Statistical Modeling of Sub-Auroral Polarization Stream (SAPS) Using Observations from Mid-Latitude SuperDARN Radars

The Sub-Auroral Polarization Stream (SAPS) is a narrow region of sunward directed plasma convection at the sub-auroral latitudes. Before the construction of the new mid-latitude chain of SuperDARN radars, a majority of the SAPS observations presented were limited to a narrow longitudinal sector. However, recent studies have demonstrated the utility of using the mid-latitude SuperDARN radars to provide simultaneous measurements of velocities in a SAPS channel over an extended longitudinal region. 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. A new empirical model based on the Dst-index to estimate the probability of occurrence of SAPS at a given latitude and MLT is developed using the statistical observations. 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 the SAPS channel being driven by different mechanisms. Furthermore, the SAPS statistical model can be applied to predict SAPS location during the periods mentioned in the CEDAR GRAND challenge and the results compared with theoretical models.