Stratosphere‐troposphere exchange at the subtropical jet: Contribution to the tropospheric ozone budget at midlatitudes

The interannual variability of the springtime maximum in free tropospheric ozone above Colorado is examined using 5‐1/2 years (1993–1998) of Differential Absorption Lidar (DIAL) data. Year‐to‐year differences of up to 20% in the monthly mean mixing ratios are shown to be correlated with changes in the 200 hPa wind speed over the eastern Pacific that are associated with the El Niño/Southern Oscillation (ENSO). This correlation is attributed to variations in the intensity of stratosphere‐troposphere exchange (STE) associated with the mean transverse circulation at the subtropical jet exit over the eastern Pacific.