TY - JOUR

T1 - Analytical investigations of horizontal meso-scale momentum equations with Newtonian nudging

AU - Cai, X. M.

AU - Steyn, D. G.

AU - Uno, Itsushi

PY - 1997/1/1

Y1 - 1997/1/1

N2 - This study presents an analytical investigation of the local behaviour of the solution to a mesoscale model with Newtonian nudging when observed winds are time varying. The analysis examines each Fourier component of the time series of observed winds. Unlike the case with a constant observed wind, the nudged wind vector does not asymptotically approach the observed wind. In response to sinusoidal oscillation of the observed wind, the nudged wind vector is always on a half circle connecting the vector ends of the observed and un-nudged modelled winds. When nudging parameter α → 0, the nudged wind vector approaches the un-nudged wind; when α → ∞, the nudged wind vector approaches the observed wind. For commonly used values of nudging parameter α, the modelled wind field always carries errors. A target nudging scheme is devised in this study in order to ensure the model result is identical to observed winds with sinusoidal oscillation. Investigation shows that such a target wind exists for a finite value of α, and the magnitude of the target-nudging term is about the same as that of a normal nudging term if α ∼ f ∼ ω, where f is the Coriolis parameter and ω is the frequency of the wind oscillation.

AB - This study presents an analytical investigation of the local behaviour of the solution to a mesoscale model with Newtonian nudging when observed winds are time varying. The analysis examines each Fourier component of the time series of observed winds. Unlike the case with a constant observed wind, the nudged wind vector does not asymptotically approach the observed wind. In response to sinusoidal oscillation of the observed wind, the nudged wind vector is always on a half circle connecting the vector ends of the observed and un-nudged modelled winds. When nudging parameter α → 0, the nudged wind vector approaches the un-nudged wind; when α → ∞, the nudged wind vector approaches the observed wind. For commonly used values of nudging parameter α, the modelled wind field always carries errors. A target nudging scheme is devised in this study in order to ensure the model result is identical to observed winds with sinusoidal oscillation. Investigation shows that such a target wind exists for a finite value of α, and the magnitude of the target-nudging term is about the same as that of a normal nudging term if α ∼ f ∼ ω, where f is the Coriolis parameter and ω is the frequency of the wind oscillation.

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U2 - 10.1007/BF01029695

DO - 10.1007/BF01029695

M3 - Article

AN - SCOPUS:0001830186

VL - 64

SP - 231

EP - 241

JO - Archives for Meteorology, Geophysics and Bioclimatology, Series A

JF - Archives for Meteorology, Geophysics and Bioclimatology, Series A

SN - 0177-7971

IS - 3-4

ER -