| Abstract: | Paleoclimatic interpretation of proxy data is complicated sometimes by the appearance of heterogeneous patterns of climatic responses across networks of sites. Modern climate analogues for the western United States, similar to those patterns of atmospheric circulation of 18,000 and 9000 yr B.P., were examined in order to explain such patterns of spatial heterogeneity. Modern analogues were defined by comparing modern atmospheric circulation patterns with those simulated by general circulation models. Maps of temperature and precipitation anomalies of the modern analogues reveal patterns of spatial heterogeneity, which resemble the patterns of effective moisture compiled from paleoclimatic data. January 1957 was found to be a reasonable 18,000 yr B.P. analogue, and it features isolated areas of increased wetness in the northern Great Basin and increased dryness in the Northwest interior. Analogues for 9000 yr B.P. from a composite of 11 Augusts display patterns of spatial heterogeneity of effective moisture over most of the mountainous areas. The analogues suggest that spatial heterogeneity of climate is the rule rather than the exception over much of the western United States, with the climatic anomalies at any particular time representing the outcome of the mediation of large-scale atmospheric circulation controls by smaller scale topographic features. |
