An EOF-Based Study of Precipitation Characteristics and Their Responses to Different Configurations of Summer Monsoon in the East Asian Monsoon Region from 1951 to 2020

Abstract

Summer precipitation in the East Asian monsoon region is significantly affected by monsoon variations.Different monsoon configurations form distinct precipitation patterns in the East Asian monsoon region by affecting regional water vapor transport.Further， the phase changes in precipitation patterns are prone to the occurrence of abnormal precipitation events， which in turn induce droughts and floods.Based on the EOF analysis， the GPCC precipitation， NCEP/NCAR reanalysis data and different monsoon indices were used to study the spatial and temporal distribution of summer precipitation in the East Asian monsoon region.The effects of four different configurations of summer monsoon on summer precipitation patterns in the East Asian monsoon region were further investigated by combining correlation analysis and water vapor flux analysis.The results show that： （1） Precipitation in the East Asian monsoon region experienced a decrease followed by an increase from 1951 to 2020.The increase in precipitation anomalies after 2010， as well as the rapid fluctuations in precipitation series， indicate a decline in regional climate stability.The EOF successfully presents the distribution of summer precipitation over the East Asian monsoon region.It mainly exhibits as the three-pole structure of north-south "-， +， -"， followed by the dipolar-type structure with north-south reversed-phase variations.Precipitation anomalies occur in the phase transition of precipitation structure， mainly tripolar type followed by dipole type.（2） The combined influence of the East Asian， South Asian， West Pacific， and westerly circulation monsoon systems results in the summer precipitation anomaly in the East Asian monsoon region.The monsoon configurations leading to anomalous increase and decrease in precipitation are Configuration 1 （WNPMI strong， EASMI and AZCI weak） and Configuration 2 （AZCI strong， EASMI and SASMI weak） respectively.（3） At Configuration 1， the subtropical high is located in the southwest， the westerly trough appears at 40°N， and the southern monsoon is strong.These combine to form precipitation in the central part of the monsoon region through shear lines as well as uplift， leading to an increase in anomalous precipitation.In Configuration 2， the westerlies are strong and the southern water vapor dynamics are too weak to penetrate deep into the continent， resulting in an anomalous decrease in precipitation.The results of this study provide a theoretical framework for investigating the mechanisms behind precipitation anomalies in the East Asian monsoon region in the context of climate change.They also provide critical scientific references for managing the region's extreme precipitation occurrences， as well as preventing and controlling floods and droughts.

Keywords

• east asian monsoon region
• monsoon index
• precipitation
• eof analysis
• water vapor fluxes