Annual And Interannual Variability Of The South China Sea Warm Water

The South China Sea Warm Water is defined the water of which sea surface temperature is larger than 28℃. The SCS warm water is external part of the Pacific Warm Water and it is also an independent part from the Pacific Warm Water. Because the atmospheric convective motion is very strong above the warm water, and air is moist and more and more clouds arise, the interaction between sea and atmosphere is very strong. So the variability of the warm water may affect the weather and climate in the SCS region and areas adjacent to SCS.On the basis of former studies with the SCS warm water, this paper is mainly to describe the characteristics of seasonal cycle of SCS warm water, to analyze and propose the ruling factor in annual cycle, and to analyze the atmospheric circulation cells associated with the SCS warm water. A new volume index is defined and the interannual fluctuations of SCS warm water are also discussed. The atmosphere circulation anomaly is associated with SCS warm water anomaly, so a possible mechanism of the warm water interannual variability is discussed.In the part of annual cycle, this paper analyzes the annual variability of SCS warm water, space distribution of the SCS warm water and the correlated aspects with the annual variability of SCS warm water, using COADS and Levitus monthly climatologies datasets. It also analyzes the atmospheric circulation associated with the warm water.According to the discussion, the SCS warm water has a large seasonal cycle. There is warm water from March to November in South China Sea. The warm water starts to develop in March. And it takes up most parts of southern SCS quickly at April. The warm water forms. With the increase the heat flux of South China Sea, thewarm water develops. The warm water takes up about all of the SCS region at June and the sea surface temperature arrives the largest. The SCS warm water becomes the strongest at July when the volume of the warm water arrives the largest. And the volume maintains the largest value until September. The SST declines in the meantime. The SCS warm water retreats to the south at October. And it disappears at about November.The variability of depth of the SCS warm water is proxy for the SST variation. However, the distribution of isobath is from northeast to southwest, and the warm water as all a part march from southeast to northwest.The annual cycle of SCS warm water is mainly responded to the interaction of sea-atmosphere of South China Sea, and the net heat flux is most important in the process. The winds of change of net heat flux are very approximate to that of SST and volume index. And the net heat flux advances 1-2 months. At the development of the SCS warm water, the net heat flux is the most important. With the sharp increase of net heat flux, SST and the volume of warm water increase quickly. Thus the warm water takes up the South China Sea quickly at April. The net heat flux is maximum at April, which leads the maximum SST appear at June, and the maximum volume of warm water at July. The net heat flux changes little from June to September, which leads to the maintenance of the volume of warm water from July to September. With the sharp decline of net heat flux, the SST and volume of warm water decrease quickly after October. The SCS warm water disappears quickly.Associated with the annual cycle of SCS warm water, the atmospheric circulation cells also has a significant seasonal variation. And the influence of the warm water to atmospheric circulation is important. In winter when there is no warm water in South China Sea, downdraft takes up the South China Sea. The largest upward motion of Hadley cell is at the equator and Indonesia. With the development of SCS warm water, it moves to the South China Sea and the warm water becomes the convective center of the atmosphere in summer. The SCS warm water develops to the heat souse of Hadley circulation taking over the Indonesia.In the part of interannual fluctuations, a volume index is calculated using SODAdatasets with cubic spline interpolation method. The interannuai fluctuations of the SCS warm water is also large compared to the annual cycle. The volume index of the warm water is proxy to SST index. Warmer SST means larger volume index. The net heat flux ceases to be the main factor in this process. However, the anomaly of atmospheric circulation is related with the warm water anomaly. In the winter of abnormal warmer years, the Hadley circulation decreases, and the downdraft decreases with the decrease of wind velocity. So the net heat flux increase and the warm water becomes stronger in later months. It is reverse in the abnormal colder years. So the anomaly of Hadley circulation cell in winter is proposed to explain the interannuai variations of SCS warm water.