Ozone Variability in the Tropical TTL Derived from SHADOZ Profiles (1998–2017): Role of Convective Processes

The tropical free troposphere (FT) and tropopause transition layer (TTL) are critical regions in changing atmospheric composition because of feedbacks among temperature (i.e., radiative forcing), dynamics and key species like water vapor and ozone. Because of these sensitivities, quantifying ozone variability and trends in the FT and TTL over the past several decades is a topic of great interest. Here we use the reprocessed SHADOZ (Southern Hemisphere Additional Ozonesondes; Thompson et al., 2017; Witte et al., 2017; 2018) ozonesonde dataset to analyze variability in FT and TTL ozone across ten tropical stations for the period 1998-2017. The vertical structure in FT and TTL ozone suggests convective influence (CI) with clear transitions in frequency 3-4 times/yr as shown in the Figure. Standard metrics (e.g., seasonal mean mixing ratio), augmented by laminar wave-identification of wave impact (Gravity Wave Index [GWI], Thompson et al., 2011) and SOM (Self-Organizing Maps; Stauffer et al., 2018), are used to quantify the role of CI in seasonal, intraseasonal and interannual variability in FT and TTL ozone. A standard Multi-variate Linear Regression Model that includes convectively-related oscillations, e.g. ENSO, IOD, MJO, is applied to monthly mean ozone. Of these, ENSO has the greatest impact on ozone variability. The implications of CI for calculation of TTL ozone trends are discussed.