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  • Kunkel, K.E., X.-Z. Liang, J. Zhu, and Y. Lin, 2006: Can CGCMs simulate the Twentieth Century “warming hole” in the central United States. J. Climate, 19, 4137–4153.

The observed lack of 20th Century warming in the central United States (CUS), denoted here as the “warming hole”, was examined in 55 simulations driven by external historical forcings and in 19 pre-industrial control (unforced) simulations from 18 coupled general circulation models (CGCMs). 20th Century CUS trends were positive for the great majority of simulations, but were negative, as observed, for 7 simulations. Only a few simulations exhibited the observed rapid rate of warming (cooling) during 1901-1940 (1940-1979). Those models with multiple runs (identical forcing but different initial conditions) showed considerable intra-model variability with trends varying by up to 1.8°C/century, suggesting that the historical forcings did not produce consistent trends while internal dynamic variability played a major role at the regional scale. The wide range of trend outcomes, particularly for those models with multiple runs, and the small number of simulations similar to observations in both the forced and unforced experiments suggest that the warming hole is not a robust response to the estimated external forcings; a more likely explanation is an unusually large realization of internal dynamic variability combined with external forcing.
The observed CUS temperature variations are positively correlated with north Atlantic (NA) sea surface temperatures (SSTs) and both NA SSTs and CUS temperature are negatively correlated with central equatorial Pacific (CEP) SSTs. Most models simulate rather well the connection between CUS temperature and NA SSTs. However, the teleconnections between NA and CEP SSTS and between CEP SSTs and CUS temperature are poorly simulated and the models produce substantially less NA SST variability than observed, perhaps hampering their ability to reproduce the warming hole.


Last Updated: 2007-02-27

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