Using a transfer function model for the earth's thermosphere, we have previously discussed the properties of different wave modes and impulsive perturbations excited by Joule heating. The thermspheric response showed the expected propagating waves, but a significant part of the perturbation, the trapped component, remained confined to the source region. In the present paper we expand the analysis to include the electric field momentum source. We discuss the effects of these excitation mechanisms on the trapped component confined to the source region and on the propagating gravity waves emanating from the source. Our analysis leads to the following conclusions: (1) for Joule/particle heating, the temperature and density perturbations contain a relatively large trapped component which has the property of a low-pass filter, with slow decay after the source is turned off. The decay time is sensitive to the altitude of energy deposition and is significantly reduced as one moves the source peak only friom 125 to 150 km. (2) For electric field momentum coupling, the trapped components in the temperature and density perturbaions are relatively small.

In the curl field of the velocity, however, the trapped component dominates, but compared with the temperature (and density), its decay time is much shorter. (3) Outside the source region the form of excitation is of secondary importance for the generation of the various propagating gravity waves modes (direct, reflected, and ducted). Different atmospheric variabiles, however, respond differently. The model has been extended to allow for incoherence in the excitation sources, which is necessary to simulate the stochastic nature of auroral processes, and a numerical experiment is presented elucidating some salent features of the thermospheric response. Observations at times show long temperature and density decay times (order of days) in the source region, yet at other times the decay time is much shorter (order of hours). Differences in the excitation mechanism studied, e.g., the altitude of energy deposition, may be responsible for the apparent disparity. ¿ American Geophysical Union