Characteristics of low-latitude Pc1 pulsations during geomagnetic storms

Abstract

We use search-coil magnetometer data from a low-latitude station in Parkfield, California (L = 1.77) to study the occurrence of Pc1 pulsations associated with geomagnetic storms. The Pc1 pulsations and storms are identified using automatic algorithms, and the statistical distributions are examined using a superposed epoch analysis technique, as a function of local time, time relative to storm main phase, and storm intensity. Results show that Pc1 pulsations are 2-3 times more likely (than normal) to be observed in the 2-4 d following moderate storms and 4-5 times more likely in the 2-7 d following intense storms. The Pc1 frequencies are higher in moderate storms than they are in nonstorm times and become even higher and occupy a greater range of local times as the strength of the storms increase. These results are consistent with the idea that the source of EMIC waves extends to lower L values as storm intensity increases. Copyright 2008 by the American Geophysical Union.