Publication Name: JGR Space Physics; First HAO Author's Name: Qian Wu

HIWIND (High altitude Interferometer WIND experiment) is a balloon borne Fabry Perot interferometer (FPI) for daytime thermospheric wind observations. In this paper, we examine the summer polar cap thermospheric winds observed by HIWIND with the RISR-C (Resolute Incoherent Scatter Radar-Canada) observed ion drifts and electron densities.

HIWIND thermospheric winds

HIWIND thermospheric winds (magenta points) and TIEGCM NSEP (green 435 solid-lines) and MSEP (green dashed-lines) simulated winds are plotted on the left. 436 RISR-C ion drift observations (yellow line) and TIEGCM NSEP (blue solid-lines) and 437 MSEP (blue dashed-lines) simulated ion drifts are on the right. Local midnight is close 438 to 6 UT and noon at 18 UT. The key point of the paper is that the TIEGCM simulation greatly overestimate thermospheric winds in the polar cap.

We also perform NCAR TIEGCM (Thermosphere Ionosphere Electrodynamics General Circulation Model) simulations to compare with the HIWIND and RISR-C observations. The standard TIEGCM underestimates the high-latitude electron density and overestimates the thermospheric winds. The discrepancies between modeled and observed meridional winds are large near midnight and noon. After increasing the energy flux in the polar cap drizzle, the simulated electron density is comparable with the RISR-C observations. However, large discrepancies with the HIWIND observed thermospheric winds persist. The cause of the model versus observation discrepancy in winds is probably due to the processes outside the polar cap.