Study of meso-scale reversed flow events in the polar ionosphere by SuperDARN radars

Abstract

In this study we have investigated Reversed Flow Events (RFEs) in the northern hemisphere polar cap. A RFE is an ∼50-250 km wide flow channel that opposes the large scale background flow. A total of 57 new RFEs were discovered using data from the Super Dual Auroral Radar Network (SuperDARN) for primarily December of 2014-2016. We found RFEs lasting up to 97 minutes, with an average duration of 11.4 minutes. Most RFEs were found in the dawn and dusk region with 26 events in the 4-10 MLT dawn region (46%) and 14 in the 14-20 MLT dusk region (25%). 12 RFEs were identified within the 10-14 MLT dayside region (21%) and only 5 in the 20-04 MLT nightside region (9%). There was no significant spread in MLT based on IMF Bz, but in our study 79% of the RFEs with stable IMF prior to onset were observed during positive IMF Bz. For By there was a strong preference towards dawn and night for negative values, and day and dusk for positive values. Most RFEs were seen stationary during their existence, while at least one RFE moved poleward. Depending on their location we have classified the reversed flow channels as either dayside RFEs, lobe cell RFEs (dawn and dusk) or nightside RFEs. Our findings agree with previous studies of dayside reconnection generated RFEs, but expand our knowledge of the phenomenon to a wider area of the polar cap.