HR: 0800h
AN: A11B-0058    [Abstracts]
TI: Factors that influence UV actinic flux in and above Arctic snow
AU: * Lefer, B L
EM: blefer@uh.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: * Lefer, B L
EM: blefer@uh.edu
AF: University of Houston, Geosciences Department 312 SRB#1 4800 Calhoun Drive, Houston, TX 77204 United States
AU: Hall, S R
EM: halls@ucar.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: Shetter, R E
EM: shetter@ucar.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: Albert, M R
EM: malbert@crrel.usace.army.mil
AF: Cold Regions Research and Engineering Laboratory, USACE Engineer Research and Development Center 72 Lyme Road, Hanover, NH 03755 United States
AU: Courville, Z R
EM: zoe.courville@dartmouth.edu
AF: Dartmouth College, Thayer School of Engineering, 8000 Cummings Hall, Hanover, NH 03755 United States
AB: Photochemical rate constants (i.e., photolysis frequencies or j-values) are principle inputs to photochemical models used to illustrate atmospheric chemistry, both in the overlaying atmosphere and within the snowpack. We have measurements of the in situ actinic flux above and within the snowpack during most of the 2003 and 2004 Summit, Greenland measurement periods from which we calculated 39 different photolysis frequencies. Since the firn (or in-snow) actinic flux observations were made at a series of discrete depths while the firn air chemical measurements reflect variable subsurface volumes, it is necessary to test the various radiative transfer models that attempt to describe the actinic flux both in the atmosphere and snowpack environments. To do this we incorporate the available measurements and estimates of factors that impact the above-snow actinic flux, such as snow surface albedo, percent cloud cover, overhead ozone column and aerosol/blowing snow optical depth into an atmospheric radiative transfer model. We also investigate the impact of physical snow characteristics (e.g., density, grain size, etc.) on the penetration of UV radiation. We use our measurements of the UV actinic flux to test these radiative transfer models for a variety atmospheric and snow conditions to help identify which of these variables are the most important inputs to the models.
DE: 0317 Chemical kinetic and photochemical properties
DE: 0360 Transmission and scattering of radiation
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting