The Impact of Tropical Forcing on Extratropical Predictability in a Simple Global Model

The impact of tropical forcing on the predictability of the extratropical atmosphere is studied. Using a two-layer spectral model, numerical experiments and diagnostic analyses have been carried out to examine the enhancement of predictability gained through knowledge of the tropical forcing. It turns out that knowing the tropical forcing induces a modest but significant improvement in extended-range predictions in middle/high latitudes. Ale enhancement of predictability can be locally large in a zonally asymmetric climate. A robust response to tropical forcing in the model, however, does not necessarily imply a strong impact on extratropical predictions.