HR: 09:25h
AN: SH51A-06    [PDF]
TI: Ion Mediated Nucleation: how is it Influenced by Changes in the Solar Activity?
AU: D'Auria, R
EM: dauria@atmos.ucla.edu
AF: Department of Atmospheric, Oceanic and Environmental Sciences, University of California, Los Angeles, Box 951565 7127 Math Sciences Bldg., Los Angeles, CA 90095-1565 United States
AU: * Turco, R P
AF: Department of Atmospheric, Oceanic and Environmental Sciences, University of California, Los Angeles, Box 951565 7127 Math Sciences Bldg., Los Angeles, CA 90095-1565 United States
AB: Recently it has been pointed out that tropospheric cloudiness can be correlated with the galactic cosmic rays (GCRs) intensity [{\it Svensmark and Friis-Christensen}, 1997]. A possible explanation for such a correlation relies on the fact that GCRs are the main ionization source in the upper troposphere, hence, throughout ionic mediated nucleation, they could possibly influence the global cloud condensation nuclei (CCN) formation [{\it e.g.}, {\it Yu}, 2001; {\it Dickinson}, 1975]. Because the GCRs are modulated by the interaction between the solar wind and the Earth's magnetosphere and their intensity generally decreases with increasing solar activity, subtle changes in the solar activity could indirectly affect the Earth's climate. We have been studying the very first steps of ionic nucleation considering the molecular species of atmospheric interest ({\it e.g.},water, nitric acid, sulfuric acid, ammonia {\it etc.}). In our approach the formation and evolution of ionic clusters is followed by resolving the time dependent kinetic aggregation process and considering the ions sources (ultimately the atmospheric ionization of neutral species) and sinks. We show how in typical atmospheric conditions stable populations of molecular ions forms. The novelty of our work consists in the determination of the kinetic parameters that govern the molecular ions growth ({\it i.e.}, the forward and reverse clustering reaction constants for each cluster type and size) at a microscopic level. In fact a thermochemistry data base is built for the species of interest by integrating laboratory measurements, quantum mechanical calculations and, when appropriate, results from the macroscopic liquid droplet model [{\it Thomson}, 1928]. Such database is than used to retrieve the reverse clustering reaction coefficients for the molecular ion type and size and for the environmental conditions (pressure and temperature) of interest. The forward reaction is instead determined by calculating the ionic-neutral collisional rate or is assumed from laboratory determinations. Here we discuss the methodology and some of the results from sensitivity tests in which the ionization rate is changed so to reflect natural variation of the GCRs as modulated by the Sun. References: Dickinson, R. E., Solar variability and the lower atmosphere, {\it Bull. Am. Meterol. Soc., 56}, 1240-1248, 1975. Svensmark, H., and E. Friis-Christensen, Variation of cosmic ray flux and global cloud coverage A missing link in solar-climate relationships, {\it J. Atmos. Sol. Terr. Phys., 59}, 1225-1232, 1997. Thomson, J. J and G. P. Thomson, Conduction of electricity through gases, {\it Cambridge University Press}, 1928. Yu, F., Altitude variations of cosmic ray induced production of aerosols: Implications for global cloudiness and climate, {\it J. Geophys. Res., 107}, 10.1029/2001JA000248, 2001.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0335 Ion chemistry of the atmosphere (2419, 2427)
DE: 1650 Solar variability
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting