Here comes the weather!

Although temperatures are low even during austral summer, quite often the sun shines for 24 hours. In a calm corner on deck, one can take a sunbath during spare time (Fig. 1). We enjoyed such conditions during our last visit (PS111) to this area 3 years ago. However, this year it is quite different. The weather is similar to the one in Fram Strait, the narrow sea between Svalbard and Greenland. The sun only shines sporadically, winds are often strong, and light snowfall hampers our regular helicopter operations. The onboard meteorologist, Steffen Schröter, explains why we face almost Arctic conditions down here in the Weddell Sea.

Those might be desperately disappointed, who have hoped for bright sunshine and high pressure during the COSMUS expedition. At the moment, the opposite dominates our weather. Above a coastal polynya in the eastern Weddell Sea, our main research area, patterns of bad weather often form. In addition, lined up like a pearl necklace, low pressure systems move regularly from Bransfield Strait to Droning Maud Land, bringing moist air from the South Atlantic and northern Weddell Sea towards the position of Polarstern (Fig. 2).

The warm, moist air mixes with cold air from the continent causing small low-pressure systems/troughs and, thus, low-altitude clouds together with snowfall (Fig. 3). Since the beginning of our cruise, the sky is grey – like in the Arctic. If high-pressure systems develop, they are weak and do not last long but lift the base of the clouds, supporting our helicopter operations. Momentarily, sunshine is rare, but the weather situation should change when sea ice formation closes the coastal polynya. As a consequence, cold and dry air dominates and high-pressure systems will form more frequently – we’ll see.