Coupled Modes of SST-Precipitation Variability in Observations, Atmospheric GCMs, and Coupled GCMs

It is well established that the atmosphere and ocean are a coupled system. However, the degree to which teleconnections between precipitation and SST anomalies represent two-way ocean-atmosphere coupling versus a forced (one-way) response to anomalous SST boundary forcing remains an open question. Here we use singular value decomposition (SVD) to identify coupled modes of global SST-precipitation variability in 20th century observations, atmospheric simulations forced with observed SST (AMIP-type simulations), and coupled (ocean-atmosphere) 20th century simulations from the IPCC Fourth Assessment Report. Atmospheric simulations forced with observed SST are shown to reproduce quite well both the spatial structure and temporal relationships of the leading coupled modes of observed SST and precipitation variability. By contrast, coupled models exhibit substantial biases in both spatial and temporal characteristics; biases are shown to arise predominately from biases in simulated SST fields. Thus while ocean-atmosphere coupling influences the development and timescale of SST anomalies, particularly in the tropics, our results suggest that precipitation teleconnections are largely a forced response to anomalous SST boundary forcing. In addition, the substantial biases in simulated modes of SST-precipitation variability in coupled climate simulations identified here suggest that these models are not directly applicable to predicting changes in precipitation teleconnections associated with global warming. Results are discussed in the context of long-range precipitation and drought prediction and global climate change.