On the Processes Leading to the Rapid Intensification of Typhoon Megi (2010)

Abstract

The processes leading to the rapid intensification (RI) of Typhoon Megi (2010) are explored with a convection-permitting full-physics model and a sensitivity experiment using a different microphysical scheme. It is found that the temporary active convection, gradually strengthened primary circulation, and a warm core developing at midlevels tend to serve as precursors to RI. The potential vorticity (PV) budget and Sawyer–Eliassen model are utilized to examine the causes and effects of those precursors. Results show that the secondary circulation, triggered by the latent heat associated with active convection, acts to strengthen the mid- to upper-level primary circulation by transporting the larger momentum toward the upper layers. The increased inertial stability at mid- to upper levels not only increases the heating efficiency but also prevents the warm-core structure from being disrupted by the ventilation effect. The warming above 5 km effectively lowers the surface pressure. It is identified that the strong secondary circulation helps to accomplish the midlevel warming within the eye. The results based on potential temperature (θ) budget suggest that the mean subsidence associated with detrainment of active convection is the major process contributing to the formation of a midlevel warm core. On the possible causes triggering the inner-core active convection, it is suggested that the gradually increased vortex-scale surface enthalpy flux has a leading role in the development of vigorous convection. The results also highlight the potentially dominant role of weak to moderate convection in the onset of RI, while the convective bursts play a supporting role. Based on the aforementioned analyses, a schematic diagram is shown to describe the plausible path leading to RI.

Impacts of SST Patterns on Rapid Intensification of Typhoon Megi (2010)

“…Updrafts stronger than 1 m s −1 reached almost 15 km altitude, and a midlevel warm core was centered around 5 km altitude. Such updrafts are known features of an intensifying storm (Rogers et al, ), and a midlevel warm core is a precursor to the RI state (Chang & Wu, ). In contrast, the FO storm kept the same intensity, although mean SST exceeded 29.0°C at all radii within 100 km (Figure b).…”

“…The evolutions of convective activity and axisymmetrization of the inner core are the features prior to the RI of Typhoon Megi (Chang & Wu, ; Wang & Wang, ). Following Wang and Wang (), we defined the axisymmetricity parameter as the ratio of the azimuthal mean kinetic energy to the total kinetic energy and calculated it for each radial band of 2 km.…”

“…The processes leading to the RI of Typhoon Megi (2010), a Category 5 typhoon with a minimum central pressure of 885 hPa, were recently investigated by using cloud‐resolving atmosphere models with a horizontal resolution of approximately 2 km (Chang & Wu, ; Wang & Wang, ). In these studies, the middle‐to‐low convection and a midlevel warm core contributed to the RI and tall and intense convection led to the formation of an upper‐level warm core.…”

Convection, latent heating and potential temperature budget in the rapidly intensifying Typhoon Mujigae (2015)

“…Recently, numerical‐model studies (Zhang and Chen, ; Chen and Zhang, ; Wang and Wang, ) have also shown that a sudden increase in deep convection elements (termed convective bursts) occurring inside the RMW may create extra LH, where the high inertial stability constrains this heat to dissipate outside. However, slightly different from these viewpoints emphasizing the importance of deep convection, Chang and Wu () suggested that the LH substantially increases within the mid‐to‐upper troposphere inside the RMW, mostly caused by the weak‐to‐moderate (WM) convection therein, and makes a significant contribution to RI.…”

Dynamics and Predictability of the Rapid Intensification of Super Typhoon Usagi (2013)

“…Statistical prediction models attempt to take advantage of the fact that a favorable enviroment is a necessity for RI, and forecast RI based on the values of large-scale environmental parameters, such as the vertical wind shear and sea surface temperature (Kaplan et al, 2010;Kaplan & DeMaria, 2003). However, many studies have shown that internal processes may also play an important role in RI, such as the initial intensity of the vortex and inner-core deep convection (e.g., Chang & Wu, 2017;Chen et al, 2017Chen et al, , 2018Rogers et al, 2016;Wang & Wang, 2014;Zagrodnik & Jiang, 2014). Idealized simulations in a no-shear environment suggest that storms with stronger vortices undergo RI earlier (Miyamoto & Takemi, 2015).…”