The Relationship Between Prior-winter SST around Austria and Summer Rainfall in the Yangtze River Valley of China

The HadISST (Hadley Centre Global Sea Ice and Sea Surface Temperature) dataset,the NCEP/NCAR (National Centers for Environment Prediction/National Center for Atmospheric Research) monthly reanalysis data,and monthly precipitation data collected at 160 stations in mainland China from 1980 to 2012 are used to study the relationship between the summer rainfall over Yangtze River valley in China and the prior-winter Sea Surface Temperature Anomalies (SSTA) around Austria.Results show that the leading mode of the monthly SSTA around Austria revealed by the Empirical Orthogonal Function (EOF) analysis exhibits the characteristics of consistent SST variation trend over the entire region,and the SSTA around Austria has a seasonal continuity,which can persist from the prior-winter through the following summer.Analysis of the Niño 3.4 index with the ENSO linear signal removed in the SST field shows that the consistent mode may be a local phenomenon that is independent of ENSO events.Based on the consistent mode of prior-winter SSTA around Austria,the Consistent Mode Index (CMI) is defined to characterize the influence of SSTA around Austria on the summer rainfall in the Yangtze River valley.The CMI has certain implications for short-term forecast of summer precipitation in the Yangtze River valley.The prior-winter SSTA around Austria may affect East Asian summer atmospheric circulations in two ways.First,the prior-winter SSTA signal around Australia can persist through the following summer and trigger a teleconnection wave train between the Northern and Southern Hemispheres,leading to an abnormal West Pacific Subtropical High (WPSH) that subsequently affects the summer precipitation in the Yangtze River valley.Second,the SSTA around Australia can result in abnormal convections in the tropics in both hemispheres,especially abnormal convection activities over the Philippine Sea,and eventually lead to anomalous changes in summer rainfall in the Yangtze River valley.