Observations of the Earth's upper atmosphere during solar eclipse represent a unique opportunity to study the response at these atmospheric altitudes to sudden variations of the solar energy input.
The multi-year CHAMP data base provides in situ measurements of the upper atmosphere for different types of eclipses in different regions. During a particular eclipse at low-latitudes at 8 April 2005 we found significant modifications of electron density distribution at ~400km. These indicate that the plasma fountain is enhanced resembling post-sunset conditions (Tomás et al., 2007). No major variations have been observed in the electron temperature, in the thermospheric mass density and in the zonal wind. The response of the equatorial electrojet to equatorial eclipses is studied by the use of CHAMP, SAC-C and Ørsted magnetic observations and by correlations with ground-based measurements during eclipse times. The observations show the formation of the counter electrojet in the wake of the eclipes (Tomás et al., 2008, JASTP, in press).