[A-AS06] Stratosphere-troposphere Processes And their Role in Climate

[AAS06-04] Study for influence of temperature at TTL on evolution of deep convection and tropical cyclones

Kenta Kobayashi¹, *Nawo Eguchi¹, Tomoe Nasuno², Yohei Yamada², Kunihiko Kodera³ (1.Kyushu University, 2.JAMSTEC, 3.Meteorological Research Institute)

Keywords:Stratosphere-Troposphere Interaction, Tropical cyclone

Previous studies based on satellite observation and general circulation model found the increase of tropical cyclone number/magnitude during a Stratospheric Sudden Warming (SSW) event [e.g., Kodera et al., ACP, 2015; Noguchi et al., GRL, 2020]. One of key factors for enhancement of deep convection and tropical cyclone is the temperature decrease at tropical tropopause layer (TTL). We evaluated the influence of stratospheric dynamical change through temperature change at TTL on the genesis/evolution of deep convection and tropical cyclones by the ensemble simulation from a global nonhydrostatic model, NICAM (Nonhydrostatic ICosahedral Atmospheric Model) [Satoh, et al., 2014] which explicitly calculates moist physics at a cloud-system-resolving resolution. We used the high-top NICAM version, approximately 50km altitude, the vertical layer is 78 number and the vertical resolution around TTL is about 380 m. The analysis period is August - September, 2019 when the tropical cyclone occurred frequently from late August to beginning September and the SSW occurred in Southern Hemisphere.

The ensemble simulation was taken each calculation with 12-hourly shifted from 00UTC 23 to 12UTC 26 August, 2019. The temperature at the tropical lower stratosphere decrease small before 24 August simulation and large after 25 August simulation [Yamada et al., personal communication], the difference is about 1 degree C on tropical average at 100 hPa. We usage the difference of temperature at TTL to analyze the change of deep convection and tropical cyclone. We mainly analyze the simulation between 00UTC 23 and 00UTC 25 Aug. From the analysis of dynamical field (geopotential height), the simulation of 25 Aug could find the amplification of planetary wave at the stratosphere, but not find that in the simulation of 23 Aug. The dynamical activation in the stratosphere enhanced the Brewer-Dobson circulation and the heat flux in 25 Aug simulation was larger than in 23 Aug simulation, in addition the temperature at TTL decrease visibly in the 25 Aug simulation. The convective activity was enhanced around 10N after the onset of SSW and six tropical cyclones occurred in the 25 Aug simulation, but two cyclones occurred in the 23 Aug simulation.