What Caused the Rapid Intensification of Typhoon Megi (2010)?

The objectives of this study are to investigate the key factors leading to the rapid intensification (RI) of Typhoon Megi (2010) and to quantify their relative contributions. The WRF model is employed to simulate the RI process associated with Megi. Our preliminary results show that the favorable synoptic environment for RI, as suggested in the literature, is prevailing during the RI of Megi, such as the reduction of vertical wind shear, the increase of low-level relative humidity, presence of the upper level easterly wind, and the upper-level divergence. Meanwhile, small upper-level relative eddy angular momentum fluxes convergence is identified, indicating less influence from the upper-level trough. Furthermore, several features found during the RI phase are generally consistent with previous studies, including the increase of latent heating, inertial stability and axisymmetricity, and the contracted eyewall with less vertical tilting.

In addition, at the convective scale, areas containing convective and stratiform precipitation both increase during the RI phase, and the area where convective bursts (CBs) can be distinctly identified also increases. These CBs contribute considerable latent heat (50%-80%) in mid-to-upper troposphere, where inertial stability is relatively high. Some of these CBs are within the radius of maximum tangential wind and can efficiently contribute to rapid intensification and formation of the warm core due to the greater heating efficiency associated with the higher inertial stability. The mean inertial stability in the CBs regions strengthens during RI, which can lead to the increase of inertial stability in the inner core. The stratiform precipitation, which contributes about 50% of the latent heat in the CBs regions at both low and high levels, may also play a role in the RI of the storm's inner core. Finally, two warm cores are recognized at levels around 6 and 16 km. It is speculated that these two warm cores may be important for the deepening of Megi's central surface pressure. Future works including sensitivity experiments of different microphysical schemes and environmental parameters will be conducted. Dynamic processes corresponding to the features identified during Megi's RI are aimed to be interpreted and discussed in the study ultimately.