Variation Characteristics Of Autumn Drought In Southern China Based On SPEI And The Possible Causes

Using the 1961 —2014 monthly Standardized Precipitation Evapotranspiration Index (SPEI),ocean temperature data from ORA-S4, and National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR)reanalysis, and different methods, such as the observational analysis, the statistical test methods and numerical experiments using NCAR CAM5.1, characteristics of drought variance over southern China and its relationship with Heat Content (HC) in the tropical Indian Ocean and SST are analyzed on this study. The results show that:(1) Main spatial distribution of SPEI change in southern China is in the same phase at all different scales, with an obvious interdecadal change from wet to dry.And the Second mode shows that the distribution of the SPEI of the west and east in southern China is opposite. And since twenty-first Century, southern China has been shown to be dry.(2) The main spatial distribution of autumn SPEI change in southern China is in the same phase, with an obvious interdecadal change from wet to dry around 1988.And the western region in southern China is drier than the eastern region from 1980s.(3) There exists a significant positive relationship between the autumn SPEI in southern China and HC in tropical western Indian Ocean, indicating that autumn drought in southern China will be corresponded to a lower HC in tropical western Indian Ocean. The lower HC in the tropical western Indian Ocean plays an important role in the decadal autumn drought in southern China.(4) The possible mechanism of the heat content in the tropical India Ocean affecting drought in southern China: The positive HC anomalies in the tropical eastern Indian Ocean, which are possibly affected by the negative HC anomalies in the tropical western Indian Ocean, are closely related to the less OLR, more precipitation and higher sea surface temperature (SST) in the tropical eastern Indian Ocean and western Pacific (TEIWP) region. These changes will give rise to an enhanced East Asian Hadley cell, and then a subsidence motion anomaly over southern China, resulting in a decadal drought in this region. A series of numerical experiments using NCAR CAM5.1 verify that the decadal warming of SST in the TEIWP region plays an important role in causing the decadal autumn drought in southern China.(5) The autumn rainfall will be more than normal in southern China in the positive IOD year, both in the years of Indian Ocean Dipole (IOD) only or IOD and ENSO concurrence. A series of numerical experiments using NCAR CAM5.1 verify that the positive IOD plays an important role in causing the decadal autumn flood in southern China.