Abstract:By analyzing the easterly waves that influence Southern China Coast during 1999—2013, the easterly waves can be classified into three types:south path easterly waves, westward easterly waves and offshore easterly.The Pacific ocean high is a key system which controls the typical paths and positions of the three types of easterly waves especially through its motions towards west and north.The composite analysis based on different types of easterly waves shows that the strong vorticity center, which mostly locates under 850 hPa level, denotes the easterly wave center.As for the structures of the easterly waves, there are a strong convergence area in its lower part and a vertical rising area over the whole level on its back side.The trough axis tilts westwards with its height for the south path easterly wave, but it is almost vertical for the westward and offshore easterly waves.The composite analysis also shows that the easterly wave tends to move towards the warmer SST area.The numerical simulation results confirm that by warming up the SST warm center in front of the easterly wave trough, it will cause minus geo-potential height at low level of the easterly wave trough area and minus center of geo-potential height at mid level of its back side.It shows that the warming up of SST would increase the intensity of the easterly wave by sensitive and latent heats.It will also increase the intensity of the easterly wave precipitation, push the rainfall area northward and add more cyclonic component of wind fields in lower part of the easterly wave.The added component will support stronger convergence at low level and maintain the rising vertical velocity over the whole level.The analysis of a typical westward easterly wave shows that the helicity is positively correlated with the intensity of the easterly wave.Potential temperature zonal difference shows that the easterly wave has a structure of warm top and cool bottom.When the vorticity of the easterly wave increases, the perturbation kinetic energy transforms to the layer perturbation potential energy;while the easterly wave weakens, the latter transforms to the former.