Thermospheric density structures over the polar regions observed with CHAMP

K. Schlegel, H. Lühr, J.-P. St.-Maurice, G. Crowley, C. Hackert
2005 Annales Geophysicae  
We report on the unexpected detection of considerable structure in high latitude thermospheric densities, as derived from an accelerometer onboard the CHAMP satellite. The width of the structures, which can either be maxima or minima, varies between a few hundred km and 2000 km. The amplitudes of these density extrema can reach 50% of ambient. Maxima cluster around 75 • (N and S), while minima are found closer to the poles. In a magnetic latitudemagnetic local time frame the maxima are found
more » ... maxima are found mainly around the cusp region. Overall, the observed structures somewhat resemble so-called density cells previously found in model calculations. However the models generate their cells around 140-300 km altitude and show little, if any remnant at 400 km or above. This has to be contrasted with the fact that the CHAMP observations were obtained near 430 km altitude. We have explored Joule heating as a possible mechanism for the generation of the structures, at least in density enhancement regions, using Hall currents measured on CHAMP and simultaneous incoherent scatter measurements with EISCAT. However, the electric fields were usually quite small during the period of observation, making the quest for an explanation for the structures all the more challenging.
doi:10.5194/angeo-23-1659-2005 fatcat:i6pgajyb5vgyzlynzhzj4c6iti