The effect of subauroral polarization streams on the mid-latitude thermospheric disturbance neutral winds: a universal time effect

Abstract

Abstract. The temporal and spatial variations in thermospheric neutral winds at an altitude of 400 km in response to subauroral polarization streams (SAPS) are investigated using global ionosphere and thermosphere model simulations under the southward interplanetary magnetic field (IMF) condition. During SAPS periods the westward neutral winds in the subauroral latitudes are greatly strengthened at dusk. This is due to the ion drag effect, through which SAPS can accelerate neutral winds in the westward direction. The new findings are that for SAPS commencing at different universal times, the strongest westward neutral winds exhibit large variations in amplitudes. The ion drag and Joule heating effects are dependent on the solar illumination, which exhibit UT variations due to the displacement of the geomagnetic and geographic poles. With more sunlight, stronger westward neutral winds can be generated, and the center of these neutral winds shifts to a later magnetic local time than neutral winds with less solar illumination. In the Northern Hemisphere and Southern Hemisphere, the disturbance neutral wind reaches a maximum at 18:00 and 04:00 UT, and a minimum at 04:00 and 16:00 UT, respectively. There is a good correlation between the neutral wind velocity and cos0.5(SZA) (solar zenith angle). The reduction in the electron density and enhancement in the air mass density at an altitude of 400 km are strongest when the maximum solar illumination collocates with the SAPS. The correlation between the neutral wind velocity and cos0.5(SZA) is also good during the northward IMF period. The effect of a sine-wave oscillation of SAPS on the neutral wind also exhibits UT variations in association with the solar illumination.

Subauroral Neutral Wind Driving and Its Feedback to SAPS During the 17 March 2013 Geomagnetic Storm

“…Enhanced westward winds are found to peak around the same latitude as SAPS flows from comparisons between ion drift and neutral wind measurements (Wang et al, , ). Different forces have been suggested to explain the acceleration of neutral wind, involving, for example, the ion drag force in the aurora zone (Wang et al, ) and on a global scale (Wang et al, ), the Coriolis force (Lühr et al, ; S.‐R. Zhang et al, ), and pressure gradient.…”

Nighttime meridional neutral wind responses to SAPS simulated by the TIEGCM: a universal time effect

“…This difference is related to the molecular viscosity in the thermospheric composition. Furthermore, as disclosed in Wang H et al (2018), the westward winds at sector of 12-24 MLT due to SAPS will not disappear at the time that the SAPS close. On the contrary, the winds will last several hours because of inertial forces, owing to the dense thermospheric density (Wang H et al, 2018).…”

“…Therefore UT variations in the responses of thermospheric winds to SAPS are really within expectations; however, delineation of the relative importance among those competing forcings responsible for longitudinal/UT variations remains a matter of significant scientific interest. Using GITM simulations, Wang H et al (2018) investigated the zonal wind response to SAPS that occurred at different UTs. They found that the westward wind disturbances exhibited a significant UT variation; the disturbances reached their maxima (minima) at 18 (04) UT and 04 (16) UT in the Northern and Southern Hemisphere, respectively.…”

Recent ionospheric investigations in China (2018–2019)

“…Wang H et al (2018) investigated the temporal and spatial variations of thermospheric neutral winds at 400 km altitude under the influence of subauroral polarization streams (SAPS) based on simulations of the global ionosphere and thermosphere model (GITM). During SAPS periods under southward IMF conditions, the westward neutral winds at subauroral latitudes are greatly strengthened at dusk.…”