Simulative study of Typhoon Chanchu (2006) using the mesoscale coupled air-sea model GRAPES_OMLM.

A new mesoscale coupled air-sea model was developed based on the Global/Regional Assimilation and Prediction System (GRAPES) with the improved Mellor-Yamada type Ocean Mixed Layer Model (OMLM) employed. Using this GRAPES_OMLM model, Typhoon Chanchu (2006) was simulated to test the ability of the GRAPES_OMLM in typhoon research and investigate the impact of local air-sea interaction on typhoon. The results show that the GRAPES_OMLM is able to catch the main physical processes of the typhoon weather. The simulated minimum surface pressure, maximum wind near the typhoon center and the typhoon’s track in the coupled model where the air-sea interaction is included are better consistent with the observation than those in the uncoupled model. Furthermore, compared to the experiment Ctrl_1 with unchanged SST condition, the results of the Ctrl_2 in which daily mean SST is adopted have a bit improvement as well. The SST simulated in the coupled model is also very close to the observation with the maximum SST cooling of more than 4.0℃, which is located at the right of Chanchu’s track. There is an inverse correlation between the change of SST and the surface wind stress, and the increasing of wind stress will induce TKE’s rise with wind-inducing mixing as the main reason for the SST cooling. Moreover, SST cooling can weaken the typhoon’s intensity and change the typhoon’s circulation structure through reducing the heat flux from the ocean, as well as change the WN-1 structure of the Potential Vorticity Tendency which affects the typhoon’s track.