Effect of Photochemical Models on Calculated Equilibria and Cooling Rates in the Stratosphere

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  • 1 The Florida State University, Tallahassee, Fla.
  • | 2 Harvard University, Cambridge, Mass.
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Abstract

Simplified models are developed for radiative heating and cooling and for ozone photochemistry in the region 22–61 km. The latter permit the inclusion of nitrogen and hydrogen reactions in addition to simple oxygen reactions. The simplicity of the scheme facilitates the use of a wide variety of cooling and reaction rates. We also consider determination of temperature and composition as a joint process. It is shown that joint radiative-photochemical equilibrium is appropriate to the mean state of the atmosphere between 35 and 60 km. Equilibrium calculations are then used to show that hydrogen reactions are important for ozone and temperature distributions primarily above 40 km while nitrogen reactions are important primarily below 50 km. Comparisons with observed distributions of temperature and ozone suggest the need for water vapor mixing ratios of from 1–5 × 10−6 and mixing ratios of (NO2+NO) of from 3–10 × 10−8 at the stratopause. At 35 km, a mixing ratio of (NO2+NO) of about 3 × 10−8 is indicated. The precise values depend on our choice of reaction and radiative cooling rate co-efficients, and the simple formulation permits the reader to check the effect of new rates as they become available.

The relaxation of perturbations from joint radiative-photochemical equilibrium is also investigated. In all cases, the coupling between temperature-dependent ozone photochemistry and radiation lead to a reduction of the thermal relaxation time from its purely radiative value. The latter, which amounts to about 10 days at 35 km and decreases to about 5 days at 50 km, is reduced to 3–7 days at 35 km and to 1.5–2.5 days at 50 km. This greatly enhances the dissipation of waves traveling through the stratosphere.

Alfred P. Sloan Foundation Fellow

Abstract

Simplified models are developed for radiative heating and cooling and for ozone photochemistry in the region 22–61 km. The latter permit the inclusion of nitrogen and hydrogen reactions in addition to simple oxygen reactions. The simplicity of the scheme facilitates the use of a wide variety of cooling and reaction rates. We also consider determination of temperature and composition as a joint process. It is shown that joint radiative-photochemical equilibrium is appropriate to the mean state of the atmosphere between 35 and 60 km. Equilibrium calculations are then used to show that hydrogen reactions are important for ozone and temperature distributions primarily above 40 km while nitrogen reactions are important primarily below 50 km. Comparisons with observed distributions of temperature and ozone suggest the need for water vapor mixing ratios of from 1–5 × 10−6 and mixing ratios of (NO2+NO) of from 3–10 × 10−8 at the stratopause. At 35 km, a mixing ratio of (NO2+NO) of about 3 × 10−8 is indicated. The precise values depend on our choice of reaction and radiative cooling rate co-efficients, and the simple formulation permits the reader to check the effect of new rates as they become available.

The relaxation of perturbations from joint radiative-photochemical equilibrium is also investigated. In all cases, the coupling between temperature-dependent ozone photochemistry and radiation lead to a reduction of the thermal relaxation time from its purely radiative value. The latter, which amounts to about 10 days at 35 km and decreases to about 5 days at 50 km, is reduced to 3–7 days at 35 km and to 1.5–2.5 days at 50 km. This greatly enhances the dissipation of waves traveling through the stratosphere.

Alfred P. Sloan Foundation Fellow

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