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Implicit Normal Mode Initialization for an Operational Regional Model

Clive TempertonRecherche en Prévision Numérique, Atmospheric Environment Service, Dorval, Québec, Canada

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Michel RochRecherche en Prévision Numérique, Atmospheric Environment Service, Dorval, Québec, Canada

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Abstract

In a previous study based on the shallow-water equations, it was shown that nonlinear normal mode initialization (NMI) can be implemented without knowing the normal modes of a model; this implicit form of nonlinear NMI is particularly useful in models for which computing the horizontal normal modes is impracticable. The present paper extends the technique to the multilevel Canadian Operational Finite-Element Regional Model. This paper shows that the method yields well-balanced initial conditions and consistent vertical velocity fields. Forecasts from these initial conditions using a semi-Lagrangian time-integration scheme with relatively large time steps are free from unrealistic high-frequency oscillations.

Abstract

In a previous study based on the shallow-water equations, it was shown that nonlinear normal mode initialization (NMI) can be implemented without knowing the normal modes of a model; this implicit form of nonlinear NMI is particularly useful in models for which computing the horizontal normal modes is impracticable. The present paper extends the technique to the multilevel Canadian Operational Finite-Element Regional Model. This paper shows that the method yields well-balanced initial conditions and consistent vertical velocity fields. Forecasts from these initial conditions using a semi-Lagrangian time-integration scheme with relatively large time steps are free from unrealistic high-frequency oscillations.

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