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 90–125 km using nearly continuously sampled measurements from
the Poker Flat Incoherent Scatter Radar (PFISR) from 2010–2019. The
average winds show consistent semidiurnal oscillations between
100–-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.