Figure 7. Strong day-to-day fluctuations of WUS free tropospheric ozone driven by meandering jet and tropopause folds during La Niña springs.

(a–c) Simulated variance in daily O₃Strat (a), median of daily O₃Strat (b) and median of daily background ozone (c) at 500 hPa in April–May for the La Niña composite (1989, 1999, 2008 and 2011). (d–f) Same as a–c but for the El Niño composite (1983, 1987, 1998 and 2010). (g–i) Same as a–c but for 1992 following the Mt. Pinatubo volcanic eruption. Locations of Edmonton (◊), Trinidad Head (⊙) and Fritz Peak-Boulder sonde sites (▵) are shown. The boxes indicate the regions where ozone variability corresponds with jet characteristics for La Niña and El Niño (Fig. 8).