Workshop: Stratospheric predictability and impact on the troposphere

Influence of stratospheric circulation changes related to sudden stratospheric warmings (SSW) on the tropical troposphere have been examined in many previous studies. However, due to small sample size of SSW and large internal variability in the tropical troposphere, influence of the SSW on the tropical troposphere is still uncertain. We examine impact of the stratospheric circulation changes related to SSW on the tropical troposphere using 5,000-year scale ensemble simulations with a 60 km global atmospheric model MRI-AGCM3.2. Thousands of SSW-like circulation change events are extracted thanks to the large ensemble simulations. A composite analysis of the SSW-like events shows significant stratospheric upwelling and cooling in the tropics. Synchronized with the upwelling, significant tropospheric signals such as increased temperature and enhanced convective activity including tropical cyclone are found. Furthermore, during the events, extratropical synoptic scale waves propagate into the tropics, and appear to affect spatial distribution of convective activity.