Robust Multi-Year Predictability on Continental Scales




Jia, Liwei

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This study identi es natural, unforced predictable components of surface air temperature (SAT) and precipitation in six continents from pre-industrial control runs of the Coupled Model Intercomparison Project phase 3 data set. The externally forced components of continental SAT also are identi ed by maximizing the variance ratio in the 20th century runs to the control runs. The leading unforced predictable components can be predicted in independent control runs with statistically signi cant skill for 3-6 years in SAT and 1-3 years in precipitation, depending on continent, using a linear regression model with global sea surface temperature (SST) as predictor. The leading unforced predictable components of SAT are related to ENSO and the persistence of SSTs near the continent itself. The only exception is Europe, which has no signi cant ENSO relation. The leading unforced predictable components of precipitation are signi cantly correlated with an ENSO-like SST pattern. No unforced predictability of land precipitation could be found in Europe. There is only one signi cant forced pattern of SAT in each continent. The largest amplitudes of these forced patterns concentrate in high latitudes. No signi cant forced pattern of continental precipitation could be identi ed on a multi-model basis. Although the forced and unforced patterns of SAT are identi ed in model simulations, they are not separable in the observations, presumably because of the large similarity between them.



Multi_Year, Predictability, Continental, Land, Climate