利用卫星遥感和再分析数据刻画2017-2018年格陵兰北部罕见冰间湖事件

以90%海冰密集度为阈值，基于卫星遥感数据，2017-2018年冰季在格陵兰北部识别了两次冰间湖事件，分别出现在冬季和夏季。冬季的冰间湖事件从2018年2月20日持续至3月3日，夏季的事件从8月2日持续到9月5日。AMSR2被动微波的海冰密集度产品表明，冬季和夏季冰间湖事件对应的最低海冰密集度分别为72%和65%。两次冰间湖事件都与格陵兰北部东西气压梯度异常引起的南风加强有关，而气压梯度的异常则与对流层中部极涡的扰动有关。冬季冰间湖事件期间，相对暖和的气温和频繁出现的冰间湖，导致冬季海冰生长不持续，海冰热力增厚较小，这为夏季海冰发生破碎并形成冰间湖创造了条件。南风减弱和新冰生成是冬季冰间湖消失的主要原因。对于夏季的冰间湖，导致其消失的主要原因则是从北部输入的浮冰增加。Sentinel-1 合成孔径雷达产品相对AMSR2被动微波观测产品更加适合于应用到冰间湖事件伴随的新冰生长，这与前者具有更高的空间分辨率有关。格陵兰北部是北冰洋多年冰的聚集地，该区域被认为是北冰洋海冰的“避难所”。因此区域在2017-2018年出现罕见的冰间湖事件，对于整个北冰洋海冰的快速减少具有重要意义，也助于北冰洋海冰，尤其是多年冰的消退。

Characterization of the unprecedented polynya events north of Greenland in 2017/2018 using remote sensing and reanalysis data

Based on an ice concentration threshold of 90%, it has been identified that two polynya events occurred in the region north of Greenland during the 2017/2018 ice season. The winter event lasted from February 20 to March 3,2018 and the summer event persisted from August 2 to September 5, 2018. The minimum ice concentration derived from Advanced Microwave Scanning Radiometer 2(AMSR2) observations was 72% and 65% during the winter and summer events, respectively. The occurrence of both events can be related to strengthened southerly winds associated with an increased east-west zonal surface level air pressure gradient across the north Greenland due to perturbation of mid-troposphere polar vortex. The relatively warm air temperature during the 2017/2018 freezing season in comparison with previous years, together with the occurrence of the winter polynya, formed favourable pre-conditions for ice field fracturing in summer, which promoted the formation of the summer polynya. Diminished southerly winds and increased cover of new ice over the open water were the dominant factors for the disappearance of the winter polynya, whereas increased ice inflow from the north was the primary factor behind the closure of the summer polynya. Sentinel-1 Synthetic Aperture Radar(SAR) images were found better suited than AMSR2 observations for quantification of a new ice product during the polynya event because the SAR images have high potential for mapping of different sea ice regimes with finely spatial resolution. The unprecedented polynya events north of Greenland in 2017/2018 are important from the perspective of Arctic sea ice loss because they occurred in a region that could potentially be the last "Arctic sea ice refuge" in future summers.