2019年夏季の熱帯低気圧の発生・発達への成層圏力学場の影響

Abstract

This study investigates the impacts of stratospheric dynamical change on the tropical convections and cyclones (TCs) by using a global nonhydrostatic global model (NICAM). Eight numerical experiments which were initialized from 0000 UTC on August 23 to 1200 UTC August 26 in 2019 at 12-hour intervals were conducted to examine possible impacts of a sudden stratospheric warming (SSW) event. In the experiments with later initial dates (25 and 26 Aug), the temperature at the upper troposphere and lower stratosphere in the tropics (Tropical Tropopause Layer; TTL) decreased larger than that in the experiments with earlier initial dates (23 and 24 Aug). In the former, the connection between the Hadley circulation and the stratospheric Brewer-Dobson circulation was clear when the TTL temperature dropped, and cumulus convection became active around 12ºN. It was also suggested that the strengthening of the Hadley circulation strengthened the subtropical high, which affected the course of TCs.