An analysis of the response of the thermospheric normal modes to temporally varying convection at high latitudes

A normal modes model that includes realistic temperature and electron density profiles, and the effects of viscosity, heat conduction, and Lorentz forcing has been used to study the response of the high‐latitude thermosphere to temporal variations in the forcing due to the plasma convection pattern. In particular, the rotation rate of the two‐cell convection pattern was varied from the usual 2π in 24 hours to produce a crude simulation of the effects of temporal variations in the forcing. The model calculation proceeds from an initial steady state at 48 hours through four 6 hour integrations, where the rotation rate is alternately decreased and increased, corresponding to decelerated and accelerated flow. The results show that the rotational wind component is only slightly modified when the plasma rotation has been varied. The divergent wind component responds more strongly to variation of the rotation rate, an effect which is greatest in the E region. Variation of the rotation rate then results in greater magnitude and phase variation with height of the divergent wind component in the E region, indicating that vertically propagating gravity waves are of importance in that height range. To the extent to which varying the rotation rate can simulate variations in the configuration of the plasma convection, as are due to substorms or variations in the interplanetary magnetic field, the model indicates that detailed consideration of such geophysical effects is necessary if the transient response of the neutral wind is to be better understood.