Stockholm university

Arctic expedition: Arrival of an atmospheric river

”The spring has finally arrived,” announced Michael Tjernström, Professor at Stockholm University and Chief Scientist of ARTofMELT2023 to the expedition participants during the routine breakfast meeting at 08.30 UTC on June 10th. Excitement mixed with relief filled the room.

Video with ARTofMELT chief scientists Michael Tjernström and Paul Zieger discussing strong inflow of warm and moist air during the expedition. Photo: Christoffer Groop

For the previous five weeks, the scientists have been eagerly awaiting a strong inflow of warm and moist air coming from further south – a so-called atmospheric river (AR) – that would trigger the sea ice melt signaling the transition to summer in the High Arctic. Studying the effects of atmospheric rivers on the ice surface is one of the main objectives of ARTofMELT2023 as such findings could help to more reliably predict future climate in the Arctic and globally.

“I was beginning to fear we would miss the melt onset since it was so late. But it came now just at the end of the expedition and it is a pity we can’t extend the expedition another week! We have been relatively unlucky with warm air intrusions so far, but we were now at the tail end of a transient atmospheric river, and it is absolutely amazing to see how fast the ice surface is now changing. One day with temperatures above zero and one can see where melt ponds are forming, one more and we already have a few azure-blue melt ponds on the ice floe next the Oden,” says Michael Tjernström.

A warm front was approaching from south, but the first pulse of warm air came almost a day earlier bringing low clouds and dense fog that enshrouded Oden and the surrounding ice floes until lunchtime the next day. Poor visibility together with several visits by curious polar bears meant that all activities on the ice had to be postponed until conditions improved.


Measuring longer-lasting fog periods

Bog bows in the Arctic
When the sun breaks through, bog bows have become more common; a cousin to the more elaborate rainbow.
Photo: Michael Tjernström

However, being forced to hunker down for the fog was not bad news for everyone onboard. The aerosol scientists from Stockholm University, led by Paul Zieger, Associate Professor and Co-Chief Scientist for ARTofMELT2023, were busy ensuring that their instruments were running smoothly to collect all-important data about the air articles present inside the fog.

“Finally, we measure longer-lasting fog periods, which is one of our research objectives here during ARTofMELT2023. Aerosol particles are essential for forming fog droplets and we want to better understand the microphysical principles that govern the development and properties of fog and clouds in general. This is important because fog and low-level clouds are key in determining how energy is transported to and from the ice, which also influences the onset of the sea ice melt,” says Paul Zieger.

Read more on the Arctic expedition ARTofMELT2023

Text: Stella Papadopoulou