Enhanced DC Electric Fields Associated with Sub-Auroral Polarization Streams and “STEVE” Auroral Displays within Evolving Sub-Storms

Abstract:

Enhanced DC electric fields, and associated E x B plasma drifts, have been identified in several data sets as a common feature of the sub-auroral ionosphere during magnetic storms, occurring in the pre-midnight evening sector on the equatorward edge of the precipitation region. The fields are always poleward, producing zonal, westward plasma flows, are confined in latitude, and are sometimes, though not always, associated with the plasmaspheric density trough as observed in the ionosphere below 1000 km altitude.

The Vector Electric Field Instrument (VEFI) on the DE-2 satellite has identified over 100 examples of this feature, with typical amplitudes of 50 to 100's of mV/m. In a few cases, the observed fields are between 300 and 400 mV/m, corresponding to plasma drifts of 6-8 km/sec, with one example of a very pronounced peak at 900 mV/m (~20 km/sec).

In this presentation, we provide a new perspective on these observations by dividing them between electric field features that are broader in latitude associated with sub-auroral polarization streams (SAPS) and those that display electric field enhancements that are very narrow in latitude, more commonly associated with sub-auroral ion drifts (SAIDs) discussed in the literature. We investigate the statistics of each class of enhanced, localized electric fields particularly with respect to how they are organized within evolving sub-storms and how they are associated with a displacement of the precipitating energetic ion and electrons. We examine groups of consecutive DE-2 passes to understand the changes between broad and narrow electric field signatures within the context of the sub-storm, and study numerous examples of conjugate observations to better understand their causal mechanism and growth.

The DE-2 data are also used to help determine how the different types of enhanced electric fields may be associated with optical auroral observations recently identified as strong thermal emission velocity enhancements (STEVE). To this end, we seek to determine how the enhanced electric fields might help identify the conditions for STEVE-related optical observations.