The effect of using limited scene-dependent averaging kernels approximations for the implementation of fast observing system simulation experiments targeted on lower tropospheric ozone

[摘要] Practical implementations of chemical OSSEs (Observing SystemSimulation Experiments) usually rely on approximations of thepseudo-observations by means of a predefined parametrization of theaveraging kernels, which describe the sensitivity of the observingsystem to the target atmospheric species. This is intended to avoidthe use of a computationally expensive pseudo-observationssimulator, that relies on full radiative transfer calculations. Here wepresent an investigation on how no, or limited, scene dependentaveraging kernels parametrizations may misrepresent the sensitivity ofan observing system. We carried out the full radiative transfer calculation fora three-days period over Europe, to produce referencepseudo-observations of lower tropospheric ozone, as they would beobserved by a concept geostationary observing system called MAGEAQ(Monitoring the Atmosphere from Geostationary orbit for European AirQuality). The selected spatio-temporal interval is characterised byan ozone pollution event. We then compared our reference withapproximated pseudo-observations, following existing simulationexercises made for both the MAGEAQ and GEOstationary Coastal and AirPollution Events (GEO-CAPE) missions. We found that approximatedaveraging kernels may fail to replicate the variability of the fullradiative transfer calculations. In addition, we found that the approximations substantially overestimate thecapability of MAGEAQ to follow the spatio-temporal variations ofthe lower tropospheric ozone in selected areas, during the mentioned pollution event. We conclude that suchapproximations may lead to false conclusions if used in an OSSE. Thus,we recommend to use comprehensive scene-dependent approximations ofthe averaging kernels, in cases where the full radiative transfer iscomputationally too costly for the OSSE being investigated.

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