SuperDARN Hokkaido radar observation of westward flow enhancement in subauroral latitudes

Abstract. Westward flow enhancement in subauroral latitudes is investigated based on the first one and a half year observation of the SuperDARN Hokkaido radar. A total of 15 events are identified with the criteria of westward flow speed of >1.0 km/s in magnetic latitude from 45 to 65 deg during geomagnetically disturbed period of K_p>3+ at 20 magnetic local time. It is found that especially during the storm recovery phase, the flow enhancement occurs in broad range of D_st amplitude, and the occurrence latitude depends on the amplitude of D_st. It is also found that the disturbed K_p condition is not sufficient for the appearance of the subauroral flow enhancement as seen by Hokkaido radar while storm-like D_st condition is necessary, supporting the idea that ring current particles play an essential role to enhance the westward flow in subauroral latitudes via magnetosphere-ionosphere coupling through the field-aligned current.