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The Beta Drift of Baroclinic Vortices. Part II: Diabatic Vortices

Yuqing WangBureau of Meteorology Research Centre, Melbourne, Victoria, Australia

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Greg J. HollandBureau of Meteorology Research Centre, Melbourne, Victoria, Australia

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Abstract

The beta drift of diabatic vortices is investigated with a three-dimensional primitive equation model with simple physical parameterizations. The vertical coupling mechanism discussed in Part I is extended to include the effects of diabatic heating and moist processes. The results show that the motion and evolution of the diabatic vortices can substantially differ from those of adiabatic vortices.

The anticyclone at the upper troposphere tends to propagate equatorward and westward due to the Rossby wave dispersion. But the continuous regeneration of an anticyclonic PV anomaly by diabatic heating keeps the upper-level anticyclone in a band stretching from the vortex core to several hundred kilometers equatorward and westward. Downward penetration of the circulation associated with these anticyclonic PV anomalies reduces the westward motion of the diabatic vortices by the vertical coupling mechanism discussed in Part I. This also rotates the lower-level beta-gyres anticyclonically, resulting in a more poleward asymmetric flow over the lower-level vortex core. As a result, diabatic vortices with a deeper and stronger outflow-layer anticyclone move in a more poleward direction than do the equivalent adiabatic baroclinic or barotropic vortices.

The asymmetric divergent flow associated with convective asymmetries within the vortex core region deflects the vortex center toward the region with maximum convection. Evolution of both the asymmetric convection and the vertical coupling may result in meandering vortex tracks.

Abstract

The beta drift of diabatic vortices is investigated with a three-dimensional primitive equation model with simple physical parameterizations. The vertical coupling mechanism discussed in Part I is extended to include the effects of diabatic heating and moist processes. The results show that the motion and evolution of the diabatic vortices can substantially differ from those of adiabatic vortices.

The anticyclone at the upper troposphere tends to propagate equatorward and westward due to the Rossby wave dispersion. But the continuous regeneration of an anticyclonic PV anomaly by diabatic heating keeps the upper-level anticyclone in a band stretching from the vortex core to several hundred kilometers equatorward and westward. Downward penetration of the circulation associated with these anticyclonic PV anomalies reduces the westward motion of the diabatic vortices by the vertical coupling mechanism discussed in Part I. This also rotates the lower-level beta-gyres anticyclonically, resulting in a more poleward asymmetric flow over the lower-level vortex core. As a result, diabatic vortices with a deeper and stronger outflow-layer anticyclone move in a more poleward direction than do the equivalent adiabatic baroclinic or barotropic vortices.

The asymmetric divergent flow associated with convective asymmetries within the vortex core region deflects the vortex center toward the region with maximum convection. Evolution of both the asymmetric convection and the vertical coupling may result in meandering vortex tracks.

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