Solutions to the Vertical Structure Equation for Simple Models of the Tropical Troposphere

David A. Ortland NorthWest Research Associates, Redmond, Washington

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M. Joan Alexander Colorado Research Associates Division, NWRA, Boulder, Colorado

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Abstract

Observation and modeling studies indicate that the wave flux from tropical heating sources that propagates into the lower stratosphere is sensitive to the buoyancy frequency profile N(z) in the troposphere. This sensitivity is explained by examining analytic solutions to the vertical structure equation for various simplified models of the tropical troposphere. An efficient method for obtaining expressions for these analytic solutions when N(z) is piecewise constant is presented. The solution is expressed in terms of reflection and transmission coefficients. It is found that the response to heating for Hough modes with small equivalent depth is quite sensitive to the shape of the heating profile, the magnitude of N(z) within the heating profile, and the internal wave reflections that result from the sharp change in N(z) at the tropopause. The location of the primary peak in the wave response, which occurs where the wavelength is twice the depth of the heating for a constant N(z) profile, is also sensitive to the occurrence of internal wave reflection.

Corresponding author address: David Ortland, NorthWest Research Associates, 4118 148th Ave. NE, Redmond, WA 98052. E-mail: ortland@nwra.com

Abstract

Observation and modeling studies indicate that the wave flux from tropical heating sources that propagates into the lower stratosphere is sensitive to the buoyancy frequency profile N(z) in the troposphere. This sensitivity is explained by examining analytic solutions to the vertical structure equation for various simplified models of the tropical troposphere. An efficient method for obtaining expressions for these analytic solutions when N(z) is piecewise constant is presented. The solution is expressed in terms of reflection and transmission coefficients. It is found that the response to heating for Hough modes with small equivalent depth is quite sensitive to the shape of the heating profile, the magnitude of N(z) within the heating profile, and the internal wave reflections that result from the sharp change in N(z) at the tropopause. The location of the primary peak in the wave response, which occurs where the wavelength is twice the depth of the heating for a constant N(z) profile, is also sensitive to the occurrence of internal wave reflection.

Corresponding author address: David Ortland, NorthWest Research Associates, 4118 148th Ave. NE, Redmond, WA 98052. E-mail: ortland@nwra.com
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