A mesoscale model intercomparison: A case of explosive development of a tropical cyclone (COMPARE III)

The performance of current mesoscale numerical models is evaluated in a case of model intercomparison project (COMPARE III). Explosive development of Typhoon Flo (9019) occurred in the case in September 1990 during the cooperative three field experiments, ESCAP/WMO-led SPECTRUM, US-led TCM-90, and former USSR-led TYPHOON-90 in the western North Pacific. Sensitivity to initial fields as well as impact of enhanced horizontal resolution are examined in the model intercomparison. Both track and intensity predictions are very sensitive to the choice of initial fields prepared with different data assimilation systems and the use of a particular synthetic tropical cyclone vortex. Horizontal resolution enhanced from 50km through 20km down to a 10km grid has a large impact on intensity prediction. This is presumably due to a better presentation of inner structure with higher resolution. There is little impact on track prediction in this target period when the typhoon was in its before-recurvature stage. While most models show large biases in underestimating central pressure deepening, some of the participating models with a particular initial field succeed in reproducing qualitatively the time evolution of central pressure, including slow deepening in the first half and rapid deepening in the second half of the simulation period of 72 hours. However, differences leading to different intensity predictions among models have yet to be identified. Intercomparison of the simulation results shows that wind field has a close relationship with precipitation distribution. This suggests that better prediction of precipitation distribution is crucial for better prediction of wind field, and vice versa. Through the COMPARE III experiments, it has become clear that precise simulation of tropical cyclone structure, especially in the inner-core region, is very important for accurate intensity prediction. Consideration, therefore, should be given to this point, when improvements in resolution, initialization, and physics of numerical models for tropical cyclone intensity prediction are reviewed