The Characteristics Of Dryness/Wetness In China And The Causal Analyses Over The Middle Loess Plateau In Autumn

Based on the monthly mean rainfall and temperature of589China stations,the National Centers for Environmental Prediction/National Centers for Atmospheric Research (NCEP/NCAR) reanalysis dataset and NOAA extended reconstructed SST data from1961to2010, the temporal evolution and spatial distribution of drought over China under global warming. The assosicated large-scale circulation anomalies and reasons are investigated over the middle Loess plateau drought with rotated empirical orthogonal function(REOF), wavelet transform, regression, composite and correlation methods. The main conclusions are as follows:The spatial characteristics of annual standard drought index can be divided into sixteen climatic subareas in China region under global warming. The middle Loess plateau is the first anmoly area. The seasonal drought index linear trend is analysed and the autumn standard drought trend is the significant (-0.29/10a).In this study two time scales are separated by:whose period is shorter than eight years as inerannual component,and whose period is longer than eight years as interdecadal component. The atmospheric circulation patterns associated with these two modes are quite different.The atmospheric circulation anomalies associated with the wet over the middle Loess plateau of the interannual component include the double blockings of mid-high latitude and the westerly jet streams shows significant negative, and the northeastern Pacific and Japan-Okhotsk Sea anticyclone is featured with an equivalent barotropic structure,and the east wind at the bottom of the anticyclone provided favorable moisture for the middle Loess plateau.And that of the interdecadal component include the negative geopotential height anomaly over East Asian and the East Asian subtropical westerly jet stream(EAWJ)turns to be weaken and northward, and the westerly water vapor transport in the middle latitude and The moisture transport that roots in the Arabian Sea and the Bay of Bengal, Turning northward at the Indo-China Peninsula, had very important contribution to the variability of the atmospheric water resource over the middle Loess plateau.Bay of Benga and South China Sea SST index (BayI) negatively correlates with the standard drought index over the middle Loess plateau in autumn(DroI) when Bayl lead DroI for5months. Nino3index(NinoI) negatively correlates with DroI when NinoI lead Drol for3months. It is found that the significant connections exist mainly at the inter-annual timescale of quasi～4a and4-6a, representing the relationships between the inter-annual BayI (Ninol) and the DroI,and significant connections exist at the interdecadal timescale of quasi～10a between BayI and DroI.The linkage between Asian-Pacific oscillation (APO)and the wet/drought over the middle Loess plateau in autumn is preliminarily addressed by using of the observed data.Results show that they correlate very well,with the positive/ngetive phase of APO tending to wet/drought the over the middle Loess plateau.Such a relationship can be explained by the autumn atmospheric circulation change over Aisian and the North Pacific in association with the anomalous summer APO. So, The summer APO variation provides a potential valuable signal for predicting the autumn wet/drought over the middle Loess plateau.