Study Of The Tropical Indian Ocean Heat Content Variability And Its Impact On The Drought And Flood Over China

As we all know, drought and flood are the greatest climate disasters in China. Since 1980s, drought, flood and other climate disasters cause economic losses of 2,000 billion Yuan every year, accounting for 3%-6% of national GDP. Therefore, it is a leading subject to carry out the research of formation mechanism and prediction theory of drought and flood, to improve the forecast level of climate anomaly, and to reduce the economic losses caused by drought and flood climate disasters.In the tropical Indian Ocean, the eastern Indian Ocean warm pool is a part of the Indian-Pacific warm pool, which is the"warm pole"in the world's oceans and affects the water vapor transmission of monsoon and distribution of rain belt. This area plays a key role in regulating drought and floor over China. It should be noted that in the past studies on oceans impact on Chinese drought and flood, a lot of scientists used the sea surface temperature (SST) as basic oceanographic parameter. However, because SST is great affected by sea surface heat flux, it is far worse than ocean heat content or subsurface temperature in reflecting the ocean dynamic process. Moreover, it is little about study of the interannual and interdecadal temporal and spatial variation of heat content anomaly field in the tropical Indian Ocean and its impact on drought and floor over China, and its physical processes is poorly understood. Therefore, it is not only important scientific significant but also practical profitable to carry out the research of inter-annual and inter-decadal temporal and spatial variation of heat content in the tropical Indian Ocean and its impact on the drought and flood over China.Based on the monthly average temperature and salinity data of Japan Meteorological Agency from 1950 to 2006, monthly average precipitation data of 160 stations over China from 1950 to 2009 and ERA-40, NCEP / NCAR monthly average reanalysis data, the inter-annual and inter-decadal temporal and spatial variation of heat content anomalies in the Indian Ocean are analyzed in this paper , and then its impact on drought and floor over China is discussed using filtering, EOF, correlation and composite analysis and other statistical methods. In addition, the relationship between the inter-annual and inter-decadal variation of heat content, El Ni?o-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), the Pacific Decadal Oscillation (PDO) and atmospheric circulation anomalies are also analyzed. The main results are as follow.(1) The inter-annual oscillation mode of the tropical Indian Ocean heat content anomalies mainly comprises two modes with different spatial structure and similar oscillation period of 2-6-yr, but the second mode appears to be the early development phase of the first mode. The inter-decadal oscillation mode of the tropical Indian Ocean heat content anomalies mainly also comprises two modes with different spatial structure and similar oscillation period of 28-yr, but the second mode appears to be the transition phase of the first mode. The inter-annual oscillation of the tropical Indian Ocean heat content may has important impact on the ENSO cycle with a 1-9-month leading and on the Indian Ocean Dipole with a 3-11-month leading, respectively. The zonal wind anomalies over the equatorial Indian Ocean are important factor for the inter-annual oscillation of the tropical Indian Ocean heat content. The PDO may have an important impact the inter-decadal oscillation of the tropical Indian Ocean heat content with 8-11-yr leading.(2) The first mode of interannual oscillation of tropical Indian Ocean heat content has about 9 months leading impact on the Chinese summer rainfall (Jun-Aug). When the first mode time coefficient of the tropical Indian Ocean heat content in autumn is positive (negative) extremes, the rain over the Yangtze River-Huaihe River valley is more (less), but the rain over the south China is less (more) in next summer. The inter-annual variation of summer rainfall over China is mainly caused by the inter-annual oscillation of circulation anomalies and atmospheric water vapor flux over Asia-India-Pacific area, which caused by the interannual oscillation of the tropical Indian Ocean heat content during the previous fall. Among them, the West Pacific subtropical high, the South Asia high, Somalia flow crossing the equator, the zonal wind anomaly over the tropical Indian Ocean, Walker circulation and the southwest monsoon all have greatly important impact on the water vapor flux.(3) The inter-decadal oscillation of heat content anomaly in the tropical Indian Ocean also has an important impact on the summer precipitation over China, which is finished through impact of the heat content on the inter-decadal variability in the summer monsoon over East Asia and South Asia. Before (after) the end of 1970s, the heat content of the tropical Indian Ocean was significantly low (high), the thermal difference between ocean and land was stronger (weaker), which leads to weaker (stronger) summer monsoon and water vapor flux. This will tend to increase (decrease) the summer rainfall over the north China and the south China, and decrease (increase) the summer rainfall in the mid-and low-reaches of the Yangtze River.