Ion-recombination nucleation and growth of ice particles in noctilucent clouds

Details Ion-recombination nucleation and growth of ice particles in noctilucent clouds Ion-recombination nucleation and growth of ice particles in noctilucent clouds

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994jgr....99.3915s&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 99, no. A3, p. 3915-3929

Physics

21

Atmospheric Chemistry, Ice Clouds, Ion Recombination, Ionospheric Electron Density, Mesosphere, Noctilucent Clouds, Nucleation, Reaction Kinetics, Computerized Simulation, Polar Regions, Summer

Scientific paper

Formation of ice particles in the polar summer mesosphere is simulated with the proton hydrate, H(+)(H2O)n, as the origin. In an ion-recombination nucleation scheme, electrons in the mesosphere play a role in removing heavy proton hydrates from the ionic system to the background neutral system, making an ionic system a steady source of neutral embryonic nuclei for condensation. Referring to the laboratory data of n less than or equal to 6, a model of reaction coefficients up to the hydration order of n = 1000 is constructed with the help of both the nucleation theory and the unimolecular reaction theory. For a model nucleation layer 600 m in thickness with a minimum temperature of 125 K, produced fluxes of embryonic nuclei are calculated as a strong function of (H2O), 10(exp 3)/sq cm/s at (H2O) = 2.16 parts per million by volume, for example. In the time dependent simulations, stable limit cycle oscillations of the cloud formation are found with periods of 3 to 4 days depending of the magnitude of diffusion. A cloud becomes bright after an active nucleation with a decay of approximately 1.3 days which is a sedimentation time of embryonic nuclei. Deposition of water vapors in ice particles switches off the nucleation, and evaporation of particles at the bottom of a cloud recovers the nucleation activity with a lag of diffusion-advection time. Out of phase oscillations are predicted between the cloud brightness and the polar mesospheric summertime echo from the region of heavy proton hydrates, which will be a crucial evidence for the in situ origin of the clouds.

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