Generation of transient dayside subauroral proton precipitation

S.A. Fuselier, S.P. Gary, M.F. Thomsen, E.S. Claflin, B. Hubert, B.R. Sandel, 
and T. Immel


The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft
obtained the first global images of the proton aurora. One of the discoveries
from these images was a region of proton precipitation equatorward of the
nominal auroral oval. This precipitation can be observed for ~10 min
immediately following a large solar wind pressure pulse. Various mechanisms have
been proposed for producing this precipitation. This study focuses on one of the
proposed mechanisms, the scattering and precipitation of protons due to
interaction with electromagnetic ion cyclotron (EMIC) waves. Using data from the
IMAGE spacecraft FUV and EUV imagers, in situ ring current data from the Los
Alamos geosynchronous spacecraft, and in situ solar wind data from the ACE
spacecraft, two features of the precipitation, the local time occurrence and
limited latitudinal extent, are explained. The local time occurrence of the
precipitation is correlated with the orientation of the pressure pulse front in
the solar wind. The limited latitudinal extent of the emissions appears to be
related to the interaction between the hot ring current protons and the cold
plasmaspheric ions that gives rise to EMIC wave growth. 

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Journal of Geophysical Research, 109, A12227, doi:10.1029/2004JA010393, 2004