Abstract:

Based on the daily precipitation data observed by six meteorological stations in the Dalian region from 1971 to 2019, the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) data, including monthly height field, wind field, water vapor field and other reanalysis data, and the data from 130 climate system monitoring indices compiled by the National Climate Center, the characteristics of anomalous atmospheric circulations with more or less than normal precipitation in July were analyzed using statistical diagnosis methods such as synthesis and correlation analysis.Furthermore, the observation truth and cause of anomalous less precipitation in July of 2018 over the Dalian region were studied.The results show that in July of 2018, the Dalian region is in the climate background with less precipitation.The precipitation in July of 2018 is the least during the same period since 1971.The geopotential height of the East Asia continent at 30°-50°N at 500 hPa is relatively high.From the south to the north along the east Asian coast, it presents a "negative-positive-negative" pattern.The geopotential height from North China-Northeast China-Japan Sea is a positive anomaly.The East Asian trough is easterly and weakly, and the western Pacific subtropical high (WPSH) is stronger.The position of the ridgeline and the northern boundary is abnormally northerly, and it is the most northward year for the same period in history.A deeper and warmer high pressure controls the high and low levels over the Dalian region and its stable maintenance which causes the continuous subsidence motions of airflows.At the same time, a cyclonic circulation of wind anomalies at 850 hPa dominates around the south of Japan and the Philippines, and the anomalous airflow divergence region of water vapor flux occurs in Dalian, so it is not favorable for the water vapor convergence to form precipitation.These are the main reasons for the abnormally less precipitation in the Dalian region, in which the stronger WPSH and its anomalous northward ridge line boundary in July play a key role in the anomalous less precipitation in the Dalian region.

Key words: Anomalous precipitation, Atmospheric circulation, Cause analysis