The satellite CHAMP with its sensitive accelerometer on board provides the opportunity to investigate the thermospheric dynamics in great detail. In this study we concentrate on density structures in the cusp. During 25 Sep. 2000, the day we take as an example, air density enhancements of almost a factor of two are observed whenever the satellite passes the cusp region. For the interpretation of these events we consider also the concurrent ionospheric Hall and field-aligned currents (FACs). As expected, sizable currents are found in the regions of dense air. Small-scale FAC filaments (1-km size) seem to play an important role in the heating. Whenever these very intense FACs with amplitudes of several hundreds of ¿A/m2 show up, density enhancements occur.