12:00 〜 12:15
[AAS02-06] Influence of Sea Surface Temperature on the Extreme Tropical Cyclones over the Western North Pacific in 1959
キーワード：熱帯低気圧、数値シミュレーション、極端現象、気候力学、非静力学正20面体格子大気モデル
Extreme tropical cyclones (TCs) are closely related to secondary disasters such as landslides and debris flows, leading to huge losses of lives and properties. Therefore, it is significant to have a better understanding of the physical mechanisms of extreme TCs. In August–October of 1959, five Category 5 (C5) TCs generated in the western North Pacific. Among these TCs, Typhoons Joan, Sarah, and Vera struck Taiwan, South Korea, and Japan, respectively, causing substantial damage. Based on the International Best Track Archive for Climate Stewardship (IBTrACS), it is shown that C5 TC records account for 14.6% of all TC records in 1959, ranked first in history. Further analysis indicates that both enhanced C5 TC number and increased mean duration in C5 stages are main contributors. However, it still remains to be investigated whether numerical models could reproduce extreme TCs in 1959, as well as how large-scale environments lead to these extreme TCs.
According to the correlation maps between sea surface temperature (SST) anomaly (SSTA) and Category 5 TC characteristics, including total duration, number, and mean duration, it is shown that warming in the central Pacific, as well as cooling in the South China Sea and Bay of Bengal, might be responsible for extreme TCs. Hence, utilizing the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), four 3-month numerical experiments with 5 ensemble members are designed: (1) HIST experiment, with 1951-1980 climatology SST; (2) REAL experiment, with 1959 SST; (3) CPW experiment, with 1959 SST in the central Pacific region (15°S–30°N, 160°E–100°W, warming in the region) but 1951-1980 SST in other regions; (4) ZDIF experiment, with 1959 SST in the central Pacific region (15°S–30°N, 160°E–100°W, warming in the region) and South China Sea-Bay of Bengal region (15°S–25°N, 85°E–140°E, cooling in the region) but 1951-1980 SST in other regions. Here, experiments 1–2 aim to investigate whether NICAM could reproduce extreme TCs in 1959, while experiments 3–4 attempt to find the key SSTA regions that contribute to extreme TCs.
The simulation results of HIST and REAL experiments demonstrate that NICAM successfully reproduces extreme TCs in 1959. The percentage of <950 hPa TC records in the REAL experiment is 12.6%, significantly exceeding the 7.1% in the HIST experiment. Meanwhile, accumulated cyclone energy, extreme TC number, and mean duration represent similar results. However, in the CPW and ZDIF experiments, the frequent occurrences of extreme TCs are not observed. This could be due to large ensemble spread or because chosen regions are not the most responsible for the extreme TCs. In the REAL experiment, TC genesis is mainly over the southeastern part of the western North Pacific basin, which could be well explained by the genesis potential index and dynamic genesis potential index. In terms of TC intensification, the increase in low-level vorticity and the decrease in vertical wind shear in the main developing regions of extreme TCs may be the main contributors.
According to the correlation maps between sea surface temperature (SST) anomaly (SSTA) and Category 5 TC characteristics, including total duration, number, and mean duration, it is shown that warming in the central Pacific, as well as cooling in the South China Sea and Bay of Bengal, might be responsible for extreme TCs. Hence, utilizing the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), four 3-month numerical experiments with 5 ensemble members are designed: (1) HIST experiment, with 1951-1980 climatology SST; (2) REAL experiment, with 1959 SST; (3) CPW experiment, with 1959 SST in the central Pacific region (15°S–30°N, 160°E–100°W, warming in the region) but 1951-1980 SST in other regions; (4) ZDIF experiment, with 1959 SST in the central Pacific region (15°S–30°N, 160°E–100°W, warming in the region) and South China Sea-Bay of Bengal region (15°S–25°N, 85°E–140°E, cooling in the region) but 1951-1980 SST in other regions. Here, experiments 1–2 aim to investigate whether NICAM could reproduce extreme TCs in 1959, while experiments 3–4 attempt to find the key SSTA regions that contribute to extreme TCs.
The simulation results of HIST and REAL experiments demonstrate that NICAM successfully reproduces extreme TCs in 1959. The percentage of <950 hPa TC records in the REAL experiment is 12.6%, significantly exceeding the 7.1% in the HIST experiment. Meanwhile, accumulated cyclone energy, extreme TC number, and mean duration represent similar results. However, in the CPW and ZDIF experiments, the frequent occurrences of extreme TCs are not observed. This could be due to large ensemble spread or because chosen regions are not the most responsible for the extreme TCs. In the REAL experiment, TC genesis is mainly over the southeastern part of the western North Pacific basin, which could be well explained by the genesis potential index and dynamic genesis potential index. In terms of TC intensification, the increase in low-level vorticity and the decrease in vertical wind shear in the main developing regions of extreme TCs may be the main contributors.