Identifying Cold Pool Scales over Complex Topography Using TaiwanVVM Simulations

In this study, our objective is to identify the appropriate cold pool scales over Taiwan’s complex topography during predominant afternoon thunderstorms under a local-circulation dominated weather regime in summer. We utilize semi-realistic TaiwanVVM simulations, which cover the entire area of Taiwan, to investigate this phenomenon. Our findings reveal that when buoyancy is defined using a conventional environmental scale (109 km), the cold pool locations do not align with the precipitation areas, instead being concentrated mainly along the mountain ridges. We hypothesize that this discrepancy arises from the environmental scale at which cold pool buoyancy operates. To assess this, we conducted systematic analyses and the results show that an optimal environmental scale of approximately 7 km to 11 km (about 3 times of the 75th and 90th percentile of the precipitation object length) can be identified. The statistics of cold pool frequency better align with precipitation hotspots, characterized by evaporative cooling over the plains and increased water loading within the core of precipitation objects over the mountains. We demonstrate that this method effectively captures the shift in cold pools associated with precipitation responses in a warming climate in Taiwan. This work highlights the importance of using an appropriate environmental scale when estimating buoyancy over complex topography.