Autocatalytic water vapor production as a source of large mixing ratios within the middle to upper mesosphere

Abstract

[1] Different measurements have shown that large water vapor mixing ratios occur in the upper mesosphere in high-latitude summer just under conditions of strongest solar insolation where photolysis should effectively reduce its value. The analysis of this finding by means of a high-resolution one-dimensional model supplies evidence that water vapor is autocatalytically formed below a crossover height of about 65 km and destroyed by photolysis above this altitude. We found three catalytic cycles of water vapor formation from the molecular hydrogen reservoir. Hydrogen radicals, resulting for the most part from water vapor by photolysis and oxidation by O( 1 D), act as catalysts. A great number of the hydrogen radicals return to water vapor, particularly under the condition of small atomic hydrogen concentration decreasing strongly with decreasing height. In the upper domain under the condition of large atomic hydrogen concentrations the formation of molecular hydrogen will be favored. Favorable conditions for large water vapor mixing ratios at high altitudes are given by an accelerated upward vertical wind. Below the crossover level the vertical wind should be weak so that H 2 and CH 4 have sufficient time to oxidize into H 2 O, a very slow process. Above this level, however, the vertical wind should be strong in order to lift the air, enriched with H 2 O, as quickly as possible to greater heights before the dissociation has an effective impact on the H 2 O distribution. Such accelerated upward vertical winds are typical of the mesosphere under certain seasonally latitudinal conditions. Calculations by means of our three-dimensional model COMMA-IAP yield seasonal-latitudinal patterns and variations approximately comparable with those of the HALOE observations. In the paper we discuss the chemical background and the interplay between dynamics and chemistry in more detail.Citation: Sonnemann, G. R., M. Grygalashvyly, and U. Berger (2005), Autocatalytic water vapor production as a source of large mixing ratios within the middle to upper mesosphere,

Retrieval of water vapor profile in the mesosphere from satellite ozone and hydroxyl measurements by the basic dynamic model of mesospheric photochemical system

“…A possible cause of the second maximum of H 2 O concentration (at 73-75 km) may be heterogeneous reactions of H 2 O molecule formation on the surface of meteorite dust hypothesized by Summers and Siskind (1999). However, Sonnemann et al (2005) showed that no heterogeneous reactions are needed to produce the high water vapor peak at 70 km or higher.…”

“…This result (a secondary role of even hydrogen compounds H 2 O 2 , H 2 and CH 4 ) may be elucidated on an example of the reaction H 2 +O( 1 D)→H+OH which is most "influential" among the omitted reactions. At the heights of 50-70 km, the concentration of H 2 O exceeds the H 2 concentration by more than 3-4 times (Sonnemann et al, 2005), and the value of the constant of this reaction is less than half of the constant of the reaction H 2 O+O( 1 D)→2OH. As a result, the contribution of the reaction H 2 +O( 1 D)→H+OH to the common source of odd hydrogen at the heights of 50-70 km turns out to be considerably smaller than that of the sum of the reactions H 2 O+O( 1 D)→2OH and H 2 O+hν→H+OH.…”

Influence of water vapour on the height distribution of positive ions, effective recombination coefficient and ionisation balance in the quiet lower ionosphere

“…The largest water vapour concentrations have been found during summer because of intensified gravity wave upward propagation. Between 65 and 75 km, an additional water vapour maximum has been observed due to the interaction between upward motions and autocatalytic water vapour formation (Sonnemann et al, 2005(Sonnemann et al, , 2012. Satellite measurements performed during the Middle Atmosphere High-Resolution Spectrograph Investigation indicated a water vapour peak between 10 and 15 ppmv at altitudes between 82 and 84 km in the polar summer mesosphere (Summers et al, 2001).…”

“…Recent research has been quite successful in mapping the water vapour pattern in the lower mesosphere and explaining possible mechanisms for cluster ion formation (Solomon et al, 1981;Gumbel and Witt, 2002;Sonnemann et al, 2005Sonnemann et al, , 2012Hervig and Siskind, 2006;Lossow et al, 2007;Grygalashvyly et al, 2009;Hartogh et al, 2010;Gabriel et al, 2011). However, the ionospheric parameter responses to water vapour variability in the mesosphere and the lower thermosphere are very complicated.…”

On the two-day oscillations and the day-to-day variability in global 3-D-modeling of the chemical system of the upper mesosphere/mesopause region

“…The influence of the turbulent diffusion on the nonlinear behavior was investigated by means of a one-dimensional model (Sonnemann andFeigin, 1999a and1999b;Sonnemann et al, 1999) using the diffusion coefficient as a control parameter. A very complicated system response has been found.…”