Global distribution of CO₂ in the upper troposphere and stratosphere

Abstract. In this study, we construct a new monthly zonal mean carbon dioxide (CO₂) distribution from the upper troposphere to the stratosphere over the 2000–2010 time period. This reconstructed CO₂ product is based on a Lagrangian backward trajectory model driven by ERA-Interim reanalysis meteorology and tropospheric CO₂ measurements. Comparisons of our CO₂ product to extratropical in situ measurements from aircraft transects and balloon profiles show remarkably good agreement. The main features of the CO₂ distribution include (1) relatively large mixing ratios in the tropical stratosphere; (2) seasonal variability in the extratropics, with relatively high mixing ratios in the summer and autumn hemisphere in the 15–20 km altitude layer; and (3) decreasing mixing ratios with increasing altitude from the upper troposphere to the middle stratosphere ( ∼ 35 km). These features are consistent with expected variability due to the transport of long-lived trace gases by the stratospheric Brewer–Dobson circulation. The method used here to construct this CO₂ product is unique from other modelling efforts and should be useful for model and satellite validation in the upper troposphere and stratosphere as a prior for inversion modelling and to analyse features of stratosphere–troposphere exchange as well as the stratospheric circulation and its variability.