Effects of high-latitude ionospheric electric field variability on global thermospheric Joule heating and mechanical energy transfer rate

Effects of high-latitude ionospheric electric field variability on the Joule heating and mechanical energy transfer rate are investigated by incorporating realistic spatial and temporal characteristics of electric field variability derived from observations into the forcing of a thermosphere ionosphere electrodynamic general circulation model. First, the characteristics of subgrid-scale variability are examined from a spectral analysis of Dynamic Explorer-2 (DE-2) plasma drift measurements. The analysis reveals that the subgrid-scale electric field varies with magnetic latitude, magnetic local time, interplanetary magnetic field (IMF), and season in a manner distinct from that of the resolved-scale electric field and of the climatological electric field. The subgrid-scale electric field varies strongly with season, and its magnitude averaged over the polar region does not depend on IMF. On the other hand, the resolved-scale electric field depends less on season but more on IMF. Second, the spatial-temporal structure of resolved-scale electric fields are characterized from various electromagnetic observations taken during the storm period of January 10-11, 1997, using a space-time covariance model derived from the DE-2 observations. Finally, the modeling results show that the amount of Joule heating and mechanical energy transfer rate in the thermosphere is significantly altered by taking into account the electric field variability and its space-time structure. Additional electromagnetic energy due to the electric field variability dissipates in the ionosphere almost exclusively as Joule heating if the variability has no spatial and temporal correlation. However, the spatially and temporally correlated electric field variability has seasonally dependent effects on the mechanical energy transfer rate.