A process-oriented evaluation of CAMS reanalysis ozone during tropopause folds over Europe for the period 2003–2018

Abstract

Abstract. Tropopause folds are the key process underlying stratosphere-to-troposphere transport (STT) of ozone, and thus they affect tropospheric ozone levels and variability. In the present study we perform a process-oriented evaluation of Copernicus Atmosphere Monitoring Service (CAMS) reanalysis (CAMSRA) O3 during folding events over Europe and for the time period from 2003 to 2018. A 3-D labeling algorithm is applied to detect tropopause folds in CAMSRA, while ozonesonde data from WOUDC (World Ozone and Ultraviolet Radiation Data Centre) and aircraft measurements from IAGOS (In-service Aircraft for a Global Observing System) are used for CAMSRA O3 evaluation. The profiles of observed and CAMSRA O3 concentrations indicate that CAMSRA reproduces the observed O3 increases in the troposphere during the examined folding events. Nevertheless, at most of the examined sites, CAMSRA overestimates the observed O3 concentrations, mostly at the upper portion of the observed increases, with a median fractional gross error (FGE) among the examined sites >0.2 above 400 hPa. The use of a control run without data assimilation reveals that the aforementioned overestimation of CAMSRA O3 arises from the data assimilation implementation. Overall, although data assimilation assists CAMSRA O3 to follow the observed O3 enhancements in the troposphere during the STT events, it introduces biases in the upper troposphere resulting in no clear quantitative improvement compared to the control run without data assimilation. Less biased assimilated O3 products, with finer vertical resolution in the troposphere, in addition to higher IFS (Integrated Forecasting System) vertical resolution, are expected to provide a better representation of O3 variability during tropopause folds.

Higher‐Resolution Tropopause Folding Accounts for More Stratospheric Ozone Intrusions

“…Recent NASA coupled chemistry-meteorology products are likewise promising for studying stratospheric intrusions (MERRA2-GMI [Global Modeling Initiative] and GEOS-CF [Goddard Earth Observing System Composition Forecasts]; Strode et al, 2015;Keller et al, 2021;Knowland et al, 2022). CAMSRA ozone is broadly consistent with upper-tropospheric observations during stratospheric intrusions over Europe, despite overestimation in some sites (Akritidis et al, 2022), and lower-tropospheric ozone in East Asia (Park et al, 2020). Stratospheric ozone in CAMSRA is parameterized using the Cariolle scheme (Cariolle & Déqué, 1986;Cariolle & Teyssèdre, 2007), and subject to data assimilation.…”

Tropospheric ozone and its natural precursors impacted by climatic changes in emission and dynamics

“…This downward transport leads to changes in tropospheric ozone levels (Xiong et al, 2022). An increase in tropospheric O 3 level is observed during the folding events, which have a stratospheric origin (Akritidis et al, 2022). Akriditis et al identified changes in tropopause fold frequencies from 1970-1999 to 2070-2099 in both hemispheres, regionally exceeding 3%, and found links with the projected changes in the position and intensity of the subtropical jet streams (Akritidis et al, 2019).…”