Global Evaluation of the Fidelity of Clouds in the ECMWF Integrated Forecast System
Aumann, Hartmut H.; Wilson, R. Chris; Geer, Alan; Huang, Xianglei; Chen, Xiuhong; Desouza-Machado, Sergio; Liu, Xu
2023-05
Citation
Aumann, Hartmut H.; Wilson, R. Chris; Geer, Alan; Huang, Xianglei; Chen, Xiuhong; Desouza-Machado, Sergio ; Liu, Xu (2023). "Global Evaluation of the Fidelity of Clouds in the ECMWF Integrated Forecast System." Earth and Space Science 10(5): n/a-n/a.
Abstract
Weather forecasting centers mainly assimilate infrared sounder data in clear-conditions or in channels with their main sensitivity to the atmosphere well above the cloud tops. Sometimes channels with stronger cloud sensitivity are used in overcast conditions, but currently no cloud information is used from infrared sounders, and all-sky assimilation approaches are still under development. However, cloudy radiances could already be used for validating the quality of clouds in forecasts. We illustrate this by comparing the brightness temperatures observed (obs) with AIRS (Atmospheric Infrared Sounder) to those calculated (cal) based on the clouds specified in the ECMWF (European Centre for Medium Range Weather Forecasting) Integrated Forecast System (IFS). Our analysis is based on a 12 hr ingest of AIRS data into the ECMWF assimilation system. We show that the standard deviation of (obs-cal) using the 1,231 cm−1 atmospheric window channel is a metric of the fidelity of the clouds in the IFS. The global standard deviation of 5 K after accounting for likely space/time interpolation errors, appears to be dominated by clouds in the IFS which are not seen in the AIRS data, and vice versa. Our metric capitalizes on the unique sensitivity of infrared sounders to clouds for the routine monitoring of the fidelity of clouds in weather forecasts.Plain Language SummaryKey to a good weather forecast is clouds of the right variety in the right places at the right time. We evaluate this for 12 hr of European Centre for Medium Range Weather Forecasting (ECMWF) data by comparing the clouds created from the temperature and water vapor profiles and first principle physics with the clouds observed with the Atmospheric Infrared Sounder (AIRS). For the global mean, there is a good match, but locally the ECMWF finds deep convective clouds which are not seen in the AIRS data, and vice versa, in clusters on a scale of hundreds of kilometers. We propose a metric for the cloud fidelity, which allows monitoring and quantifying improvements as new algorithms or data are included in the Integrated Forecast System.Key PointsWe compare the clouds observed from space to the clouds in a medium range weather forecast system, where clouds are created from first principle physics aloneWe propose a metric, which allows the numerical assessments of the cloud fidelity of the current forecast system to be compared with future upgradesOn average, the agreement between the forecast clouds and Atmospheric Infrared Sounder (AIRS) observations is very good, but, particularly in areas prone to deep convection, there are large cloudy areas which are not seen in the AIRS data, and vice versaPublisher
Wiley Periodicals, Inc.
ISSN
2333-5084 2333-5084
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