2021年2月北美极端低温暴雪的卫星遥感监测

利用气象卫星数据和欧洲中期天气预报中心ERA5再分析数据，在开展卫星数据误差分析的基础上，研究2021年2月北美冬季风暴乌里发生的气候背景、发展演变、极涡活动对乌里的触发作用及造成极端低温和降雪的大气影响因子等。结果表明:与ERA5温度相比，FY-3D/VASS温度在北美地区100，400 hPa和850 hPa的平均绝对偏差分别为1.14℃，1.44℃和2.63℃，可满足冬季极端冷事件监测服务需求；2021年2月北美大陆冷空气活动关键区（50°~80°N，50°~150°W）西部温度较历史同期偏低4~8℃，2月上旬冷空气强度最强，温度距平百分比达70%；在东北太平洋暖高压脊引导下，极涡加强南下，极涡中心西侧横槽转竖过程中冷空气向南爆发，对流层中高层高位涡异常南伸为乌里的生成提供了高层动力强迫，低层冷空气南下和墨西哥湾沿副热带高压西侧向北输送的暖湿气流在美国南部交汇，触发了乌里低层低涡及云系的快速发展；造成强降雪的风暴乌里云系具有对流特征，冷锋云带和头部云顶亮温大部分低于-40℃，部分低于-52℃，闪电活跃。

Extreme Cold and Snowstorm Event in North America in February 2021 Based on Satellite Data

Using meteorological satellite data and the reanalysis dataset from European Centre for Medium Range Weather Forecasts(ERA5) and others, based on the accuracy evaluation of FY-3D/VASS temperature in North America, the climatic background, development and evolution of North America winter storm Uri in 2021, the triggering effects of polar vortex activities on Uri and the characteristics of atmospheric environment causing extreme low temperature and snowfall are studied. The results show that the average absolute error of FY-3D/VASS temperature at 100, 400 hPa and 850 hPa are 1.14℃, 1.44℃ and 2.63℃ respectively. It shows that FY-3D/VASS temperature can meet the demand of global extreme cold event monitoring, and it is an important data source in regions where conventional meteorological observation is insufficient. FY-3D/VASS temperature analysis shows that in February 2021, when winter storm Uri is active, the temperature in the western part of the key area of polar cold air activity in North America (50°-150°W, 50°-80°N) is 4-8℃ lower than climate mean. The cold air intensity is the strongest in the first ten days of February, and the maximum percentage of temperature anomaly is about 70%. Under the guidance of the warm high ridge in the northeast Pacific, the polar vortex intensifies and extends southward, and the cold air breaks out southward during the vertical rotation of the horizontal trough on the west side of the polar vortex center. The abnormal southward extension of the upper troposphere potential vorticity in high latitude provides upper-level dynamic forcing for the formation of Uri. The cold air in the low layer extends southward and intersects with the warm and humid airflow transported northward over the Gulf of Mexico along the west side of the subtropical high in southern United States. They trigger the low-level vortex of storm Uri and the rapid development of cloud system. The cloud causing strong snowfall of storm Uri shows convective characteristics, with the cloud top brightness temperature reaching lower than -40℃ and even lower than -52℃ in some areas. Lightning is also active in the storm cloud system which causes heavy snow.