Dynamics and energetics in the early development of Super Typhoon Megi (2010)

Through cloud-resolving simulations with the Weather Research and Forecast (WRF) model, along with observations from the Impact of Typhoons on the Ocean in the Pacific (ITOP) field experiments, this study examines the dynamics and energetics in the early development of Super Typhoon Megi, the strongest tropical cyclone over the globe in 2010. It is found that there are three phases in the initial development of Megi: (i) initial burst of convection, (ii) low- to mid-tropospheric moistening and warming, and (iii) reinvigoration of moist convection and rapid intensification. The time variation of the 360-km area-mean vorticity and vertical velocity shows that the distinct enhancement of the low-level vorticity usually occurs following the burst of deep convection, which indicates that the increase of the low-level vorticity is mainly ascribed to the surface-based moist convection, and therefore, the genesis of Megi is essential a “bottom-up” process. During the rapid intensification of Megi, the convective-induced positive potential vorticity (PV) anomalies were continuously swept into the storm-centered area by the system-scale confluent flow and caused the strengthening of low-level PV of the storm. Before the presence of a persistent PV ring around the storm center, the low-level PV alternates between a ring-shape and a monopolar structure. This initial development of Megi to some extent resembles Hurricane Dolly, a 2008 Cat-2 storm in the Atlantic basin, whose formation was examined in details in Fang and Zhang (2010, 2011). We are also currently examining the conversion and transfer of eddy/mean kinetic and available potential energy to further understand the dynamics and energetics occurred in the early development of Megi in the viewpoint of the interaction between the symmetric and asymmetric processes.