Direct observation of the F region dynamo currents and the spatial structure of the EEJ by CHAMP

The satellite CHAMP in its low-altitude polar orbit, and with its high-resolution magnetic field measurements, provides the opportunity to investigate ionospheric currents in great detail. In this study we focus on average features of equatorial current systems during day time. Considering quiet time observations from the period Aug. 2000 to Oct. 2004 we determined the mean spatial structure of the EEJ current. The existence of reverse currents at the flanks of the primary eastward current is confirmed. More importantly, average characteristics of the F region dynamo driven currents are observed for the first time throughout the daytime. The meridional current system, driven by westward thermospheric winds, peaks around noon. Similar meridional currents, but flowing in the opposite sense, are observed at the dusk sector. At CHAMP altitudes we find over the dip equator in the F region a vertical sheet current of about 6 mA/m oriented downward at noon and an upward current of 4 mA/m around sunset.