Detection and Adjustment of Undocumented Discontinuities
in Chinese Temperature Series Using a Composite Approach |
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Authors: | LI Qingxiang and DONG Wenjie |
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Institution: | Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100049;
National Meteorological Information Center, China Meteorological Administration, Beijing 100081;Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100049; State Key Laboratory of Earth Surface Processes and Ecology Resource, Beijing Normal University, Beijing 100875 |
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Abstract: | Annually averaged daily maximum and minimum surface temperatures from southeastern China
were evaluated for artificial discontinuities using three different tests for undocumented changepoints.
Changepoints in the time series were identified by comparing each target series to a reference
calculated from values observed at a number of nearby stations. Under the assumption that no trend
was present in the sequence of target-reference temperature differences, a changepoint was assigned
to the target series when at least two of the three tests rejected the null hypothesis of no
changepoint at approximately the same position in the difference series. Each target series then
was adjusted using a procedure that accounts for discontinuities in average temperature values from
nearby stations that otherwise could bias estimates of the magnitude of the target series step change.
A spatial comparison of linear temperature trends in the adjusted annual temperature series suggests
that major relative discontinuities were removed in the homogenization process. A greater number of
relative change points were detected in annual average minimum than in average maximum temperature
series. Some evidence is presented which suggests that minimum surface temperature fields may be
more sensitive to changes in measurement practice than maximum temperature fields. In addition,
given previous evidence of urban heat island (i.e., local) trends in this region, the assumption
of no slope in a target-reference difference series is likely to be violated more frequently in
minimum than in maximum temperature series. Consequently, there may be greater potential to
confound trend and step changes in minimum temperature series. |
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Keywords: | temperature series China urban heat island changepoints |
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