Simulation of the interannual variation of seasonal northwest Pacific typhoon activity with a regional climate model

The majority of current approach for using dynamical model to project seasonal tropical cyclone (TC) activity involves counting the number of TC-like systems simulated in the model. While this may seem an obvious approach to take, it assumes that dynamical model realistically represent the nature of TCs and their interaction with the environment. However, it is known that many of the most important processes relating to TC formation and to intensity change in reality occur at scales less than 50 km. This would certainly cast some doubts on the ability of current relatively coarse resolution system in capturing the realistic nature of TC frequency, distribution and intensity.

A new 18 km grid regional model has been demonstrated to be able to successfully reproduce the observed multi-decadal increase and interannual variations of Atlantic hurricane activity since 1980, using large-scale interior nudging toward the NCEP reanalysis. Here we shifted the model domain to the northwest Pacific basin to further investigate the model's capability in downscaling and simulating the seasonal typhoon activity. Longer and more active typhoon seasons are typically found over the Pacific. The characteristics of long-term trend of TC activity over the northwest Pacific are rather different from the Atlantic. The relation between tropical storm counts to ENSO is also opposite over the two ocean basin. With revised ocean surface parameterization to improve the pressure-wind relationship simulated in the model, we will discuss whether the model can still reliably capture the TC-climate interactions under different large-scale environment in the northwest Pacific. The relative roles of dynamical (e.g., vertical shear) and thermodynamical (e.g., potential intensity) factors in shaping the variability will also be assessed.