Long-term ozone and temperature changes in the upper stratosphere

Changes in temperature and ozone in the upper stratosphere are closely coupled. Chlorine-induced ozone loss leads to a change in short-wave heating and a reduction of temperature. However, a decrease in temperature reduces the ozone loss rate and damps the change in ozone mixing ratio. At the same time, increased greenhouse gases lead to more long-wave cooling and lower temperatures that cause an increase in ozone that damps the temperature decrease through increased short-wave heating. Simulations show that, by the end of this century, these changes together will lead to an increase in ozone above its level when man-made chlorofluorcarbons were negligible, greenhouse gas concentrations were lower, and the temperature was warmer. This overall increase in upper stratospheric ozone is termed "super-recovery".

We have examined the time evolution of the relationship between ozone and temperature in the upper stratosphere in simulations using our coupled chemistry climate model (GEOS CCM). The seasonal cycle in a given year shows a negative slope of ozone vs. temperature. The magnitude of that slope decreases from the beginning of the simulation in 1950, reaching a minimum in about 2000. After 2000, the magnitude of the negative slope again increases. This effect comes directly from chlorine-driven loss processes that have smaller temperature dependence than either nitrogen-driven or direct oxygen-driven loss processes. We will compare the time dependence of these seasonal slopes to that derived from data from the Limb Infrared Monitor of the Stratosphere on Nimbus 7, the Halogen Occultation Experiment and the Microwave Limb Sounder (MLS), both on the Upper Atmosphere Research Satellite, and the MLS on Aura.