Formation and development of North Atlantic Storm Eunice revealed by satellite remote sensing

The North Atlantic winter storm Eunice brought severe disasters to central and western Europe in February 2022. Based on satellite data, the environmental fields, the dry intrusion characteristics on satellite water vapor images, and the impact of potential vorticity forcing in the upper and middle troposphere on explosive development are studied in this paper. The results show that during the Eunice activities, western/eastern part of the northern hemisphere high latitudes was abnormally cold/warm. The polar vortex shifted towards the northern part of the North American continent, and the average air temperature was lower than the climatological value near the North American polar region. The generation of Eunice was related to the cold air-mass splitting from polar vortex in the North American polar region and its eastward propagation along the westerlies. During the explosive development, the sea level pressure decreased by about 40 hPa/(24 h), which far exceeded the indicator of explosive development (24 hPa/(24 h)) and occurred over the ocean with positive sea surface temperature anomalies. The polar cold air-mass from the cyclone in the south of Greenland formed strong northwesterly to westerly winds over the North Atlantic Ocean surface, which was particularly important for the explosive development. Corresponding to the strong northwesterly to westerly winds, a large range of well-arranged cellular cumulus clouds extended to the vicinity of the Eunice center on satellite true color images, and rapidly enhanced dry intrusion features accompanied by strong positive potential vorticity anomalies displayed on satellite water vapor images. When Eunice reached its strongest stage, the strong positive potential vorticity extended downwards, with the maximum center at 400 hPa located directly above the storm center. Below 500 hPa, the strong positive potential vorticity tilted to the southeast, accompanied by strong descending in the middle and lower troposphere that provided energy for the enhancement of low- level wind to a certain extent. The intrusion of positive potential vorticity was also in favorable for the cyclone development below it.