Polar Ozone Depletion and Subtropical Precipitation

Research conducted by S M Kang andcolleagues this year has further demonstrated the varied climatic influence polar ozone depletion can have; not just in Antarctica but extending to the tropics.

Kang and colleagues compared the results of four contrasting models to the observed trend in global precipitation between 1979-2000 (years in which ozone depletion has occurred). Observational data showed that in austral summer (December to February) precipitation was increasing between the latitudes 15S and 35S. 

The models were constructed using the Canadian Middle Atmosphere Model (CMAM); one was coupled with ocean-atmosphere interactions and the other uncoupled – therefore using prescribed data on sea surface temperature and other parameters. Another two models were run using the NCAR Community Atmosphere Model, again one was coupled to atmosphere-ocean processes and the other was uncoupled. This fourth model also only had the inputs of ozone depletion southwards of 40S latitude in order to clarify whether polar ozone was in fact the main driver of the results.

All four models spatially agreed with the observed trend that subtropical precipitation was increasing (Figures 1 and 2). This agreement across varying models added to the robustness of the study’s findings and interpretations, which was vital due to the model dependent nature of precipitation results. Kang’s results supported that of previous studies in suggesting a shift in the southern hemisphere’s extra tropical westerly jet stream was responsible for changes in precipitation. This shift of the jet stream (Figure 3), suggested to be caused by polar ozone depletion, alters the storm track that brings increased precipitation to areas such as eastern Australia.

The most important conclusions from this study demonstrate that the hydrological cycle of the tropics can be dramatically influenced by interactions at high latitudes. From an anthropogenic perspective, changes in weather patterns that have been caused by ozone depletion again adds to the ever increasing list of feedbacks that human activity can cause.