Impact of lower stratospheric ozone on seasonal prediction systems
South African Journal of Science
South African Weather Service - Research, Pretoria, South Africa; Council for Scientific and Industrial Research, Natural Resources and the Environment, Pretoria, South Africa; Department of Geography, Geoinformatics and Meteorology, University of Pretoria, Pretoria, South Africa
We conducted a comparison of trends in lower stratospheric temperatures and summer zonal wind fields based on 27 years of reanalysis data and output from hindcast simulations using a coupled oceanatmospheric general circulation model (OAGCM). Lower stratospheric ozone in the OAGCM was relaxed to the observed climatology and increasing greenhouse gas concentrations were neglected. In the reanalysis, lower stratospheric ozone fields were better represented than in the OAGCM. The spring lower stratospheric/ upper tropospheric cooling in the polar cap observed in the reanalysis, which is caused by a direct ozone depletion in the past two decades and is in agreement with previous studies, did not appear in the OAGCM. The corresponding summer tropospheric response also differed between data sets. In the reanalysis, a statistically significant poleward trend of the summer jet position was found, whereas no such trend was found in the OAGCM. Furthermore, the jet position in the reanalysis exhibited larger interannual variability than that in the OAGCM. We conclude that these differences are caused by the absence of long-term lower stratospheric ozone changes in the OAGCM. Improper representation or non-inclusion of such ozone variability in a prediction model could adversely affect the accuracy of the predictability of summer rainfall forecasts over South Africa. © 2014. The Authors. The Authors.
accuracy assessment; annual variation; atmospheric general circulation model; climate modeling; climate prediction; data set; El Nino-Southern Oscillation; greenhouse gas; hindcasting; jet stream; oceanic general circulation model; ozone; ozone depletion; polar vortex; rainfall; seasonal variation; stratosphere; troposphere; wind field; zonal wind; South Africa