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Detecting inhomogeneities in the Twentieth Century Reanalysis over the central United States
Journal of Geophysical Research, 117 (D5): D05123+ (10.03.2012)
DOI: 10.1029/2011jd016988
Аннотация
The Twentieth Century Reanalysis (20CR), which spans the 138 year period from 1871 to 2008, was intended for a variety of
climate applications, including long-term trend assessment. Because over land 20CR only assimilates surface pressure observations
and their count increases by an order of magnitude over the course of the record, a key question is whether the 20CR is homogenous
and hence suitable for detecting climate-related changes. We use three statistical methods (Pettitt and Bai-Perron tests and
segmented regression) to detect abrupt shifts in multiple hydrometeorological variable mean and uncertainty fields over the
central United States. For surface air temperature and precipitation, we use the Climate Research Unit (CRU) time series data
set for comparison. We find that for warm-season months, there is a consensus change point among all variables between 1940
and 1950, which is not substantiated by the CRU record. While we cannot say with certainty that these shifts in the 20CR analysis
fields are artificial, our statistical analyses, coupled with a visual inspection of the underlying assimilated observational
count time series, strongly point to this conclusion. Our recommendation is therefore for users to restrict climate trend
applications over the central United States to the second half century of the 20CR record, after observational density has
stabilized.
