Mechanism For The Impact Of North Atlantic SSTA On The Interannual Variation Of GIIE

The interface between the East Asian summer monsoon (EASM) and the Indian summer monsoon(ISM) quantitatively describes the interaction of the two Asian monsoon subsystems, its interannual variation is vital for understanding and forecasting Asian summer monsoon circulation and associated rainfall. Based on the generalized potential temperature, first we improve the definition of the interface between the EASM and the ISM and proposed the definition of the generalized interface of the East Asian summer monsoon and the Indian summer monsoon (GIIE). Secondly, the impact of preceding and concurrent Atlantic SST anomaly on interannual variation of GIIE is investigated. Based on NOAA 20th Century Reanalysis data V2、the Met Office Hadley Centre’s sea ice and sea surface temperature (SST) data set, a comprehensive study is performed focusing on the influence mechanism of preceding and simultaneous north Atlantic SST anomaly on GIIE with the application of composite analysis, empirical orthogonal function (EOF), singular value decomposition (SVD) and numerical modeling. The key physical processes that North Atlantic Tripole SST anomaly impact GIIE through the North Atlantic-silk road pattern is investigated.The main conclusions are summarized as follows:(1) General formula of generalized potential temperature and the associated generalized definition of GIIE. In order to better describe the incomplete saturation state of the inhomogeneous real atmosphere, we obtain general formula of generalized potential temperature by extracting weights of various wet conditions by EOF and linear combination various wet conditions according to the weight. We recalculated the interface between the EASM and ISM of previous study, and define it as the generalized interface between the EASM and ISM (GIIE). This improvement will allow the interface between the monsoon subsystem representating inhomogeneous saturated conditions in the real atmosphere.(2) The leading mode of North Atlantic SST anomaly influencing GIIE.The singular value decomposition between spring and summer North Atlantic SST anomaly and GIIE distribution showed that the North Atlantic Tripole pattern is the leading mode of their coupling relationship. Further research on Composite analysis result confirmed that the Tripole SST anomaly pattern in North Atlantic has a significantly connection with GIIE variation.(3) The physical processes of North Atlantic tripole SST anomaly impact on GIIE. Based on SVD1 left field (SST) time series and the right field (GIIE) time series, composite analysis on wind anomaly, geopotential height anomaly and T-N flux has been done, and the physical mechanism of the North Atlantic Tripole pattern impact GIIE variation — the North Atlantic-Silk road teleconnection pattern is identified. Results reveal that the physical mechanism can be summarized as: preceding North Atlantic Tripole SST anomly pattern "+,-,+" ("-,+,-") lasting to summer, and excite North Atlantic-silk road teleconnection pattern. This wave train characterized by geopotential height anomly exhibits "negative-positive-negative-positive-negative-positive’("positive-negative-positive-negative-positive-negative") pattern along Great circle path, and wind field anomaly exhibits"cyclone-anticyclone-cyclone-anticyclone-cyclone-anticyclone"(anticyclone-cyclone-anticyclone-cyclone-anticyclone-cyclone)pattern, which can lead to the Western Pacific subtropical high enhanced and shifted southward(weakend and northward), and further lead to GIIE position shift eastward(westward) than normal.(4) Numerical simulation of the North Atlantic Tripole SST anomaly impact GIIE interannual variability. The selected numerical model can simulate the basic characteristics of the North Atlantic SST well. Response of wind anomaly, geopotential height anomaly and T-N flux of the coupled model to North Atlantic Tripole SST anomaly is also analyzed, and the results show that numerical model successfully reproduced the North Atlantic-Silk road teleconnection pattern and the GIIE zonal movement associated with it. The physical model that, the North Atlantic Tripole SST impact GIIE through exciting the North Atlantic-Silk road pattern which lead to influence of intensity and position of the Western Pacific subtropical high, is verified.