Editorial Type:
Article
Article Type:
Research Article

Forecast of Operational Forecast Skill with the Adjoint of a Primitive Equation Model

Yves Bouteloup Météo-France/SCEM, Toulouse, France

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Print Publication:
01 Nov 1997
DOI:
https://doi.org/10.1175/1520-0493(1997)125<2984:FOOFSW>2.0.CO;2
Page(s):
2984–2997
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Abstract

In this article the author demonstrates the feasibility of a local skill forecast system based on the use of the adjoint of the tangent linear equations. A six-level adiabatic primitive equations spectral model of the atmospheric circulation, truncated at T42, is used. Local skill forecast from 1 to 3 days ahead is computed for a 3-month period, using the T42 model and the adjoint of its tangent linear equations. To highlight the effect of model error, the trajectories required by the adjoint model are chosen in various ways. First, it is the result of the integration of the direct low-resolution model. The trajectory is then interpolated from the forecast of the operational 24-level T119 variable resolution model used at Météo-France. Finally, the trajectory is interpolated from successive analyses. The initial error covariance matrix is built from the analysis error produced by the operational optimal interpolation system used at Météo-France and a simple correlation function. The weaknesses of the method are discussed, in particular the weak day-to-day variability of these variances. The large day-to-day variability of the forecast error variances is shown, in connection to the characteristics of the flow. The impact (from 48 h ahead) of the trajectory used by the adjoint model is also shown. Finally, a large set of variances is produced. Statistical connections between predicted variances and the skill of the forecasts of the model are described. The results show the potential usefulness of this product to help the forecaster to predict the evolution of the flow.

Corresponding author address: Dr. Yves Bouteloup, Météo-France/SCEM, 42 Av. G. Coriolis, 31057 Toulouse Cedex, France.

Abstract

In this article the author demonstrates the feasibility of a local skill forecast system based on the use of the adjoint of the tangent linear equations. A six-level adiabatic primitive equations spectral model of the atmospheric circulation, truncated at T42, is used. Local skill forecast from 1 to 3 days ahead is computed for a 3-month period, using the T42 model and the adjoint of its tangent linear equations. To highlight the effect of model error, the trajectories required by the adjoint model are chosen in various ways. First, it is the result of the integration of the direct low-resolution model. The trajectory is then interpolated from the forecast of the operational 24-level T119 variable resolution model used at Météo-France. Finally, the trajectory is interpolated from successive analyses. The initial error covariance matrix is built from the analysis error produced by the operational optimal interpolation system used at Météo-France and a simple correlation function. The weaknesses of the method are discussed, in particular the weak day-to-day variability of these variances. The large day-to-day variability of the forecast error variances is shown, in connection to the characteristics of the flow. The impact (from 48 h ahead) of the trajectory used by the adjoint model is also shown. Finally, a large set of variances is produced. Statistical connections between predicted variances and the skill of the forecasts of the model are described. The results show the potential usefulness of this product to help the forecaster to predict the evolution of the flow.

Corresponding author address: Dr. Yves Bouteloup, Météo-France/SCEM, 42 Av. G. Coriolis, 31057 Toulouse Cedex, France.

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