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The accelerometer onboard CHAMP enables us to derive the thermospheric zonalwind at orbit altitudes (~400 km). Numerous equatorial overflights(~45 250) are used to investigate the influence of nonmigrating tideson the thermospheric zonal wind. In a previous study a so called "wave-4"longitudinally signal observed in the satellite frame was identified in thezonal wind residuals during equinox. Using four years of data (2002–2005), wedetermine the annual variation of this prominent feature which is strongestduring the months of July through October and has a smaller second maximumduring March/April. Due to the large data set we were able to separate theobserved wavenumbers into the tidal components. Thereby, we can identify theeastward propagating diurnal tide with zonal wavenumber <I>s</I>=3 (DE3) as theprime cause for the observed wave-4 pattern in the zonal wind. Analyzing thezonal wind along the geographic and the dip equator revealed that the largestamplitudes of DE3 are found along the dip equator. Besides DE3 we present thefull spectrum of nonmigrating tides in the upper thermosphere

Nonmigrating tidal signals in the upper thermospheric zonal wind at equatorial latitudes as observed by CHAMP