| The main characteristics of the general atmospheric circulation in the spring of 2021 (from March to May) are as follows. The polar vortex was characterized by a dipole pattern in the northern hemisphere and was stronger than the average. The westerlies in the middle and high latitudes are 4-wave pattern. In March, the intensity of cold air was weak which caused sea fog occurred frequently during the month. In April, North China sea was affected by surface high pressure system, the circulation was stable, thus the activity of cold air was weak. In May, the surface wind was affected by extratropical cyclones. There were 5 gale processes above 8-grade over offshore areas of China, including 2 produced by cold air, 1 jointly induced by cold air and extratropical cyclones, and 2 generated by extratropical cyclones. Eight obvious sea fog processes occurred over offshore areas, including 3 in March, 2 in April, and 3 in May. There were 8 rough sea wave processes above two meters, and the lasting days of these processes were less than average. Two tropical cyclones was active over the western North Pacific and the South China Sea．The sea surface temperature over the offshore areas was increasing during spring, the increasing rates in eastern and southern seas were more significant which enhanced the gradient of sea surface temperature between the North and South China sea. |