Study On The Impact Of Tropical Pacific-Indian Ocean Upper Layer Heat Content Variation On Drought And Flood Over China

Based on the monthly average temperature and salinity data of JapanMeteorological Agency from1950to2006, the monthly average sea surfacetemperature data from Hadley Center, the monthly average precipitation data of160Chinese stations provided by the National Climate Center, and the NCEP/NCARmonthly average atmospheric reanalysis data, the temperal and spatial variations ofboth tropical Pacific-Indian Ocean heat content and sea surface temperature anomalyfields and the relationship between them are analyzed utilizing the empiricalorthogonal function decomposition, composite analysis and other statistical methods.Also the impact of the heat content’s first two modes on China’s summer rainfall andits accompanying atmospheric circulation anomalies are discussed. The main findingsare as follows:1. The interannual oscillation of the tropical Pacific-Indian Ocean heat contentanomaly is mainly comprised of two modes with similar change period but differentspatial structure. And these two modes correspond to the mature and transit phase ofENSO (El Ni o and the Southern Oscillation) events respectively. The interannualoscillation of the tropical Pacific-Indian Ocean SST anomaly is mainly comprised oftwo modes whose spatial structure and change period are both different, and only thefirst mode corresponds to the mature phase of ENSO events. Although there is a closepositive correlation between the first mode of heat content and SST anomaly fileds,the interannual changes of heat content and SST in tropical eastern Indian Ocean andin the equatorial central Pacific are out of phase.2. The first two modes of tropical Pacific-Indian heat content variations both havegreat influence on China’s summer rainfall in the following year although their affectareas and degrees are different. The first mode’s affect area is relatively larger and ismainly in the North and Northeast of China, the Yangtze River basin, the Southwestof China, the Yangtze-Huaihe River basin and Jiangnan area. The second modes’ affect area is smaller and only contains Yangtze River basin, the South China and theYangtze-Huaihe River basin.3. The two modes’ impacts on the atmospheric circulation, the wind fields, thevapor transport and the vertical motion are also different. They both impact the SouthAsia High, the West Pacific Subtropical High(WPSH), the wind fields, the vaportransport and vertical motion, but the first mode also affects the Ural and Okhotskridges, the East Asia Trough.4. The variation of tropical Pacific and Indian Ocean heat content influencesChina’s summer rainfall about six months to a year in advance. And the impaction ismainly achieved by affecting the atmospheric circulation, the wind fields, the vaportransport and the vertical motion. When the main modes of the heat content field arein positive phase, in the next summer the South Asian High strengthens and moveseastward, the West Pacific Subtropical High(WPSH) intensifies and moves westward,the Ural and Okhotsk ridges strengthens, the East Asia trough deepens and thenorthward vapor transport increases causing floods in Yangtze River basin anddroughts in both Yangtze-Huaihe River basin and South China. When the two modesare in negative phase, the situation just reverses.