Sun glint during September equinox

Sunglint during September equinox

22 September 2016 06:00 and 14:27 UTC

Sun glint during September equinox
Sun glint during September equinox

In 2016, 22 September was the autumnal equinox in the Northern Hemisphere and the vernal equinox in the Southern Hemisphere.

Last Updated

10 August 2021

Published on

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.

Enhancement on the sunglint area

Enhanced Met-10 Natural Colour RGB,22 September 14:15 UTC compare1

Figure 2: Comparison of Meteosat-10 Natural Colour RGB images showing the sunglint.

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.

 Meteosat-8 Natural Colour RGB, 22 September 14:27 UTC
Figure 1: Meteosat-8 Natural Colour RGB, 22 September 14:27 UTC

Image scanning with Meteosat takes 12 minutes, and the equator area was scanned at the equinox precise minute.

 Meteosat-10 Natural Colour RGB, 22 Sept 06:00 UTC
Figure 3: Meteosat-10 Natural Colour RGB, 22 Sept 06:00 UTC

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).

Related Content

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)