Cooperative Institute for Research in Environmental Sciences

Auroral Forms that Extend Equatorward from the Persistent Midday Aurora during Geomagnetically Quiet Periods

J. V. Rodriguez (1), H. C. Carlson, Jr. (2), R. A. Heelis (3)

(1) CIRES and NOAA NGDC, (2) USTAR Space Weather Center, Utah State University, (3) William B. Hanson Center for Space Sciences, University of Texas at Dallas

Auroral forms ('crewcuts') that extend equatorward from the persistent midday aurora have been characterized based on a survey of Svalbard 630.0-nm all-sky images from eight December solstice seasons. The 630.0-nm forms are directly related to a mix of precipitating magnetosheath and plasma sheet electrons embedded in a population of boundary layer ions, as observed by NOAA 6. The associated midday aurora lies at the equatorward edge of poleward velocity-dispersed cusp 'ion plumes' observed by DMSP F7 at 10 magnetic local time. In this survey, crewcuts are found to occur for Kp ≤ 3. Distinct in many salient ways (including dynamics, orientation and associated IMF polarity) from the poleward-moving auroral forms (PMAFs) associated with transient dayside merging, crewcuts represent a solar wind-magnetosphere interaction that is more characteristic of quiet geomagnetic conditions. Crewcuts are most likely to be observed when IMF Bx and By (GSM) are dominant. Considering these observations in the context of magnetic merging topologies, we suggest crewcuts observed at Svalbard are most likely to lie at the foot of overdraped field lines recently opened by patchy, quasi-steady merging in the southern hemisphere.