Representing twentieth-century space-time climate variability. Part I: Development of a 1961-90 mean monthly terrestrial climatology

The construction of a 0.5 degrees lat x 0.5 degrees long surface climatolog y of global land areas, excluding Antarctica, is described. The climatology represents the period 1961-90 and comprises a suite of nine variables: pre cipitation, wet-day frequency, mean temperature, diurnal temperature range, vapor pressure, sunshine, cloud cover, ground frost frequency, and wind sp eed. The climate surfaces have been constructed from a new dataset of stati on 1961-90 climatological normals, numbering between 19 800 (precipitation) and 3615 (wind speed). The station data were interpolated as a function of latitude, longitude, and elevation using thin-plate splines. The accuracy of the interpolations are assessed using cross validation and by comparison with other climatologies. This new climatology represents an advance over earlier published global te rrestrial climatologies in that it is strictly constrained to the period 19 61-90, describes an extended suite of surface climate variables, explicitly incorporates elevation as a predictor variable, and contains an evaluation of regional errors associated with this and other commonly used climatolog ies. The climatology is already being used by researchers in the areas of e cosystem modelling, climate model evaluation, and climate change impact ass essment. The data are available from the Climatic Research Unit and images of all th e monthly fields can be accessed via the World Wide Web.