Characteristics Of The Principle Modes Of Climatology Intraseasonal Oscillation Of Chinese Precipitation During Its Rainy Season

This study reveals the characteristics of Climatology Intraseasonal Oscillation (ISO) of Chinese precipitation via Empirical Orthogonal Function (EOF) analyzing the data from rainfall data of 436 Chinese weather stations, NCEP/NCAR reanalysis data, the Asian monsoon precipitation from Highly-Resolved Observational Data Integration towards Evaluation of the Water Resources Project and sea surface temperature of Hadley center. The first principle mode (PC1) reflects the asymmetric distribution of ISO between the south and north sides of Yangtze River during June and July, while the second principle mode (PC2) reveals the ISO difference between Yangtze-Huaihe River Basin and Southeastern China from May to July. With four polarities located in the mid-east of Arabian sea, the mid-north of Bay of Bengal, the center of South China Sea and the regions from the south of Yangtze River to the southern Japan, respectively, the clamitological intraseasonal teleconnection anchoring in the low latitude is of great responsibility to the PCI. The climatological intraseasonal teleconnection originating in the exit region of westerly jet in the northeast of Atlantic plays an important role in the formation of the CISO in Yangtze-Huaihe River basin from the end of June to the mid of July.A new index (Climatology Intraseasonal Oscillation Intensity, CISOI) reflecting the climatological evolution characteristics of the CISO of Chinese precipitation is defined via the combination of PCI and PC2 which are able to depict the features of the CISO with the mainly oscillating periods in 56 days together. The amplitudes of CISO become pronounced mainly in June and July with predominant phase-lock to the East Asian summer monsoon. The CISO signals in East Asian have close relationship with the ones in the Arabian Sea and the Bay of Bengal. The propagation of CISO in the center of South China Sea varies with the phases. During phase-1 to phase-3, it strengthens the convective anomaly in southeastern China following its northeastward propagating to Western North subtropical Pacific of which the convective anomaly is enhanced then. From phase-4 to phase-6, the CISO convection originating from the tropical regions in the south of South China Sea is famous with its northwestward propagation. The abruptly westward jumping of the Western north Pacific anticyclone anomaly in phase 4 is of most responsibility to the former's northwestward propagation as well as the formation of the PC1. The establishments of the positive anomalies of geopotential height over both of the northeast Atlantic and the Baikal Lake play a critical role on the genesis of the barotropic intraseasonal teleconnection in the mid and high latitudes.In order to understand the available preceding and present conditions of PC1 and PC2, the spatial correlations are employed to categorize the PC-related years. There are 7 years, namely 1962,1964,1977,1988,1992,1995 and 1998, associated with PC1, and 7 years, namely 1968,1969,1972,1975,1983,1996 and 1999, related to PC2. The composite maps of seasonal and monthly anomalies reveal that the PC1-related spatial-temporal distribution of the CISO of Chinese rainfall mainly comes out in the summer of the year when El Nino converts to La Nina. In June, the low-level anticyclone anomaly over the Western North Pacific benefits the northwestward propagation of convective anomaly arising in the Western tropical Pacific. In PC2-related years, the pronounced high anomaly in the exit region of Westerly Jet Stream, perturbed by the near-surface warm anomaly, benefits the establishment of the intraseasonal fluctuation in situ. The high anomaly in the middle of the Siberia, triggered by the upstream cyclone pair, acts as a bridge to guide the upstream Rossby wave train equatorwardly to influence the CISO of precipitation in Yangtze-Huaihe River Basin from the end of June to the mid of July. The near-surface cold anomalies in the north of the Urals and over the Pamirs are of great responsibility to the genesis of the cyclone pair.