A Numerical Sensitivity Study on the Energetics of Tropical Cyclone Megi(2010) during Intensification

This work studies the intensification of Tropical Cyclone Megi (2010) from the energetics point of view and its sensitivity to boundary layer schemes. Here, we presented the kinetic energy budget as the volume-integrated kinetic energy tendency of an axisymmetric system balanced by the sum of the energy conversion from the available potential energy and energy loss due to friction.  In particular, a 2-km resolution simulation is performed with Deardorff boundary layer scheme using the MRI/JMA nonhydrostatic model. Numerical experiments are conducted by increasing the momentum exchange coefficient (Cd) by 50% and changing the vertical mixing scheme to Mellor-Yamada-Nakaniishi-Niino Level 3 (MYNN) scheme. The sensitivity experiments show substantial impacts to KE balance by introducing perturbations on the inflow (v_r) and tangential winds (v_ϕ) upon changing Cd and the boundary layer scheme. Changes on v_r , and hence on mass stream function, affect energy conversion; while variations on v_ϕ , subsequently on momentum flux, affect energy loss. In this work, both experiments intensified the volume-integrated mass stream function which in turn enhanced energy conversion. However, lower energy tendency, and subsequently slower intensification, is still observed due to a higher increased in the frictional dissipation. It was found that the energy loss for the case of the increased surface drag coefficient is mainly due to the enhancement of the inward momentum flux. On the otherhand, the increased energy loss in the MYNN was largely controlled by the enhancement of the downward momentum flux due to a larger diffusivity coefficient.