HR: 0800h
AN: A41A-0017    [Abstracts]
TI: Surface Radiative Forcing by Clouds and Diamond Dust Measured During Winter 2006-2007 at Eureka, Canada
AU: * Lesins, G
EM: glen.lesins@dal.ca
AF: Dalhousie University Department of Physics and Atmospheric Science, Dunn Building, Halifax, NS B3H 1Z9, Canada
AU: Bourdages, L
EM: line.bourdages@gmail.com
AF: Dalhousie University Department of Physics and Atmospheric Science, Dunn Building, Halifax, NS B3H 1Z9, Canada
AU: Duck, T
EM: tom.duck@dal.ca
AF: Dalhousie University Department of Physics and Atmospheric Science, Dunn Building, Halifax, NS B3H 1Z9, Canada
AU: Eloranta, E W
EM: eloranta@lidar.ssec.wisc.edu.
AF: University of Wisconsin Space Science and Engineering Center, 1225 W. Dayton St., Madison, WI 53706, United States
AU: Walden, V P
EM: vonw@uidaho.edu
AF: University of Idaho Department of Geography, PO Box 443021 McClure 305A, Moscow, ID 83844-3021, United States
AB: During the Arctic winter, in the absence of sunlight, most cloud and diamond dust layers exert a positive (warming) radiative forcing at the ground by blocking the longwave infrared window and thus help to prevent surface temperatures from dropping to even lower values. As part of the Canadian Network for the Detection of Atmospheric Change (CANDAC) and the NOAA Study of Environmental Arctic Change (SEARCH), surface based remote sensing measurements are being taken of the cloud properties and the radiative forcing at Eureka (80N, 86W) in the Nunavut Territory in the Canadian High Arctic. Here we present results obtained during the winter of 2006-2007 using the University of Wisconsin Arctic High Spectral Resolution Lidar (AHSRL) and Polar Atmospheric Emitted Radiance Interferometer (P-AERI) demonstrating the importance of cloud radiative forcing. Even under clear sky conditions the measured diamond dust surface infrared downward radiative forcing ranged from 7 to 32 W/m2 in the wavelength band from 4 to 20 microns for visible optical depths ranging from 0.23 to 1.7. Lidar extinction and depolarization ratios showed that these events are dominated by ice crystals. This is an important difference for earlier studies at other Arctic locations which concluded that significant radiative forcing from diamond dust occurred only if liquid water clouds were also present. At Eureka the diamond dust events can produce high enough optical depths even in the absence of liquid water. In addition there are events where a thin layer of supercooled cloud water caps a layer of ice crystals which extends to the surface. The differences in the radiative forcing of these events will also be examined. These results have important implications for atmospheric processes in the winter Arctic including Arctic smog, dehydration effect, minimum attainable temperature, surface energy balance and regional climate change.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting