Numerical Study On The Sudden Change Of Typhoon MEGI(2010):Roles Of The Meso-scale Convective System Within The Typhoon Circulation

Several significant studies on Tropical Cyclones (TCs) have been reviewed comprehensively, mainly including the researches on TC structure, TC track variety, changing TC intensity and the mesoscale convective systems with TC circulation.There is an obvious sudden change of track and intensity happened after the super typhoon Megi of2010moving into the South China Sea, which was unpredicted before. And there is a mesoscale convective system of high strength and long lifetime within the typhoon circulation observed unexpectedly according to the satellite dataset. It is the inter-reaction between the mesoscale convective system and the typhoon matrix that may play an important role in that sharp change progress of typhoon Megi.Isentropic potential vorticity (PV) analyses for the asymmetric structure of super typhoon Megi of2010are derived from double-nested numerical simulation using non-hydrostatic WRF model Afterwards a contrastive analysis of the asymmetric PV structure before, during and after the sharp change of track of Megi is designed in order to help understand the relationship between the asymmetric turbulence of tropical cyclones (TCs) and TC movement and improve forecasting skills. And the isentropic PV reveals nearly symmetries on each level before and after the sudden track change of Megi, while the isentropic PV structure displays strong asymmetries when it changed to move northwards suddenly. Besides the evolutions of asymmetric wind field and the whole kinematic energy prove the above results. It is indicated that the asymmetric turbulence located in the southeast of typhoon circulation as well as the advection and convection led by it make contributions to Megi’s sudden translation. Afterwards, based on the double-nested numerical simulation results, five sensitive experiments that the location of mesoscale convective system within typhoon circulation changed are designed in order to study the effect of asymmetric turbulence to typhoon evolution. And it turns out that the different position of MCS becomes important for TC intensity changing while it plays a minor role in determining the turning TC motion. The PV distribution in middle and upper troposphere evidences that typhoon should be enhanced when TC and surrounding MCS are merged according to the energetics of geostrophic adjustment in rotating flow.