Towards an unbiased stratopsheric analysis
Presenter:
Patrick Laloyaux
ECMWF
ECMWF
Talk
A new set of diagnostics based on GPS-RO revealed the presence of systematic large-scale errors in the stratospheric temperature of the IFS model used at ECMWF for numerical weather forecasting. A weak-constraint 4D-Var formulation has been developed where a model-error forcing term is explicitly estimated to take into account model imperfections. This approach reduces up to 50% the bias in the analysis departures of all observations sensitive to stratospheric temperature.
The importance of anchoring data (accurate observations that do not require bias correction) such as GPS-RO is indisputable to ensure the good behaviour of the method. Weak-constraint 4D-Var also allows to have a more consistent way to treat the source of the different biases, ensuring that the Variational Bias Correction (VarBC) corrects only systematic errors from data and observation operators.
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