In this study, we investigated potential solutions to these problems by providing further constraints using potential available information, such as constraints on the size of the bias correction and innovative bias correction metrics using uncertainty estimation from calibration and radiative transfer. This has been studied in CMA’s GRAPES (Global/Regional Assimilation PrEdiction System) 3D-Var system and the full ECMWF global 4D-Var system, using data from microwave sounders which are sensitive to stratospheric temperature. The data assimilation experiments showed that this scheme improved GRAPES analyses and medium range forecasts. The resulting enhanced bias corrections in the full ECMWF global 4D-Var was assessed in the context of other assimilated observations (in particular radiosondes and GPS radio occultation measurements), and through comparisons of MLS temperature retrieval data in stratosphere and mesosphere in the full ECMWF global 4D-Var system.
The constrained bias correction of AMSU-A stratospheric sounding channels reduces the biases in stratosphere and improves the medium range forecasts in both stratosphere and troposphere.