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Point Vortices In A Low‐Order Model of Barotropic Flow On the Sphere
Author(s) -
Egger Joseph
Publication year - 1992
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49711850507
Subject(s) - barotropic fluid , vortex , baroclinity , anticyclone , geology , climatology , orography , physics , forcing (mathematics) , vorticity , northern hemisphere , atmospheric sciences , polar vortex , eddy , mesocyclone , meteorology , westerlies , mechanics , turbulence , precipitation , doppler effect , doppler radar , astronomy
A low‐order model of global barotropic flow with intrinsic long‐term variability is presented. the model is based on the barotropic vorticity equation with Newtonian forcing of the zonal flow and realistic orography. Subgrid eddy motion is represented by point vortices which move within the low‐order flow of the model and affect it through their own circulation. the vortices are inserted at locations of maximum flow speed and are removed after a prescribed lifetime has elapsed. In the absence of Newtonian forcing, mid‐latitude westerlies and strong polar easterlies are induced if there are only cyclonic vortices. Anticyclonic vortices create equatorial easterlies. If ‘realistic’ Newtonian forcing is added, two stationary orographic troughs dominate the model's mean flow in the northern hemisphere. Cyclones are generated downstream of the troughs, and pronounced storm tracks extend eastward from these genesis areas. the model atmosphere exhibits slow variability of a realistic order of magnitude with maxima over the ‘oceans’. This long‐term variability is due to the interaction of long‐lived circulation patterns, like blocks, with the point vortices. Moreover, cyclone generation is important in inducing slow motions. In the southern hemisphere there is little variation of flow statistics with longitude. All in all the low‐order model is surprisingly successful in simulating the observed patterns of atmospheric transience. This suggests that a low‐order model with point vortices might be a useful tool in climate research.