Observation of large scale waves in the thermosphere-ionosphere system

Kurzfassung

Atmospheric waves as tides, atmospheric gravity waves and planetary waves are important for the coupling between the lower and middle atmosphere and the thermosphere. Consequently, large scale periodic variations observed in the ionosphere are supposed to be the effect of planetary waves originating below. Regional hemispheric maps of the ionospheric total electron content (TEC), which are regularly produced by the DLR Neustrelitz since 2002, are a new opportunity to investigate the planetary wave type oscillations on a hemispheric scale. Relative differences of the TEC to monthly median values are analysed for large scale wave like disturbances. A few quasi periodic variations are forced by the sun, as the 27day solar rotation period and subharmonics. They are localized and filtered in the wavelet spectrum using a comparison to the wavelet spectra of the F10.7cm radioflux index and the solar wind speed, measured with the solar wind experiment. The contribution of solar forced quasi periodic variations to the variability of the relative differential TEC in middle to high latitudes on the northern hemisphere is estimated with 38-42%. The variability of the filtered relative differential TEC show some typical characteristics of planetary waves in the middle atmosphere, as the same seasonal dependency and periods corresponding to the atmosphere’s Eigenfrequencies. Thus, planetary waves may have an important effect on the variability in the thermosphere-ionosphere system. The SWARM mission may deliver new essential data for the analysis of planetary wave type oscillations in the ionosphere.