Precipitation of Energetic Protons at High Latitudes: Dependence on the Interplanetary Magnetic Field

The data of particle measurements onboard the low-orbit NOAA satellites are used to investigate the occurrence of energetic (>30 keV) proton precipitation at latitudes above 80° and the dynamics of the poleward boundary of the precipitation as a function of the interplanetary magnetic field (IMF). The occurrence of proton precipitation in both hemispheres is shown to rise as the IMF Bz component increases. The mean latitude of the poleward boundary of the precipitation for positive Bz is higher by a few degrees than for negative Bz The By component affects the occurrence of energetic protons in the morning and evening sectors: when By > 0, the poleward precipitation boundary shifts poleward in the evening (morning) sector of the northern (southern) polar cap; when By < 0, the latitude is higher in the morning (evening) sector of the northern (southern) polar cap. The probability to observe protons in these regions changes accordingly. Similar dependencies were established earlier at the same latitudes for polar-cap aurorae. Intense localized bursts of low-energy (0.3-20 keV) electrons are observed inside the energetic proton precipitation regions. These observations corroborate the previously found relation between polar cap aurorae and the regions of precipitation of energetic protons, as well as the hypothesis on the localization of the source of polar cap aurorae in the magnetospheric plasma sheet.