Wave forcing in the stratosphere under doubled-CO2 conditions in a 100-year coupled chemistry-climate model study

Abstract

The impact of doubling atmospheric CO2 on the resolved-wave forcing of the stratospheric flow, and thus on the Brewer-Dobson circulation (BDC), is investigated with 100-year timeslice simulations using a chemistry-climate model, the IGCMFASTOC, coupled to a mixed-layer slab ocean. The Arctic lower stratosphere in winter warms by up to 4 K, with associated weakening of the polar vortex and enhancement of the BDC. This change is related to a significant increase in the wave forcing near the vortex core starting in January, followed by an increased wave forcing at the lower edge of the polar vortex in February. Maximum wave forcing is found both to occur earlier in the winter and to be distributed over a longer period of time in the 2 × CO2 climate. The sensitivity to surface conditions is studied by repeating the CO2-doubling experiments with prescribed interannually varying and fixed annual cycle monthly mean surface temperatures. In the absence of interannual variability, the BDC response is strongly attenuated. With interannual variability, the monthly mean prescribed surface temperatures lead to a similar dynamical response in the stratosphere as found with the interactive surface but with reduced magnitude. Copyright 2010 by the American Geophysical Union.