Dependence of neutral winds on convection E‐field, solar EUV, and auroral particle precipitation at high latitudes

Abstract

We use the Global Ionosphere Thermosphere Model (GITM) to investigate the thermospheric neutral winds and their relationship to the high‐latitude ionospheric convection, auroral precipitation, and solar activity. Each simulation is run for 24 hours, allowing an approximate steady state to be reached. Our results show that the duskside vortex and the antisunward polar cap neutral winds are prominent. The interplanetary magnetic field (IMF) southward Bz control of the polar cap winds is evident in both dusk cell and polar cap. When the IMF Bz changes from −1 to −10 nT, at the auroral region both the root of mean square (RMS) of Vn and Vi increase more than 50% at 300 km altitude, the ratio of R2 (RMS(Vn · (E × B))/RMS(E × B)2) increases, while R1 (RMS(Vn)/RMS(E × B)) changes little. In the polar cap region, since the ion flow is in the same direction as the neutral pressure gradient, above around 160 km altitude, ∣Vn∣ is larger than ∣Vi∣. When the F10.7 increases from 70 to 250, in the auroral region, the magnitude of ∣Vn∣ increases close to 20% at 300 km altitude. At lower latitudes, where ∣Vn∣ > ∣Vi∣ and the ions act as a load to the neutral winds, as a consequence of increases in F10.7, the drag on the neutrals becomes greater and therefore slows the neutrals down. The altitude dependent change of R2 is associated with the multiple effects of the F10.7 to the neutral winds, including the increased day‐to‐night pressure gradient and ion drag. The impact of hemispheric power (HP) to the low thermosphere is pronounced. At 150 km altitude, the neutral winds increase 30% in magnitude at auroral latitudes. When HP is raised from 10 to 100 GW, a dawn cell forms, concurrent with an enhancement in the dusk cell. The dawn and dusk cells show an obvious asymmetry both in the average neutral winds and the sensitivity of neutral winds to the HP. It is shown that at 250 km altitude, the magnitude of the southward IMF Bz has a positive correlation with the magnitude of the polar cap winds and the sensitivity increases with F10.7. A negative correlation between the magnitude of Vn and F10.7 with small southward IMF Bz becomes positive when the southward IMF Bz increases. This change is presumably due to the momentum balance between ion drag and advection. The dawn (dusk) convection cell is enhanced when By is negative (positive). In response to the effect of the Coriolis force, the By negative winds are not exactly mirror reflections of the By positive winds. For northward IMF Bz, the neutral winds flow sunward at the highest latitudes near noon. When the northward Bz increases from 10 nT to 20 nT, the distribution of the polar cap potential becomes more symmetric and the sunward neutral flow is enhanced and expanded.