[A-AS06] Advances in Tropical Cyclone Research: Past, Present, and Future

[AAS06-04] NICAM Simulation Study of Large-Scale Circulation Underlying Tropical Cyclone Genesis in the Western North Pacific in September 1959 and September 2023

*Xu Chen¹, Masaki Satoh¹ (1.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords:Typhoon

Tropical cyclones (TCs) represent extremely active and inactive periods, which are closely linked with the large-scale environmental factors affected by subtropical high and monsoon. September 1959 and 2023 are good examples. Typhoons Sarah and Vera stroke Japan successively and led to enormous losses in 1959, while TCs fail to generate over the western North Pacific (WNP) for approximately 20 days in 2023. Based on reanalyses and 1-month global simulations of Nonhydrostatic Icosahedral Atmospheric Model (NICAM) with 14 km horizontal resolution, the possible physical mechanisms causing the TC genesis in September 1959 and 2023 are investigated.
NICAM succeeds in reproducing the extreme TCs in 1959, and few TC genesis in 2023. To be more specific, 3 simulated TCs over the North Pacific all exceed 45 m s^-1 in 1959, while only 2 TCs form over the WNP in the simulation of 2023. However, there exist biases on the genesis positions of TCs in 1959, which are more eastward in NICAM. This could be due to the inactive convection over the WNP basin, which needs further verification.
It is indicated in both reanalyses and NICAM simulations that subtropical high in 1959 shows a weak intensity and a small coverage, while is intense and covers a vast region over the North Pacific in 2023. In addition, reanalyses represent that convections over the WNP basin (South of Japan) are strong (weak) in the September of 1959 (2023). The combined effects of subtropical high and convection activities might result in the features of TC genesis in 1959 and 2023.