An appropriate sampling frequency for each model variable is obtained by comparing the estimates of first- and second-moment climate statistics determined at intervals ranging from 2 to 24 hours with the "best" estimates obtained from hourly sampling. Relatively accurate estimation of first- and second-moment climate statistics (10 percent errors in means, 20 percent errors in variances) can be achieved by sampling a model variable at intervals that usually are longer than the bandwidth of its time series, but that often are shorter than its characteristic time scale.
For the surface variables, sampling at intervals that are non-integral divisors of a 24-hour day yields relatively more accurate time-mean statistics because of a reduction in errors accociated with aliasing of the diurnal cycle and higher-frequency harmonics. The superior estimates of first-moment statistics are accompanied by inferior estimates of the variance of the daily means due to the presence of sytematic biases, but these probably can be avoided by defining a different measure of low-frequency variability. Estimates of the intradiurnal variance of accumulated precipitation and surface run-off also are strongly impacted by the length of the storage interval. In light of these results, some alternative strategies for storage of the EMWF model variables are recommended.(pdf file)