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

北极夏季的气旋格外猛烈，因为它们在该地区最脆弱的时候袭击。冬季保护海洋表面免受暴风雨侵袭的海冰覆盖层因夏季融化而变薄，这使得风可以将冰层分开，并将更温暖的次表层水混合在一起，从而促进进一步融化。夏季冰盖的缺乏也允许风驱动海浪侵蚀海岸线，近几十年的变暖已经融化了那里的永久冻土，并移除了陆地冰的保护层。幸运的是，夏季北极气旋比冬季气旋弱，但最近的研究表明，夏季有加强的趋势。在30年来的泛北极气象卫星观测记录中，2012年8月的“北极大气旋”比除十几个冬季气旋以外的所有气旋都要强。北极气旋的影响及其与海冰下降的联系引发了人们对它们的结构、动力学和云微物理的兴趣。自然，它们与更常见的中纬度气旋有许多共同之处，但也有有趣的不同之处：它们往往更大，有时覆盖北极盆地的大部分地区，它们与温度反差大和急流速度快的地区没有密切联系，它们即使在遮挡后也可以继续增强，它们的云层中含有异常丰富的液滴(而不是冰粒)。云层中丰富的液态水增加了它们产生的下行红外辐射，使低层大气变暖，促进海冰融化。该奖项的工作结合卫星观测和气象数据(包括风、海平面气压、湿度和温度)来研究处于生命周期不同阶段的夏季北极气旋。NASA A-Train卫星星座上的云雷达和激光雷达仪器提供了气旋的横截面，并根据其海平面气压确定气旋生命周期特定阶段的数据。观测分析得到了使用天气研究和预报模型的计算机模拟的补充。讨论的一个问题是，在大尺度环境中是否有线索可以用来确定哪些气旋将发展到极端大小和强度。如上所述，由于夏季气旋对北冰洋海冰和海岸侵蚀的强烈影响，该项目具有更广泛的影响。该项目还支持两名研究生，并按小时雇用本科生，从而促进这一领域下一代研究人员的教育。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.