Tropical cyclones have strong impact on the extreme precipitation and drought over the East Asia and Taiwan region. To improve the TC land-falling frequency simulation over the Asian East Coast, this study systematically investigated the impact of high horizontal resolution in the simulation of TC land-falling frequency over the Asian East Coast from High Resolution Model (HiRAM) at 25 km and 50 km horizontal resolutions. Ensemble (simple average) HiRAM-50km simulation overestimate the TC genesis numbers over the western North Pacific (WNP). Through GPI estimation, we found that the overestimation of GPI and TC genesis numbers by ensemble HiRAM-50km simulation were mainly contributed by the overestimation of mid-level relative humidity. The overestimation of low-level cyclonic vorticity and mid-level ascending motion play a secondary role. HiRAM-25km model not only improved the mid-level relative humidity simulation, but also improved the low-level monsoon and subtropical high simulation which lead to more accurate TC genesis location and frequency simulation. The spatial distribution of TC track frequency over the WNP was well captured by ensemble HiRAM-50km and 25km simulations. Observed and simulated TC main tracks were mainly steered by large-scale environmental flows and could be divided into three main land-falling regions: South China Sea region including part of Philippines (SCS), Taiwan and the coastal areas of East China (TWCN), and the vicinity of Japan (JP). TC land-falling frequency in the TWCN region was well captured by ensemble HiRAM-50km and 25km simulations. However, ensemble-50km and 25 km simulations underestimated land-falling frequency in SCS, while significantly overestimated the land-falling frequency in JP. The former was attributed to the weaker subtropical high steering flow simulated by Ensemble-50km model which induced the westerly anomalous steering flows and further restricts TC to propagate westward into SCS region. On the other hand, the weaker (stronger) subtropical high steering (monsoon) flow lead to more TC formation in the WNP, eastward shifting in TC genesis location and more recurving tracks moving to JP region. HiRAM-25km model improved the TC land-falling frequency simulation in JP by improving the simulation in TC genesis frequency and steering flows.
|Effective start/end date||2019/08/01 → 2021/07/31|
- Genesis Potential Index (GPI)
- Tropical cyclone Land-falling frequency
- Steering Flow
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