Response of the thermospheric density to auroral heating during geomagnetic disturbances

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Assuming an impulse-type heat input into a small band of latitude within the auroral ovals during local night in order to simulate the heat input during geomagnetic disturbances, the corresponding response of the thermospheric density has been calculated. The result in terms of a series of spherical harmonics shows that the components with large wave domain numbers (n, m) decay rapidly within the first hour after the onset of the geomagnetic storm, whereas the two zonal components (0, 0) and (2, 0) and the two associated components (1, 1) and (3, 1) are predominant during the slow tail phase of the disturbance. It is the slow tail of the density disturbance beginning about one hour after the onset of the storm that contains most of the spectral energy and that is responsible for the observed worldwide response of the thermospheric density during geomagnetic storms. Its dependence on storm time, latitude, and longitude is discussed and compared with available satellite drag data.