Evaluation of the Jacobians of Infrared Radiation Models for Variational Data Assimilation

Abstract In this paper, linearized versions of fast infrared radiative transfer schemes for variational data assimilation are studied. A neural network–based infrared broadband radiation model (NeuroFlux) is compared with the European Centre for Medium-Range Weather Forecasts operational radiation model. Also, the Radiative Transfer for Television and Infrared Observation Satellite Operational Vertical Sounder (RTTOV) scheme for satellite brightness temperature computation is compared with a more physically based scheme: the narrowband Synsatrad model developed at the European Organization for the Exploitation of Meteorological Satellites. The Jacobians are examined. They are converted into flux perturbations with the tangent-linear approximation and into atmospheric variable increments with a one-dimensional variational assimilation system. For NeuroFlux and RTTOV, despite accurate flux and radiance computation, the sensitivity with respect to water vapor needs to be improved. However, the random structu...

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