Global variations of thermospheric winds and temperatures caused by substorm energy injection

Two numerical simulations of the thermospheric response to magnetospheric energy injection have been performed using a zonally averaged, time-dependent model of neutral composition, dynamics, and energy budget. The simulations are distinguished by the duration of the source. The first simulation has an energy injection of 1 hour, representative of substorm type forcing, and the second one has a 12-hour energy injection, representative of main storm type forcing. They were performed under the condition of equinox at solar minimum, In the first simulation, large-scale atmospheric gravity waves (AGWs), generated by the substorm energy via Joule heating of ionospheric currents, are clearly identified in the wind-field in a meridional plane as well as in the temporal and spacial variations of the total energy density of air above about 130 km height. These waves reach the equator after about 3 hours and propagate into the opposite hemisphere, The horizontal propagation speed is close to the speed of sound (for example, roughly 440 m/s at about 150 km altitude and 670 m/s at about 260 km altitude). Snapshots of the wind system affected by the substorm energy injection show a ''four-cell'' pattern between the poles. Above 260 km the cells have the opposite rotational direction to those below. These small-scale features in the wind system are indicative of the internal atmospheric gravity waves with the vertical phase propagation. From a term analysis of the energy conservation equation, it is identified that the dominant energy process associated with the propagation of AGWs is adiabatic compressional heating and/or expansive cooling process. If call be concluded that the energy oscillations at middle and low latitude are mainly produced by AGWs propagating from high latitude during the substorm. The second simulation indicated that horizontal and vertical advections. vertical heat conduction, and infrared radiative cooling by nitric oxide are important in addition to adiabatic compressional heating and/or expansive cooling. It is suggested that short-duration energy injection preferentially generates AGWs which dominate the energy oscillations at low latitudes through adiabatic heating and cooling. Long-duration energy injection is more effective in generating a meridional circulation which transfers energy by both advective and adiabatic processes.