Just a short update with the weekend coming up. The humidity I talked about yesterday gave us a nasty surprise.

Shortly after sunset we approached an area with colder water, probably a cold water eddy of the Malvinas Current. Water temperature dropped by more than 2°C within less than three hours and the dew point did the same, and air temperature dropped even more.

Soon air temperature reached dew point, and that means fog, and a low stratus established that escorted us until Friday morning, with only short periods when visibility was a little better.

On Thursday morning there was a gap of some hours, beginning with sunrise, but soon we approached new fog patches (see figure 1), and the remaining day we stayed inside the area of the low stratus, which was clearly recognisable in the satellite image (figure 2). More stratus advected from the north-west so it lasted until Friday morning before we left the area of grey.

At about nine local time we had an ascent of water temperature from 14°C to 21°C within 20 minutes. It took another 30 minutes or so for the dew point and air temperature to follow (with a rise from abut 15 to 19°C), but then the stratus lifted and we got a horizon again (figure 3).

Fig. 1: Approaching The Fog Patches (Morning of 23 March)

Fig. 2: METOP-AVHRR Image (RGB) Of 23 Mar 2017, 19:22 UTC; Polarstern’s position is marked

Another interesting experience was the fact that strong wind and fog do not exclude each other.

On Thursday our position was between a high, east of Rio de la Plata, and a trough that extends from the south over the Falkland Islands towards the area behind us, resulting in a north-westerly wind that increased to Beaufort 6 to 7 on Thursday afternoon – with fog patches all day and a poor to moderate visibility.

For the first time on this journey, we had a little more sea (about 2 m significant wave height) – see figure 4, but of course it’s extremely hard to fix the impression of the sea on a photo. Until Friday morning the wind decreased again to Beaufort 5 and is expected to further decrease when we come nearer to the high.

Fig. 3: The end of grey is near!

Fig. 4: Sea after some hours with 6 to 7 Beaufort

Posted by Oliver Sievers, DWD

Dr Oliver Sievers of the Deutscher Wetterdienst (DWD) is a forecaster specialising in sea-surface and wave models and ship-route forecasts

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