Abstract
Abstract This paper presents an analysis of the diurnal density variations between ~200 km and 400 km as evidenced by a data set of unique characteristics, namely the density data collected by the Drag Balance Instrument (DBI, Broglio et al. , 1989; Arduini et al. , 1993) on board the San Marco III (SM3) satellite (launched 1971) and San Marco V (SM5) satellite (launched 1988). The measurements are covering similar seasonal periods and different solar cycle conditions. They have, in addition, very high space and time resolution and very good relative accuracy. These characteristics allow us to appreciate fine details of the diurnal variation. In the present paper, besides the data presentation, a few points will be addressed, namely: 1. —Midnight Density Maximum (MDM) feature as related to the diurnal tides; 2. —persistence and variability of the diurnal bulge on the long period; 3. —persistence and variability of the diurnal bulge on the short period; 4. —comparison with model results.
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