Effects of High-Latitude Electric Fields on Neutral Winds

The thermospheric winds are driven by a combination of forces such as pressure gradient force produced by local and global heating and drag force resulting from collisions between the ions and the neutrals. In addition, Coriolis and horizontal momentum advection accelerations also contribute to the overall thermospheric wind system. At high latitudes, strong electric fields and precipitating energetic particles are important sources of energy and momentum to drive the winds in the upper thermosphere where the ions tend to move faster than the neutrals and they also respond quickly to changes in magnetospheric electric fields. In the lower thermosphere, however, upward propagating atmospheric tides play an important role in regulating the energy and momentum transfer between the ions and the neutrals. Consequently, the ion-neutral coupling processes are altitude-dependent. This paper presents a detailed analysis of various forcing terms that contribute to the vertical neutral wind distributions. In particular, we show the relative importance of the different forces at various altitudes based on the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations. The TIEGCM incorporates nonlinear ion-neutral interactions, allowing us to elicit a better understanding of the vertical coupling in the ionosphere-thermosphere system. The feedback effects of the winds on energy transfer and field-aligned currents will also be discussed.