Azimuthal Variations of the Convective-scale Structure in a Simulated Tropical Cyclone Principal Rainband

Previous numerical simulations have focused mainly on the mesoscale structure of the principal rainband in tropical cyclones with a relatively coarse model resolution.In this study,the principal rainband was simulated in a semi-idealized experiment at a horizontal grid spacing of 1/9 km and its convective-scale structure was examined by comparing the convective elements of the simulated principal rainband with previous observational studies.It is found that the convective scale structure of the simulated principal rainband is well comparable to the observation.The azimuthal variations of the convective scale structure were examined by dividing the simulated principal rainband into the upwind,middle and downwind portions.Some new features are found in the simulated principal rainband.First,the overturning updraft contains small-scale rolls aligned along the inward side of the outward-leaning reflectivity tower in the middle portion.Second,the inner-edge downdraft is combined with a branch of inflow from the upper levels in middle and downwind portions,carrying upper-level dry air to the region between the overturning updrafts and eyewall,and the intrusion of the upper-level dry air further limits the altitude of the overturning updrafts in the middle and downwind portions of the principal rainband.Third,from the middle to downwind portions,the strength of the secondary horizontal wind maximum is gradually replaced by a low-level maximum of the tangential wind collocated with the low-level downdraft.