Simulation of secular temperature trends in the stratosphere, mesosphere and lower thermosphere

Abstract:

Anthropogenic emissions of greenhouse gases (GHG) warm the troposphere and cool the upper layers of the atmosphere above about 100 hPa. The pattern of temperature change with altitude depends, not just on the rate of emission of GHG, but also on changes in ozone brought about by decreases in the halogen burden of the atmosphere and by the changing temperature itself. We use the Whole Atmosphere Community Climate Model (WACCM) to investigate secular trends in temperature over the last 30 years and to project these changes into the rest of the 21st century. We compare model results against observations and show that WACCM reproduces many details of the observed trends, including the region of small or insignificant temperature trends near the mesopause; these changes may be understood in terms of the interplay among GHG, ozone, temperature, and the global circulation. The vertical profile of the temperature trend changes substantially in the course of the 21st century compared to the last 30 years as ozone responds to the curtailment of halogen emissions and as changing temperatures modify its photochemical equilibrium concentration.