| The interannual variability of the RegCM2 regional climate model, with a U.S. centered domain, forced by the NCAR CCM3 global climate is the main focus of this study. A 6 member 10 year CCM3 ensemble, from January 1, 1968 to December 31, 1978, forced globally by reconstructed observed sea surface temperatures, provides RegCM2 boundary conditions.; An understanding of how RegCM2 responds to CCM3 interannual variability is developed using an anomaly pattern correlation (APC) analysis of the CCM3 and RegCM2 monthly averaged 500 mb heights, surface temperature, and precipitation. All three variables show a distinct APC annual cycle.; The effect of regional climate modeling on simulated climate reproducibility compared using the modeled ensemble run variances. In certain regions RegCM2 surface temperature normalized ensemble run variance is significantly lower than CCM3, suggesting higher reproducibility in these regions. RegCM2 precipitation reproducibility is found to be lower than CCM3 in all regions, indicating higher resolution simulations have lower reproducibility.; A empirical orthogonal function (EOF) analysis of the dominant precipitation and surface temperature modes of variability is also presented. The EOF analyses use 60 years (6 ensemble members x 10 years) of RegCM2, CCM3, and a gridded observed data. RegCM2 does not significantly alter the primary modes of CCM3 surface temperature variability. Furthermore, the observed primary modes of surface temperature variability are similar to those modeled. Neither model captures the primary mode of winter precipitation variability. The modeled primary mode of precipitation variability, focused on the west U.S. coast, is similar to the observed second mode. The RegCM2 increases the amplitude of the CCM3 mode, improving the simulation of winter precipitation variability relative to the observations.; The analysis of summer surface temperature and precipitation variability reveals that regional scale forcing, such as the low-level jet, plays an important role in modifying the locations of the primary modes of variability. The RegCM2 significantly improves the jet simulation, shifting the precipitation variability to midwestern and eastern U.S. Despite these changes, the results show the CCM3 interannual variability signal is present in the RegCM2 signal throughout the year. |
