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EP: Fachverband Extraterrestrische Physik

EP 2: Near Earth Space

EP 2.7: Talk

Monday, March 30, 2009, 16:30–16:45, Zahnklinik

Nonmigrating tidal signals in the thermospheric zonal wind as observed by CHAMP — •Kathrin Häusler and Hermann Lühr — Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum - GFZ

Accelerometer measurements taken onboard the satellite CHAMP (orbit altitude ∼400km) are used to investigate the influence of nonmigrating tides on the dynamics of the upper atmosphere and in particular on the zonal wind. The presence of nonmigrating tides in the zonal delta wind (deviations from the zonal average) was identified in a previous study as a wave-4 signal. Using four years of data (2002-2005), we could disclose the annual variation of this prominent feature which is strongest during the months of July through October with a second smaller maximum during March/April. Due to the large data set (∼45250 equatorial overflights are available) we were able to separate the observed wavenumbers into the single tidal components. Thereby, we could identify the eastward propagating diurnal tide with zonal wavenumber 3 (DE3) as the prime cause for the observed wave-4 pattern in the zonal wind. The DE3 tide is primarily excited by latent heat release in the tropical troposphere in deep convective clouds. Here we report on the latitudinal behavior (up to ±50^∘) of various nonmigrating tides in the geomagnetic as well as in the geographic frame. A possible dependence on the solar flux is also discussed.