Magnetic signatures and conjugate features of low-latitude plasma blobs as observed by the CHAMP satellite

Abstract

We investigated the magnetic signatures of plasma blobs, as observed by the CHAMP satellite. In total, we have identified 52 blobs with clear density enhancements and magnetic signatures. In each blob the magnetic field strength was depressed, and the components perpendicular to the main magnetic field direction showed fluctuations. The variation in magnetic field strength implies that the enhanced plasma pressure is balanced by a magnetic pressure reduction, and the deflection in the perpendicular components indicates the presence of field-aligned currents. Both characteristics are consistent with bubble magnetic signatures. Concurrent observations of CHAMP (at similar to 350 km altitude) with ROCSAT-1 (similar to 600 km), STSAT-1 (similar to 680 km), and DMSP F15 (similar to 840 km) strongly suggest that the blobs have a field-aligned structure spanning several hundred kilometers. We also investigated the seasonal/longitudinal distribution of the detected blob events. From that a rough coincidence with the bubble occurrence distribution is found, although the blob distribution is biased heavily toward the winter hemisphere. Plasma blob encounters at CHAMP altitude are quite frequent, even after local midnight. We believe that our results corroborate the close relationship between equatorial plasma bubbles and blobs.