Proton precipitation related to Pc1 pulsations

Abstract

By the analysis of one-year data from the low-altitude NOAA satellite and on the basis of comparison with observations of Pc1 pulsations at Sodankyla Geophysical Observatory, Finland, we have for the first time found and described a type of proton precipitation closely related to Pc1. It is characterised by a localised (∼1° of latitude) burst of both precipitating and locally trapped energetic (>30 keV) protons situated within the anisotropic precipitation zone. We found that intense Pc1 on the ground can be observed at any distance (in MLT) from the footprint of satellite detecting the precipitation burst, but the probability of the Pc1 observations strongly decreases with the distance. The frequency of the ground Pc1 pulsations decreases with the increase of the proton burst latitude. These findings strongly confirm the idea that Pc1 pulsations are the result of ion-cyclotron instability of energetic ring current protons.