The hydrogen budget of the stratosphere inferred from ATMOS measurements of H2O and CH4

The total hydrogen budget of the stratosphere and lower mesosphere has been examined using vertical mixing ratio profiles of H 2 O and CH 4 measured by the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment from four space shuttle missions. The oxidation of CH 4 and H 2 is investigated by evaluating the quantity H (=H 2 O + 2 CH 4 ) entering the stratosphere, and examining its conservation with altitude in the upper atmosphere. Data from all four ATMOS missions indicate H to be nearly conserved in the lower stratosphere and to exhibit a broad maximum in the 35‐ to 65‐km range. The observations provide evidence of a secondary source of H 2 O from H 2 oxidation at altitudes from 35 to 55 km, and net production of H 2 at altitudes above ∼55 km. ATMOS measurements of H 2 O and CH 4 permit the first evaluation of a sickle‐shaped vertical profile of H 2 that is qualitatively consistent with profiles calculated using two‐dimensional models.