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Abstract

Novel possibilities to detect Equatorial Spread-F (ESF) events are given by the magnetic signatures of the depleted plasma tubes. The diamagnetic effect enhances the total magnetic field in regions of low plasma density. We use 7 years (2001-2007) of almost continuous high quality magnetic field observations on board the CHAMP satellite to reconstruct the global climatology of the ESF magnetic signatures at about 400 km altitude. Our results compare very well with existing ESF climatologies based on satellite observations of electron density, especially in longitudinal and seasonal (S/L) dependences. We find an excellent agreement with the S/L distribution of the equatorial prereversal vertical plasma drift velocity derived from ROCSAT-1 observations. These results prove that the vertical plasma drift acting on the F-layer height is the dominant contributor to the ESF occurrence. The increasing CHAMP data set spanning different solar cycle phases reveals the existence of more, larger and stronger ESF events for high solar flux level conditions. These characteristics are reflected in the extended local time and the higher L-values where ESFs are observed at high solar flux levels. CHAMP also provides observations of the transverse magnetic ESF signatures. These deflections imply the existence of field-aligned currents. Such observations will be used for characterizing the electrodynamic state of the ESF event.