The development of the Antarctic ozone hole over the late 20th century has not only been linked to climate trends at stratospheric levels but also to a poleward shift in the Southern Hemisphere (SH) mid-latitude tropospheric jet stream during summer months. This study provides the first attempt to quantify the changes in the clouds and radiation budget associated with the poleward shift in the tropospheric circulation. Single forcing climate model integrations are performed using the Community Atmosphere Model (CAM3), in which only stratospheric ozone depletion is specified. The results indicate that 1) high- and mid-level clouds closely follow the poleward shift in the SH mid-latitude jet and 2) low-level clouds decrease across most of the Southern Ocean. The hemispherically averaged radiation anomaly associated with the cloud changes is calculated to be approximately +0.25 W m-2, which arises largely from the reduction of the total cloud fraction at mid-latitudes.
These dynamically induced cloud and radiation anomalies are considerable and may be an important “indirect effect” of the ozone hole. However, the results are highly model dependent. An examination of the cloud-radiative anomalies from 20 global climate models from the Coupled Model Intercomparison Project (CMIP5) reveals two distinct model behaviors. The first class of CMIP5 models, like CAM3, possesses a strong cloud-induced warming effect in association with a poleward jet shift in the SH.
In contrast, the second class of CMIP5 models does not include this effect. Observational analysis of two independent satellite data sets reveals that the behavior of the second class of CMIP5 models (i.e., those without the “indirect effect”) is more realistic. Implications of these model biases for historical and future climate projections will be discussed.