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

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By utilizing magnetic field measurements from the Swarm constellation during the years 2014–2019, average characteristics of the height‐integrated ionospheric zonal and meridional currents at middle and low latitudes are investigated. We provide for the first time the detailed dependencies of these currents on location, local time, and season. The main results obtained are: (a) Large parts of the ionospheric currents flow in the F‐region, particularly on the nightside and in the winter hemisphere. (b) Clearly outstanding zonal current is the equatorial electrojet (EEJ) around noon, accompanied by currents in opposite direction at middle latitudes. At night, eastward currents are prevailing in the summer hemisphere, and westward in winter. During equinox the nighttime zonal currents show a lot of hemispheric similarity, with westward currents around pre‐midnight and eastward currents post‐midnight at mid latitudes. These features can be attributed to the meridional thermospheric wind effects. (c) The meridional currents are weak at night, exhibiting a preferred direction toward the summer hemisphere. At daytime the meridional currents flow toward equator in the pre‐noon sector and opposite current directions prevail in the afternoon, which is consistent with the closing of the EEJ current circuit. Large hemispheric differences in meridional currents are found during December solstice, suggesting that most of the EEJ current is closed through the winter, northern hemisphere. (d) The zonal and meridional currents at middle latitude exhibit clear signatures of solar tides at daytime. Most prominent are the non‐migrating tidal components DE3 in the zonal currents and SW5 in the meridional.

Section: Tidal Features Of Ionospheric Currents At Middle Latitudesmentioning

confidence: 87%

Average Ionospheric Mid‐ and Low‐Latitude Currents From E‐ and F‐Region Altitudes, Derived by the Swarm Constellation

Zhou

Lühr

2023

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“…Additionally, Holappa and Buzulukova (2022) studied the IMF B y effect on the energetic proton flux specifically in the dusk sector, focusing on the 12 to 24 MLT interval. In this work, the MLT of peak PEJ is used to define the events, following previous works (e.g., Wang & Lühr, 2023, 2024).…”

Section: Data and Processing Methodsmentioning

confidence: 99%

“…This article is a follow‐on work of our previous research (Wang & Lühr, 2023, 2024), wherein we employed a consistent 6‐hr MLT interval. The motivation for using such a broad MLT bin width is to ensure sufficient statistics in all MLT bins.…”

Section: Data and Processing Methodsmentioning

confidence: 99%

“…Field‐aligned currents (FACs) play an important role in the magnetosphere‐ionosphere coupling system. They remain a hot topic in space weather since satellite observations confirmed their existences (e.g., Friis‐Christensen & Wilhjelm, 1975; Iijima & Potemra, 1976; Vennerstrøm et al., 2002, 2005; Wang & Lühr, 2023; Wang et al., 2005, 2014). Region 1 (R1) FACs flows into the ionosphere on the dawn side and out of the ionosphere on the dusk side.…”

Section: Introductionmentioning

confidence: 99%

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Interplanetary Magnetic Field B_y Effects on the Strength and Latitude of Field‐Aligned Currents in Different Magnetic Local Time Sectors

Wang,

Sun,

Lühr

2024

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In this work, IMF By effects on field‐aligned currents (FACs) are examined in different local time sectors, seasons, and hemispheres. At dusk and 09–14 MLT, when the eastward polar electrojet (PEJ) prevails, the northern FACp (poleward side FACs) are stronger when IMF By < 0 than when IMF By > 0. Conversely, at dawn, 21–02 MLT, and 09–14 MLT with westward PEJ, the northern FACp are stronger with IMF By > 0 compared to IMF By < 0. The southern FACp shows a reversed relationship with IMF By direction. The dependence of FACe (equatorward side FACs) on IMF By is weaker, except for the midday FACe, which shows opposite variations with respect to IMF By when compared to FACp. Stronger IMF By effect is observed in local summer in most of local times. The northern FACs are located at higher latitude for IMF By > 0 than for IMF By < 0 in local times with eastward PEJ, while the opposite trend is observed in other local times and in the Southern Hemisphere. The hemispheric difference in the peak latitude of FACs demonstrates an inverse relationship with its intensity, with stronger FACs located at lower latitudes. Overall, the local time and hemispheric differences in FACs strength and latitude are discussed in the context of interhemispheric field‐aligned currents linked to IMF By.

“…IHFACs are predominantly confined to the dayside and are strongest at low latitudes (below ± 35°magnetic latitudes). Their intensity and direction (northward or southward) are dependent on latitude, longitude, local time, and season (Fillion et al, 2023;Park et al, 2011Park et al, , 2020Wang et al, 2023). Model studies carried out by Fukushima (1979) suggested that the most intense IHFACs are located around the Sq focus in two hemispheres, flowing from the summer to the winter hemisphere during noon hours.…”

Section: Quasi 16 Days Oscillations In Ionospheric Currentsmentioning

confidence: 99%

Quasi 16‐Day Wave Signatures in the Interhemispheric Field Aligned Currents: A New Perspective Toward Atmosphere‐Ionosphere Coupling

Jadhav,

Yamazaki,

Gurubaran

et al. 2024

Quasi 16‐day waves (Q16DWs) are a prominent and recurrent phenomenon in the middle atmosphere, typically observed over winter mid and high latitudes. This study investigates the intense Q16DW event during the 2018–2019 Northern Hemisphere (NH) winter, and explores its propagation in the middle atmosphere and its notable influence on the E‐region ionosphere. Long‐term geopotential height estimates of Aura Microwave Limb Sounder (MLS) reveal that the wave activity under consideration exhibited the largest amplitudes in the mesosphere for past 16 years. An analysis of wind data obtained from medium frequency (MF) and meteor radars, as well as from Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) reanalysis, reveals the presence of a westward‐propagating Q16DW with zonal wavenumber 1 exhibiting notable asymmetry about the equator, with the majority of the wave activity being confined to the NH. The prominently large amplitudes and vertical wavelengths of the wave suggest potential for the wave propagation to extend deep into the E‐region ionosphere. Swarm satellite observations reveal concurrent ∼16‐day oscillations in the eastward component of the geomagnetic field at low latitudes. These oscillations can be attributed to the periodic variations in interhemispheric field‐aligned currents (IHFACs). The ∼16‐day oscillations in the IHFACs are likely a consequence of asymmetric wind‐dynamo action, which is directly or indirectly associated with the Q16DW. These findings suggest that planetary waves originating in the middle atmosphere can cause interhemispheric coupling in the ionosphere.