The Relationship of High‐Latitude Thermospheric Wind With Ionospheric Horizontal Current, as Observed by CHAMP Satellite

Abstract

The relationship between high‐latitude ionospheric currents (Hall current and field‐aligned current) and thermospheric wind is investigated. The 2‐D patterns of horizontal wind and equivalent current in the Northern Hemisphere derived from the CHAMP satellite are considered for the first time simultaneously. The equivalent currents show strong dependences on both interplanetary magnetic field (IMF) By and Bz components. However, IMF By orientation is more important in controlling the wind velocity patterns. The duskside wind vortex as well as the antisunward wind in the morning polar cap is more evident for positive By. To better understand their spatial relation in different sectors, a systematic superposed epoch analysis is applied. Our results show that in the dusk sector, the vectors of the zonal wind and equivalent current are anticorrelated, and both of them form a vortical flow pattern for different activity levels. The currents and zonal wind are intensified with the increase of merging electric field. However, on the dawnside, where the relation is less clear, antisunward zonal winds dominate. Plasma drift seems to play a less important role for the wind than neutral forces in this sector. In the noon sector, the best anticorrelation between equivalent current and wind is observed for a positive IMF By component and it is less obvious for negative By. A clear seasonal effect with current intensities increasing from winter to summer is observed in the noon sector. Different from the currents, the zonal wind intensity shows little dependence on seasons. Our results indicate that the plasma drift and the neutral forces are of comparable influence on the zonal wind at CHAMP altitude in the noon sector.

Seasonal and Temporal Variations of Field‐Aligned Currents and Ground Magnetic Deflections During Substorms

“…Furthermore, our results show that prior to onset, the increase in FACs is concentrated on the duskside. The asymmetries observed in the total FACs derived from AMPERE in this study are different from the asymmetries in the current density from CHAMP reported by Huang et al (), with the current densities in the Region 2 currents being up to 40% stronger at dawn. As noted in section 2, AMPERE predominantly detects large‐scale currents, whereas single‐spacecraft measurements of FACs can detect much smaller current systems; thus, these differences may arise from the underlying FAC calculations.…”

Fabry‐Perot Interferometer Observations of Thermospheric Horizontal Winds During Magnetospheric Substorms

“…In the statistical study based on CHAMP satellite measurements by Förster et al (2011), they found that the outer boundary of the wind vorticity on the duskside generally overlaps with the boundary between the Region 1 (R1) and Region 2 (R2) currents. Along the boundary, the Hall current flows eastward, which is equivalent to the EEJ observed by the ground-based magnetometers (Huang et al, 2017). The westward wind in our observations should be a part of the duskside vortex, and the westward acceleration indicates that the vortex is strengthened with continued solar wind energy input during the GP.…”

“…The westward wind in our observations should be a part of the duskside vortex, and the westward acceleration indicates that the vortex is strengthened with continued solar wind energy input during the GP. Our observations are also in agreement with the statistical study by Huang et al (2017), who showed that the westward winds are anti-correlated with the EEJ along the latitudes. The speed of the westward wind rely on the duration of the acceleration.…”

High‐Latitude Observations of a Localized Wind Wall and Its Coupling to the Lower Thermosphere

“…This location corresponds to strong zonal winds as seen in wind maps presented by Dhadly et al (2017) and Huang et al (2017). Between longitudes of 100°and 200°and 60°and 70°southern latitudes there exists a wind wall of extreme velocity reversals to westward in the zonal and southward in the meridional winds, regularly À400 m/s and À200 m/s, respectively, but the zonal wind can reach À600 m/s.…”

“…To compare the WINDII observations with existing data, the authors chose two recent papers with highlatitude wind maps, Dhadly et al (2017; with data from many sources including WINDII) and Huang et al (2017) They are especially strong for the June solstice, all of which is consistent with the WINDII observations. The patterns shown by Huang are similar for positive By, showing the strongest zonal winds around 80°magnetic latitude and noon magnetic local time.…”