The atmospheric response to variations in tropical latent heating extends well beyond its source region, and therefore it is thought that a reduction of tropical forecast errors should also benefit subsequent forecasts over the extratropics. In this presentation, we employ the use of “relaxation experiments” to quantify the remote influence of tropical forecast errors, which is implemented on the National Centers for Environmental Prediction (NCEP) unified forecast system (UFS). This approach involves nudging forecasts towards reanalyses over a tropical region, while allowing the model to run freely elsewhere. By comparing nudged to free running forecasts, this type of experiment generally shows that midlatitude forecasts are improved in association with reducing tropical forecast errors. For example, Week 2-4 forecast errors over the North Pacific and North America in particular are reduced by tropical nudging. The sensitivity of changes in remote forecast errors to nudging parameters is discussed with focus on the location of the nudging region as well as on which state variables are nudged. In addition, potential modulations of the pattern and amplitude of remote error reductions by ENSO as well as by the Madden Julian oscillation are investigated.
