IONOSPHERE-THERMOSPHERE INTERACTIONS BASED ON NCAR-TIEGCM: THE INFLUENCE OF THE INTERPLANETARY MAGNETIC FIELD(IMF)-DEPENDENT IONOSPHERIC CONVECTION ON THE HIGH-LATITUDE LOWER THERMOSPHERIC WIND

Abstract

To better understand how high-latitude electric fields influence thermospheric dynamics, winds in the high-latitude lower thermosphere are studied by using the Thermosphere-Ionosphere Electrodynamics General Circulation Model developed by the National Center for Atmospheric Research (NCAR-TIEGCM). The model is run for the conditions of 1992-1993 southern summer. The association of the model results with the interplanetary magnetic field(IMF) is also examined to determine the influences of the IMF-dependent ionospheric convection on the winds. The wind patterns show good agreement with the WINDII observations, although the model wind speeds are generally weaker than the observations. It is confirmed that the influences of high-latitude ionospheric convection on summertime thermospheric winds are seen down to 105 km. The difference wind, the difference between the winds for IMF$\neq$0 and IMF=0, during negative IMF ${\rm B}_y$ shows a strong anticyclonic vortex while during positive IMF ${\rm B}_y$ a strong cyclonic vortex down to 105 km. For positive IMF ${\rm B}_z$ the difference winds are largely confined to the polar cap, while for negative IMF ${\rm B}_z$ they extend down to subauroral latitudes. The IMF ${\rm B}_z$-dependent diurnal wind component is strongly correlated with the corresponding component of ionospheric convection velocity down to 108 km and is largely rotational. The influence of IMF by on the lower thermospheric summertime zonal-mean zonal wind is substantial at high latitudes, with maximum wind speeds being 60 ms$^{-1}$ at 130 km around $77^\circ$ magnetic latitude.