On Binary Vortex Self-organization And Tropical Cyclone Torrential Rainfall

The interaction of binary vortices can result in either the abnormal track of tropical cyclone (TC) or TC-related torrential rainfall, both of which are difficult to forecast. Three issues are addressed in this dissertation to understand the phenomena in the context of binary vortex interaction and vortex self-organization dynamics.First of all, the binary vortex interaction is studied with a shallow-water model to find out the factors that can affect the mergence of two vortices. Six numerical experiments are carried out with different vortex structure, strength, horizontal size or distance between the two vortices. Results show that the interaction of two vortices can make them cyclonically rotate around each other, away from each other, close-up or merge into one stronger vortex. The initial distance between the two vortices and the initial asymmetric distributions are found to be the two kinds of factors affecting vortices merging. The critical distance for mergence is 300 km for symmetric vortices and 400 km for quasi-symmetric vortices, while the situation becomes complicated for asymmetric vortices with the critical distance changing with the asymmetric distributions.Secondly, nineteen experiments are performed using the quasi-geostrophic barotropic vorticity equation in the context of advection dynamics to explore how a larger scale vortex self-organize. Results show that the self-organization process can be classified into two types. One is that the relative vorticity of the merged vortex banking in the inner region is caused by initially two axisymmetric vortices while its spiral band rooted in the stretch of the relative vorticity fringe wing. The other is that initial elliptical vortex contributes to the relative vorticity piling-up in the merged vortex inner region and initial eccentric vortex stretch and rupture time and again gives rise to the spiral band in the outer region.Thirdly, two typical cases are diagnosed to explore the vortex self-organization phenomenon and its role in the TC abnormal track or TC-related heavy rain. A new way of thinking in the forecast is established with the predictand changing from large-, or synoptic scale system tovortex system on the basis of vortex dynamics, which makes the 'fine forecast' possible by scaling down the predictand.In conclusion, the vortex self-organization dynamics provide us an efficient tool to understand the mechanism of TC abnormal track and torrential rainfall. The output of this study can be helpful in improving the forecast skill.