A large vertical wind in the thermosphere at the auroral oval/polar cap boundary seen simultaneously from Mawson and Davis, Antarctica

Abstract

Ground-based Fabry–Perot spectrometer observations from the Australian Antarctic stations of Davis and Mawson show an upward wind ≥100 m s −1 in the thermosphere at ∼240 km altitude on the night of Day of Year 159 in 1997. The wind was from a region located poleward of the poleward edge of the discrete auroral oval, and is identified as a further event of the type seen at Mawson, and elsewhere, in earlier work. The upward wind was first seen over Davis station at ∼22:00 UT. As the auroral oval moved northward the region of upward wind followed, and was seen at Mawson (some 4° magnetically north of Davis) just over 1 h later. It is shown that the presence of the large upward wind does, at times, affect the horizontal wind inferred from the off-zenith observations. Correcting the affected measurements for the non-zero upward wind leads to a horizontal wind field more consistent with that derived from observations before and after the vertical wind event. A lower limit of the area of the region of upward wind over Mawson and Davis on this night is estimated as ∼6×10 11 m 2. The estimated power required to drive the upward wind over this area at 240 km altitude is of order 6×10 9 W. We estimate that this represents between 3 and 7% of the geomagnetic power input in the southern hemisphere during this interval.