Improved Field‐Aligned Current and Radial Current Estimates at Low and Middle Latitudes Deduced by the Swarm Dual‐Spacecraft

Wang, Fengjue; Lühr, H.; Xiong, Chao; Zhou, Yunliang

doi:10.1029/2022ja030396

Cited by 8 publications

(27 citation statements)

References 15 publications

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“…But these authors also find an influence of the lunar tide M2 at this time of the year, in particular during years with stratospheric sudden warming events. These afore mentioned tidal features are also found in the recent work by Wang et al (2022) and in this study.…”

Section: Tidal Signatures Of Ihfacsupporting

confidence: 92%

“…(2019), and Wang et al. (2022). Only around the longitudes of the South Atlantic Anomaly (SAA) this pattern is somewhat disturbed.…”

Section: Resultsmentioning

confidence: 97%

“…The comparison shown here indicates that the updated IRC and FAC data are more reliable. However, by a systematic survey based on the 5‐year data period of version 04, this spurious morning signature partly remains in the average values of descending orbits, as was the case in data of version 03 (see Figure 6 of Wang et al., 2022). Since the hours around 04:00–06:00 MLT are not of main concern for our current study and the mean bias ranges only around 2 nA/m 2 , we do not think this effect is influencing our main results.…”

Section: Data and Processing Approachesmentioning

confidence: 83%

“…(2019) and Wang et al. (2022), were limited to magnetic latitudes below about ±40° MLat. Park et al.…”

Section: Resultsmentioning

confidence: 99%

“…In this study, we used the 1 Hz Level-1b magnetic field data with product identifier "MAGx_LR" and the 1 Hz Level-2 FAC data with product identifier "FACx_TMS." The small "x" in the product names represents a placeholder for the spacecraft names, A, B, C. Of particular interest for this work are IRC and FAC estimates both derived from the combined magnetic field measurements of Swarm A and C. These results exhibit clear advantages over the corresponding estimates from single satellites, as has been shown by Wang et al (2022). Methods and assumptions on how the FAC and IRC are calculated from the magnetic measurements of single satellite and dual spacecraft have been described by Lühr et al (2020).…”

Section: Swarm Satellites and Ionospheric Current Productsmentioning

confidence: 94%

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

et al. 2023

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The solar quiet daily variation (Sq) currents are known to cause prominent magnetic field variations at low and middle latitudes (Campbell, 1989). These currents in the dayside ionospheric E-layer flows clockwise in the southern hemisphere and counter-clockwise in the northern hemisphere, with vortices centered at about ±35° magnetic latitude (MLat). As the atmospheric wind and ionospheric conductivity depend on the intensity of solar extreme ultraviolet (EUV) radiation, ionospheric currents show prominent seasonal dependence. Compared to equinoxes, the summer hemispheric atmosphere during solstice is more effectively ionized and with that the hemispheric difference in ionospheric current intensity is larger (Van Sabben, 1964). As a consequence, inter-hemisphere field-aligned currents (IHFAC) were predicted to flow from one hemisphere to the other, connecting the vortices of the Sq current systems in order to balance the potential differences between the two hemispheres (Fukushima, 1979).Earlier studies used mainly the magnetic signatures from ground magnetometers (Forbes, 1981;Rastogi, 1989), or sounding rocket (e.g., Onwumechili, 1992), to investigate the characteristics of ionospheric currents. However, Fukushima et al. (1976) pointed out that the magnetic signatures from ground magnetometers cannot effectively distinguish contributions from the magnetospheric and ionospheric currents. Therefore, in situ magnetic measurements from low-Earth orbit (LEO) satellites became an important data source for resolving these currents (e.g., Cain & Sweeney, 1973;Langel et al., 1993;Lühr et al., 2004), as all LEO satellites fly above the E-region current but below the magnetospheric current, for example, the ring current. Compared to ground magnetometer and rocket, LEO satellites pass very rapidly over the ionospheric current system and their measurements thus can be regarded as a snapshot of the spatial structures. The F-region currents during daytime are much weaker compared to the E-region current, for example, Sq currents or equatorial electrojet (EEJ), therefore, magnetic field measurements with high resolution are required to resolve the F-region currents.

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Section: Tidal Signatures Of Ihfacsupporting

confidence: 92%

“…(2019), and Wang et al. (2022). Only around the longitudes of the South Atlantic Anomaly (SAA) this pattern is somewhat disturbed.…”

Section: Resultsmentioning

confidence: 97%

Section: Data and Processing Approachesmentioning

confidence: 83%

“…(2019) and Wang et al. (2022), were limited to magnetic latitudes below about ±40° MLat. Park et al.…”

Section: Resultsmentioning

confidence: 99%

Section: Swarm Satellites and Ionospheric Current Productsmentioning

confidence: 94%

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

et al. 2023

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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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Influence of the Polar Electrojet on Field‐Aligned Current Estimates From Single Satellite Magnetic Field Measurements

et al. 2023

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There are in general two kinds of intense ionospheric currents at auroral latitudes: one is the field-aligned current (FAC) that flows along the magnetic field lines, and the other is the auroral or polar electrojet (PEJ) that flows horizontally in the ionospheric E-region at about 110 km. As a connection between the magnetosphere and ionosphere, FACs are the dominant transport mechanism for energy and momentum, and they are thus of fundamental importance for our understanding of the solar wind-magnetosphere-ionosphere-thermosphere coupling (e.g., Birkeland, 1908;Iijima & Potemra, 1976b). Differently, the PEJs are part of the horizontally Hall current vortices that close over the polar cap. Along the auroral oval the PEJ currents are concentrated and their intensity is related to the substorm activity (e.g., Akasofu et al., 1965;Kisabeth, 1979).According to Ampere's law, electric currents cause magnetic signatures perpendicular to the current direction. Therefore, measuring the magnetic variations is a possible way to quantify the ionospheric currents. Davis and Sugiura (1966) proposed the auroral electrojet (AE) index to monitor the electrojet activity, which is widely used today as an indicator reflecting the state of polar ionosphere as well as the activity phase of a substorm. Later studies, for example, Kamide et al. (1981) and Friis-Christensen et al. (1985), have also successfully derived the full Hall current vortices from the ground-based magnetic observations. However, one weakness of magnetic observations from ground is that they can only estimate the equivalent currents, representing horizontal currents that close in the ionosphere. Conversely, currents connected with FACs cannot be sensed. An additional limitation is the patchy distribution of ground stations, which restricts the investigation of large-scale current circuits, and they cannot reflect well the global variations. Therefore, magnetic observations taken at satellite altitude have become an important data source for retrieving the ionospheric currents on a global scale, especially for the FAC distribution. Zmuda et al. (1966) first reported the magnetic signatures in the 1963-38C satellite data, shown as persistent perturbations of the east-west magnetic components whenever the satellite crossed the auroral latitudes. These signatures were later identified as the FAC sheet crossings. Potemra (1976a, 1976b) were the

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Improved Field‐Aligned Current and Radial Current Estimates at Low and Middle Latitudes Deduced by the Swarm Dual‐Spacecraft

Cited by 8 publications

References 15 publications

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

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

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

Influence of the Polar Electrojet on Field‐Aligned Current Estimates From Single Satellite Magnetic Field Measurements

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