Preconditioning for stratospheric sudden warmings - Sensitivity studies with a numerical model

The phenomenon of preconditioning for sudden stratospheric warming events is investigated using a 3D primitive equation model adapted from the model used by Rose and Brasseur (1989). In order to identify the conditions that make the flow preconditioned, the model was initialized alternately with observed and with artificially constructed 'hybrid' stratospheric flow patterns. Two observed warmings were investigated, February 1979 and February 1989. The artificially constructed hybrid flow fields used upper-level winds (above 10 mb) from one period and lower-level winds (below 10 mb) from another. The results of model simulations indicate that the flow in the lower and middle stratosphere is capable of serving as a predictor of the potential for a major sudden warming, with the occurrence of a warming depending only on the lower-level winds.