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Steady Linear Response to Thermal Forcing of an Anomaly Model with an Asymmetric Climatology

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  • 1 IMGA—CNR, Modena, Italy
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Abstract

An anomaly model linearized around the observed winter climatology is used to study the steady response of the atmosphere to diabatic heating. The model is an R7, nine vertical levels, primitive equations, fully spectral model, derived from the GFDL GCM (Geophysical Fluid Dynamics Laboratory's General Circulation Model). The anomaly model is capable of treating basic states that depend on latitude, longitude and height. The Krylov technique is used to solve the linear equations. This generality allows the treatment of the important problem of linear waves in the atmosphere from a more general paint of view; a larger class (zonally asymmetric) of basic states can now be treated for the baroclinic primitive equations. The (R7) linear anomaly model is used to investigate the linear response to equatorial and midlatitude prescribed heating. The results indicate that the solution is affected by the presence of the stationary waves in the basic state. In particular, in the case of midlatitude heating large responses can be obtained for some locations of the heating. However, because of the low resolution used in these experiments no firm conclusion can be drawn on the role of baroclinic effects.

The most sensitive areas are identified in some preliminary sensitivity experiments. In the equatorial heating case they correspond to equatorial heating positioned south of the main jet stream. In the midlatitude heating case, a large response is obtained with shallow heating placed at the beginning of the Asian jet stream.

Abstract

An anomaly model linearized around the observed winter climatology is used to study the steady response of the atmosphere to diabatic heating. The model is an R7, nine vertical levels, primitive equations, fully spectral model, derived from the GFDL GCM (Geophysical Fluid Dynamics Laboratory's General Circulation Model). The anomaly model is capable of treating basic states that depend on latitude, longitude and height. The Krylov technique is used to solve the linear equations. This generality allows the treatment of the important problem of linear waves in the atmosphere from a more general paint of view; a larger class (zonally asymmetric) of basic states can now be treated for the baroclinic primitive equations. The (R7) linear anomaly model is used to investigate the linear response to equatorial and midlatitude prescribed heating. The results indicate that the solution is affected by the presence of the stationary waves in the basic state. In particular, in the case of midlatitude heating large responses can be obtained for some locations of the heating. However, because of the low resolution used in these experiments no firm conclusion can be drawn on the role of baroclinic effects.

The most sensitive areas are identified in some preliminary sensitivity experiments. In the equatorial heating case they correspond to equatorial heating positioned south of the main jet stream. In the midlatitude heating case, a large response is obtained with shallow heating placed at the beginning of the Asian jet stream.

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