Factors That Influence North Pacific Tropopause Folds and Their Changes in a Future Warmer Climate

Rossby wave breaking over the North Pacific is associated with folds in the tropopause, which influence the strength and position of the jet stream. Deep tropopause folds can bring dry stratospheric, ozone-rich air down into the troposphere in so-called stratospheric ozone intrusion events, with impacts on the tropospheric ozone budget. Using a tropopause fold frequency dataset based on ERA-interim reanalysis, we consider how low-frequency modes of atmospheric variability, such as the El Nino-Southern Oscillation and the Quasi-biennial Oscillation, influence the occurrence, depth, and location of deep tropopause folds over the North Pacific and western United States during boreal spring. We also examine model simulations using the Whole Atmosphere Community Climate Model (WACCM) that are designed to isolate these influences. Finally, we consider how tropopause folds and the factors that influence them change in a simulation with increased greenhouse gases.