THE RELATIVE IMPORTANCE OF DIFFERENT HEAT-EXCHANGE PROCESSES IN THE LOWER STRATOSPHERE

Wan-cheng Chiu New York University

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Richard S. Greenfield New York University

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Abstract

The temperature variation at a fixed point in the free atmosphere or at a point which moves vertically with an isobaric surface is a result of the combined effect of radiation, horizontal advection of heat, vertical convection of heat, and other heat-exchange processes. A method is presented by which the 12-hr local temperature change that would have resulted from radiative processes alone may be estimated. This method and the conventional method of determining the 12-hr local temperature change due to the horizontal advective process lead to a way of estimating the relative importance of different heat-exchange processes.

Following these methods, the 12-hr local temperature changes in the lower stratosphere over a portion of the United States due to radiation, horizontal advection, and the vertical convective and eddy heat exchange processes combined are separately estimated from many years of radiosonde data and daily isobaric maps. The results of this study show that over the southeastern United States, at least, and probably over a much wider area, the horizontal advective process is more important than radiation in influencing the 12-hr local temperature change at the 200-mb and the l00-mb levels. These two processes are probably of equal importance near the 50-mb level. At the 200-mb and the 100-mb levels. These two processes are probably of exchange processes combined are estimated to be as important as, or even more important than, the radiative processes over the same area. These conclusions are probably true for both winter and summer, but especially for winter.

Abstract

The temperature variation at a fixed point in the free atmosphere or at a point which moves vertically with an isobaric surface is a result of the combined effect of radiation, horizontal advection of heat, vertical convection of heat, and other heat-exchange processes. A method is presented by which the 12-hr local temperature change that would have resulted from radiative processes alone may be estimated. This method and the conventional method of determining the 12-hr local temperature change due to the horizontal advective process lead to a way of estimating the relative importance of different heat-exchange processes.

Following these methods, the 12-hr local temperature changes in the lower stratosphere over a portion of the United States due to radiation, horizontal advection, and the vertical convective and eddy heat exchange processes combined are separately estimated from many years of radiosonde data and daily isobaric maps. The results of this study show that over the southeastern United States, at least, and probably over a much wider area, the horizontal advective process is more important than radiation in influencing the 12-hr local temperature change at the 200-mb and the l00-mb levels. These two processes are probably of equal importance near the 50-mb level. At the 200-mb and the 100-mb levels. These two processes are probably of exchange processes combined are estimated to be as important as, or even more important than, the radiative processes over the same area. These conclusions are probably true for both winter and summer, but especially for winter.

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