HR: 0800h
AN: A41D-0743    [Abstracts]
TI: Changes in Aerosol and Aerosol Direct Radiative Effects Near Clouds
AU: * Coakley, J A
EM: coakley@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University 104 COAS Admin Bldg, Corvallis, OR 97331-5503, United States
AU: Twohy, C H
EM: twohy@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University 104 COAS Admin Bldg, Corvallis, OR 97331-5503, United States
AU: Tahnk, W R
EM: tahnk@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University 104 COAS Admin Bldg, Corvallis, OR 97331-5503, United States
AU: Hayes, C R
EM: chayes@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University 104 COAS Admin Bldg, Corvallis, OR 97331-5503, United States
AB: Aerosols and their radiative effects change in the vicinity of clouds. The high relative humidity (RH) of the environment near low-level clouds causes hygroscopic aerosols to swell, thereby changing their optical properties. Aircraft observations of relative humidity and particle concentrations taken during INDOEX are used to document the increases in RH and the changes in particle concentrations in the vicinity of clouds. These changes along with the chemical composition of the aerosol are used to estimate the changes in optical properties and the effect of these changes on the aerosol direct radiative effects as a function of distance from low-level clouds. Observations from the multichannel cloud radiometer (MCR) during INDOEX are used to compare the calculated changes with those observed. Part of the changes in the observed radiances are due to changes in particle concentrations and to particle growth, but part is also due to the increased illumination of the cloud-free column as a result of radiation reflected by the sides and tops of nearby clouds. Visible and near infrared radiances from the MCR are used to estimate the relative magnitudes of the different contributions to the changes. As such effects decrease with distance from cloud, daytime CALIPSO lidar observations are used to determine the sizes of cloud-free ocean regions in which low-level clouds reside. This distribution provides the probability of distances to cloud for aerosols in the cloud-free regions. The observed changes and the distribution of sizes for cloud-free ocean regions are used to estimate the contribution of the changes in the direct radiative effects of aerosol in the vicinity of low-level clouds to the total direct radiative effects of aerosols for oceans. These changes are estimated to be comparable to the ~1 Wm^-2 uncertainty in the ~4.6 Wm^-2 direct aerosol effect derived from CERES observations.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 3311 Clouds and aerosols
DE: 3359 Radiative processes
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting