Analysis on the causes of positive precipitation anomaly in Shandong in the autumn of 2021

Abstract

Based on daily precipitation data of 123 national stations in Shandong province from 1961 to 2021, ERA5 monthly reanalysis data and NOAA sea surface temperature data, the causes of the positive precipitation anomaly in Shandong in autumn 2021 were analyzed. The results showed that there was a "two ridges and one trough" double-resistance circulation pattern over mid-high latitudes at the geopotential height of 500 hPa. The long-wave trough in the west of Lake Baikal was deepened and strengthened, which was conducive to the southward and eastward transmission of cold air from the west road to affect Shandong. The Western Pacific Subtropical High had larger area and stronger intensity than usual, with the ridge point to the west and the ridge line to the north, which transported sufficient warm and wet air from the periphery northward to the Huanghuai area and provided sufficient water vapor for Shandong. The intersection of cold air and warm and wet air flow in the Huanghuai area leaded to abnormally more precipitation. Further analysis showed that under the synergistic influence of the cold water state in the equatorial Middle Eastern Pacific and the warm sea surface temperature phase in the Indian Ocean, the Western Pacific Subtropical High was stronger, more westerly and northerly, thus providing favorable water vapor conditions for the transport of warm and wet air. The stronger and northerly Western Pacific Subtropical High anomaly, the warm SST anomaly over the east coast of South America and the north Pacific Ocean, and the cold SST anomaly over the central equatorial Pacific Ocean were the main reasons for the positive precipitation anomaly in Shandong in September of 2021.

Keywords

• autumn precipitation
• west pacific subtropical high
• atmospheric circulation
• sea surface temperature anomalies