Arctic Mixed Phase Clouds and a Melting Greenland

Last night, Dave Turner from the National Severe Storms Laboratory presented some brand new research just published in Nature.  The research involves a particular type of clouds that occur in the Arctic called mixed phase clouds, because they contain both ice and water particles.  The various processes that occur to create and sustain these clouds are complex, and difficult to model accurately.  To improve the understanding of high latitude clouds, Turner and collaborators installed a measurement facility at the peak of the Greenland ice sheet, called Summit Station.  The instruments there measure quantities such as air temperature, moisture, wind speeds and cloud properties, and using many instruments together, the team was able to deduce that mixed phase clouds in the Arctic played a critical role in a historic melting event on July 12, 2011, when nearly all of the ice sheet experienced some melting.  The last time this occurred in the ice record was in the 1890s.  Through measurements and model experiments, Turner and collaborators were able to determine that if the clouds had been thicker or thinner, this melting event would almost certainly not have happened, earning them the name "Goldilocks Clouds".  Using other data sets and models, Turner's group is able to predict that the Goldilocks setup occurs a significant fraction of the time all over the Arctic, which means more extreme melting events like this one could occur as heatwaves like the summer of 2011 become more prevalent on a warming world.  Turner cautioned that there is little understanding of how these clouds themselves will respond to a warmer world, and that increased warming could cause the clouds to be thicker, or not exist at all, which would short circuit the effects seen last summer.