Interannual Variations of the Stratosphere and Troposphere during Northern Winter as Simulated by WACCM

Abstract

This study explores interannual variations (IAVs) of the stratosphere and troposphere during Northern Hemisphere (NH) winter using a 50-yr simulation of Sassi et al. with the Whole Atmosphere Community Climate Model (WACCM). The simulation is forced with observed sea surface temperature (SST) and sea ice distributions from 1950 to 1999. The focus herein is on tropical tropospheric variations correlated with NH stratospheric variations and El Niño?Southern Oscillation (ENSO). The discussed correlation analysis generally reproduces the following features as obtained in observational studies by Salby and Callaghan: an intensification of the Brewer?Dobson (BD) circulation driven by enhanced planetary wave (PW) drag in the NH stratosphere is accompanied by intensification of the Hadley circulation and anomalous warming of the tropical troposphere. It is further revealed that the tropical tropospheric warming is a reflection of the ENSO variability resulting from a positive correlation between the PW driving/BD circulation and ENSO, whereas the Hadley circulation does intensify with the BD circulation even when ENSO?s effects are removed.