Comparison Study On The Developing Mechanism Of Spring And Autumn Cyclones In Eastern China Sea

The cyclones which develop on the Eastern sea of China during spring and autumn in 2008--2014 are statistically analyzed. According to seasons when cyclones are on the sea; the cyclones are divided into two categories:spring developing cyclones and autumn developing cyclones. Respectively, the basic statistical characteristics of the two types of cyclones are compared. Then, the features of cyclonic synthetic structure are diagnosed and analyzed by the synthetic analysis method. For investigating the cyclone developing mechanism on the sea, the dynamic impact of cyclone jet and the influence of environmental factors are systemically analyzed. Finally, WRF model is used to simulate the spatial and temporal changes of the two types of cyclones in the process of the development on the sea, including the structure configuration and the intensity change of the cyclone jet stream, and the strong rainfall of cyclone, and their impact on the development of the cyclone on the sea. The results showed as follows::(1) The numbers of developing cyclones on the sea did not have an obvious interannual variance trend. Overall, the two types of Sea cyclones are a kind of relatively shallow system. Spring cyclones can be roughly divided into two categories according to their vertical depth, one is relatively shallow with a vertical scale up to 850hPa, another kind is with a thickness up to 700 hPa. Generally, the autumn sea cyclones is thicker to 700hPa. Both spring and autumn sea cyclones are mainly with 1500 km in horizontal scales, only a few can reach more than 2500 km. The sea cyclones have two kinds of moving path basically:moving eastwards through Japan and moving northeastwards through South Korea. The kinds of developing sea cyclone here is different from the explosive cyclone, their intensity variance is only 2-3hPa/6hr and their active area is mainly within mid latitude zone. (2) The sea cyclone’s weather is strong winds, high waves and heavy precipitation. The cyclone precipitation area in spring is significantly larger than in autumn, the precipitation area is more concentrated in the spring, while the precipitation area is more dispersed in the autumn. The high wave area and the strong wind area are located in the southeast or east of the cyclone in the spring; But the high wave area and strong wind area are mainly located in the cyclone center area in the autumn.(3) The warm center and warm advection are important influence factors on the development of sea cyclone in the spring and autumn. The warm advection in the spring is stronger than in the autumn. The Latent heating position can indicate the distribution of cyclone rainfall area. Convective instability is not an important influence factor on the development of cyclones in the spring and it just a key factor to the development of cyclones in the autumn.(4) The cyclone jet is important factor impacting the development of sea cyclone in the spring and autumn, it is also an important carrier of water vapor transport to cyclone. In cyclone structure the cyclone jet axis area is with an average speed over 10m/s on 1000hPa and over 16m/s on 850hPa. The cyclone jets of several levels configure the sea cyclone construction with a top large and base small funnel shape in the vertical. The structure is asymmetry and stronger in southeastern part of the cyclone. The left side of the low level cyclone jet is conducive to maintaining the center intensity of the cyclone, and the left side of the upper cyclone jet is corresponding to the right side of the low level cyclone jet, which helps cyclonic pumping. With the multi cyclone jets overlapping, it results in strong vertical ascending motion area in southeastern cyclone and other parts of cyclone are without cyclone jet, such cyclone structure causes the cyclone funnel shaped with a strong spiral upwards motion branch and a weak downwards motion branch. Other main factors which are conducive to the development of the cyclone are the downwards transport of the upper level jet momentum, the SST sensible heating over the sea.(5) Numerical simulation results show that the area size of the strong precipitation at the southeastern of the sea cyclone is promotional to the cyclone intensity, and the latent heat released from the cyclone is enhanced cyclone intensity. So Spring sea cyclone rainfall area is larger than that in the autumn, which will support the enhancement of spring sea cyclone. The evolution of the cyclone jet and the maintenance and enhancement of the asymmetric structure strongly promote the strengthening of the cyclone on the sea. The configuration of the spring cyclone jet is larger than that of the autumn cyclone jet, which is conducive to the expansion of the spring cyclone scale.