Sensitivity of eyewall structure and intensification of tropical cyclones to the boundary layer turbulent mixing

The importance of boundary layer vertical turbulent transport to the evolution of tropical cyclones has been long recognized. However, how does boundary layer turbulent mixing regulate eyewall structure and affect storm intensification is still not well understood. The problem becomes more complicated in numerical simulations since the turbulent mixing is not resolved but parameterized in models. Thus, the regulation of boundary layer processes on eyewall structure and intensification in simulations depends on the way of how turbulent mixing is parameterized. To address this issue, a series of numerical experiments of an idealized hurricane vortex are performed using the multiple nested state-of-the art Weather Research and Forecast (WRF) model. In addition to the four boundary layer schemes, namely, Yonsei University (YSU), Mellor-Yamada-Janjic (MYJ), Mellor-Yamada-Nakanishi-Niino 2.5 level (MYNN-2.5), and Mellor-Yamada-Nakanishi-Niino 3 level (MYNN-3.0) schemes, being tested in the simulations, More experiments are performed on the YSU scheme with the adjusted the eddy exchange coefficient, a parameter that mainly determines the vertical turbulent mixing ability. It is found that the eddy exchange coefficient is a key that modulates the eyewall Rossby waves and barotropic instability of eyewall mesovortices. By adjusting eddy exchange coefficient, the simulations with the YSU scheme can reproduce the main characteristics of eyewall structure shown in the simulations with other boundary layer schemes. The relation of parameterized boundary layer processes to eyewall dynamics and storm intensification is also discussed in this study.