Interannual variations of the general circulation and polar stratospheric ozone losses in a general circulation model

Interannual variations of the general circulation and polar stratospheric ozone losses are investigated by using a general circulation model (GCM) developed at Kyushu University. The GCM includes simplified ozone photochemistry interactively coupled with radiation and dynamics in the GCM. Polar ozone depletion is brought about in the GCM by a parameterized ozone loss term. We performed an 'ozone depletion experiment' over 50 successive years with stratospheric ozone losses occuring over the Arctic and Antarctic polar regions. In addition, a 50-year 'control experiment' without such losses was also performed. Results of the ozone depletion experiment show large interannual variations of the general circulation and polar ozone losses, especially in the Northern Hemisphere winter and spring. It is found that stratosphere-troposphere coupled interannual variations are caused not only by dynamical conditions, e.g., strength of the polar vortex and planetary wave activities, but also by interaction mechanisms between dynamical and ozone depletion processes. The resultant interannual variability of the general circulation in the stratosphere becomes larger than that in the control experiment. Moreover, influences of the stratospheric polar night jet extend to the troposphere during late spring; overall three-dimensional patterns of the interannual variations in dynamical fields seem to coincide well with those of the Arctic Oscillation. On the other hand, for the Southern Hemisphere, it is found that there exists a remarkable interaction between meridional transport of ozone controlled by polar night jets and UV heating in the polar lower stratosphere. Strong and cold polar vortices lead to less ozone abundance in the polar region, resulting in less UV heating and lower temperatures, along with strengthening of the polar vortices themselves. As a result, even in the control experiment, interannual variability of ozone and temperature fields in the polar lower stratosphere is comparable to that for the ozone depletion experiment.