Observations of D-region structure and atmospheric tides with PFISR during active aurora

Abstract

We report on combined spectral measurements of the D-region ionosphere and the polar summer mesosphere and lower thermosphere performed on 9 June 2007 with the 450 MHz Poker Flat Incoherent Scatter Radar (PFISR) under active auroral conditions. Observations during the first 7 h occurred at nighttime and revealed strong temporal correlations between enhanced auroral precipitation, the occurrence of polar mesosphere summer echoes (PMSE), and enhanced electron densities ( N e ) extending to much lower altitudes ( ∼ 60 – 80 km ) than the previously reported at these latitudes without the presence of a polar cap absorption (PCA) event. PMSE and lower D-region echoes most often occurred together and PMSE were more often visible to PFISR before the N e of the D-region was sufficiently high to be detected. These measurements also enabled definition of high precision horizontal winds (errors of 2 – 3 m s - 1 ) in the ∼ 64 – 90 km altitude range, which has previously been possible only with MF and HF radars, with the Arecibo 430 MHz IS radar (ISR), or with other ISRs during PCA events. This observing technique allowed for ∼ 24 h of almost continuous measurements of the meridional and zonal wind fields and thus permitted the measurements of atmospheric tides over this large altitude range. We determine amplitude and phase for both the diurnal and semi-diurnal tides showing the latter to be stronger as expected at these latitudes. We also present observations of a gravity wave during a quiet period indicating that PFISRs sensitivity is sufficiently high to obtain reliable spectral information even when electron densities are not enhanced by aurora or a PCA event and are as low as 10 9 e - / m 3 . These results show the capabilities of PFISR to study the neutral dynamics in the polar D-region and mesosphere and lower thermosphere (MLT) over an unprecedented altitude range.