Analysis Of The Relationship Between Intraseasonal SST Over The Northwest Pacific And Summer Intraseasonal Rainfall In Eastern China

By using the NOAA daily sea surface temperature data (SST), NCEP/NCAR wind fields and specific humidity, OAFlux net heat flux, and the daily rainfall data from National Meteorological Information Center, the low frequency significant cycle of the climatic SST fields over the northwest Pacific was discussed, and the channel that the SST Intraseasonal Oscillation (ISO) over the northwest Pacific affecting the ISO rainfall anomaly in eastern China is also investigated. We also analyzed the distribution of the ISO rainfall in detail and study the possible impact mechanisms. The results show that1)The Western North Pacific SST have the main low frequency cycle about10-20d and30-60d during June to November and the intraseasonal oscillation is more significant. The stronger SST ISO more likely appeared because of the shallower ocean mix layer and the latent heat flux is one of the most important factors causing the change.2) most significant regions of the anomalous ISO precipitation in eastern China affected by the northwest Pacific SST ISO are the middle reaches of the Yangtze River, the coastal areas of South China, the Yangtze-Huaihe regions and most regions of north China.3) There is interaction between the northwest Pacific SST ISO and the850hPa circulation field. The wave train with the structure of cyclone-anticyclone-cyclone (anticyclone-cyclone-anticyclone) gradually forms from south to north in East Asia coast, which cause vapor convergence or divergence that induce the summer ISO rain belt advancing from Yangtze-Huaihe region to north China (retreating from north China to the middle reaches of the Yangtze River and the coastal of South China).4) There is significant intraseasonal oscillation in Jingnan region during the summer time. The positive (negative) SST ISO induces (suppress) the upward net heat flux and then heat (cool) the low level atmosphere that lead to the convergence (divergence) in low level and divergence (convergence) in upper air. What more, It also triggers the cyclone (anticyclone) in Jiangnan region which causes the water vapor convergence (divergence) in there and promote (suppress) the ISO precipitation.5) The negatively anomalous net heat flux caused by the previous SST ISO induced the intraseasonal cyclone in Yangtze-Huaihe region, along with the anticyclone in north and south. The low-frequency waves bring large vapor to the Yangtze-Huaihe region and there is also significant ascending motion. All this favor the intraseasonal rainfall in Yangtze-Huaihe region.