HR: 0800h
AN: A11B-0043    [Abstracts]
TI: A coupled physical, optical, and photochemical model of snow: relating measurements of specific surface area to snow optical properties.
AU: * Phillips, G
EM: ffgjp@uaf.edu
AF: Geophysical Institute and Department of Chemistry and Biochemistry University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775 United States
AU: Simpson, W R
EM: ffwrs@uaf.edu
AF: Geophysical Institute and Department of Chemistry and Biochemistry University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775 United States
AU: Taillandier, A
EM: tailland@lgge.obs.ujf-grenoble.fr
AF: Glaciology Laboratory CNRS, 54 Rue Moliere, Grenoble, 38402 France
AU: Domine, F
EM: Florent.Domine@lgge.obs.ujf-grenoble.fr
AF: Glaciology Laboratory CNRS, 54 Rue Moliere, Grenoble, 38402 France
AB: Recent experiments and modeling studies have shown that chemical processes in the snow pack have significant impacts on the chemistry of the atmosphere. Solar ultraviolet radiation penetrating the snow pack is the driving force for some of these chemical processes. Therefore, factors controlling photochemical processes in the snowpack need to be understood. Here, we present field investigations of the relationship between physical and optical properties of the snowpack and laboratory studies validating radiation models that predict photochemical reaction rates within the snowpack. A critical parameter in modeling snow photochemistry is the scattering coefficient for the snow. Steve Warren (University of Washington) proposed that the best physical measurement that correlates with scattering is the specific surface area (SSA); however, this correlation has not been tested to our knowledge. Therefore, we performed field experiments comparing optical measurements of scattering and the SSA. The measurement of the snow SSA was achieved by using the Brunauer-Emmett-Teller method to analyse CH$_4$ adsorption onto snow samples. The optical determination of scattering in the snowpack used a variation of the method of Beaglehole. In this method, the light penetration of a snow sample was measured using decreasing thicknesses of the sample on a black base. In the thin layers, the scattering dominates the light attenuation within the snow. In the thicker layers both the absorption and scattering determine the light attenuation. Kubelka-Munk two-flux theory was used to model the data and calculate the scattering and absorption within the samples. This determination of the scattering was found to be proportional to the measured SSA. This linkage between SSA and optical properties confirms Warren`s hypothesis and allows the literatures of optical and physical properties of snow to be coupled. A laboratory study of the performance of snow radiation models was also carried out. A delta-Eddington model and the TUV-Snow model of Lee-Taylor and Madronich were used to calculate the photolysis rate coefficient of an actinometer molecule in an artificial snow analog. The total depth integrated photolysis rates calculated by the models were compared with photolysis rates determined from the conversion of the actinometer. The models were found to be in good agreement with the experiments. The validated models will made available to the wider research community via the www. Through the combination of these field and laboratory experiments, we are now able to quantify snow photochemistry either by optical measurements or by simply knowing snow physical properties.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting