Distortion Effects of the Anomaly Method of Removing Seasonal or Diurnal Variations from Climatological Time Series

Abstract

In the environmental sciences, observations time series usually include important contributions from the annual and daily variations. A commonly used procedure to eliminate these cycles is a form of prewhitening known as the ?anomaly? method. This method is shown to be equivalent to a digital filtering process. An expression is derived for the corresponding response function that shows that for short time series the anomaly method introduces spurious modifications to the residual series. Use of the method is best avoided when only a small number of cycles is included in the sample.