Abstract
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)
Highlights
Vertical winds in the thermosphere have a number of possible sources. Smith (1998) identified a diurnal expansion and contraction of the thermosphere, localized heating, and wave motions
We have shown that mean vertical winds are linked to the auroral oval, consideration should be given to thermospheric circulation
Only ∼600 km separates the stations on the ground, mean thermospheric vertical winds are quite different at the two stations
Summary
Vertical winds in the thermosphere have a number of possible sources. Smith (1998) identified a diurnal expansion and contraction of the thermosphere, localized heating (for ex-ample, auroral heating), and wave motions. Vertical winds in the thermosphere have a number of possible sources. Smith (1998) identified a diurnal expansion and contraction of the thermosphere, localized heating The diurnal cycle is in response to the daily solar heating and is expected to be ∼1–3 m s−1 (Smith, 1998). Large vertical winds, ∼100– 200 m s−1 , have been observed at auroral latitudes with both satellite Price et al, 1995; Innis et al, 1999). Thermospheric waves manifest in vertical winds with amplitudes of up to 100 m s−1 (Johnson et al, 1995). Waves are seen propagating both equatorward and poleward of the auroral oval, and relevant observations have been reviewed by Innis et al (2001)
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