HR: 16:45h
AN: A24B-04    [Abstracts]
TI: Detection of the Arctic Dehydration-Greenhouse Feedback Using Satellite Observations and a Regional Climate Model
AU: * Grenier, P
EM: grenier@sca.uqam.ca
AF: Universite du Quebec a Montreal, 201, av. President-Kennedy, Montreal, QC H3C 3P8, Canada
AU: Blanchet, J
EM: blanchet.jean-pierre@uqam.ca
AF: Universite du Quebec a Montreal, 201, av. President-Kennedy, Montreal, QC H3C 3P8, Canada
AU: Munoz-Alpizar, R
EM: rodrigo@sca.uqam.ca
AF: Universite du Quebec a Montreal, 201, av. President-Kennedy, Montreal, QC H3C 3P8, Canada
AU: Girard, E
EM: girard.eric@uqam.ca
AF: Universite du Quebec a Montreal, 201, av. President-Kennedy, Montreal, QC H3C 3P8, Canada
AU: Jones, C
EM: jones.colin@uqam.ca
AF: Universite du Quebec a Montreal, 201, av. President-Kennedy, Montreal, QC H3C 3P8, Canada
AU: Bertram, A
EM: bertram@chem.ubc.ca
AF: University of British Columbia, 2210, West Mall, Vancouver, BC V6T 1Z4, Canada
AU: Stephens, G L
EM: stephens@atmos.colostate.edu
AF: Colorado State University, 1371, Campus Delivery, Fort Collins, CO 80523, United States
AB: Datasets from the CloudSat radar reflectivity and the CALIPSO lidar backscattering measurements have provided a new regard on Arctic winter cloud systems, as well as on the way aerosols determine their formation and evolution. In this presentation, we emphasize the role of sulfates in the cooling and dehydrating air masses from cold low pressure systems entering the Arctic during the cold season. Using combined information from satellite instruments and the Northern Aerosol Regional Climate Model (NARCM), we show that a high sulfate fraction in the aerosol field is much likely to favour the production of bigger ice crystals which, by increased precipitation rates, accelerate both the depletion of atmospheric water content and the reduction of its greenhouse effect. This is linked to the property of sulfuric acid to lower the freezing point of haze droplets, leading to a type of thin ice clouds (TIC-2) extending deeply in the troposphere and increasing the radiative cooling rate with further strenghtening of water deposition and sedimentation of large ice crystals. This enhanced dehydration-IR cooling induced by acidic IFN is a case of dehydration-greenhouse feedback (DGF). In contrast, pristine aerosols favour the formation of large amounts of small crystals and non-precipitating thin ice cloud (TIC-1) systems. Because of their high sensitivity to discriminate crystal sizes, TIC-2 types are easily detected by both instruments, lidar and radar, whereas TIC-1 type is only seen by the lidar due to its capability to detect smaller crystals. Therefore, CloudSat and CALIPSO datasets are used to heuristically discriminate Arctic TIC in two crystal size categories (radar/lidar versus lidar-only). A calculation of the correlation between the occurrence of these cloud types and the aerosol sulfate fraction is obtained by joining satellite information to an aerosol field simulation from NARCM. Humidity field from the Atmospheric InfraRed Sounder (AIRS) is also used to analyse a cold cyclone dehydration case over the Arctic Ocean in January 2007. Results show that the DGF process could be responsible for climatic tropospheric cooling when a cold region is subject to an increase in sulfuric acid concentrations.
DE: 3311 Clouds and aerosols
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting