Evaluation of the CFSv2 45 day forecasts to capture stratospheric events and usefulness for intra-seasonal forecasts of stratospheric winter hemispheric conditions

The NCEP Climate Forecast System version 2 (CFSv2) (Saha, 2010) is a coupled atmosphere, land, ocean model. At every 6 hour cycle the system uses the high resolution (T574L64) analysis from the CFS reanalysis to generate one 9-month lower resolution (T126L64) run and 4-45 day runs. We will present an evaluation of how well the 45-day runs are able to capture significant stratospheric events such as sudden stratospheric and final warmings in the winter hemisphere. We will evaluate how far in advance the model captures these events, their downward propagation, and influence upon the troposphere. We will also present how well the CFSv2 forecasts stratospheric conditions for subtle or enhanced ozone depletion in the SH and any ozone depletion in the NH during their respective late winter/early spring seasons. Initial results indicate that the CFSv2 only captures events once the trigger has taken place. The model does a good job thereafter, modifying the thermal and wind fields and the downward propagation. However, the model fails to extend the events across the tropopause and influence the tropospheric polar temperatures and wind fields.

Saha, Suranjana, and Coauthors, 2010: The NCEP Climate Forecast System Reanalysis. Bull. Amer. Meteor. Soc., 91, 1015.1057. doi: 10.1175/2010BAMS3001.1