The Spring Transition of the North Pacific Jet and its Relation to Deep Stratosphere-to-Troposphere Mass Transport over Western North America

Abstract:

Stratosphere-to-troposphere mass transport to the planetary boundary layer (STT-PBL), and the associated ozone transport, peaks over the western United States during boreal spring, when deep stratospheric intrusions are most frequent. The tropopause-level jet structure modulates the frequency and character of intrusions, although the precise relationship between STT-PBL and jet variability has not been extensively investigated. In this presentation, we demonstrate how the north Pacific jet transition from winter to summer leads to the observed peak in STT-PBL. We find that the transition enhances STT-PBL through an increase in storm track activity which produces highly-amplified Rossby waves and more frequent deep stratospheric intrusions over western North America. We find that La Niña conditions in late winter are associated with an earlier jet transition and enhanced STT-PBL due to deeper and more frequent tropopause folds. An opposite response is found during El Niño conditions. ENSO conditions also influence STT-PBL in late spring/early summer, during which time La Niña conditions are associated with larger and more frequent tropopause folds than both El Niño and ENSO neutral conditions.