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  • DelSole, T., 2006: Low-Frequency Variations of Surface Temperature in Observations and Simulations. J. Climate, 19, 4487-4507.

This paper documents the low-frequency (i.e., decadal) variations of surface temperature
for the period 1899-1998 in observations, and in simulations conducted as part of the
Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The
space-time structure of low-frequency variations are extracted using Optimal Persistence
Analysis, which is a technique that linearly decomposes a vector time series into a set of
uncorrelated components, ordered such that the first component maximizes the decorrelation
time, the second maximizes the decorrelation time subject to being uncorrelated with the first,
and so on. The results suggests that only the first two optimal persistence patterns (OPPs) in the
observation-based record are statistically distinguishable from white noise. These two
components can reproduce the spatial structure of local linear trends over various multi-decadal
periods, indicating that they give an efficient representation of the observed change in surface
temperature. In contrast, most simulations suggest the existence of a single physically significant
OPP, all with qualitatively similar time series but each with somewhat different spatial structure.
The leading OPP computed from the full model grid, and from the observation based grid and
missing data masked out, are surprisingly consistent with each other, suggesting that the
observation-based grid does not pose a serious barrier to extracting the dominant low-frequency
variations in the global climate system. The regions in which the leading optimal persistence
patterns agree in their predictions of warming coincides with the regions in which warming has
in fact been observed to occur.


Last Updated: 2007-09-06

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