The dynamical interactions which occur in the atmospheric region around the mesopause (~90 km) determine the boundary characteristics for the thermospheric region above. A significant data base of radar wind measurements exists which characterizes the global circulation at altitudes between 70 and 110 km. In the present work, using an empirical model of Eulerianmean meridional motions based on monthly climatological winds from these radar data, the net vertical motions in this atmospheric regime are derived from the continuity equation. Assuming empirical prescriptions of the mean density and temperature fields, mean heat flux divergences and momentum flux divergences are estimated which exhibit very specific characteristics in the height versus latitude domain for winter, summer, and equinox conditions in both hemispheres. A numerical circulation model including gravity wave/mean flow and tide/mean flow interactions is utilized to examine possible origins of these heat and acceleration sources. At low latitudes (≤30¿), it is evident that atmospheric tides represent the the primary wave source contribution to zonal mean acceleration and heating of this region of the atmosphere; similarly, at middle and high latitudes (≥30¿) below about 90 km, dissipation of vertically propagating gravity waves appears to provide the dominant momentum source for the mean zonal circulation. However, above approximately 90 km and between about 40¿ and 70¿ latitude, very significant regions of mean heating and acceleration exist which are not accounted for by the effects of vertically propagating gravity waves and tides. The possible origins of these effects are examined. We suggest that the two most likely candidates to explain these observed features are (1) obliquely propagating gravity waves and/or (2) planetary scale waves. ¿ American Geophysical Union 1991