The Seasonal and Latitudinal Behavior of Trace Gases and O3 as Simulated by a Two-Dimensional Model of the Atmosphere

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  • 1 Atmospheric and Environmental Research, Inc., Cambridge, MA 02139
  • | 2 Rutherford Appleton Laboratory, England
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Abstract

A two-dimensional zonal-mean model with parameterized dynamics and an advanced photochemical scheme is used to simulate the stratospheric distributions of atmospheric trace gases including ozone. The model calculates the distributions of 37 species that are photochemically coupled via 140 reactions with rate data from WMO/NASA. A full diurnal treatment is used to calculate the diurnal variations of the short-lived species and the diurnal mean of the production/loss rates for the long-lived species. The calculated concentrations are compared with a wide range of observations with emphasis on the seasonal and latitudinal features. In this work, no post hoc adjustment of the dynamical parameters has been attempted to improve agreement with observations.

In general, the model results are in good agreement with observations, although several discrepancies are noted. Rather than focusing on any individual species, we look for systematic agreements and discrepancies between model and observations for a wide range of species. The model appears to successfully simulate the major features of the mixing ratio surfaces for the long-lived species. However, at the equatorial region, the model tends to underestimate the concentrations of upward diffusing species (e.g., CFCs, CH4, N2O) and overestimate the column abundances of the downward diffusing species (HNO3, HCl, O3). These discrepancies are systematically examined and their implications for transport parameterization assessed.

The model successfully simulates the general latitudinal and seasonal behavior of the local concentration and column abundance of O3. Apart from the overestimation of the column abundances at the equator, the model also underestimates its seasonal contrast at high latitudes. There are difficulties in explaining the observed low concentrations of NO2 in winter at high latitudes. It is shown that errors in the simulation of NO2 concentration in these regions can significantly affect the calculated seasonal and latitudinal behavior of the column abundance of ozone in the middle and high latitudes.

Abstract

A two-dimensional zonal-mean model with parameterized dynamics and an advanced photochemical scheme is used to simulate the stratospheric distributions of atmospheric trace gases including ozone. The model calculates the distributions of 37 species that are photochemically coupled via 140 reactions with rate data from WMO/NASA. A full diurnal treatment is used to calculate the diurnal variations of the short-lived species and the diurnal mean of the production/loss rates for the long-lived species. The calculated concentrations are compared with a wide range of observations with emphasis on the seasonal and latitudinal features. In this work, no post hoc adjustment of the dynamical parameters has been attempted to improve agreement with observations.

In general, the model results are in good agreement with observations, although several discrepancies are noted. Rather than focusing on any individual species, we look for systematic agreements and discrepancies between model and observations for a wide range of species. The model appears to successfully simulate the major features of the mixing ratio surfaces for the long-lived species. However, at the equatorial region, the model tends to underestimate the concentrations of upward diffusing species (e.g., CFCs, CH4, N2O) and overestimate the column abundances of the downward diffusing species (HNO3, HCl, O3). These discrepancies are systematically examined and their implications for transport parameterization assessed.

The model successfully simulates the general latitudinal and seasonal behavior of the local concentration and column abundance of O3. Apart from the overestimation of the column abundances at the equator, the model also underestimates its seasonal contrast at high latitudes. There are difficulties in explaining the observed low concentrations of NO2 in winter at high latitudes. It is shown that errors in the simulation of NO2 concentration in these regions can significantly affect the calculated seasonal and latitudinal behavior of the column abundance of ozone in the middle and high latitudes.

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