Autocatalityc water vapor production

Die autokatalytische Wasserdampf-Produktion (Beschreibung z.Zt. nur in englisch verfügbar)

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 model supplies evidence that water vapor is autocatalytically formed below a height of about 65 km and destroyed by photolysis above this altitude. Three catalytic cycles of water vapor formation from the molecular hydrogen reservoir were proposed by Sonnemann. Hydrogen radicals act as catalysts, resulting mainly from water vapor by photolysis and oxidation by O(1D). 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 cross-over level the vertical wind is weak so that H2 and CH4 have sufficient time to oxidize into  H2O- a very slow process. Above this level, however, the vertical wind is strong in order to lift the H2O enriched air to greater heights before the dissociation has an effective impact on the H2O-distribution. Such accelerated upward vertical winds are typical for the mesosphere under certain seasonal-latitudinal conditions.

Calculations by means of our 3D-model COMMA-IAP yield seasonal-latitudinal patterns and variations approximately comparable with those of the HALOE (HALogen Ocultation Experiment) observations. The model output mirrors typical seasonal-latitudinal patterns of water vapor distribution as measured by HALOE of the Upper Atmosphere Research Satellite (UARS) observing H2O-maxima in the upper mesosphere.

Figure shows a seasonal section of the distribution of the water vapor at 67.5° N. The figure impressively illustrates the double maximum of the water vapor mixing ratio during late summer with very high values above 70 km. Exactly such a feature was measured at ALOMAR (69.29° N, 16.03° E) by microwave measurements of Hartogh.

variation of water vapor

Annual variation of water vapor mixing ratio [ppmv] at 67.5° N.