Representing twentieth-century space-time climate variability. Part II: Development of 1901-96 monthly grids of terrestrial surface climate

The authors describe the construction of a 0.5 degrees lat-long gridded dat aset of monthly terrestrial surface climate For the period of 1901-96. The dataset comprises a suite of seven climate elements: precipitation, mean te mperature, diurnal temperature range, wet-day frequency, vapor pressure, cl oud cover, and ground frost frequency. The spatial coverage extends over al l land areas, including oceanic islands but excluding Antarctica. Fields of monthly climate anomalies, relative to the 1961-90 mean, were interpolated from surface climate data. The anomaly grids were then combined with a 196 1-90 mean monthly climatology (described in Part I) to arrive at grids of m onthly climate over the 96-yr period. The primary variables-precipitation, mean temperature, and diurnal temperat ure range-were interpolated directly from station observations. The resulti ng time series are compared with other coarser-resolution datasets of simil ar temporal extent. The remaining climatic elements, termed secondary varia bles, were interpolated from merged datasets comprising station observation s and, in regions where there were no station data, synthetic data estimate d using predictive relationships with the primary variables. These predicti ve relationships are described and evaluated. It is argued that this new dataset represents an advance over other product s because (i) it has higher spatial resolution than other datasets of simil ar temporal extent, (ii) it has longer temporal coverage than other product s of similar spatial resolution, (iii) it encompasses a more extensive suit e of surface climate variables than available elsewhere, and (iv) the const ruction method ensures that strict temporal fidelity is maintained. The dat aset should be of particular relevance to a number of applications in appli ed climatology, including large-scale biogeochemical and hydrological model ing, climate change scenario construction, evaluation of regional climate m odels, and comparison with satellite products. The dataset is available fro m the Climatic Research Unit and is currently being updated to 1998.