The role of the stratosphere on the multi-year predictability of the climate system

Aim of this study is to examine the decadal variability and predictability of the climate system, associated with processes occurring in the stratosphere. We base our analysis on a set of near-term predictions performed with a state- of-the-art stratosphere-resolving climate models, initialized with a realistic estimate of the ocean and atmosphere. In order to fully establish the impact of a realistic model initialization, results from decadal integrations are contrasted against a twin set of historical, non-initialized, climate projections covering the same time period. The set of hindcasts used are based on the CMCC-CMS and MPI-ESM-MR coupled models. These two systems differ for the adopted initialization procedure, with the CMCC-CMS model being initialized in the ocean only, while MPI-ESM-MR model is initialized in both atmosphere and ocean. The different initialization of the model components makes it possible an analysis of the individual effects associated with atmosphere and ocean. Understanding the role played by the stratosphere on decadal scale climate predictability is a topic which has received relatively little attention, so far. Here, the decadal predictability associated with the occurrence of SSWs in the extra-tropical stratosphere, and a possible role of QBO on extra-tropical predictability will be inspected through the novel approach represented by decadal predictions.