Troposphere-Stratosphere Coupling Processes

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Among the most challenging global environmental problems is the threat that chemical pollution may cause significant depletion of the stratospheric ozone layer during the next century. Because of the complex chemical, radiative, and dynamical processes that together determine the global budget of ozone, many physical mechanisms must be understood before a comprehensive model can be developed for prediction of the evolution of the ozone layer. The budget of stratospheric ozone is strongly influenced by global transport within the stratosphere and by transfer of various trace chemicals between the troposphere and stratosphere. Thus an understanding of the mechanisms and global distribution of troposphere.stratosphere coupling is essential for an understanding of the global circulation of the stratosphere, and its influence on the ozone layer. Cumulonimbus convective storms can contribute to troposphere.stratosphere coupling through production of vertically propagating wave motions that transfer momentum from the troposphere to the stratosphere, and through transfer of chemical trace constituents into the stratosphere by convective overshooting of individual cloud turrets, followed by turbulent mixing. Professors Holton and Durran will study these processes with the aid of a numerical model designed to simulate the dynamical, microphysical, and radiative properties of cumulonimbus cloud systems in the tropics. Observations from recent field experiments will be used to help specify initial conditions, and to validate the model results. Professors Holton and Durran will also evaluate the possible role of high altitude cirrus anvil clouds formed by cumulonimbus convection in dehydrating the stratosphere through radiative destabilization and resultant ice particle growth and fallout.