Analysis of the Genesis of Tropical Cyclones Simulated by SAM0-UNICON

Most of extreme precipitation events on the Earth are associated with tropical cyclones (TC). To obtain insights into the large-scale environmental conditions responsible for the genesis of tropical cyclones, we analyzed tropical cyclones simulated by the Seoul National University Atmosphere Model Version 0 with a Unified Convention Scheme (SAM0-UNICON) at the 0.5°lat x 0.5°lon resolution for 100 years over the globe. The UNICON (Unified Convection Scheme) is a subgrid convection scheme that can simulate all dry-moist, forced-free, and shallow-deep convection in a seamless, consistent and unified way. UNICON consists of diagnostic multiple convective updrafts, diagnostic multiple convective downdrafts, and prognostic subgrid cold pool and associated mesoscale organized flow. Previous studies showed that without degrading the mean climate, UNICON successfully simulates the observed Madden-Julian Oscillation, diurnal cycle of precipitation, and tropical cyclones, all of which are known to be notoriously difficult to be simulated in typical GCMs.

At every 6-hour, we first identified the embryo vortex (EV) that has persisted for one day with the 850 hPa relative vorticity, ξ₈₅₀ ≥ 2 CVU (where 1 CVU = 10^-5 [s^-1]) and then computed composite anomalies of various environmental conditions at the 2.5°lat x 2.5°lon resolution for the EVs that evolve into the TC stage with persisting ξ₈₅₀ ≥ 20 CVU (e.g., strong cyclonic vortex) and ξ₈₅₀ - ξ₂₅₀ ≥ 20 CVU (e.g., strong warm core) at least for two days. Following previous studies, the environmental variables are grouped into the four categories characterizing vortex dynamics, atmospheric moisture, vertical instability, and vertical wind shear. The dependency of simulated TC genesis on these environmental variables, including geographical variations of these dependency, will be shown.