OBSERVED VERSUS SIMULATED 2ND-MOMENT CLIMATE STATISTICS IN GCM VERIFICATION PROBLEMS

The observed and simulated (by the Hamburg GCM) Northern Hemisphere mo nthly surface air temperatures, averaged within different latitude ban ds, are statistically analyzed and compared. The objects used for the analysis are the two-dimensional spatial-temporal spectral and correla tion characteristics, the multivariate autoregressive and linear regre ssion model parameters, and the diffusion equation coefficients. A qua litative comparison shows that, generally, the shapes of the correspon ding spectra and correlation functions are quite similar but that thei r numerical values and some features differ markedly, especially for t he tropical regions. The spectra reveal a few randomly distributed max ima (along the frequency axis), the periods of which were not identica l for both types of data. A comparative study of the estimates of the diffusion equation coefficients shows a significant distinction betwee n the character of the meridional circulations of the observed and sim ulated systems. The approach developed gives approximate stochastic mo dels and reasonable descriptions of the temperature processes and fiel ds, thereby providing an opportunity for solving some of the vital pro blems of the theoretical and practical aspects surrounding validation, diagnosis, and application of the GCM. The methodology and the result s presented make it clear that the formalization of the statistical de scription of the surface air temperature fluctuations can be achieved by applying the standard techniques of multivariate modeling and multi dimensional spectral and correlation analysis to the data, which have been averaged spatially and temporally.