Abstract:Based on the NCEP/NCAR daily reanalysis product and daily precipitation and temperature data collected at observational stations,the circulation characteristics and causes of anomalous the high temperature and drought in the summer of 2018 over Liaoning Province have been investigated using a diagnostic analysis method.The results demonstrate that in the summer of 2018 Liaoning Province experienced a record-breaking event since 1962.The precipitation in the entire region showed a negative anomaly,and the anomalous precipitation was -127.72 mm.The precipitation anomaly percentage in the western and eastern parts of Liaoning Province was 10%~30%,while that in the central part was 30%~60%.In particular,the precipitation anomaly percentage in the northern and southern parts of Liaoning Province was less than 60%.Meanwhile,unusually high temperature influenced Liaoning Province mainly from mid-July to early August.The high temperature was developing from the northeastern part of Liaoning Province and gradually spreading to the southwestern part while strengthening in intensity,and reaching its peak in early August.The temperature in the northern part of Liaoning Province was more than 2.4 degrees greater than its mean climatology;that in the central part was more than 3.2 degrees greater;and that in the southern part was more than 4 degrees greater.Under the influence of abnormally high temperature and abnormally low rainfall,the drought situation in Liaoning Province intensified rapidly.The anomalous anticyclonic circulation with equivalent barotropic structure is the local circulation cause.Liaoning Province was controlled by an abnormal anticyclone from the lower troposphere to the upper troposphere.The anomalous cyclonic circulation on the southern side of the anomalous anticyclonic circulation blocks the warm and humid airflow from the Bay of Bengal and South China Sea to Liaoning Province,which is conducive to precipitation in Liaoning Province.Moving in opposite directions of the South Asia High(SAH) and Western Pacific Subtropical High(WPSH) and overlapping over Liaoning Province was the large-scale circulation caused by the hot and drought-ridden summer of 2018.As a result,Liaoning Province was continuously affected by the downdraft.The East Asia Pacific/Pacific Japan (EAP/PJ) and Eurasian (EU) pattern was one of the direct causes for the abnormal development of the WPSH.The positive geopotential height anomaly center in Liaoning Province was strengthened by the EAP/PJ and EU pattern,thus contributing to the northward positioning of the WPSH.The dispersion of Rossby wave energy is one of the fundamental causes for the formation and perpetuation of the EAP/PJ and EU pattern.The Rossby wave energy originating from the North Atlantic dispersed eastward to East Asia along the waveguide area of the high-altitude westerly jet,thereby resulting in the abnormal enhancement of the geopotential height in northern China,including Liaoning Province.Meanwhile,there was a quasi-meridional dispersion of Rossby wave energy from northeastern China to the Korean Peninsula and Japan,which is conducive to maintaining and developing the EAP/PJ and EU pattern,thus making Liaoning Province controlled by a positive geopotential height anomaly,and in turn the WPSH developed abnormally.The persistence of the heat and drought event over Liaoning Province was due to the perpetuation of the quasi-stationary waves at mid-high latitudes,which originated from the North Atlantic Ocean.