Abstract
Approximately four hundred neutral wind profiles of the lower thermosphere, obtained by rocket-borne techniques since 1957, have been analysed in terms of diurnal and latitudinal variability. Some 15 of these measurements have been carried out during daytime conditions, providing an insight into the dynamics of the daytime thermosphere.
The dominant tidal modes (1, 1), (1, -2), (2, 2) and (2, 4) have each been identified in the statistical analysis, and their amplitudes and phases determined as a function of altitude within the lower thermosphere. Agreement is found between the characteristics of the data and recent models of the tides in the lower thermosphere. The (1, -2) mode, for example, appears more strongly in the meridional than zonal components; however, its phase appears to be 3 to 4hr advanced compared with model calculations. This mode may be strongly enhanced after even moderate geomagnetic activity, indicating that the high latitude energy source responsible for the enhancement may also cause the phase advancement relative to models of the (1, -2) tide as generated only by in situ solar EUV heating.
