HR: 0800h
AN: A41C-09    [Abstracts]
TI: CCN Concentration Variations Even in Clean Air Affect Cloud Microphysics
AU: * Mishra, S
EM: smishra@dri.edu
AF: Desert Research Institute, 2215 Raggio Pkwy., Reno, NV 89512-1095, United States
AU: Hudson, J G
AF: Desert Research Institute, 2215 Raggio Pkwy., Reno, NV 89512-1095, United States
AB: The Rain in Cumulus over the Ocean (RICO) campaign in Dec-Jan, 2004-05 investigated warm rain initiation. Measurements were made on the NCAR C-130 based in Antigua, at the northeast corner of the Antilles, where northeast trade winds provide clean air. As expected Colon-Robles et al. (2006) found giant nuclei to be well correlated with low level wind speed. However, they found that large cloud droplet concentrations were anti- correlated with low level winds and giant nuclei. They also found a high correlation between horizontal and vertical winds (w) and between w and total cloud droplet concentrations (N_c), which should be controlled by w and cloud condensation nuclei (CCN). In lieu of CCN, Colon-Robles et al. (2006) presented Condensation Nuclei (CN) and accumulation mode particle concentrations. Since they found no correlation between these concentrations and either wind speed they concluded that N_c was predominantly controlled by w, which seemed to negatively control large cloud droplet concentrations. Low level CCN concentrations during these same 12 RICO flights varied by a factor of three, which was more than expected for clean air. Contrary to the Colon-Robles et al. (2006) aerosol measurements, we find a correlation coefficient between CCN concentrations and N_c that is similar to the w-N_c correlation (0.64 versus 0.66). Moreover, the correlation coefficient of the product of w and CCN with N_c was 0.78! So, as expected, N_c is controlled by both CCN and w. These RICO results suggest that: 1) there are enough variations in CCN concentrations even in clean air masses to cause appreciable differences in cloud droplet concentrations, 2) large cloud droplet concentrations (i.e., precipitation) are controlled by CCN rather than giant nuclei as Hudson and Yum (2001) and Yum and Hudson (2002) demonstrated in less-clean air masses. Low CCN concentrations promote precipitation. 3) CN or accumulation mode aerosol cannot be used as surrogates for CCN as proposed by Dusek et al. (2006). Colon-Robles et al., (2006), Geophys. Res. Letts., 33, L20814, doi:10.1029/2006GL926476, Dusek et al., (2006), Science, 312, 1375-1378. Hudson and Yum, (2001), J. Atmos. Sci., 58, 915-926. Yum and Hudson, (2002), Tellus, 54B, 61-73.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly