Seasonal and Geomagnetic Activity Dependence of Auroral E-Region Neutral Winds at Poker Flat

Abstract

In this paper, we investigated the seasonal and geomagnetic dependence of the auroral $E$-region neutral winds and the tidal components between 90 and 125 km using nearly continuously sampled measurements from the Poker Flat Incoherent Scatter Radar (PFISR) from 2010 to 2019. The average winds show consistent semidiurnal oscillations between 100 and 115 km and diurnal oscillations above 115 km in all seasons with some seasonal and geomagnetic activity dependencies. In general, the semidiurnal oscillation in zonal and meridional directions is strongest in summer and weakest in winter. The diurnal oscillation is strongest in winter and weakest in spring. More details on the seasonal and geomagnetic activity dependencies are revealed in the tidal decomposition results. Tidal decomposition results show eastward mean wind below 115 km in summer, fall, and winter and westward mean wind above 115 km in all seasons. The meridional mean is northward below 115 km and southward above in all seasons. The diurnal amplitudes are small below 110 km and increase with altitude above 110 km in all seasons with larger enhancements in the meridional direction. The semidiurnal amplitudes increase with altitude below 110 km and reach a maximum at around 110 km, then decrease or keep stable (depending on the geomagnetic activity) above 110 km in both directions and all seasons. The diurnal phases shift to earlier times with the increase of geomagnetic activity but show different variations with altitudes in zonal and meridional directions. The semidiurnal phases show a downward progressing trend in both directions and in all seasons.