Climatology and Latitudinal Gradients of Nighttime F-Region Neutral Winds Over Millstone Hill

Physics

Scientific paper

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3309 Climatology (1620), 3369 Thermospheric Dynamics (0358)

Scientific paper

We use extensive Fabry-Perot interferometer measurements of Doppler shifts in the OI 630 mm nightglow from Millstone Hill to study the local time, seasonal, and solar cycle dependence of nighttime mid-latitude thermospheric winds. We also study latitudinal gradients by comparing results from north-looking and south-looking observations (a 5 degree spread). Our results show that the quiet-time meridional winds are mostly equatorward and peak at 01-02 LT, with average peak values ranging from 40 m/s for December solar maximum conditions to 120 m/s during equinox solar minimum and June solstice conditions. There are very strong latitudinal gradients in the meridional winds: The nighttime peak winds to the north of Millstone Hill are 40-120 m/s stronger than corresponding winds south of the observatory, with the largest gradients occurring during solar minimum. These gradients are roughly the same under geomagnetically quiet and disturbed conditions. The quiet-time zonal winds are generally eastward in the pre-midnight sector and turn westward at 04 LT in December and around 22 LT in June. The December solstice winds are strongest during solar minimum, with average peak eastward values of 130 m/s occurring at 22 LT. The June solstice winds are largely independent of solar flux, and monotonically change from 30-40 m/s eastward near dusk to 30-40 m/s westward near dawn. Latitudinal gradients in the quiet-time zonal winds are very small for December solar minimum conditions, but during June solstice or solar maximum, the pre-midnight winds to the north of Millstone Hill are 40-60 m/s more westward than corresponding south-looking observations. During disturbed conditions, these gradients increase substantially, with differences of up to 120 m/s. In addition to presenting the climatology of the Fabry-Perot winds, we will compare our results with corresponding results derived from incoherent scatter radar measurements and Dynamics Explorer-2 zonal wind observations.

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