Ozone trends in the Upper Troposphere - Lower Stratosphere using dynamical coordinate systems

Despite decades of measurements, ozone trends in the upper troposphere/lower stratosphere (UTLS) remain highly uncertain. This uncertainty arises from sharp spatial gradients and significant variability caused by competing transport, chemical, and mixing processes near the upper tropospheric jets and extra-tropical tropopause. Additionally, observations in this region are spatially and temporally limited, which further complicates the interpretation of trends.

The World Climate Research Programme's (WCRP) Atmospheric Processes And their Role in Climate (APARC) Observed Composition Trends and Variability in the UTLS (OCTAV-UTLS) activity aims to reduce uncertainties in UTLS composition trend estimates by evaluating and using a diverse set of dynamical coordinate systems to account for atmospheric variability.

The 20-year contemporaneous UTLS ozone measurements from the Aura Microwave Limb Sounder (MLS) and the Atmospheric Composition Experiment Fourier Transform Spectrometer (ACE-FTS) enable us to evaluate these dynamical coordinates across two datasets with contrasting sampling approaches. When using dynamical coordinates, we observe much better coherence in trend analysis between these datasets compared to conventional geographical coordinates (e.g., latitude-pressure). Using dynamical coordinates also reveals consistent seasonal features in ozone trends across the UTLS.