Intraseasonal Characteristics of Water Vapor Transport Associated with Low‐Frequency Rainfall Regimes over Southern China in Summer

Abstract

AbstractThe intraseasonal characteristics of the water vapor transport associated with two low‐frequency rainfall regimes over southern China in summer is investigated by composite analysis on historical cases using the daily NCEP/NCAR reanalysis dataset for the period 1962‐2006. The one of the rainfall regimes is the South of the Yangtze River (SY) regime with a rainbelt located to the south of the Yangtze River, and the other regime is the Yangtze‐Huaihe valley (YH) regime with a rainbelt along the Yangtze‐Huaihe River valley. The results show that the total water vapor transport associated with the SY regime primarily comes from the Bay of Bengal, while that associated with the YH regime mainly comes directly from the South China Sea but originally from the Indian monsoon region. The anomalous water vapor transports associated with the two regimes are significantly different from each other. The northward anomalous water vapor transport originates from the tropical Western Pacific Ocean (WPO) and the South China Sea plays a leading role in supplying anomalous water vapor associated with the SY regime, as well as the mid‐latitude eastward and mid‐and high‐latitude southward anomalous water vapor transports are also important for this regime. The anomalous water vapor supply associated with the YH regime mainly comes from the contribution of the northward anomalous water vapor transport originating from the tropical and subtropical WPO, and the contribution of the eastward anomalous water vapor transport from mid‐latitude is next to those of the northward anomalous water vapor transport. In addition, the anomalous water vapor has a contribution of about 50% to the total regional water vapor budget corresponding to the SY regime, while the anomalous water vapor has a contribution as high as of about 70% to the total regional water vapor budgets corresponding to the YH regime. Although the total water vapor transport is dominated by the climate‐mean water vapor transport, the anomalous water vapor transport has a same contribution as the climate‐mean water vapor transport to the regional water vapor budget corresponding to the SY regime. Particularly for the YH regime, the total regional water vapor budgets are dominated by the anomalous water vapor transport, which may be one of the reasons for the major difficulty in prediction of summer rainfalls over the Yangtze‐Huaihe River valley since that the anomalous water vapor transport is more complicated than the mean water vapor transport.