| Based on the auroral electron/ion precipitation boundary database observed by the Defense Meteorological Satellite Program (DMSP) satellites during 1984 and 2009, the characteristics of the nightside equatorial boundaries of the electron precipitation (ble) and the ion precipitation (bli) in the Northern/Southern Hemispheres (NH/SH) are statistically investigated. The results show:That most of the boundaries are located between magnetic latitude (MLAT) of 60°～70° with the mean MLAT for ble/bli to be 64.30°/63.22° and -64.48°/-63.26° in the NH and SH, respectively, indicating that ble and bli in both hemispheres are located in conjugated magnetic field lines with ble～1.2° poleward of bli; that the MLATs of ble and bli in both hemispheres shift to lower MLATs (from ～70。 to ～55。) as geomagnetic activity increases; that MLATs of both ble and bli and their differences slowly decrease from dusk to midnight with some differences in both hemispheres during different levels of geomagnetic activities; that ble and bli in both hemispheres decrease linearly with Kp and exponentially with Dst, AE and SYM-H, respectively, demonstrating that auroral particle precipitation is closely related with geomagnetic activity; that in different magnetic local time (MLT) sectors, the changing rates of the boundaries with Kp are different, and the rates of ble are generally larger than those of bli, implying that the difference between ble and bli reduce with increasing geomagnetic activity. In order to understand the origin of the precipitation particles, the locations of ble/bli are traced onto the magnetic equator using dipolar magnetic field model, and the results are compared with empirical plasmapause models. Statistical results show that the traced lines on magnetic equator move to Earth with increasing geomagnetic activities and the geocentric distances of the traced lines for ble are generally 2.0 RE larger than those of bli on both hemispheres. |
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