Influences of Different PBL Schemes on Secondary Eyewall Formation and Eyewall Replacement Cycle in Simulated Typhoon Sinlaku (2008)

The effects of different planetary boundary layer （PBL） processes on the secondary eyewall formation （SEF） and eyewall replacement cycle （ERC） in Typhoon Sinlaku （2008） are investigated by using the Weather Research and Forecasting （WRF） model with six different PBL schemes. The SEF and ERC have been successfully simulated with all the six PBL schemes and the mechanism for the SEF and ERC proposed in our previous study has been reconfirmed. It is demonstrated that both the intensification of the storm and the inward-moving outer spiral rainband contribute to the SEF. After the SEF, the associated diabatic heating enhances the secondary eyewall further, and the transfer of moist air from outer region to the primary eyewall is cut off by the secondary eyewall. In such a way, the primary eyewall dies and an ERC completes. It is found that some simulated features of the SEF and ERC, such as the time and location of the SEF and duration of the ERC, do vary from one simulation to another. In order to describe the features of the SEF and ERC quantitatively, a concentric eyewall index （CEI） is defined and a threshold of the CEI is suggested to determine the onset of the secondary eyewall. The differences in the simulated SEF and ERC are discussed and some possible causes are suggested. In addition, based on the CEI threshold and the conservation law of angular momentum, a formula to predict the location of SEF is also proposed and applied to all the six simulations. The success and failure of the formula are then discussed.

NUMERICAL STUDIES OF PLANETARY BOUNDARY LAYER PARAMETERIZATION SCHEMES ON SUPER TYPHOON SANBA(2012)DURING ITS INITIAL STAGE

The formation and development of typhoons are closely related to the disturbed low vortexes at the planetary boundary layer(PBL). The effects of five PBL parameterization schemes(PBL schemes hereinafter) on the trajectory,intensity, and distribution of physical quantities are studied using the mesoscale WRF model on Super Typhoon Sanba(2012) during its initial stage. Results show that the five PBL schemes exhibit significant different effects on the simulated intensity and path. The results simulated by QNSE and ACM2 without the Bogus method are close to the best track data in the numerical experiments. When the Bogus method is adopted, the simulated trajectories improve significantly because the initial field is close to the true data. Among the five PBL schemes, QNSE and ACM2 with the Bogus method present improved simulated path and intensity compared with the three other schemes. This finding indicates that the two schemes deal with the initial PBL process satisfactorily, especially in the formation and development of disturbed low vortexes. The differences in the treatment methods of the five PBL schemes affect the surface layer physical quantities and the middle and upper atmospheres during the middle to late periods of the typhoon.Although QNSE and ACM2 present better simulation results than other schemes, they exhibit a few differences in the internal structure of the typhoon. The results simulated by MYJ are worse, and this method may be unsuitable for studying the formation and development of typhoons.

The Numerical Simulation on the PBL Structure and Its Evolution over Small-Scale Concave Terrain

A high resolution, nonhydrostatic, three dimensional diagnostic PBL model over small scale concave terrain was established in this paper. A two dimensional prognostic model was developed based on the diagnostic model. The hydrostatic approximation was abandoned and the simple energy ( E e ) closure scheme was used in both models. Using the two models, characteristics of PBL structure and its evolution were fully studied. The main characteristic of the PBL is the circulation, and it fairly affects the distribution of the pollutant in the pit.