Momentum and Energy Budgets in the High‐Latitude Lower Thermospheric Wind System

This paper summarizes our recent progress in the study of momentum and energy budgets in the high-latitude lower thermospheric wind system in response to steady-state magnetospheric forcing. Model-based studies, using the NCAR TIE-GCM, have enabled us to gain a better understanding of the physical processes that drive and maintain high-latitude lower thermospheric wind dynamics: High-latitude lower thermospheric winds are sustained by the gradient-wind balance among divergent/convergent pressure gradient, Coriolis, and horizontal momentum advection accelerations. The dominant contribution to the wind tendency is the rotational component of the ion-drag acceleration. High-latitude lower thermospheric wind is strongly dominated by rotational flow rather than horizontally divergent flow and the vertical vorticity depends on the IMF direction. The vertical vorticity variations are forced primarily by ion convection and can be contributed by the horizontal advection. Generation of high-latitude lower thermosphere potential vorticity and available energy (kinetic energy plus available potential energy) is dominated primarily by momentum forcing, but has contributions from heating that increase in relative importance with descending altitude and with increasingly negative IMF B-z.