Derivation of the full current density vector in the Earth's ionosphere low- and mid-latitude F region using ESA's Swarm satellites (original) (raw)
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Advances in Space Research, 2019
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Journal of Geophysical Research: Space Physics, 2019
We present statistical investigation of the high‐latitude ionospheric current systems in the Northern Hemisphere (NH) and Southern Hemisphere (SH) during low (Kp < 2) and high (Kp ≥ 2) geomagnetic activity levels. Nearly 4 years of vector magnetic field measurements are analyzed from the two parallel flying Swarm A and C satellites using the spherical elementary current system method. The ionospheric horizontal and field‐aligned currents (FACs) for each auroral oval crossing are calculated. The distributions of the mean values of FACs as well as the horizontal curl‐free and divergence‐free currents in magnetic latitude and magnetic local time for each hemisphere and activity level are presented. To estimate the NH/SH current ratios for the two activity levels, we remove seasonal bias in the number of samples and in the Kp distribution by bootstrap resampling. This is done in such a manner that there are equal number of samples from each season in each Kp bin. We find that for the...
Parallel Electrical Conductivity in the Topside Ionosphere Derived From Swarm Measurements
Journal of Geophysical Research: Space Physics, 2021
Our knowledge of the physical properties of the topside ionosphere is still incomplete. A key point still not fully understood is how field‐aligned currents are generated, evolve and dissipate in the ionosphere. Answering to this question is fundamental for a better understanding of the mechanisms regulating the coupling between magnetosphere and ionosphere and to shed light on the physical processes inherent to space weather events occurring in the Earth's ionosphere. In this framework a relevant role is played by the ionospheric conductivity. The purpose of this study is to analyze the main properties of the electrical conductivity parallel to the geomagnetic field from a climatological point of view. The statistical study of the electrical conductivity is proposed using four years of in‐situ electron density and temperature measurements at 1 Hz acquired by the European Space Agency's Swarm A satellite. Variations due to seasonal effects are also investigated. Finally, sta...
Ionospheric midlatitude electric current density inferred from multiple magnetic satellites
Journal of Geophysical Research Space Physics, 2013
1] A method for inferring zonal electric current density in the mid-to-low latitude F region ionosphere is presented. We describe a method of using near-simultaneous overflights of the Ørsted and CHAMP satellites to define a closed circuit for an application of Ampère's integral law to magnetic data. Zonal current density from sources in only the region between the two satellites is estimated for the first time. Six years of mutually available vector magnetic data allows overlaps spanning the full 24 h range of local time twice. Solutions are computed on an event-by-event basis after correcting for estimates of main and crustal magnetic fields. Current density in the range˙0.1 A/m 2 is resolved, with the distribution of electric current largely matching known features such as the Appleton anomaly. The currents appear unmodulated at times of either high-negative Dst or high F 10.7 , which has implications for any future efforts to model their effects. We resolve persistent current intensifications between geomagnetic latitudes of 30 and 50 ı in the postmidnight, predawn sector, a region typically thought to be relatively free of electric currents. The cause of these unexpected intensifications remains an open issue. We compare our results with current density predictions made by the Coupled Thermosphere-Ionosphere-Plasmasphere model, a self-consistent, first-principles, three-dimensional numerical dynamic model of ionospheric composition and temperatures. This independent validation of our current density estimates highlights good agreement in the broad spatiotemporal trends we identify, which increases confidence in our results.
Pressure-Gradient Current at High Latitude from Swarm Measurements
Remote Sensing, 2022
The pressure-gradient current is among the weaker ionospheric current systems arising from plasma pressure variations. It is also called diamagnetic current because it produces a magnetic field which is oriented oppositely to the ambient magnetic field, causing its reduction. The magnetic reduction can be revealed in measurements made by low-Earth orbiting satellites flying close to ionospheric plasma regions where rapid changes in density occur. Using geomagnetic field, plasma density and electron temperature measurements recorded on board ESA Swarm A satellite from April 2014 to March 2018, we reconstruct the flow patterns of the pressure-gradient current at high-latitude ionosphere in both hemispheres, and investigate their dependence on magnetic local time, geomagnetic activity, season and solar forcing drivers. Although being small in amplitude these currents appear to be a ubiquitous phenomenon at ionospheric high latitudes characterized by well defined flow patterns, which ca...
Annals of Geophysics, 2018
The high−latitude ionosphere is characterised by plasma density irregularities with typical lengths in a wide range of scales (from ~1 m up to ~1000 km). The enhancement of these irregularities caused for instance by severe Space Weather conditions can affect trans−ionos− pheric communications between ground facilities and satellites. For this reason, an accurate characterisation of the dynamic properties of electron density and their variation with the geomagnetic activity level is of particular interest for the Space Weather especially at high latitudes. In this framework, taking advantage of high resolution in situ measurements by the recent ESA−Swarm space mission orbiting in the ionospheric F−layer, we study both the dynamical properties of the electron density and the scaling properties of the electron den− sity fluctuations at high latitudes in the Northern and Southern Hemispheres in response to changes in the geomagnetic activity levels via nonlinear techniques involving the first−order structure functions. Indeed, it has been shown that the turbulent character of the ionos− pheric plasma density plays an important role in the generation and dynamics of ionospheric plasma density irregularities and the study of the scaling properties of the electron density fluctuations permits us to characterise the possible turbulent state of the ionospheric elec− tron density. The obtained results are consistent with the turbulent character of the ionospheric dynamics, and with the presence of dif− ferent turbulent regimes that show a dependence on the geomagnetic activity levels, magnetic latitude and MLT values.
Curl-B technique applied to Swarm constellation for determining field-aligned currents
Earth, Planets and Space, 2006
The constellation of the Swarm satellites provides for the first time the opportunity to determine field-aligned currents in the ionosphere uniquely. This is achieved by employing the curl-B relation of Ampere's law directly to measurements of a satellite pair flying side-by-side. The new technique is applied to a set of consistent magnetic field and current data generated by a global magnetospheric model. Using a realistic Swarm constellation the current distribution is determined along the orbit from the synthetic magnetic field data. The resulting currents are tested against the input currents. The agreement between input model and recovered field-aligned currents is excellent and much improved compared to the single-satellite estimates. Due to the spatial separation of the sampling points, only the distribution of large-scale field-aligned currents can be determined. These investigations demonstrate one important aspect of the broad capabilities provided by the upcoming space mission.
Earth, Planets and Space, 2006
We have used a global model of the solar wind magnetosphere interaction to model the high latitude part of the external contributions to the geomagnetic field near the Earth. The model also provides corresponding values for the electric field. Geomagnetic quiet conditions were modeled to provide simulated external contributions relevant for internal field modeling. These have proven very valuable for the design and planning of the upcoming multi-satellite Swarm mission. In addition, a real event simulation was carried out for a moderately active time interval when observations from the Ørsted and CHAMP sattelites were available. Comparisons between the simulation results and the satellite observations for this event demonstrate the current level of validity of the global model. We find that the model reproduces quite well the region 1 current system and nightside region 2 currents whereas it consistently underestimates the dayside region 2 currents and overestimates the horizontal ionospheric closure currents in the dayside polar cap. Furthermore, with this example we illustrate the great benefit of utilizing the global model for the interpretation of Swarm external field observations and, likewise, the potential of using Swarm measuremnets to test and improve the global model.
High-latitude ionospheric currents during very quiet times: their characteristics and predictability
Annales Geophysicae, 2004
CHAMP passes the geographic poles at a distance of 2.7 • in latitude, thus providing a large number of magnetic readings of the dynamic auroral regions. The data of these numerous overflights were used for a detailed statistical study on the level of activity. A large number of tracks with very low rms of the residuals between the scalar field measurements and a high degree field model were singled out over both the northern and southern polar regions, independently. Low rms values indicate best model fits and are therefore regarded as a measure of low activity, although we are aware that this indicator also has its limitations. The occurrence of quiet periods is strongly controlled by the solar zenith angle at the geomagnetic poles, indicating the importance of the ionospheric conductivity. During the dark polar season, about 30% of the passes can be qualified as quiet. The commonly used magnetic activity indices turn out not to be a reliable measure for the activity state in the polar region. Least suitable is the D st index, followed by the K p . Slightly better results are obtained with the P C and the IMAGE-AE indices. The latter is rather effective within a time sector of ±4 hours of magnetic local time around the IMAGE array.
Spatial Gradients in Geomagnetic Storm Time Currents observed by Swarm Multi-Spacecraft Mission
Journal of Geophysical Research: Space Physics, 2019
This paper presents a comprehensive study of geomagnetic storm time currents using magnetic field recorded by multispacecraft polar-orbiting mission, Swarm. During geomagnetic storm period, the magnetic field variations obtained after removing the internal geomagnetic field and quiet time contributions can be considered as a proxy for storm time currents and are found to follow the temporal profile of Dst index very closely. These variations at the equatorial crossings recorded by multiple-spacecraft are used to estimate the Dst values and are found to have a good match with the ground-based Dst index. The average deviation between these two is around 4-13%. We have estimated the asymmetry by taking the difference between the magnetic field variations at two local time sectors separated by 12 hr. The estimated asymmetry shows a good match with the AsyH-index, especially when satellite traverses in the dawn-dusk sector. In general, the magnetic field variations are stronger in the night-to-dusk sector than day-to-dawn sector, which could be due to the larger pressure-gradients near night-to-dusk caused by ion movements. The important advantage of Swarm mission is that it provides an opportunity to investigate the longitudinal gradients in the storm time magnetic fields. It is observed that in general, the gradients are stronger during the main phase of the storm, centered near the equator with a latitudinal width of~20-30°in both the hemispheres, and are supportive to the scenario of particle-injection from the magnetotail. The stronger gradients are observed at higher latitudes (~40°) during the episodes of substorms and might be associated with the ionospheric/field-aligned currents. Plain Language Summary The space weather events such as geomagnetic storms can have a huge impact on the terrestrial magnetic and plasma environment, producing large currents, which in turn, impact spaceborne communication, navigation systems, aviation and satellite operations, and electric power grids, etc. The paper presents a new approach to estimate geomagnetic indices equivalent to Dst and AsyH during geomagnetic storms, making use of the increased observations from space-based instruments in recent times, and demonstrates their utility in quantifying the geomagnetic environment. The important advantage of multispacecraft Swarm mission is that it provides an opportunity to investigate the spatial gradients in the storm time magnetic fields. The paper reports that strong azimuthal gradients in the magnetic field, near the equatorial sector, are associated with particle injection from the magnetotail. The paper demonstrates the utility of space-based measurements in understanding the geomagnetic environment.