The Structure, Evolution, Dynamics and Cloud and Precipitation Characteristics of Extreme Summer Arctic Cyclones Revealed Through Comprehensive Life Cycle Studies

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

The cyclones of the Arctic summer pack an extra punch as they strike when the region is at its most vulnerable. The sea ice cover that protects the ocean surface from storm winds in winter is thinned by summer melt, allowing the winds to push the ice apart and mix up warmer subsurface water that promotes further melting. The lack of ice cover in summer also allows the winds to drive ocean waves which erode coastlines, where the warming of recent decades has thawed permafrost and removed the protective skirt of landfast ice. Fortunately summer Arctic cyclones are weaker than their winter counterparts, but recent work suggests a strengthening trend in summer. The "Great Arctic Cyclone" of August 2012 was stronger than all but a dozen of the winter cyclones in the 30 year record of pan-Arctic observations from weather satellites. The impacts of Arctic cyclones and their connection to sea ice decline has prompted interest in their structure, dynamics, and cloud microphysics. Naturally they have much in common with the more familiar cyclones of the middle latitudes, but there are interesting differences: they are often larger, sometimes covering most of the Arctic basin, they are not closely connected to regions of strong temperature contrast and fast jet streams, they can continue to intensify even after they occlude, and their clouds are unusually abundant in liquid droplets (as opposed to ice particles). The abundance of liquid water in the clouds increases the downwelling infrared radiation they generate, warming the lower atmosphere and promoting sea ice melt. Work under this award uses a combination of satellite observations and meteorological data (including winds, sea level pressure, moisture, and temperature) to investigate summer Arctic cyclones at various stages in their lifecycles. The cloud radar and lidar instruments on the NASA A-Train satellite constellation provide cross sections through the cyclones, and data for specific stages of cyclone lifecycles are identified according to their sea level pressure. The observational analysis is complemented by computer simulations using the Weather Research and Forecasting model. One question addressed is whether there are clues in the large-scale environment that could be used to determine which cyclones will grow to extreme size and intensity. The project has broader impacts due to the strong impacts of summer cyclones on Arctic sea ice and coastal erosion, as noted above. The project also supports two graduate students and employs undergraduate students on an hourly basis, thereby promoting the education of the next generation of researchers in this area. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.