Structured subauroral polarization streams and related auroral undulations occurring on the storm day of 21 January 2005

Abstract

AbstractWe investigate structured subauroral polarization streams (SAPS) and their impacts on the midlatitude trough and auroral regions during the 21–22 January 2005 geomagnetic storm. This was a storm with two sudden commencements occurring under varying interplanetary magnetic field (IMF) conditions and three main phases, two of them unfolding during northward IMF. Its onset at ~1700 UT allowed us to investigate SAPS wave structures (WS) and their impacts during the local evening hours under both southward and northward IMF conditions in the American sector. Results suggest that during southward IMF, SAPS‐WS might be related with standing (toroidal) Alfven waves and structured most intensively the stagnation trough. During northward IMF, the trough was created by SAPS electric (E) field effects only and became less structured by SAPS‐WS that were of Alfvenic origin. Auroral wave structures and undulations occurred in the structured and unstructured oval regions, respectively, and triggered the subauroral region's response to produce SAPS‐WS. Spectrogram images (only one shown) confirmed ring current injections implying magnetotail reconnections during the four SAPS‐WS events investigated. Periodic tail connections are also evidenced by the periodic increases seen in both the solar wind‐magnetosphere coupling function (ε) and the energy input efficiency. Finally, we conclude for the time period investigated that (1) the nature of SAPS‐WS was informative of IMF orientation, (2) plasma stagnation enhanced SAPS E field and SAPS‐WS development, and (3) more efficient energy input into the magnetosphere contributed to the better development of auroral undulations and SAPS‐WS.