Statistical characterization of the Sub-Auroral Polarization Stream (SAPS) using large scale observations from mid-latitude SuperDARN radars

The Sub-Auroral Polarization Stream (SAPS) is a latitudinally narrow region of westward directed flows observed equatorward of the auroral oval. A majority of SAPS observations presented in earlier studies were limited to a narrow longitudinal sector due to the lack of extended spatial coverage. Recent studies have demonstrated the utility of using the new mid-latitude chain of SuperDARN radars to provide simultaneous measurements of velocities in a SAPS channel over an extended longitudinal sector. These studies have been limited to isolated events. In the current study, data from the mid-latitude SuperDARN radars between January 2011 and August 2012 was used to compile a database of large scale SAPS events. The events were observed during widely varying levels of geomagnetic activity and were divided into different bins based on the Dst-index. We present spatial maps of various parameters of interest such as the probability of occurrence and average velocities for different Dst-index levels. These results have been coded into a new empirical model based on the Dst-index to estimate the probability of occurrence of SAPS at a given latitude and MLT. The results show SuperDARN radars make observations of SAPS channels even during periods of low geomagnetic activity. Moreover the characteristics of SAPS channel exhibit significant differences during periods of low geomagnetic activity as compared to periods with high geomagnetic activity, suggesting the possibility of different driving mechanisms for SAPS.