Combined Modes of the Northern Stratosphere, Tropical Oceans, and East Asian Spring Rainfall: A Novel Method to Improve Seasonal Forecasts of Precipitation

Seasonal forecasting models have a harder time accurately predicting regional precipitation anomalies in East Asia than the large-scale drivers of these precipitation anomalies. These large-scale drivers include both sea surface temperature (SST) anomalies and conditions in the polar stratosphere. A maximum covariance analysis is used to isolate the SST and stratospheric patterns most associated with anomalous East Asian precipitation, which are employed to correct seasonal forecasts by projecting the forecasted stratospheric circulation and SST onto the observed combined modes. The nonuniform predictability of East Asian rainfall in seasonal forecast models is improved after error correction with the observed linkage between the stratosphere–tropical ocean modes and East Asian rainfall. This method should be helpful for improving rainfall forecasts in other regions as well.