The Role of Spatial and Temporal Variability in Determining the Magnitude and Structure of Thermospheric Vertical Winds

Vertical winds in the thermosphere can occur in various spatial scales and vary in very short time-scales. They are typically associated with barometric, divergent, and nonhydrostatic motions. Increasing number of observational studies suggest that vertical winds are temporally and spatially highly variable and their magnitudes and structures are overall not captured well enough by contemporary general circulation models (GCMs) that are based on the hydrostatic assumption and have coarse spatial resolutions and relatively large time steps. In this study, using the 3-D nonhydrostatic Global Ionosphere Thermosphere Model (GITM) developed at the University of Michigan, we investigate the physical mechanisms that control the magnitudes and structures of the thermosphere neutral vertical winds, focusing on the role of spatial and temporal variability simulated by GITM. To identify the response of the high-latitude thermosphere-ionosphere (TI) to variable magnetospheric inputs, such as the IMF Bz, the associated Joule and auroral heating are analyzed. In a series of systematic simulations, the magnitude and temporal variations of Bz are modulated. Additionally, the effects of random electric field variability are investigated by implementing first constant and then temporally variable noise term in the electric fields. Vertical winds are found to be sensitive to spatial resolution as well as to the specific form of temporally varying magnetospheric input and random noise in the electric field input.