Global observation of traveling atmospheric disturbances (TADs) in the thermosphere

Densities derived from accelerometer measurements on the CHAMP satellite near 400 km are used to elucidate global- scale characteristics of traveling atmospheric disturbances (TADs) in connection with 3 sudden injections of energy at high latitudes on 29 May 2003. Dayside TADs with typical amplitudes similar to 20 - 30% propagate towards the equator from the northern hemisphere (southern hemisphere) auroral region with phase speeds of order 730 ms(-1) (460 ms(-1)). Some evidence is found for TAD penetration from the northern to the southern Hemisphere, and for the first time for transpolar propagation. Nighttime TAD signatures are less well defined, but have phase speeds similar to the dayside TADs. The above day- night and hemisphere differences possibly reflect dependencies on direction and intensity of the prevailing solar- driven circulation, and on generation efficiency and ion drag dissipation with respect to solar zenith angle.