On the Differences between the Lifecycles of Some Baroclinic Waves Using the Primitive and Quasi-Geostrophic Equations on a Sphere

M. K. MacVean Department of Meteorology, Reading University, Reading RG6 2AU, U.K.

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I. N. James Department of Meteorology, Reading University, Reading RG6 2AU, U.K.

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Abstract

Lifecycles of baroclinic waves obtained by integrating the primitive and quasi-geostrophic equations on the sphere are compared. Two basic states are considered. The first is based on Northern Hemisphere winter climatology, while the other has a maximum baroclinicity at midlevels, but no temperature gradients on the upper and lower boundaries. The earlier part of the lifecycles are broadly similar for both equation sets, although there are significant quantitative differences. In the later stages, the momentum fluxes of the decaying waves can differ greatly. Moreover, we are unable to identify any systematic pattern in these differences. We conclude that the use of quasi-geostrophic results to parameterize the modification of the mean flow by baroclinic wave activity is likely to be subject to large errors.

Abstract

Lifecycles of baroclinic waves obtained by integrating the primitive and quasi-geostrophic equations on the sphere are compared. Two basic states are considered. The first is based on Northern Hemisphere winter climatology, while the other has a maximum baroclinicity at midlevels, but no temperature gradients on the upper and lower boundaries. The earlier part of the lifecycles are broadly similar for both equation sets, although there are significant quantitative differences. In the later stages, the momentum fluxes of the decaying waves can differ greatly. Moreover, we are unable to identify any systematic pattern in these differences. We conclude that the use of quasi-geostrophic results to parameterize the modification of the mean flow by baroclinic wave activity is likely to be subject to large errors.

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