GLOBAL VARIATIONS OF THERMOSPHERIC WINDS AND TEMPERATURES CAUSED BY SUBSTORM ENERGY INJECTION

Two numerical simulations of the thermospheric response to magnetosphe ric energy injection have been performed using a zonally averaged, tim e-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 injecti on, representative of main storm type forcing. They were performed und er the condition of equinox at solar minimum, In the first simulation, large-scale atmospheric gravity waves (AGWs), generated by the substo rm energy via Joule heating of ionospheric currents, are clearly ident ified in the wind-field in a meridional plane as well as in the tempor al and spacial variations of the total energy density of air above abo ut 130 km height. These waves reach the equator after about 3 hours an d propagate into the opposite hemisphere, The horizontal propagation s peed is close to the speed of sound (for example, roughly 440 m/s at a bout 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 featu res in the wind system are indicative of the internal atmospheric grav ity 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 co mpressional heating and/or expansive cooling process. If call be concl uded that the energy oscillations at middle and low latitude are mainl y produced by AGWs propagating from high latitude during the substorm. The second simulation indicated that horizontal and vertical advectio ns. vertical heat conduction, and infrared radiative cooling by nitric oxide are important in addition to adiabatic compressional heating an d/or expansive cooling. It is suggested that short-duration energy inj ection preferentially generates AGWs which dominate the energy oscilla tions at low latitudes through adiabatic heating and cooling. Long-dur ation energy injection is more effective in generating a meridional ci rculation which transfers energy by both advective and adiabatic proce sses.