HR: 1340h
AN: A23A-0915    [Abstracts]
TI: Using Ship Tracks to Characterize the Effects of Haze on Cloud Properties
AU: * Segrin, M S
EM: msegrin@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg Oregon State University, Corvallis, OR 97331-5503 United States
AU: Coakley, J A
EM: coakley@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg Oregon State University, Corvallis, OR 97331-5503 United States
AU: Christensen, M W
EM: chrismat@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg Oregon State University, Corvallis, OR 97331-5503 United States
AU: Tahnk, W R
EM: tahnk@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg Oregon State University, Corvallis, OR 97331-5503 United States
AB: 1-km MODIS observations of ship tracks off the west coast of the U.S. are used to characterize changes in droplet effective radius, cloud visible optical depth, pixel-scale cloud cover fraction, and column cloud liquid water amount as low-level marine clouds respond to particle pollution from underlying ships. The study re-examines findings of earlier studies based on 1-km AVHRR observations showing that when restricted to pixels overcast by low-level, single-layered cloud systems, polluted clouds in the ship tracks had, on average, 15 - 20% less liquid water than the nearby uncontaminated clouds. In addition to using MODIS instead of AVHRR radiances, this new study uses a retrieval scheme that accounts for the effects of partial cloudiness within the 1-km pixels on the retrieved cloud properties. The new study also employs an improved automated track finding scheme that allows the selection of unpolluted clouds to be closer to the clouds identified as being polluted. Results obtained with the partly cloudy pixel retrieval scheme show that the pixel-scale cloud cover within the ship track is almost always greater than that found in the surrounding region containing the unpolluted clouds. In addition, when restricted to overcast pixels, as was done in earlier studies, preliminary results from the Terra MODIS indicate that cloud liquid water amount is the same in the polluted and the nearby uncontaminated clouds. The liquid water amount appears to be constant regardless of the wavelengths of the channels used in the retrieval scheme. The discrepancy with the loss of liquid water found in the earlier study probably results from the limited sample of Terra observations examined thus far. Results from a larger ensemble of cases for both the Terra and Aqua MODIS instruments, and for the sensitivity of polluted clouds to additional particle loading, as occurs when ship tracks cross, will be presented.
DE: 0319 Cloud optics
DE: 3311 Clouds and aerosols
DE: 3360 Remote sensing
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005