A study of teleconnections in state-of-the-art seasonal forecast systems

We describe some of the seasonal forecasting activities taking place at ECMWF since the implementation of SEAS5, ECMWF's fifth generation seasonal forecast system. Compared to SEAS5's tropical SST and precipitation prediction skill, prediction of variability over the North Atlantic and Europe remains challenging. This motivates an analysis of winter tropical to extratropical teleconnections in SEAS5 and other models from the Copernicus Climate Change Service's (C3S) multi-system seasonal forecast.

Following the Molteni et al. (2015) study of teleconnections in a previous ECMWF seasonal forecast model, we study the covariance of northern hemisphere Z500 with tropical precipitation indices. Most models successfully represent the covariance of precipitation in the Nino4 region with Z500 over the North Pacific and North America, but only some have the correct pattern over the North Atlantic and Europe. Representing the covariance with Indian Ocean precipitation is more challenging for the models. We further explore these results by using techniques such as EOFs to separate modes of precipitation variability in the Pacific and Indian Ocean and analyse their teleconnection patterns. We will also briefly summarize other research and development at ECMWF that will contribute to the next seasonal forecast system.