Radiative effect of ozone change on stratosphere-troposphere exchange

Abstract

The potential radiative impact of ozone changes on stratosphere-troposphere exchange (STE) is investigated by a series of climate model simulations. The impact of an arbitrary 15% O3 change on temperature, stratospheric water vapor, and cross-tropopause mass flux are compared to the corresponding effects from a doubling of atmospheric CO2. Our analysis shows that a 15% global O3 decrease can cause a maximum cooling of 2.4 K in the stratosphere and ~7.2% increase in the tropical upwelling. This cooling also results in a higher tropical tropopause and lower tropopause temperatures, and hence less stratospheric water vapor and smaller amplitude of the so-called tape recorder signal. A global 15% O3 increase gives rise to ~2.1 K stratospheric warming and ~4% decrease in the tropical upwelling. This O3 increase results in more water vapor entering the stratosphere owing to a lower tropopause and higher tropopause temperatures. The effect of a ±15% change in O3 below 100 hPa is relatively small. However, the effect of a 15% O3 increase between 200 and 70 hPa is similar to that of a 15% O3 increase through the whole domain, suggesting that ozone increases in the UTLS dominate the impacts on temperature and tropical upwelling. Sea surface temperature (SST) changes associated with increasing atmospheric greenhouse gases (GHG) have a profound impact on the STE. Without corresponding SST changes, the radiative effects of the CO2 doubling on the STE is less significant than a global 15% O3 increase. When the SST changes are considered in the doubled CO2 experiment, the tropical upwelling is significantly increased (by 20.4%) with a much higher, but warmer, tropopause. Copyright 2008 by the American Geophysical Union.