Chemistry-climate model simulations of twenty-first century stratospheric climate and circulation changes

In the Antarctic lower stratosphere the models simulate an increase in low temperature extremes required for polar stratospheric cloud (PSC) formation, but the positive trend is decreasing over the twenty-first century in all models. In the Arctic, none of the models simulates a statistically significant increase in Arctic PSCs throughout the twenty-first century. The subtropical jets accelerate in response to climate change and the ozone recovery produces a westward acceleration of the lower-stratospheric wind over the Antarctic during summer, though this response is sensitive to the rate of recovery projected by the models.

There is a strengthening of the Brewer-Dobson circulation throughout the depth of the stratosphere, which reduces the mean age of air nearly everywhere at a rate of about 0.05 yr decade⁻¹ in those models with this diagnostic. On average, the annual mean tropical upwelling in the lower stratosphere (70 hPa) increases by almost 2% decade⁻¹, with 59% of this trend forced by the parameterized orographic gravity wave drag in the models.

This is a consequence of the eastward acceleration of the subtropical jets, which increases the upward flux of (parameterized) momentum reaching the lower stratosphere in these latitudes.