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

Abstract

[1] 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 $350 km altitude) with ROCSAT-1 ($600 km), STSAT-1 ($680 km), and DMSP F15 ($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.

The impact of FORMOSAT-5/AIP observations on the ionospheric space weather

“…At ionosphere mid-latitudes, the nighttime electron density enhancement has been observed and reported by previous studies (e.g., Bailey et al 1991;Farelo et al 2002;Dabas and Kersley 2003;Luan et al 2008;Park et al 2008;Chen et al 2011Chen et al , 2012Chen et al , 2013Lin et al 2011;Rajesh et al 2016). This density-enhanced ionospheric feature appeared more frequently during solar minimum conditions (Bailey et al 1991), and it is suggested to be caused by larger downward plasma flux from the plasmasphere during the nighttime (Mikhailov et al 2000;Farelo et al 2002;Dabas and Kersley 2003).…”

Field-aligned current associated with low-latitude plasma blobs as observed by the CHAMP satellite

“…Kil and Heelis, 1998;Huang et al, 2001;Park et al, 2005;Stolle et al, 2006), and in the Southern winter Hemisphere where blobs are frequently observed (e.g. Watanabe and Oya, 1986;Park et al, 2008b). This event is accompanied by EPBs between ±3 • GLAT showing magnetic field deflections outward and westward.…”

“…For the other one (near 04:10 UT on 18 January 2002, shown in Fig. 1 of Park et al, 2008b), the polarization angle is 150 • (i.e. westward tilt) and the peak FAC density is of the order of 0.1 µA/m 2 .…”

“…Although Park et al (2008b) addressed already the magnetic signatures of blobs, the focus of that study was put on the decrease in magnetic field strength and the maintenance of pressure balance in the region of enhanced plasma density. The perpendicular magnetic deflections (FAC signatures) were not discussed in detail, such as the polarization, amplitude, or associated FAC density.…”

“…It was also shown that blob latitudes are higher when the yearly solar activity is higher, implying a close relationship between EIA and blobs. Using magnetic field data from the CHAMP satellite (at about 400 km altitude) Park et al (2008b) reported that blobs show reduced magnetic field strength as well as magnetic deflections associated with field-aligned current (FAC). At CHAMP altitude blobs also occurred predominantly in the winter hemisphere.…”