionally constrains the sheet’s orientation.

Here, we apply VALOR to 1 Hz magnetic field observations from Swarm Alpha and Charlie and base the association measure on a vectorial version of the mean squared deviation. By means of a sample auroral oval crossing event we demonstrate that the incorporation of vectorial and polarization information helps to focus the association measure in the time-lag parameter plane leading to a smaller FAC spatial scale estimate. This result seems to hold in a statistical context including over 9000 quasi-perpendicular auroral oval crossings from 2014 to 2020. The fact that the VALOR derived FAC locations reflect the known ellipsoidal shapes of the auroral ovals speaks to the overall plausibility of the method as well as the independently supported finding that large-scale FACs (>300 km) dominate the dawn and dusk sectors while smaller scale FACs gain importance at noon and midnight. Among the various opportunities for future work are an application to 50 Hz high-resolution Swarm data as well as the investigation of the solar controlling parameters.

How to cite: Pick, L., Vogt, J., Blagau, A., and Stachlys, N.: Introducing the “VALOR” analysis framework for auroral field-aligned current sheets using observations from Swarm Alpha and Charlie, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1263, https://doi.org/10.5194/egusphere-egu21-1263, 2021.

Paola De Michelis, Giuseppe Consolini, Tommaso Alberti, Vincenzo Carbone, Roberta Tozzi, Igino Coco, and Fabio Giannattasio

Magnetic helicity, which is a measure of twist and linkage of magnetic field lines, is a useful quantity to investigate some processes occurring in space plasmas. In particular, there is a strong link between magnetic helicity, magnetic flux structures, turbulence and dissipation. We investigate the connection between the reduced magnetic helicity and the structure of field-aligned currents in the high-latitude ionosphere using high resolution (50 Hz) magnetic data collected on board the ESA Swarm constellation. We show the existence of a clear link between the multiscale coarse-grained structure of reduced magnetic helicity and the field-aligned currents. This finding strongly supports the idea that turbulence processes might be at the origin of the observed small-scale current structures. A discussion of the relevance of our results in the framework of the filamentary nature of the field-aligned current is also presented.

This work is supported by Italian PNRA under contract PNRA18_00289-A “Space weather in Polar Ionosphere: the Role of Turbulence ".

How to cite: De Michelis, P., Consolini, G., Alberti, T., Carbone, V., Tozzi, R., Coco, I., and Giannattasio, F.: On Magnetic Helicity and Field-Aligned Currents in the Polar Ionosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12667, https://doi.org/10.5194/egusphere-egu21-12667, 2021.

Masatoshi Yamauchi, Magnar Johnsen, Shin-Ichi Othani, and Dmitry Sormakov

Solar flares are known to enhance the ionospheric electron density and thus influence the electric currents in the D- and E-region.  The geomagnetic disturbance caused by this current system is called a "crochet" or "SFE (solar flare effect)".  Crochets are observed at dayside low-latitudes with a peak near the subsolar region ("subsolar crochet"), in the nightside high-latitude auroral region with a peak where the geomagnetic disturbance pre-exists during solar illumination ("auroral crochet"), and in the cusp ("cusp crochet").  In addition, we recently found a new type of crochet on the dayside ionospheric current at high latitudes (European sector 70-75 geographic latitude/67-72 geomagnetic latitude) independent from the other crochets.  The new crochet is much more intense and longer in duration than the subsolar crochet and is detected even in AU index for about half the >X2 flares despite the unfavorable latitudinal coverage of the AE stations (~65 geomagnetic latitude) to detect this new crochet (Yamauchi et al., 2020).  

The signature is sometime s seen in AL, causing the crochet signature convoluting with substorms.  From a theoretical viewpoint, X-flares that enhances the ionospheric conductivity may influence the substorm activity, like the auroral crochet.  To understand the substorm-crochet relation in the dayside, we examined SuperMAG data for cases when the onset of the substorm-like AL (SML) behavior coincides with the crochet.  We commonly found a large counter-clockwise ∆B vortex centered at 13-15 LT, causing an AU peak during late afternoon and an AL peak near noon at higher latitudes than the high-latitude crochet.  In addition, we could recognize a clockwise ∆B vortex in the prenoon sector, causing another poleward ∆B, but this signature is not as clear as the afternoon vortex.  With such strong vortex features, it becomes similar to substorms except for its local time.  In some cases, the vortex expends to the nightside sector, where and when nightside onset starts, suggesting triggering of onset.  Thus, the crochet may behave like pseudo-onset at different latitude than midnight substorms, and may even trigger substorm onset.

How to cite: Yamauchi, M., Johnsen, M., Othani, S.-I., and Sormakov, D.: High-latitude crochet (Solar flare effect) as a trigger of pseud-substorm onset, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2741, https://doi.org/10.5194/egusphere-egu21-2741, 2021.

Aude Chambodut

The K index was devised by Bartels et al. (1939) to provide an objective monitoring of irregular geomagnetic activity at subauroral latitudes. K indices are based upon geomagnetic disturbances, measured in horizontal geomagnetic components at magnetic observatories, after « eliminating » the regular daily variation. An individual K index is an integer in the range 0 to 9 corresponding to a class that contains the largest range of geomagnetic disturbances (in either of the two horizontal components) during a 3-hour UT interval. Limits of range vary from one observatory to another since they depend on the corrected geomagnetic latitude of the observatory.

A great number of Space Weather applications rely on K-derived magnetic activity indices at subauroral latitudes. These historical indices; endorsed by IAGA such as Kp, aa and am; represent unprecedented homogeneous time series, up to more than 150 years, highly valuable for all studies related to long-term geomagnetic activity.

However, one has to keep in mind that local K indices and subauroral related ones (K-derived) were developed during other time, under specific societal and technological conditions.

We recall the local K indices derivation processes and characteristics to enlight possible nowadays drawbacks and their simple mitigations.

How to cite: Chambodut, A.: K indices and K-derived magnetic activity indices:  context’s reminder, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15692, https://doi.org/10.5194/egusphere-egu21-15692, 2021.

Veronika Haberle, Aurélie Marchaudon, Pierre-Louis Blelly, and Aude Chambodut

The Earth’s magnetic field as measured from ground-based magnetometers is composed of a variety of fields generated by diverse sources, spanning a broad amplitude and frequency spectrum. Long-term variable sources induce smooth changes, whereas short-term variable sources are able to induce rapid spikes in the geomagnetic field. An important aspect of Space Weather research is to understand the contribution and impact of each of these sources. In particular, knowing the amplitude and frequency of steady-like sources, like diurnal variations, enables us to determine the impact of sudden and hazardous events such as solar storms. The basic approach to this challenge is to identify the quiet magnetic field information within the recorded time-varying signal.
In this work, we examine the variance of the magnetically quiet diurnal and semi-diurnal components of the geomagnetic field, as recorded by ground-based magnetic observatories of the INTERMAGNET network. These variations are extracted by applying appropriately designed digital filters on the geomagnetic field time series. The residual signal is analysed in terms of local time and seasonal variations for selected locations under quiet magnetic conditions. This approach allows us to evaluate the applicability of the introduced filtering method. The obtained results improve our understanding of the driving sources of quiet currents such as the Sq current and the variations of their distributions with respect to regular solar irradiance variations. They will also contribute to a better extraction and description of the remaining/residual signal related to solar wind stimuli (e.g. ICMEs, CIRs) causing magnetic storms.

How to cite: Haberle, V., Marchaudon, A., Blelly, P.-L., and Chambodut, A.: Local diurnal variations of the geomagnetic field during magnetically quiet conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2169, https://doi.org/10.5194/egusphere-egu21-2169, 2021.

Yasmina Bouderba, Ener Aganou, and Abdenaceur Lemgharbi

In this work we will show the behavior of the horizontal component H of the Earth Magnetic Field (EMF) along the seasons during the period of solar cycle 24 lasting from 2009 to 2019. By means of  continuous measurements of geomagnetic components (X, Y) of the EMF, we compute the horizontal component H at the Earth’s surface. The data are recorded with a time resolution of one minute at Tamanrasset observatory in Algeria at the geographical coordinates of 22.79° North and 5.53° East. These data are available from the INTERMAGNET network. We find that the variation in amplitude of the hourly average of H component at low latitude changes from a season to another and it is greater at the maximum solar activity than at the minimum solar activity.

Keywords: Solar cycle 24, Season, Horizontal component H. 

How to cite: Bouderba, Y., Aganou, E., and Lemgharbi, A.: Seasonal behavior of H component during solar cycle 24, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7756, https://doi.org/10.5194/egusphere-egu21-7756, 2021.

Dmitrii Vishniakov, Ivan Lygin, and David Arutyunyan

To solve many geological and geophysical problems, it is very important to study variations of the Earth's magnetic field. The observed variations are usually obtained from data from observatories or temporary variation stations. However, while performing various regional magnetic prospecting works, the network of observatories is not complete enough to account for the variation field correctly.

In this regard, it is becoming necessary to interpolate the data on variations from the points of irregular network. At the same time, obtaining the optimal algorithm is an ambiguous task, its solution requires taking a whole list of factors into account that determine regularity of distribution of physical parameters over the area.

This project represents an interpolation algorithm using method of complex weighting coefficients. The technique was tested on data from the Intermagnet observatories for central Europe, and the obtained accuracy was ± 2 nT. Comparative analysis with known interpolation methods by interpolation methods was carried out.

How to cite: Vishniakov, D., Lygin, I., and Arutyunyan, D.: Algorithm for interpolation of magnetic field variations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12047, https://doi.org/10.5194/egusphere-egu21-12047, 2021.

Vasilis Pitsis, Georgios Balasis, Ioannis Daglis, and Dimitris Vassiliadis

We show that changes in the magnetospheric ring current and auroral currents during the magnetic storms of March 2015 and June 2015, are recorded in several specific ways by ground magnetometers. The ring current changes are detected in geomagnetic field measurements of ground stations at magnetic mid-latitudes from -50 to +50 degrees. The auroral currents changes are detected at high magnetic latitudes from 50 to about 73 degrees. Finally, for stations between 73 and about 85 degrees the measurements of the ground magnetometers seem to be directly correlated with the convection electric field VBSouth of the solar wind. Using the correlations among magnetic fields measured at stations ordered by latitude, a correlation diagram is obtained where the maximum correlation values for fields determined by the ring current form a distinct block. High-latitude magnetic fields from stations at higher latitudes, which are mainly determined by auroral currents, form a different block in the same diagram. This is in agreement with our earlier work using wavelet transforms on ground magnetic-field time series, where mid-latitude fields stations that are influenced mainly by the ring current, give a critical exponent greater than 2 while higher-latitude fields show a more complex dependence with two exponents. The maximum correlation values for mid-latitude fields correlated with the SYM-H index vary from 0.8 to 0.9, and, thus, we infer that those geomagnetic disturbances are mainly due to the ring current. The maximum correlations between the same fields and the solar wind VBSouth vary from 0.5 to 0.7. Fields at magnetic latitudes between 50 and 73 degrees exhibit greater correlation values for the AL index rather than the SYM-H index. This is expected since in the auroral zone, the convection- and substorm-associated auroral electrojets contribute significantly to the deviation of the geomagnetic field from its quiet-time value. In this case, maximum correlations vary between 0.6 and 0.7 for auroral latitude stations when compared with AL, as opposed to 0.4–0.5 when compared with SYM-H. Our results show how different measures of ground geomagnetic variations reflect the time evolution of several magnetospheric current systems and of the solar wind – magnetosphere coupling.

How to cite: Pitsis, V., Balasis, G., Daglis, I., and Vassiliadis, D.: Identification of the ground signatures of magnetospheric current systems as a function of latitude during intense magnetic storms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1436, https://doi.org/10.5194/egusphere-egu21-1436, 2021.

Diana Saturnino, M. Alexandra Pais, João Domingos, and Fernando J. G. Pinheiro

The separation of different sources  in the geomagnetic field signal measured at satellite altitude is still an open issue. One approach to tackle this problem may be non-parametric statistical methods, such as the Principal Component Analysis (PCA). Here, PCA is applied to Virtual Observatories (VO) geomagnetic time series, computed from an enlarged Swarm dataset  covering all local times and geomagnetic activity levels, from January 2014 to December 2019. For each 30-days time window, an Equivalent Source Dipole mathematical model is fitted to the data to reduce a cloud of satellite data points inside a cylinder to one single 'observation' at its axis and 500 km altitude. A VO mesh is constructed with 3394 VOs, with 2 degrees radius each and 3.5 degrees apart in latitude. We study the distribution of satellite data among the cylinders to test if any spatial or temporal sampling asymmetries can be present in the VO dataset and propagate to the PCA results. We also compare observed time series at ground level with VO time series at satellite altitude for the same latitude and longitude. After subtracting a main field model to both series, comparison of the residuals can give further insight on the dependence of external fields with altitude, with a 30-day time resolution.

How to cite: Saturnino, D., Pais, M. A., Domingos, J., and Pinheiro, F. J. G.: Altitude dependence of geomagnetic external fields using Swarm and ground observatories data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13239, https://doi.org/10.5194/egusphere-egu21-13239, 2021.

Eija Tanskanen, Tero Raita, Joni Tammi, Jouni Pulliainen, Hannu Koivula, Thomas Ulich, Reko Hynönen, Ilmo Kukkonen, and Annakaisa Korja

The near-Earth environment is continuously changing by disturbances from external and internal sources. A combined research ecosystem is needed to be able to monitor short- and long-term changes and mitigate their societal effects. Observatories and large-scale infrastructures are the best way to guarantee continuous 24/7 observations and full-scale monitoring capability. Sodankylä Geophysical Observatory takes care of continuous geoenvironmental monitoring in Finland and together with national infrastructures such as FIN-EPOS and E2S enable extending and expanding the monitoring capability. European Plate Observing System of Finland (FIN-EPOS) and flexible instrument network of FIN-EPOS (FLEX-EPOS) will create a national pool of instruments including geophysical instruments targeted for solving topical questions of solid Earth physics. Scientific and new hardware building by FLEX-EPOS is essential in order to identify and reduce the impact of seismic, magnetic and geodetic hazards and understand the underlying processes.


New national infrastructure Earth-Space Research Ecosystem (E2S) will combine measurements from atmosphere to near-Earth and distant space. This combined infrastructure will enable resolving how the Arctic environment change over the seasons, years, decades and centuries. We target our joint efforts to improve the situational awareness in the near-Earth and space environments, and in the Arctic for enhancing safety on ground and in space. This presentation will give details on the large-scale Earth-space infrastructures and research ecosystems and will give examples on how they can improve the safety of society.

How to cite: Tanskanen, E., Raita, T., Tammi, J., Pulliainen, J., Koivula, H., Ulich, T., Hynönen, R., Kukkonen, I., and Korja, A.: New Earth-space infrastructures enable full-scale monitoring capability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15343, https://doi.org/10.5194/egusphere-egu21-15343, 2021.

Raffaello Foldes, Alfredo Del Corpo, Ermanno Pietropaolo, and Massimo Vellante

Monitoring the plasmasphere is an important task to achieve in the Space Weather context. A consolidated technique consists of remotely inferring the equatorial plasma mass density in the inner magnetosphere using Field Line Resonance (FLR) frequency estimates derived from Ultra-Low Frequency (ULF) measurements. FLR frequencies can be obtained via cross-phase analysis of magnetic signals recorded from pairs of latitude separated stations. In the last years, machine learning (ML) has been successfully applied in Space Weather, but this is the first attempt to estimate FLR frequencies with these techniques. EXtreme Gradient Boosting (XGB) is a recent ensemble-based algorithm that is resulted in being highly efficient in regression/classification competitions and many real-world applications. Here we employ XGB for identifying FLR frequencies by using measurements of the European quasi-Meridional Magnetometer Array (EMMA). Our algorithm takes as input the 30-min cross-phase spectra of magnetic signals and returns the FLR frequency as output; we evaluated the algorithm performance on four different station pairs from L=2.4 to L=5.5. Results show that XGB algorithm can be a robust and accurate method to achieve this goal. Its performances slightly decrease with increasing latitude and tend to deteriorate during nighttime. However, at high latitudes, the error increases during highly disturbed geomagnetic conditions such as the storm's main phase. Finally, we compare the equatorial plasmaspheric mass density obtained by XGB estimates with the density profiles by Del Corpo et al. (2019) for a case study, the geomagnetic storm of the 1st June 2013. Our approach may represent a prominent space weather tool included in an automatic monitoring system of the plasmasphere. This work represents only a preliminary step in this direction; applying this technique on a more extensive data set and on more pairs of stations is straightforward and necessary to create more robust and accurate models.

How to cite: Foldes, R., Del Corpo, A., Pietropaolo, E., and Vellante, M.: XGBoost Algorithm for Estimating Equatorial Plasmaspheric Mass Density Using ULF Wave Measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10693, https://doi.org/10.5194/egusphere-egu21-10693, 2021.

Pierdavide Coïsson, Vladimir Truhlik, Janusz Mlynarczyk, Gauthier Hulot, Laura Brocco, Olivier Bonnot, Pierre Vigneron, Dalia Burešová, Jaroslav Chum, Pawel Rzonca, and Andzej Kulak

The magnetic component of electromagnetic signals in the Extremely Low Frequencies (ELF) has been rarely observed from space. The Swarm satellites have the capability of observing part of this spectral band during burst sessions of the Absolute Scalar Magnetometer (ASM), when the sampling frequency of the instrument is raised to 250 Hz. Burst sessions of one week duration have been acquired regularly since 2019. Swarm satellites drift slowly in local time, therefore it has been possible to progressively acquire burst data to cover all hours at all latitudes. This is a unique opportunity at Low Earth Orbits (LEO) in recent years.

This study focuses on whistlers excited by lightning strikes generated by strong storm systems in the troposphere. The ELF component of the lightning signal propagates in the neutral atmosphere at very long distances. We used data from the ground stations of the World ELF Radiolocation Array (WERA) in order to estimate lightning locations and intensity for remarkable events. Part of the lightning signal penetrates into the ionosphere, where the ionospheric plasma produces its dispersion, depending on the spatial distribution of the plasma and the direction of the magnetic field.

We selected events to simulate their propagation through the ionosphere, using ionosonde data, IRI Real-Time Assimilative Mapping (IRTAM) and International Reference Ionosphere (IRI) model as backgrounds, along with the latest version of the International Geomagnetic Reference Field (IGRF). This technique allows to use these signals to sound the ionosphere and validate ionospheric models.

A database of whistler occurrences and parameters has been constructed and a new Swarm L2 product has been defined to make this data accessible to the scientific community.

How to cite: Coïsson, P., Truhlik, V., Mlynarczyk, J., Hulot, G., Brocco, L., Bonnot, O., Vigneron, P., Burešová, D., Chum, J., Rzonca, P., and Kulak, A.: Observation and modelling of whistlers in the ELF as observed by Swarm satellites during regular ASM burst sessions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12740, https://doi.org/10.5194/egusphere-egu21-12740, 2021.

Alexandra Parmentier, Antonio Cicone, Mirko Piersanti, Roberta Tozzi, Matteo Martucci, Alessandro Sotgiu, and Paola De Michelis

Still today vaguely defined, the South Atlantic Anomaly (SAA) is the vast
geographic region where the Earth’s magnetic field is weakest relative to an
ideal Earth-centered dipole field, and the inner radiation belt comes closest
to the planet. Nonetheless it represents a major concern to the space science
community, since the local reduced magnetic intensity often results in satellite
outages and radiation hazard to humans, especially in geomagnetically disturbed
Since 1958, relentless investigation of the various morphological and dynamic
features of the SAA has been taking place, robustly relying on field, plasma and
particle measurements from Low-Earth-Orbit (LEO) satellites since the late
New readings provided by magnetometers operating at LEO altitudes show that,
within the past decade, an apparent second center of minimum field intensity
has begun to be clearly resolved southwest of Africa, suggesting a possible rapid
splitting of the SAA into two cells. In addition to magnetic determinations, the
tracking of fluxes of sub-MeV electrons that are lost to the atmosphere when
drifting into the SAA due to its increased bounce loss cone, offers a specular
view of the same phenomenon. This multi-messenger approach from different
platforms is best suited to catch fine details of the splitting.
Directly stemming from the data-adaptive Empirical Mode Decomposition (EMD)
developed at NASA in the 1990s for the analysis of non-stationary signals, the
Fast Iterative Filtering (FIF) class of signal mode decompositions is recently
taking center stage due to enhanced rigorous formalization in terms of con-
vergence and stability. Multidimensional and Multivariate FIF (MMFIF) is a
brand-new extension that handles multidimensional and multichannel datasets.
The application of MMFIF techniques to magnetic-field and particle data from
an ensemble of LEO satellites has allowed us to best characterize the dynamic
evolution of the SAA lobes in the 2010s, and compare it to analogous data in
the literature from the previous decades.

How to cite: Parmentier, A., Cicone, A., Piersanti, M., Tozzi, R., Martucci, M., Sotgiu, A., and De Michelis, P.: Tracking the split: a non-linear iterative approach to the monitoring of recent SAA evolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1781, https://doi.org/10.5194/egusphere-egu21-1781, 2021.