Climatology-based chemical tropopauses from global O3 and N2O observations since 1980

Long-term global trace gas observations can be used to define chemical tropopauses, which are not limited by the availability or resolution of vertical profiles or reanalysis data sets. Tracers that can be used for these definitions need to show clearly defined differences in stratospheric vs. tropospheric characteristics with notable examples being O₃, N₂O, CO or H₂O.

We focus on two approaches: (1) the definition of an O₃-based tropopause using a clearly defined climatology expressed as mixing ratios relative to the tropopause and (2) the filtering of stratospheric data by applying an iterative baseline filter on N₂O measurements. Our objective is to provide clear, globally applicable definitions of these chemical tropopauses, that can be easily applied to new measurement data and provide a representative distance to the tropopause.

We analyse globally distributed ozone sonde measurements, as well as aircraft and balloon measurements of N₂O, in combination with meteorological parameters from interpolated ERA5 reanalyses. By evaluating profiles for each month and geographical region, a representative distance to the tropopause can be assigned to any measurement of O₃ or N₂O. We further investigate the sensitivity of these assignments to spatial and temporal factors and apply these to separate measurement data sets.

Tropopause-relative coordinates are beneficial for trace gas analysis in regions close to the tropopause. However, this effect diminishes with greater distances. We examine for which lower and upper boundaries tropopause-relative coordinates remain beneficial.