Total hydrogen mixing ratio anomaly around the mesopause region

Abstract

[1] The strong turbulent mixing within the middle atmosphere should prevent a change of the value of the total hydrogen mixing ratio regardless of the transformation of the hydrogen species in one another within the homosphere. Within the heterosphere the corresponding mixing ratio should drastically increase due to the action of molecular diffusion. We show on the basis of a global three-dimensional model of the dynamics and chemistry of the middle atmosphere that the total mixing ratio decreases under certain conditions when an (escape) flux flows through the domain. The effect occurs particularly above and around the mesopause region, reaching a distinct minimum at about 108 km height. Hunten and Strobel [1974] also found a small reduction on the basis of simplified model calculations, but they stated that the total mixing ratio of hydrogen atoms remains nearly the same. The cause of this apparently paradoxical behavior lies in the fact that under the condition of a hydrogen flux just in the domain of transition of predominant turbulent diffusion to predominant molecular diffusion, a strong decomposition of the heavier H 2 O component into the light hydrogen constituents takes place, and the temperature increases strongly with height above the mesopause. The marked reduction of the total hydrogen mixing ratio within the extended mesopause region is extremely important for all questions concerning the physics and chemistry of this domain.

The roles of vertical advection and eddy diffusion in the equatorial mesospheric semi-annual oscillation (MSAO)

“…The April H densities are approximately two-thirds the August values over most of the altitude region. From 88 to 100 km the H mixing ratio is approximately constant, in agreement with model calculations by Sonnemann and Körner (2003), so reducing the signature of the diurnal tide. Around 85 km, where the H mixing ratio does change appreciably with altitude, the H density exhibits a diurnal tidal effect with maximum H values occurring several hours after ground-level sunset.…”

“…Instances of such studies are those of Vlasov and Kelley (2010) for the effects of turbulence on the O vertical profile, and similarly by Sonnemann and Körner (2003) for the H profile. The seasonal variation of eddy diffusion at low latitude, the target latitude for the current study, was derived from mesospherestratosphere-troposphere (MST) radar observations by Sasi and Vijayan (2001), with maximum turbulence observed at solstice periods.…”

Impact of a stratospheric warming event in January 2001 on the minor constituents in the MLT region calculated on the basis of a new 3D-model LIMA of the dynamics and chemistry of the middle atmosphere

“…All model versions were designed for investigations of the physical processes in the MLT region. The older versions were described in more detail among other publications in the papers of Berger and Dameris, 1993, Berger 1994, and Berger and von Zahn, 1999 and in Sonnemann et al, 1998, Ko¨rner and Sonnemann, 2001, Sonnemann and Ko¨rner, 2003, Hartogh et al, 2004, and Sonnemann et al, 2005 (additionally including chemistry). The older versions are based on spherical coordinates.…”

Solar influence on mesospheric water vapor with impact on NLCs

“…However, in the mesopause region and above, atomic hydrogen becomes a main hydrogen-carrying constituent. The hydrogen flux through the domain (escape flux) and the increasing influence of the molecular diffusion gives rise to a decrease of the total hydrogen mixing ratio around the turbopause and, due to the separation by the molecular diffusion, an adjacent increase of it (Sonnemann and Ko¨rner, 2003).…”