HR: 16:35h
AN: A44A-03    [Abstracts]
TI: Observed Cloud Microphysical Characteristics in India and the Arabian Peninsula: High droplet concentrations does not always retard coalescence
AU: * Bruintjes, R T
EM: roelof@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 United States
AU: Jensen, T
EM: jensen@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 United States
AU: Breed, D
EM: breed@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 United States
AU: Salazar, V
EM: vidal@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 United States
AU: Piketh, S
EM: stuart@crg.bpb.wits.ac.za
AF: University of Witwatersrand, Privte Bag 2050, WITS, Johannesburg, 2050 South Africa
AU: Ross, K
EM: kristy@crg.bpb.wits.ac.za
AF: University of Witwatersrand, Privte Bag 2050, WITS, Johannesburg, 2050 South Africa
AU: Al Mandoos, A
EM: AMandoos@almiyah.gov.ae
AF: Department of Water Resources Studies, P.O.Box 4815, Abu Dhabi, none United Arab Emirates
AU: Al Mangoosh, A
EM: AMangoosh@almiyah.gov.ae
AF: Department of Water Resources Studies, P.O.Box 4815, Abu Dhabi, none United Arab Emirates
AB: In-situ aerosol and cloud microphysical measurements in convective clouds in India, the United Arab Emirates, Sultanate of Oman and Saudi Arabia over the past four years have shown large spatial and temporal variations in microphysical characteristics. These variations can be linked to variations in temporal and spatial atmospheric aerosol characteristics. While the concentrations of cloud droplets near cloud base are fairly similar precipitation formation processes (especially condensation-coalescence process) differ substantially from one region to the other and also temporally in the same region based on aerosol characteristics and the thermodynamic structure of the atmosphere. Observational studies have shown that large nuclei (between 0.8 and 5μm diameter) which are ingested into clouds broaden the cloud droplet spectrum and accelerate the production of raindrops by coalescence. The effect of large cloud condensation nuclei (CCN) on the process and rate of drizzle and rain formation in warm clouds is investigated using the observational data and a one-dimensional cloud parcel model. Large nuclei are found to be essential for initiating coalescence in polluted environments. Once coalescence has been initiated, the rate at which cloud liquid water is transferred to precipitation-size drops depends on the amount of drizzle which forms in the cloud. Drizzle production is retarded when accumulation mode aerosol concentration is high, but is promoted when coarse mode aerosol concentration is high. Giant and ultra-giant CCN (diameter >10 micron) accelerate the onset of coalescence but suppress drizzle production, and result in a slower production of raindrops. Larger nuclei slow the rate of drizzle formation but condensate is converted to precipitation-size drops, and may fall out of the cloud before most of the available water has been harvested. These results in turn determine the ice processes in clouds once they grow to temperatures colder than 0oC and the overall precipitation formation and possibly efficiency and amount of precipitation that will reach the surface. These results have implications for both advertent and inadvertent weather modification.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 3311 Clouds and aerosols
DE: 3314 Convective processes
DE: 3354 Precipitation (1854)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005