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Ann. Geophys., 20, 1987-2001, 2002
www.ann-geophys.net/20/1987/2002/
© European Geosciences Union 2002
Thermospheric vertical winds in the auroral oval/polar cap region
P. A. Greet1, J. L. Innis1,2, and P. L. Dyson3
1Australian Antarctic Division, Kingston, Tasmania, 7050, Australia
2Geophysical Institute, University of Alaska, Fairbanks, USA
3Department of Physics, La Trobe University, Victoria, 3086, Australia
Correspondence to: P. A. Greet
(pene.greet@paradise.net.nz)
Abstract. Thermospheric mean
vertical winds from high-resolution Fabry-Perot Spectrometer observations of
the l630 nm emission (from ~ 240 km altitude), over
a four year interval 1997–2000, from Mawson (67.6° S, 62.9° E, Inv 70.5°
S) and Davis (68.6° S, 78.0° E, Inv 74.6° S) are presented. Combining the
four years of data shows Mawson mean hourly vertical winds vary between -10 ms-1
and +4 ms-1, while Davis mean hourly vertical winds vary between - 0
ms-1 and +10 ms-1. Mean hourly vertical winds from Mawson
show little change with Kp, while at Davis the range of
variation increases with increasing geomagnetic activity. Histograms of
frequency distributions of such winds, and their variations with Kp
and l630 nm emission intensity, are presented and
discussed. Variations in mean hourly thermospheric winds and l630
nm emission intensities show at least three significant associations between
mean vertical winds and the auroral oval. Mean vertical winds within the
auroral oval are smaller than those outside the oval, particularly those in the
polar cap. A downward wind associated with entry of the observing region into
the auroral oval can be seen in both Mawson and Davis hourly mean vertical
winds. Large vertical winds are seen poleward of the auroral oval/polar cap
boundary, most significantly upward winds occur within ± 2 hr of magnetic
midnight. Under moderately quiet geomagnetic conditions Davis passes through
the auroral oval into the polar cap in the evening, but at higher Kp
it passes into the polar cap earlier and larger, and more sustained mean
vertical winds are observed.
Key words. Meteorology and
atmospheric dynamics (thermospheric dynamics)
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