The predictability of stratospheric warming events: More from the troposphere or the stratosphere?

The relative roles of the stratosphere and the troposphere in determining the predictability of Southern and Northern Hemisphere-like stratospheric final warming events and stratospheric sudden warming events are evaluated in an idealized dynamical model. Initial conditions 10 and 20 days prior to warming events are separately perturbed in the troposphere and the stratosphere. It is found that the stratosphere affects predictions of warming onset prediction primarily by providing the initial state of the zonal winds, while the troposphere has a large impact through the generation and propagation of planetary waves. These results correspond to the roles played by the initial conditions and eddy forcings in a zonally symmetric version of the model. The initial stratospheric zonal flow influences stratospheric wave driving, but generally this does not significantly affect the timing of the the warming onset, except for initial conditions very 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 events.