Models for Some Aspects of Atmospheric Vortices

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  • 1 Lewis Research Center, NASA, Cleveland, Ohio 44135
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Abstract

The growth of random vortices in an atmosphere with buoyant instability and vertical wind shear is examined by using a previous analysis of the author. A study is also made of the velocities in a single gravity-driven vortex; a frictionless adiabatic model which is supported by laboratory experiments is first considered. The effects of axial drag, heat transfer and precipitation-induced downdrafts are then estimated. Heat transfer and axial drag tend to have stabilizing effects; they reduce the downdrafts or updrafts due to buoyancy. It is found that downdrafts of tornadic magnitude might occur in negatively buoyant columns. The radial-inflow velocity required to maintain a given maximum tangential velocity in a tornado is determined by using a turbulent vortex model. Conditions under which radial inflow velocities become sufficiently large to produce tangential velocities of tornadic magnitude are determined. The radial velocities in the outer regions as well as the tangential velocities in the inner regions may be large enough to cause damage. The surface boundary layer, which is a region where large radial inflows can occur, is studied, and the thickness of the radial-inflow friction layer is estimated. Finally, a tornado model which involves a rotating parent cloud, as well as buoyancy and precipitation effects, is discussed.

Abstract

The growth of random vortices in an atmosphere with buoyant instability and vertical wind shear is examined by using a previous analysis of the author. A study is also made of the velocities in a single gravity-driven vortex; a frictionless adiabatic model which is supported by laboratory experiments is first considered. The effects of axial drag, heat transfer and precipitation-induced downdrafts are then estimated. Heat transfer and axial drag tend to have stabilizing effects; they reduce the downdrafts or updrafts due to buoyancy. It is found that downdrafts of tornadic magnitude might occur in negatively buoyant columns. The radial-inflow velocity required to maintain a given maximum tangential velocity in a tornado is determined by using a turbulent vortex model. Conditions under which radial inflow velocities become sufficiently large to produce tangential velocities of tornadic magnitude are determined. The radial velocities in the outer regions as well as the tangential velocities in the inner regions may be large enough to cause damage. The surface boundary layer, which is a region where large radial inflows can occur, is studied, and the thickness of the radial-inflow friction layer is estimated. Finally, a tornado model which involves a rotating parent cloud, as well as buoyancy and precipitation effects, is discussed.

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