December solstice near the southern polar circle

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December solstice occurred in 2018 at 22:23 UTC on 21 December and could be 'seen' in satellite imagery.

Date & Time
21 December 2018 03:00 UTC
Meteosat-10, Sentinel-3, GOES-16
High Resolution Visible (HRV), Infrared Channel, Ocean Colour

By Vesa Nietosvaara and José Prieto (EUMETSAT)

An astronomical event marking the maximum inclination of the north-south Earth axis and the solar rays, the December solstice has no impact on weather other than announcing the start of longer days in the northern hemisphere (shorter in the southern). As a consequence, there is higher solar illumination and more heating on the Earth's surface in the northern hemisphere.

Satellite solar images from geostationary satellites show sunglint areas close to the polar circle around the time of the lowest sun, as seen in the animation from HRV channel of Meteosat-11 at 0 degrees (Figure 1).

Figure 1: Meteosat-11 HRV animation, 21 Dec 19:15–22:30 UTC

The first strong sunglint shows on the western side of the image at 20:45 UTC, then it moves eastwards (the sun being on the other side of Earth) to the ocean-free area east of Argentina.

Sunglint appears as an artificial bright artifact for three/four consecutives time slots, not to be confused with cloud.

GOES-16, at 75 °W, picks up different areas of strong direct reflection from the sun during the low-sun period of the day.

On Figure 2, the sunglint area shifts at roughly 2000 km/h. We see a sudden glare at 04:30 UTC on the more liquid and flat parts of the ocean in the Antarctic peninsula.

Image comparison
GOES-16 image from 04:45 UTC GOES-16 image from 04:30 UTC
Figure 2: GOES-16 0.5µm channel sunglint around 04:45 UTC (right panel) on 21 December, compared with the image at 04:30 UTC before the sunglint.

Also, Sentinel-3, through its OLCI instrument at 300 m resolution, shows Antarctic areas in 24 hour solar illumination. In Figure 3, some shades indicate the presence of high ice slopes, for instance under the North arrow. Drifting ice combines icy and liquid parts in the sea in the northern part of the image.

Figure 3: OLCI RGB composite for the area in the inset close to the Antarctic peninsula, 19 December, 09:00 UTC. Long shades point to a low sun from the south-easterly direction at the time of the image
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