Observing system experiments within the operational ECMWF data assimilation framework have been performed for summer 2008 when the largest recorded number of Global Navigation Satellite System (GNSS) radio occultation observations from both operational and experimental satellites were available. Constellations with 0%, 5%, 33%, 67%, and 100% data volume were assimilated to quantify the sensitivity of analysis and forecast quality to radio occultation data volume. These observations mostly

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... ain upper-tropospheric and stratospheric temperatures and correct an apparent model bias that changes sign across the upper-tropospherelower-stratosphere boundary. This correction effect does not saturate with increasing data volume, even if more