Multispacecraft Current Density Estimates in the Low‐ and Mid‐Latitude F‐Region Ionosphere Using the Swarm Constellation

Fillion, Martin; Hulot, Gauthier; Alken, Patrick; Chulliat, Arnaud; Vigneron, P.

doi:10.1029/2020ja028872

Cited by 5 publications

(8 citation statements)

References 54 publications

(113 reference statements)

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“…Various closely related methods using groupings of the spacecraft at the high latitude regions of LEO have been compared in an assessment of key events by Trenchi et al (2020). A time shifted configuration, tailored to the low latitude regions covered by Swarm has also been applied to extract low latitude currents (Fillion et al, 2021).…”

Section: Adaption To Leo Data: Use Of Time Stationaritymentioning

confidence: 99%

Curlometer Technique and Applications

Dunlop

Dong²,

Wang³

et al. 2021

JGR Space Physics

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We review the range of applications and use of the curlometer, initially developed to analyze Cluster multi‐spacecraft magnetic field data; but more recently adapted to other arrays of spacecraft flying in formation, such as MMS small‐scale, 4‐spacecraft configurations; THEMIS close constellations of 3–5 spacecraft, and Swarm 2–3 spacecraft configurations. Although magnetic gradients require knowledge of spacecraft separations and the magnetic field, the structure of the electric current density (for example, its relative spatial scale), and any temporal evolution, limits measurement accuracy. Nevertheless, in many magnetospheric regions the curlometer is reliable (within certain limits), particularly under conditions of time stationarity, or with supporting information on morphology (for example, when the geometry of the large scale structure is expected). A number of large‐scale regions have been covered, such as: the cross‐tail current sheet, ring current, the current layer at the magnetopause and field‐aligned currents. Transient and smaller scale current structures (e.g., reconnected flux tube or dipolarisation fronts) and energy transfer processes. The method is able to provide estimates of single components of the vector current density, even if there are only two or three satellites flying in formation, within the current region, as can be the case when there is a highly irregular spacecraft configuration. The computation of magnetic field gradients and topology in general includes magnetic rotation analysis and various least squares approaches, as well as the curlometer, and indeed the added inclusion of plasma measurements and the extension to larger arrays of spacecraft have recently been considered.

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Section: Adaption To Leo Data: Use Of Time Stationaritymentioning

confidence: 99%

Curlometer Technique and Applications

Dunlop

Dong²,

Wang³

et al. 2021

JGR Space Physics

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“…The main result is the identification of the eastward drift of IHFACs at the same speed as the rotation of the Earth. This eastward drift will need to be confirmed using the Level-2 FAC Swarm product (Ritter et al, 2013), although some limitations could arise due to known uncertainties in this product (Fillion et al, 2021;F. Wang, Lühr, et al, 2022).…”

Section: Discussionmentioning

confidence: 99%

“…The main result is the identification of the eastward drift of IHFACs at the same speed as the rotation of the Earth. This eastward drift will need to be confirmed using the Level‐2 FAC Swarm product (Ritter et al., 2013), although some limitations could arise due to known uncertainties in this product (Fillion et al., 2021; F. Wang, Lühr, et al., 2022). Other characteristics such as the increase of total amount of current over the Pacific Ocean—particularly significant in summer—or the occurrence of a WN‐5 longitudinal structure in summer are also important.…”

Section: Discussionmentioning

confidence: 99%

“…In the mid‐ and low‐latitude F region, interhemispheric field‐aligned currents (IHFACs) arise from the electrostatic difference between geomagnetic conjugate points and connect the E‐region dynamo current systems in the Northern and Southern Hemispheres (Fukushima, 1978; Takeda, 1982; Van Sabben, 1966). These currents mostly flow on the dayside and have been extensively studied using ground and satellite data (Bolaji et al., 2012; Fillion et al., 2021; Lühr et al., 2015, 2019; Park et al., 2011; Park, Stolle, et al., 2020; Park, Yamazaki, & Lühr, 2020; Ranasinghe et al., 2021; Shinbori et al., 2017; Yamashita, 2002). At high latitudes, field‐aligned currents are about one order of magnitude more intense and connect the high‐latitude E‐region current system to magnetospheric currents.…”

Section: Introductionmentioning

confidence: 99%

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

2023

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The Earth's magnetic field is the sum of magnetic fields produced by many different sources. It can be measured at the Earth's surface, in the geomagnetic observatories, or on board of satellites (Hulot et al., 2015). Such data are used to build models of the Earth's magnetic field and to study their sources. One main challenge, however, is to single out the signal from each source. This is particularly true for the ionospheric field produced by the electric currents that flow in the ionosphere-the ionized layer of the atmosphere, from 80 to 1,000 km. Because of its high variability in space and time, and of an incomplete space-time data coverage, this field and associated electric currents are still only partially understood (Finlay et al., 2017).One of the dominant ionospheric currents at mid and low latitudes are called Solar quiet (Sq) currents (Matsushita, 1968;Yamazaki & Maute, 2017). They flow in the ionospheric E region-between 90 and 150 kmand mainly consist of two vortices, each flowing in one hemisphere and in opposite directions. They are generated by a physical mechanism called the ionospheric wind dynamo (Richmond, 1979) and are therefore referred to as dynamo currents. This system is reinforced at the magnetic equator where the equatorial electrojet flows (Lühr et al., 2021). Several approaches have been proposed to build data-based models of the mid-and low-latitude E-region ionospheric field. The Comprehensive Model series (Sabaka et al., 2002(Sabaka et al., , 2020 and the DIFI model (Chulliat et al., 2013(Chulliat et al., , 2016 use spherical harmonics and Fourier series to represent the global climatological variations of the low and mid latitude E-region ionospheric field. More recently, some alternative approaches were developed. They rely on a priori information allowing for a better characterization of individual Earth's magnetic field component. Among these, one can mention correlation-based modeling techniques (Baerenzung et al., 2020;Holschneider et al., 2016) and techniques that rely on physics-based models (Alken et al., 2017;Egbert et al., 2021).Other important ionospheric currents flow in the F region, between 150 and 1,000 km. These currents are of particular interest to this study. The dominant currents in the F region are the field-aligned currents that flow along the highly conductive field lines of the Earth's main magnetic field. They exist both at high latitudes

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“…For example, due to the overlap of its spatial scales with those of the core field on the night side of the Earth, accurately removing the magnetospheric field is an essential step in building modern core field models used to constrain physical processes in the Earth's core and the geodynamo (Finlay et al., 2017). Magnetospheric field models are also used in ionospheric magnetic field and electrodynamics studies (Fillion et al., 2023; Stolle et al., 2016). Additionally, in a certain frequency range, the near‐Earth magnetospheric field is one of the main sources for the electromagnetic induction studies of the Earth's interior (A. Kuvshinov et al., 2021) as well as a signature of the interactions between the solar wind and the magnetosphere (Milan et al., 2017).…”

Section: Introductionmentioning

confidence: 99%

A Model of Hourly Variations of the Near‐Earth Magnetic Field Generated in the Inner Magnetosphere and Its Induced Counterpart

Fillion,

Chulliat,

Alken

et al. 2023

JGR Space Physics

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We present a new model of the near‐Earth magnetospheric field produced by electric currents in the inner magnetosphere and the associated induced magnetic field. The model is designed to track hourly variations of these fields and accounts for their local time asymmetries. It is built by applying spherical harmonic analysis to vector measurements from the ground observatory network at low and mid‐latitudes. The primary and induced fields are separated with an approach in the time domain that uses a a priori radially‐symmetric electric conductivity model of the Earth. The model coefficients are computed at one‐hour time steps between 1997 and 2022. This model is shown to be consistent to within a few nT with previously developed indices which track the magnetospheric ring current. It is also validated against data from the Swarm, CHAMP and Øersted satellites. The fit to satellite data is comparable to that of the CHAOS‐7.15 model for geomagnetically quiet times, and improved by up to 20% on some components for geomagnetically moderate and active times. We attribute these differences mostly to a better representation of local time asymmetries, both on average and during individual geomagnetic storms. This model can be used in various applications, such as investigating the properties of the magnetospheric field and its sources and separating the magnetospheric field from the fields of other sources in geomagnetic field modeling.

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Multispacecraft Current Density Estimates in the Low‐ and Mid‐Latitude F‐Region Ionosphere Using the Swarm Constellation

Cited by 5 publications

References 54 publications

Curlometer Technique and Applications

Curlometer Technique and Applications

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

A Model of Hourly Variations of the Near‐Earth Magnetic Field Generated in the Inner Magnetosphere and Its Induced Counterpart

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