HR: 11:05h
AN: A22C-04    [Abstracts]
TI: Where Does Firn Air Come From?
AU: * Albert, M R
EM: mary.r.albert@erdc.usace.army.mil
AF: Cold Regions Research & Engineering Lab, 72 Lyme Road, Hanover, NH 03755 United States
AU: * Albert, M R
EM: mary.r.albert@erdc.usace.army.mil
AF: Thayer School of Engineering, Dartmouth College, Hanover, NH 03755 United States
AU: Courville, Z R
EM: zoe.r.courville@erdc.usace.army.mil
AF: Cold Regions Research & Engineering Lab, 72 Lyme Road, Hanover, NH 03755 United States
AU: Courville, Z R
EM: zoe.r.courville@erdc.usace.army.mil
AF: Thayer School of Engineering, Dartmouth College, Hanover, NH 03755 United States
AU: Perron, F E
EM: frank.e.perron@erdc.usace.army.mil
AF: Cold Regions Research & Engineering Lab, 72 Lyme Road, Hanover, NH 03755 United States
AU: Dibb, J E
EM: jed@unh.edu
AF: Institute for Study of Earth, Oceans, Space, University of New Hampshire, Durham, NH 03824 United States
AU: Lefer, B L
EM: lefer@uh.edu
AF: Department of Geosciences, University of Houston, Houston, TX 77204-5007 United States
AB: Understanding linked physical and photochemical interactions in the near-surface snow is required both to assess the impact of the reactions on the composition of the atmosphere above the snow and to understand post-depositional processes for ice core interpretation. Field campaigns in 2003 and 2004 at Summit, Greenland have focused on simultaneous measurements of many chemical species, actinic flux, and temperature in and above the snow pack. The measured concentrations depend on the snow and interstitial air chemical content, and the volume from which samples are collected depends on the stratigraphy and microphysical characteristics of the snow pack as well as flow characteristics induced by the sampler. The layered nature of snow and firn has a large impact on chemical interactions. A critical element of understanding snow pack photochemistry is an understanding of airflow through the snow pack, under both natural conditions and the perturbed state during sampling. In situ experiments were conducted using SF6 as an inert tracer gas to verify flow paths in the near-surface snow. To gather non-reactive scalar data, vertical arrays of fine-gauge thermocouples were installed to record firn temperatures, both for model verification and for examining temperature versus photochemical effects. Finite element calculations using measured firn properties and boundary conditions were conducted for computation of flow field and resulting advective-diffusive temperature profiles a variety of conditions corresponding to the conditions of the group sampling. Measurements and modeling are shown for several scenarios, including group shading experiments and experiments conducted over long times in the near surface as well as deeper in the firn. The model results compare well with measured temperatures. Possible effects of stratigraphy, flow paths and flow rates on chemical measurements are discussed.
DE: 3322 Land/atmosphere interactions
DE: 3210 Modeling
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting