The Mechanism Of Tropical Indo-Western Pacific Warm Pool Precipitation Anomalies Influencing The Interannual Variability Of Winter East Asian Atmospheric Circulation

The tropical Indo-Western Pacific Warm Pool (WP), which has huge warm waterabove28°C, is the basin where the convective activities are the strongest from the globe.The WP is one of the most important basins where the ocean heats the atmosphere. Thus,the WP is very important for the global climate system. The heating anomalies over theWP in summer (JJA) can induce Pacific-Japan pattern (PJ) to impact the climate in China,Korean Peninsula and Japan. Using EOF, regression, correlation, SVD and variousstatistical methods, the process of WP precipitation anomalies influencing the borealw．．in．．te．．r．(D．．JF．．)East Asia (EA) atmospheric circulation interannual variability isinvestigated in this paper, based on the resent more than60-year observational datasets.The differences of this process among different periods are also examined. Themechanism of WP precipitation influencing the EA atmospheric circulation is confirmedwith simple atmospheric model and atmospheric general circulation model (AGCM)experiments. Some new results are found as follows:1. It is shown that the leading mode of the interannual variability of winter WPprecipitation is a west-east dipole mode, which is called WPD mode. During its positivephase, it shows more precipitation over the western Indian Ocean and less precipitationover the Indo-Western Pacific warm pool. The sea surface temperature anomalies (SSTA)induced WPD are ENSO-like pattern. The Indian Ocean Dipole mode in the previous fall(SON) also can influence the WPD mode.Corresponding to the WPD mode, the leading mode of EA winter geopotentialheight anomalies at200hPa (H200) is a wave train pattern. The H200show “positive-negative-positive” from WP to EA during the positive phase (WP-EA pattern). The WP- EA pattern is vertical quasi-barotropic, but it is the most obvious at the upper level,especially the negative anomaly center above East China. A series of atmospheric modelexperiments are performed to confirm that this winter teleconnection pattern is theresponse of atmosphere to the heating anomalies associated with the WPD.Duing the WPD positive phase, there are positive height anomalies at500hPa overthe northeastern China/Japan Sea, and anomalous anticyclonic circulation at lower levelover the tropical northwestern Pacific. Both the two anomalous circulations favor warmertemperature over most regions in China, and more precipitation over southeastern andnorthern China. The anomalies are opposite during the WPD negative phase.2. It is found the WP-EA wave train is weaker during1948-1976and stronger during1977-1998. The main cause is that the amplitude of ENSO is stronger during1977-1998.From1999to now, the mean SST in tropical Pacific is colder. The colder SST canstrengthen the Walker Cell and lead to more (less) precipitation over the tropical WesternPacific (western Indian Ocean). Besides, the La Ni a is more frequent. As a result, theWP region still has strong precipitation anomalies and can induce strong WP-EA pattern.3. The WP precipitation anomalies and the WP-EA wave train are very strong bothin the1997/98winter and January2014. The results of AMIP experiments from11CMIP5models also show that the models basically can simulate the WP-EA wave train.The above analyses verify that the WP-EA wave train is the atmospheric response to WPprecipitation anomalies.The study in this paper reveals the importance of WP precipitation, which acts as abridge in the process of tropical SSTA influencing EA atmospheric circulation. Thus, anew mechanism of how the tropical SSTA impact EA climate is given in this study. Thiswill be a new approach for the EA winter climate prediction.