In 2016, 22 September was the autumnal equinox in the Northern Hemisphere and the vernal equinox in the Southern Hemisphere.
10 August 2021
22 September 2016
By Jose Prieto and Ian Mills (EUMETSAT)
Equinox is either of two astronomical moments in the year when the Sun hits vertically on the Earth's equator. The one at 14:21 UTC on 22 September 2016 marks the start of the astronomical autumn in the northern hemisphere.
Figure 1 (above, right) is the Meteosat-8 Natural Colour RGB, taken as close to the actual time of the equinox as possible — on 22 September at 14:27 UTC.
Meteorologically the image at the equinox is of no special value, apart from the fact that the sunglint area, which characterises the ocean area mirroring solar radiation straight into the Meteosat sensors, is centred on the equator too, moving west roughly half the apparent speed of the Sun.
Sunglint areas indicate, in the absence of cloud, where winds are stronger (darker brown pixels in the enhanced zoom of Figure 2) and weaker or calm (brighter brown pixels). This applies in a radius of roughly 500 km around the point of specular reflection.
Meteosat-8 at 40 °E (Figure 1) and Meteosat-10 (Figure 2) show different sunglint areas. For Meteosat-10, the area is further to the west.
Image scanning with Meteosat takes 12 minutes, and the equator area was scanned at the equinox precise minute.
Figure 3 is the Meteosat-10 Natural Colour RGB from earlier in the day, at 06:00 UTC, and shows the terminator straight along the zero degree meridian (equal day and night).
Solstices & Equinoxes (Time and Date website)
Previous case studies
Autumn equinox 2015
Seeing solstices and equinoxes from space (21 June 2011)
End of winter 2013/2014 (20 March 2014)
Meteosat sunglint on the Southern Ocean around solstice (21 Dec 2103)
Northern summer solstice 2012 (21 June 2012)
Autumn equinox 2012 (22 September 2012)
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