The Impact Of SST Difference Between The Tropical Indian Ocean And Western-central Pacific On The IIE

The Asian monsoon which contains the Indian monsoon and the East monsoon is the most energetic monsoon system in the world. From the perspective of its members, there is an interface between the Indian monsoon and East Asian monsoon in summer. In this paper, on the basis of previous studies, possible impacts of sea surface temperature difference between the tropical Indian Ocean and tropical western-central Pacific on the interface between the Indian summer monsoon and East Asian summer monsoon (IIE) are studied. The conclusions are as follows:(1) In this paper, the SST averaged over (50°100°,10°S—12°N) is defined as the tropical Indian Ocean (TIO) index TIOI; that over (100°E-170°W,10°S-12°N) as the tropical western-central Pacific (TWCP) index TWCPI, and an index SSTDI (SSTDI=TIOI-TWCPI) which simply describes the SST difference between TIO and TWCP is defined. The leading SSTDI is significantly related to IIE, with good persistence.(2) By using regression analysis between several meteorological elements and SSTDI in winter and spring, as well as IIE, We can get this conclusion:when the SSTDI is positive (negative) in either winter or spring, namely relative warming (cooling) in the TIO and relative cooling (warming) in the TWCP, the mean sea level pressure, vertical velocity and geopotential height in the Bay of Bengal (BOB) and the region from the South China Sea to the western North Pacific are positive (negative) with prevalence of updraft (downdraft), controlled by anomalous anticyclone (cyclone) circulation. Such a pattern of anomalous circulations, the southwest summer monsoon from the BOB is weaker (stronger) than normal; the southeast summer monsoon from the South China Sea is stronger (weaker). Thus, the IIE will shift eastward (westward) than normal.(3) The summer anomalous atmospheric circulations in1997and1998are reconstructed, using respectively the SSTDI in winter and spring. By comparing, it is evident that the SSTDI really can be a factor affecting the abnormal interface location, which is the same with regression analysis.(4) We designed2sensitivity tests that SST anomaly on the TIO and TWCP is added to climate average state of SST, and then simulated for30years using the atmospheric circulation model ECHAM6. The differential analysis of several meteorological elements of2integral test results and the simulating position of HE show that:when the TIO is relatively warming (cooling), while the TWCP is relatively cooling (warming), the IIE will shift eastward (westward) than normal. The atmospheric circulation analysis results match well with the interface position of numerical simulation tests. The results of statistical diagnosis analysis are certified.