The Predictability of Stratospheric Warming Events: More from the Troposphere or the Stratosphere?

Abstract

he roles of the stratosphere and the troposphere in determining the predictability of stratospheric final warming and sudden warming events are evaluated in an idealized atmospheric model. For each stratospheric warming event simulated in the model, a number of forecast experiments are performed from 10 or 20 days prior to the warming onset with perturbations in the troposphere and in the stratosphere separately. It is found that the stratosphere affects predictions of warming onset primarily by providing the initial state of the zonal winds, while the tropospheric initial conditions have a large impact through the generation and propagation of planetary waves. These results correspond to the roles played by the initial zonal flow and the evolution of eddy forcings in a zonally symmetric model. The initial stratospheric zonal flow has some influence on stratospheric wave driving, but in most cases this does not significantly affect the timing of the warming, except when the initial condition is close to the onset date. These results highlight the role of the troposphere in determining stratospheric planetary wave driving and support the importance of tropospheric precursors to the stratospheric warming events.