Physics
Scientific paper
May 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995jatp...57..597a&link_type=abstract
Journal of Atmospheric and Terrestrial Physics (ISSN 0021-9169), vol. 57, no. 6, p. 597-609
Physics
19
Annual Variations, Arctic Regions, Diurnal Variations, Geomagnetism, Magnetic Effects, Solar Cycles, Thermosphere, Vertical Air Currents, Wind Velocity, Doppler Effect, Error Analysis, Fabry-Perot Interferometers
Scientific paper
The vertical wind component is frequently used to determine the zero-velocity baseline for measurements of thermospheric winds by Fabry-Perot and other interferometers. For many of the upper atmospheric emission lines from which Doppler shifts are determined, for example for the OI 630 nm emission, available laboratory sources are not convenient for long-term use at remote automatic observatories. Therefore, the assumption that the long-term average vertical wind is zero is frequently used to create a baseline from which the Doppler shifts corresponding with the line-of-sight wind from other observing directions can then be calculated. A data base consisting of 1242 nights of thermospheric wind measurements from Kiruna (63 deg N, 20 deg E), a high-latitude site, has been analyzed. There are many interesting short-term fluctuations of the vertical wind which will be discussed in future papers. However, the mean vertical wind at Kiruna also has a systematic variation dependent on geomagnetic activity, season and solar cycle. This means that the assumption that the average value of the vertical wind is zero over the observing period cannot be used in isolation to determine the instrument reference or baseline. Despite this note of caution, even within the auroral oval, the assumption of a zero mean vertical wind can be used to derive a baseline which is probably valid within 5 m/s during periods of quiet geomagnetic activity (K(sub p) less than 2), near winter solstice. During other seasons, and during periods of elevated geomagnetic activity, a systematic error in excess of 10 m/s may occur.
Aruliah Anasuya L.
Rees David
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