The relationship between the intensity of East-Asian summer monsoon in the mid-lower Yangtze Valley and sea surface temperature anomalies in the previous winter

Using ECMWF ERA40 reanalysis, daily rainfall measurements from 740 stations across China, NOAA monthly sea surface temperature (SST) data, NCEP/NCAR monthly outgoing long wave radiation (OLR) data, China NMC-provided daily positions of the western-Pacific subtropical high's ridge, we defined the regional intensity of East-Asian Summer Monsoon (EASM) and calculated the intensity of EASM in the mid-lower Yangtze valley (MLYV) by the definition. The intensity exhibits stronger inter-annual and inter-decadal variability. Analysis is performed of the difference in the circulation, geopotential height and OLR fields between years of strong, weak and normal EASM in MLYV, with preliminary study on the mechanism for key-region SST impacting the monsoon intensity, discovering the intensity in higher positive (negative) correlation with previous winter SST anomalies (SSTA) over the tropical Indian Ocean, waters off East China, and equatorial eastern Pacific (SSTA over waters east of the Philippines), that is, warmer-than-normal SST in the tropical Indian Ocean, and equatorial eastern Pacific and colder-than-normal SST in the east of the Philippines make the western-Pacific subtropical high's ridge southward of mean, its west stretching point westward of normal and intensity higher in comparison to mean, and meanwhile a blocking high is prone to appear around Lake Balkhash, allowing the cold air to move south frequently, therefore, the cold and warm air flows meet in MLYV, converging and rising, leading to the monsoon intensity stronger and the serious floods occur there and vice versa. The findings can serve as an important criterion for the forecasting of the EASM's intensity in MLYY.