THE ROLE OF STRATOSPHERIC INTRUSIONS IN COLORADO CYCLOGENESIS

Isentropic composites and correlation analyses are employed to investi gate the impact of stratospheric air intrusions during Colorado cyclog enesis, A sample of cold-season Colorado cyclones is partitioned into evolution categories (early, late, and nondeveloping systems) and exam ined far relationships between surface intensity measures and depressi on of the tropopause. Maps of isentropic potential vorticity for time periods prior to and up to 48 hours following cyclogenesis are utilize d to determine the mean evolution of the stratospheric intrusion For e ach development type. Correlations are calculated to elucidate further the tropopause and surface variable associations suggested by the com posites. Composite patterns and correlation results provide strong cli matological evidence of a substantial contribution from stratospheric intrusion to surface development. Developing cyclones are characterize d by progressive, intensifying depressions of the tropopause, while no ndeveloping systems exhibit retreating or static patterns. Further, th e influence of stratospheric intrusion upon surface development appear s to be strongest during the initial 24 hours following cyclogenesis.