A review of homogenisation procedures
Mestre, O.
Many long instrumental climate records are available and can provide useful information in climate research. These datasets are essential since they are the basis of the description of the past climate. But in most cases, these series are altered by changes in the measurement conditions, such as evolution of the instrumentation, relocation of the measurement site, modification of the surroundings, instrumental inaccuracies, poor installation, and observational and calculation rules. These modifications manifest themselves as shifts (inhomogeneities) in the time series. As these artificial shifts often have the same magnitude as the climate signal, such as long-term variations, trends or cycles, a direct analysis of the raw data series might lead to wrong conclusions about climate evolution. A homogenisation method is a procedure that allows the detection and removal of possible effects of artificial changes in the measuring conditions. The problem at hand is tackled in two steps, detection of the inhomogeneities and correction of the series. We provide a review of the various methods currently used, with their advantages and drawbacks, including techniques for daily data.
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