Study of the occurrence characteristics of SAPS observed by the SuperDARN Hokkaido Pair of Radars

Abstract:

We make a statistical study on the occurrence characteristics of Sub-Auroral Polarization Streams (SAPS), using the Super Dual Auroral Radar Network (SuperDARN) data. Our ultimate goal is to use several years of SuperDARN data and to study the longitudinal dependence of SAPS occurrence characteristics, by comparing the data obtained by the Hokkaido radars in the East Asian sector and those in other longitudinal sectors such as the North American continent. We identify the equatorward aurora oval boundary using the precipitating energy fluxes data of the NOAA POES satellites and use only the SuperDARN echoes equatorward of this boundary. We set criteria to identify SAPS events, i.e., the flow speed exceeds 150 m/s [Nagano et al., 2015] and has a westward component (-45 deg < Δθ < +45 deg). We obtained the overall characteristics of SAPS, i.e., an equatorward shift of high occurrence rate region for later MLT and magnetically disturbed period. Some of the characteristics are different from previous studies (e.g., Kunduri et al., 2017); SAPS regions seem to be located at higher latitudes than the previous studies, and SAPS occurrence peak regions are located at later MLT. These differences might be due to the difference in geographic longitude, as well as the relative values between geographic and geomagnetic latitudes (Far-East Siberia to Pacific vs North American region). We also found new features, i.e., westward flows from midnight to morning at relatively low geomagnetic latitudes that could not be caught in the past studies probably due to the limitation of radars fields of view, especially lower latitude boundary.