The Physical Mechanism of Baroclinic Instability and Its Downstream Propagation Based on the Splitting Method

Qui-Shi Chen Department of Meteorology, The Pennsylvania State University, University Park 16802

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Abstract

Large-scale atmospheric motion develops under the interaction between inertia-gravity waves and Rossbywaves. The continuous variation of the large-scale motion can be divided into a set of variations over short time intervals., In each interval the way in which the geostrophic wind is destroyed and in which theageostrophic wind strives toward the balance again, should be studied in some detail. The total variation in each short time interval is the sum of these two processes. If the adjusting rate toward the balance ismuch larger than the rate of addition of a geostrophic wind through the advection process, the quasi-geostrophic motion must be maintained. If not, the adjusting rate is much smaller, and a relitively stronggeostrophic wind should be observed in the atmosphere.

In this paper, we first introduce some basic concepts of the splitting method for the large-scale motion, then we analyze some characteristics of the advection and adjustment processes and their interaction. Thephysical mechanism of baroclinic instability is illustrated from a positive feedback between the development of the barotropic part and the baroclinic part. This feedback process can also propagate to the downstream region resulting in the downstream propagation of the development of unstable waves.

Abstract

Large-scale atmospheric motion develops under the interaction between inertia-gravity waves and Rossbywaves. The continuous variation of the large-scale motion can be divided into a set of variations over short time intervals., In each interval the way in which the geostrophic wind is destroyed and in which theageostrophic wind strives toward the balance again, should be studied in some detail. The total variation in each short time interval is the sum of these two processes. If the adjusting rate toward the balance ismuch larger than the rate of addition of a geostrophic wind through the advection process, the quasi-geostrophic motion must be maintained. If not, the adjusting rate is much smaller, and a relitively stronggeostrophic wind should be observed in the atmosphere.

In this paper, we first introduce some basic concepts of the splitting method for the large-scale motion, then we analyze some characteristics of the advection and adjustment processes and their interaction. Thephysical mechanism of baroclinic instability is illustrated from a positive feedback between the development of the barotropic part and the baroclinic part. This feedback process can also propagate to the downstream region resulting in the downstream propagation of the development of unstable waves.

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