Higher‐Resolution Tropopause Folding Accounts for More Stratospheric Ozone Intrusions

Abstract

Ozone in the troposphere is a pollutant and greenhouse gas, and it is crucial to better understand its transport from the ozone-rich stratosphere. Tropopause folding, wherein stratospheric air intrudes downward into the troposphere, enables stratosphere-to-troposphere ozone transport (STT). However, systematic analysis of the relationship between folding and tropospheric ozone, using data that can both capture folding's spatial scales and accurately represent tropospheric chemistry, is limited. Here, we compare folding in high-resolution reanalysis ERA5 (0.25° horizontal, <21 hPa vertical) and low-resolution chemical reanalysis CAMSRA (0.75°, <40 hPa), against CAMSRA ozone, over 1 year. Folding becomes dramatically more frequent at high resolution, with vertical resolution overwhelmingly responsible. Deeper, more filamentary folding is almost entirely unrepresented at low resolution. Higher-resolution folding is better-correlated with tropospheric ozone (especially along midlatitude storm tracks, where deep folding is most common); STT is therefore likely more attributable to tropopause folding than coarsely-resolved folding can capture.