Shock aurora: FAST and DMSP observations

X.-Y. Zhou, R.J. Strangeway, P.C. Anderson, D.G. Sibeck, B.T. Tsurutani, 
G. Haerendel, H.U. Frey, and J. K. Arballo


Global signatures of the aurora caused by interplanetary shocks/pressure pulses
have been studied in recent years using ultraviolet imager data from polar
orbiting spacecraft. The signatures include the occurrence of the aurora first
near local noon and then propagation antisunward along the auroral oval at very
high speeds. To better understand the mechanisms of particle precipitation, in
this paper we study shock auroras using near- Earth observations of the FAST and
DMSP satellites. We have studied the events that occurred during 1996-2000 where
FAST and/or DMSP crossed the dawnside or duskside auroral zone within 10 min
after shocks/pressure pulses arrived at the nose of the magnetopause. It is
found that the electron precipitation increased significantly above the dawnside
and duskside auroral oval zone after the shock/pressure pulse arrivals. The
precipitation structure is low-energy electrons (<~1 keV) at higher latitudes
(~75-83 degrees ILAT within 0600-0900 MLT) and high-energy electrons (~1Ð10 keV)
at lower latitudes (~65-79 degreesILAT) of the auroral zone. There are a few
degrees (1-4 degrees ILAT) of overlap between these two categories of
precipitated electrons. The precipitation of low-energy electrons was along
highly structured field-aligned currents. The precipitation of the high-energy
electrons was highly isotropic filling the loss cone. Possible mechanisms of
field-aligned current generation are some dynamic processes occurring on the
dayside magnetopause, such as magnetic shearing, magnetopause perturbation,
magnetic reconnection, and Alfve«n wave generation. Adiabatic compression might
have caused the high-energy electron precipitation. On the basis of observations
of FAST and DMSP, shock auroras are speculated to be diffuse auroras at the
lower latitudes of the dayside auroral oval and discrete auroras on the poleward
boundary of the oval with a few latitude degree overlap of the two types of
auroras. 

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Journal of Geophysical Research, 108(A4), 8019, doi:10.1029/2002JA009701, 2003.