The EMIC wave-driven proton precipitation and related effects on the ionosphere

Protons of tens of keV can be resonantly scattered by EMIC waves excited in the magnetosphere and further precipitate down to the upper atmosphere. In this study, we show a case event that shows direct linkage of the EMIC waves, proton precipitation, and ionospheric ionization using space-borne and ground-based measurements. On Oct 11, 2012, the POES observed that the precipitating flux of the proton much larger than that of the electrons in the night sector around magnetic latitude of 65°. Around the same time and location, ground-based magnetometer detected clear signature of EMIC waves, indicating the causal relation to the proton precipitation. We further simulate the impact of this tens of keV proton precipitation on the upper atmosphere, and found good agreement with PFISR observations of electron density and conductivity. On the other hand, the large ionization rate cannot be accounted for by the electron precipitation at that location. This study shows a clear evidence of the precipitating coupling processes within the magnetosphere-ionosphere system.