Institute of Meteorology and Climate Research

Oxidation of hydrogen contributes by ~ 0.4 ppm to the water vapour budget in the equatorial upper stratosphere

The figure shows measured mean time series of H2O and 2*CH4 at 3.2 hPa for 10S-10N from HALOE (black), MIPAS (red), and ACE_FTS (blue), as well as time series of the derived quantities H2, H2O+2*CH4, and Hy (= H2O +2 *CH4 + H2).

Multi-year time series of water vapor and methane in the upper tropical stratosphere from HALOE, ACE-FTS and MIPAS have shown that the sum H2O + 2*CH4 is not constant over time and altitude. The gain in water vapor is consistently larger than two times the loss in methane, as it would be expected if methane oxidation was the only source of water vapor in the upper stratosphere. We use this relationship to infer molecular hydrogen mixing ratios from the observations which shows that its mixing ratio decreases with altitude above 5 hPa. This net loss in molecular hydrogen drives additional water vapor production so that multiyear average profiles of H2O + 2*CH4 increase by ~0.4 ppmv between 5 hPa and 1.5 hPa.
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