The Relationship Between Summer Rainfall Anomalies In Yangtze-Huaihe Valley And Atmospheric Circulation Anomalies Over Western Indian Ocean

The characteristics of summer rainfall anomalies in Yangtze-Huaihe valley, the variation of the annual relationship between the rainfall anomalies and the vertical circulation anomalies over Western Indian Ocean region and the relationship between the vertical circulation and the sea surface temperature of the Western Indian Ocean and other regions are investigated, in terms of the NCEP/NCAR reanalysis data and the160stations monthly precipitation data from China National Center of Climate. Results show as follows:(1) There exist more (less) than normal blocking high at high-latitudes and low trough activities at mid-latitudes, West Pacific Subtropical High and East Asian summer monsoon are stronger (weaker), more than normal rainfall may occur in Yangtze-Huaihe areas, vice versa.(2) When there exist more (less) than normal precipitation in Yangtze-Huaihe areas, the sea surface temperature of Western Indian Ocean region have significant positive (negative) anomalies from early winter to spring, and the positive (negative) anomaly area moves from the equator to the Arabian sea. In summer, the SSTA of the West Indian Ocean have the maximum Significant positive (negative) anomalies with the strongest signal.(3) The vertical circulation over Western Indian Oceans has close relation to the rainfall in Yangtze-Huaihe valley, when the anomalous descending (ascending) motions occur over Western Indian Ocean, more (less) summer precipitation in Yangtze-Huaihe areas. But the relation is influenced by the climate background clearly. The vertical motion over Western Indian Oceans is opposed to the rainfall in Yangtze-Huaihe valley during the period1979-1993with correlation coefficient of-0.43, but coincident from1994to2010with positive correlation coefficient of0.71.(4)When the anomalous descending (ascending) motions occur over Western Indian Ocean, Western Pacific Subtropical High tends to be weaker and move eastward (stronger and move farther westward), and the East Asian summer monsoon is weaken (strengthen) and the rain belt is likely to shift southward (northward). The summer rain belt is in the north (south) China inl979-1993(1994-2010), so when there exists descending (ascending) motions over Western Indian Ocean, the anomaly rain belt will tend to move southward (northward) in the Yangtze-Huaihe valley from the north (south) China. As a result, negative (positive) relationship between the ascending motion over Western Indian Ocean and the summer precipitation in Yangtze-Huaihe at the background with strong (weak) Western Pacific Subtropical High and related monsoon.(5)There exist significantly positive (negative) anomaly SST in the Western Indian Ocean in the early autumn, and the strongest one occurs in the early winter, starting to wane in the early spring and summer. The SSTA in Western Indian Ocean appears5months earlier than the vertical circulation anomalies over the Western Indian Ocean, so the vertical circulation anomalies over the Western Indian Ocean is strongest in the summer. It means that, The SSTA in the Western Indian Ocean in leading winter is one of the important precursors and factors resulting in the vertical circulation anomalies over the Western Indian Ocean. The signal is advisable in the prediction of summer rainfall in Yangtze-Huaihe areas.