Drivers and surface signal of inter‐annual variability of boreal stratospheric final warmings
Résumé
Springtime stratospheric final warming (SFW) variability has been suggested to be linked to the tropospheric circulation, particularly over the North Atlantic sector. These findings, however, are based on reanalysis data that cover a rather short period of time (1979‐present). The present work aims to improve the understanding of drivers, trends and surface impact of dynamical variability of boreal SFWs using chemistry‐climate models. We use multi‐decadal integrations of the fully coupled chemistry‐climate models CESM1(WACCM) and EMAC‐O. Four sensitivity experiments are analyzed to assess the impact of external factors; namely the Quasi‐Biennial Oscillation (QBO), sea surface temperature (SST) variability and anthropogenic emissions. SFWs are classified into two types with respect to their vertical development; i.e. events which occur first in the mid‐stratosphere (10‐hPa first SFWs) or first in the upper stratosphere (1‐hPa first SFWs). Our results confirm previous reanalysis results regarding the differences in the time evolution of stratospheric conditions and near‐surface circulation between 10‐hPa and 1‐hPa first SFWs. Additionally, a tripolar SST pattern is, for the first time, identified over the North Atlantic in spring months related to the SFW variability. Our analysis of the influence of remote modulators on SFWs revealed that the occurrence of major warmings in the previous winter favors the occurrence of 10‐hPa first SFWs later on. We further found that QBO and SST variability significantly affect the ratio between 1‐hPa first and 10‐hPa first SFWs. Finally, our results suggest that ozone recovery may impact the timing of the occurrence of 1‐hPa first SFWs.
Origine : Fichiers produits par l'(les) auteur(s)