Linkages of Changes in Ozone to Arctic Climate Change in the Stratosphere and Troposphere

Stratospheric ozone depletion is a well-known phenomenon, largely because of the Antarctic ozone hole and concerns over adverse effects on ecosystems and human health. But ozone depletion also occurs in the Arctic stratosphere, where reductions of 10% to 20% can be seen in satellite data, for example in differences between the means for years 2000 to 2005 and 1979 to 1984. Unlike the Antarctic, where a single ozone hole extends from altitudes below 15km to above 20km, Arctic ozone depletion has two distinct maxima, one in the upper stratosphere between 35km and 45km (roughly 5mb to 1mb) and one in the lower stratosphere between 10 and 15km (roughly 200 to 100mb). Research by the PIs and others has produced compelling evidence that the Antarctic ozone hole has produced substantial changes in the climate and atmospheric circulation of the stratosphere and troposphere. These changes include stratospheric cooling and a southward shift of the westerly winds around Antarctica that extends from the stratosphere to the Earth's surface. However, analogous climate and circulation impacts of the more subtle Arctic ozone depletion have not been identified, owing partly to lack of research effort and partly to discrepancies in the satellite-derived ozone estimates over the Arctic.

Work conducted here addresses the impact of Arctic stratospheric ozone loss by combining three satellite derived datasets with stand-alone radiative transfer codes and the Whole Atmosphere Community Climate Model (WACCM), an atmospheric circulation model with a well-resolved stratosphere and optional stratospheric ozone chemistry. The first stage of the research is to use radiative transfer models to calculate radiative heating rates from the ozone concentrations found in the three observational datasets, in order to determine the magnitude of the heating and the extent to which differences in ozone concentrations yield differences in heating.

These radiative heating calculations are followed by WACCM simulations in which the ozone concentrations from the three datasets are be imposed, using the Specified Chemistry version of WACCM. Experiments will be performed using ozone changes restricted to the stratosphere above and below 10mb, to determine the extent to which ozone changes in the upper stratosphere affect the lower stratosphere and the extent to which upper- and lower-level heating affect the troposphere. These experiments are motivated by the dual-maximum structure of the ozone depletion. Finally, WACCM will be integrated with interactive gas-phase chemistry, so that the model can simulate ozone loss internally, allowing the ozone chemistry to be affected by the temperature and circulation changes which it produces.

The research seeks to develop a better understanding of the mechanisms driving for climate variability and change in the Arctic, and the Arctic climate change has broad linkages to societally-relevant impacts on ecosystems, the cryosphere, and human activities in the Arctic. Moreover, changes in atmospheric circulation over the Arctic can have substantial consequences for the weather and climate of the middle latitudes of the Northern Hemisphere. In addition, the project provides support and training for a graduate student, thereby providing for the next generation of scientists working in this area.