HR: 1340h
AN: A53A-0144    [Abstracts]
TI: Aerosol-Cloud Interactions and the Role of Clouds in Modifying Atmospheric Composition during INTEX-NA
AU: * Anderson, B E
EM: b.e.anderson@larc.nasa.gov
AF: NASA Langley Research Center, MS 483, NASA LaRC, Hampton, VA 23681
AU: Thornhill, K L
EM: k.l.thornhill@larc.nasa.gov
AF: NASA Langley Research Center, MS 483, NASA LaRC, Hampton, VA 23681
AU: Chen, G
EM: gao.chen-1@nasa.gov
AF: NASA Langley Research Center, MS 483, NASA LaRC, Hampton, VA 23681
AU: Barrick, J D
EM: j.d.barrick@larc.nasa.gov
AF: NASA Langley Research Center, MS 483, NASA LaRC, Hampton, VA 23681
AU: Winstead, E L
EM: e.l.winstead@larc.nasa.gov
AF: NASA Langley Research Center, MS 483, NASA LaRC, Hampton, VA 23681
AU: Diskin, G S
EM: g.s.diskin@larc.nasa.gov
AF: NASA Langley Research Center, MS 483, NASA LaRC, Hampton, VA 23681
AU: Sachse, G W
EM: g.w.sachse
AF: NASA Langley Research Center, MS 483, NASA LaRC, Hampton, VA 23681
AU: Vay, S A
EM: s.a.vay@larc.nasa.gov
AF: NASA Langley Research Center, MS 483, NASA LaRC, Hampton, VA 23681
AU: McNaughton, C
EM: cameronm@soest.hawaii.edu
AF: University of Hawaii, Manoa, 1000 Pope Road, Marine Sciences Building, Honolulu, HI 96822
AU: Clarke, A D
EM: tclarke@soest.hawaii.edu
AF: University of Hawaii, Manoa, 1000 Pope Road, Marine Sciences Building, Honolulu, HI 96822
AU: Dibb, J E
EM: jack.dibb@unh.edu
AF: University of New Hampshire, Morse Hall 39 College Road , Durham, NH 03824-3525
AB: During the summer 2004 INTEX-NA mission, extensive measurements of atmospheric composition were recorded aboard the NASA DC-8 aircraft as it flew sampling missions within the North American tropospheric airshed. Clouds were often encountered along the flight paths, as wet convection was quite active throughout the study area. To examine the impact of these clouds upon trace gas distributions and chemistry as well as to search for links between aerosols and cloud properties (indirect effects), particle size distribution data recorded aboard the DC-8 were used to derive a number of important cloud microphysical parameters including cloud water content, extinction, effective radius, and particle mean volume and number diameters. We have also analyzed UV-Dial aerosol profiles to calculate cirrus cloud frequency, optical depth, wavelength dependencies, and depolarization ratios. Results of the study indicate that the aircraft flew within clouds somewhere between 5 and 10% of the time at most flight levels. The largest cloud particles, highest cloud water concentrations, and greatest average extinctions were found at temperatures between -20 and 0 C. Most of the cumulus clouds sampled during the mission contained low liquid water contents (< 0.2 g/m3), had relatively small particles (< 20 um), and exhibited small values of light extinction. Many cloud penetrations occurred at the top of the planetary boundary layer, where convective overshoot had produced high levels of water vapor saturation. Assuming these clouds grew in parcels that contained roughly the same aerosol particle concentrations as the air just below cloud base, we investigated the relationship between submicron particle densities and cloud microphysical properties and found that there were significant differences in median cloud extinction, effective radius, volume mean diameter, and total particle concentrations between the "clean", low aerosol and "polluted", high aerosol cases. Thin cirrus clouds were often encountered at high altitudes during INTEX. Most of these clouds contained < 0.01 g/m3 of particles that were, on average, 20 um in diameter. Calculated extinctions were typically < 1.0/km, which corresponds to "sub-visual" clouds. If the clouds are grouped according to their level of interstitial submicron particles, the clouds that contained low levels of ambient aerosols were more likely to exhibit lower extinctions and larger effective radii for a given amount of ice water content. The polluted cirrus also tended to form at slightly lower relative humidities than clean cirrus. Finally, higher levels of pollutants and nanometer-sized aerosols were often found in the vicinity of cirrus anvils; nitric acid was the only measured gas-phase species that appeared to be lost to ice particle surfaces.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005