Reinvigoration of moist convection in the early development of Super Typhoon Megi (2010)

The formation of a tropical cyclone usually consisted of three consecutive stages phases: (i) initial burst of convection, (ii) low- to mid-tropospheric moistening and adjustment, and (iii) reinvigoration of moist convection and rapid intensification. Through the cloud-resolving simulation with the Weather Research and Forecast (WRF-ARW) model, this study examines the reinvigoration of moist convection that finally led to the development of a self-sustained low-level cyclonic vortex in the early development of Megi (2010). It is found that, as the storm evolved into Stage 2, which began with typical stratiform development, the low-level cold pool resulted from the previous convection bursts induced evident geostrophic adjustment of the wind and pressure fields. During the adjustment, the convergence usually appeared following the distinct divergence associated with the cold pool in the inner-core area of incipient Megi, which could act as a trigger of convection when the lower troposphere is thermodynamically recovered via the sensible heat and moist flux from the ocean. The positive feedback between the convection and low-level convergence favored the development of low-level wind surge near the inner core of incipient Megi, which together with the cold pool associated with the mesoscale convective system in the southwest of incipient Megi led to noticeable low-level southwesterly jet penetrating to the inner-core area of the storm. The southwesterly jet produced distinct convergence in the southeast side of the storm and then led to the reinvigoration of moist convection.