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Dr. Zachary Handlos
Summary Sentence: A seminar by Dr. Melissa Breeden, School of Earth and Atmospheric Sciences
Full Summary: No summary paragraph submitted.
Melissa BreedenThe Spring Transition of the North Pacific Jet and its Relation to Deep Stratosphere-to-Troposphere Mass Transport over Western North America
Deep stratosphere-to-troposphere mass transport (deep STT) can advect high stratospheric ozone values down to the surface over western North America during boreal spring, often reducing air quality to unhealthy levels. The peak during spring coincides with the time when deep stratospheric intrusions are most common. The tropopause-level jet structure modulates the frequency and character of intrusions, although the precise relationship between deep STT and jet variability has not been extensively investigated.
In this study, we demonstrate how the north Pacific jet transition from winter to spring leads to the observed peak in deep STT. We show that the transition enhances deep STT 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 deep STT due to deeper and more frequent tropopause folds.
An opposite response is found during El Niño conditions. ENSO conditions also influence deep STT 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.
These results suggest that knowledge of ENSO state and the north Pacific jet structure in late winter could be leveraged for predicting the strength of deep STT in the following months.
