Abstract:

Based on temperature and precipitation data of seven meteorological stations from 1951 to 2018 in the Dalian area, the daily precipitation data of the 220 automatic stations during July and August of 2018, the NCEP/NCAR (National Centers for Environmental Prediction-the National Center for Atmospheric Research Reanalysis) daily mean reanalysis data during 1948-2018, the features of the persistent and serious high temperature and drought from July 1 to August 31 of 2018 in Dalian and its causes of atmospheric circulation anomalies were analyzed. The results show that it records a breaking extreme value of the number of long persistent high-temperature days and no-precipitation days in the midsummer of 2018 in the Dalian area. The rainfall is at least 70%-80% lower than the historical average. The Dalian area is controlled by an unusual anticyclone from the lower troposphere to the upper troposphere and jointed the teleconnection pattern over the Eurasia continent (EU pattern). At the same time, the pattern of "-+-" of 500 hPa geopotential height anomaly along the East Asian coast from south to north, which means to show a negative East Asia Pacific teleconnection pattern, a cyclonic circulation of wind anomalies at 850 hPa dominates around the south of Japan and Philippines. The abnormally westward and northward Western Pacific Subtropical high exist a tendency to move in opposite directions and the South Asian high, which is abnormally eastward and northward, their intensity enhance at the same time and overlap over the Dalian area, which causes atmospheric warming of the entire troposphere. Meanwhile, the East Asian subtropical westerly jet lies significantly northward compared with the average situations, so it is not favorable for the cold air moving southwards. Under the combined impacts of the subtropical and mid-high latitude atmospheric circulation over Eurasia, the Dalian region is affected by an abnormal anticyclone. The anomalous cyclonic circulation on the southern side of the anomalous anticyclonic circulation blocks the warm and humid airflow to Dalian, and its anomalous airflow divergence area of water vapor flux occurs in the region, combined with the descending motion effects, which result less precipitation. All the key reasons bring about the anomalous high-temperature and drought weather in Midsummer of 2018 over the Dalian area.

Key words: High temperature and drought, EU pattern, Atmospheric circulation anomaly