Vol. 39, issue 08, article # 7

Abstract:

Observed growth of the atmospheric concentration of gases, such as CO₂ and CH₄, strengthens the greenhouse effect in the atmosphere and impacts on climate. One of the characteristics of the greenhouse effect is the radiative forcing of the atmospheric gases which is defined as the difference between the longwave radiative fluxes at different concentrations of gases other parameters of the atmosphere being constant. From 1990 to 2023, the radiative forcing of long-lived greenhouse gases due to their concentration grow from the pre-industrial period (1750 year) has increased by more than 50%. In the work, the impact of atmospheric water vapor content variability on the CO₂ and CH₄ radiative forcing for summer and winter conditions of south Western Siberia is investigated. The longwave IR radiative fluxes are calculated on the basis of upper-air sounding data of meteorological station in Novosibirsk for 10 years. The maximum of absolute value of the CO₂ radiative forcing was observed at the top of troposphere, at that, in summer, it was higher by 50% than in winter conditions, and relation of CH₄ radiative forcing to CO₂ forcing at this altitude was about 12%. The sign of the forcing is negative, which means heating of the troposphere. At the top and bottom of the atmosphere, a decrease in CO₂ and CH₄ radiative forcing is observed with an increase in atmospheric water vapor content, which is caused by overlapping of H₂O bands and continuum absorption with CO₂ and CH₄ absorption bands. The contribution of H₂O continuum absorption to the CO₂ radiative forcing increases from 30 to 70% when the water vapor atmospheric total column increases from 1 to 4 g/cm². For winter cases with low water vapor content, the average CO₂ radiative forcing at the bottom of the atmosphere increases by 1.5 times in comparison with summer conditions, which leads to additional warming of the surface.

Keywords:

carbon dioxide, methane, water vapor, atmospheric radiative forcing, IR radiation flux

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