Characteristics of Shaanxi Summer Precipitation Anomalies in ENSO Developing and Decaying Stages

Based on Shaanxi summer precipitation data from 1961 to 2008, NCEP/NCAR monthly reanalysis data, the influence of developing stage and decaying stage of ENSO events on Shaanxi summer precipitation is analyzed through composite analysis. It shows that the response of Shaanxi summer precipitation to ENSO in developing stage is very different from that of the decaying stage. During El Niño developing stage and La Niña decaying stage, the precipitation in Shaanxi is less than normal. During La Niña developing stage and El Niño decaying stage, Shaanxi has more precipitation than normal, and the most significantly impacted period by ENSO is July. The response of Shaanxi summer precipitation anomalies to La Niña developing stage and El Niño decaying stage is more remarkable than that of El Niño developing stage and La Niña decaying stage. There is a significant difference in atmospheric circulation in developing and decaying stages of ENSO, especially with regard to the western Pacific subtropical high and the East Asia monsoon strength. During El Niño developing stage and La Niña decaying stage, the western Pacific subtropical high is stronger and more west than normal and the East Asia monsoon is weaker than normal. During La Niña developing stage and El Niño decaying stage, the situation is the opposite. When the subtropical high is stronger and further west, Shaanxi has southwest wind anomalies which transport water vapor, the northern part has the north wind anomalies that bring cold air, and the precipitation would be higher. ENSO developing and decaying stages affect on the change of atmospheric circulation and the East Asia monsoon, and contribtute to Shaanxi summer precipitation. During El Niño developing stage and La Niña decaying stage, the East Asia monsoon is stronger, and Shaanxi has less precipitation. During La Niña developing stage and El Niño decaying stage, the East Asia monsoon is weaker and Shaanxi has more precipitation. In comparison, the East Asia summer monsoon is greatly affected by El Niño events than La Niña events. At the same time, Shaanxi summer precipitation is also affected by El Niño events more greatly. This is an evidence that ENSO affect Shaanxi summer precipitation through changing the East Asia summer monsoon strength.