Extreme Updraft And Parcel Trajectories In Inner-core Of Tropical Cyclone Planetary Boundary Layer In The Large-eddy Simulation

With the application of high-resolution satellite and radar observation,It has been found that there are various synoptic-scale and fine-scale weather phenomena in the tropical cyclone core region such as eyewall mesovortices,hot tower,rolls and tornado-scale vortices.At present,we know little about these structures.In this study,numerical experiments by incorporating the large eddy simulation(LES)technique with different finest horizontal resolutions of 333m(LES-333),111m(LES-111),37m(LES-333)are conducted to study characteristics of extreme vertical velocity related to fine-scale structures in the boundary layer and mixing processes between the eye and the eyewall.On the basis of the ideal simulation,the simulate of typhoon " Rammasun" with LES framework is carried out.Main conclusions are as follows:In this study,three idealize numerical simulations with resolutions from the sub-kilometer(1/3 km)to sub-hundred meter(1/27 km)are conducted to investigate the low-level updraft extreme near the eyewall.Results show that the strongest updrafts near the eyewall are located in the inner side of the radius of the maximum wind(RMW).Increasing the horizontal resolution in the large eddy experiment,the magnitude(frequency)of the extreme updraft increases.In addition,when the horizontal resolution of a large eddy experiment reaches 111 meter,the spatial distribution and magnitude of the extreme updraft are comparable to the observation.Whether high entropy air inside the low-level eye affects TC intensity through mixing with the eyewall remains controversial.Through the analysis of the trajectory,we found that there are parcels inside the eye entrain the eyewall at different heights and mainly distribute on the strong convection side.The mixing from the low-level eye to the eyewall is dominated by high entropy air,however it only accounts for a small part of the overall circulation in TC comparing to the high-speed airflow in the eyewall.Based on previous study,we conducted numerical experiment on typhoon " Rammasun" with horizontal resolution of 74 m.After using the LES framework,the intensity and track of the simulated TC are very close to the observation.The fine-scale structure and gust can be well simulated and close to the observation.