Origins of tropospheric ozone interannual variation over Réunion: A model investigation

Abstract

International audienceObservations from long-term ozone sonde measurements show robust variations and trends in the evolution of ozone in the middle and upper troposphere over Réunion Island (21.1°S, 55.5°E) in June–August. Here we examine possible causes of the observed ozone variation at Réunion Island using hindcast simulations by the stratosphere-troposphere Global Modeling Initiative chemical transport model for 1992–2014, driven by assimilated Modern-Era Retrospective Analysis for Research and Applications meteorological fields. Réunion Island is at the edge of the subtropical jet, a region of strong stratospheric-tropospheric exchange. Our analysis implies that the large interannual variation (IAV) of upper tropospheric ozone over Réunion is driven by the large IAV of the stratospheric influence. The IAV of the large-scale, quasi-horizontal wind patterns also contributes to the IAV of ozone in the upper troposphere. Comparison to a simulation with constant emissions indicates that increasing emissions do not lead to the maximum trend in the middle and upper troposphere over Réunion during austral winter implied by the sonde data. The effects of increasing emission over southern Africa are limited to the lower troposphere near the surface in August–September

Tropospheric Ozone Assessment Report: Assessment of global-scale model performance for global and regional ozone distributions, variability, and trends

“…Recent developments in global chemistry models towards representing tropospheric and stratospheric chemistry as a single entity (Morgenstern et al, 2017 and references therein) will allow the uncertainty in the stratospheric impact on the troposphere to be evaluated more comprehensively (e.g., CCMI). Extensive evaluation of these models against more meaningful diagnostics that provide information on transport between the stratosphere and troposphere (e.g., Neu et al, 2014;Orbe et al, 2015;Liu et al, 2016) will help build confidence in the model simulated stratospheric contribution to tropospheric ozone.…”

Stratospheric ozone intrusion events and their impacts on tropospheric ozone in the Southern Hemisphere

“…Models show that stratospheric ozone depletion has propagated to the upper troposphere . However, work based on the Southern Hemisphere Additional OZonesonde (SHADOZ) network suggests stratospheric mixing may be increasing upper-tropospheric ozone near southern Africa (Liu et al, 2015;Thompson et al, 2014). Uncertainties in the various processes which produce tropospheric ozone limit predictions of future ozoneinduced radiative forcing.…”

“…While the frequency, seasonality, and impacts of STT events have been well described in the tropics and Northern Hemisphere (NH), observational estimates from the SH extratropics are noticeably absent in the literature. The role of STT in the SH remains highly uncertain due to the more limited data availability compared to the NH and the temporal sparsity of these datasets (Mze et al, 2010;Thompson et al, 2014;Liu et al, 2015).…”

The ENSO and QBO Impact on Ozone Variability and Stratosphere‐Troposphere Exchange Relative to the Subtropical Jets

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