HR: 1330h
AN: A22A-1037    [PDF]
TI: Morphology of Tropical Cirrus Crystals Derived from Single Particle and Bulk Property Analysis
AU: Raga, G B
EM: raga@servidor.unam.mx
AF: Universidad Nacional Autonoma de Mexico, Centro de Ciencias de la Atm¢sfera - UNAM Universidad Nacional Aut¢noma de M‚xico Circuito Exterior s/n, Ciudad Universitaria, Mexico City, DF 04510 Mexico
AU: * Baumgardner, D
EM: darrel@servidor.unam.mx
AF: Universidad Nacional Autonoma de Mexico, Centro de Ciencias de la Atm¢sfera - UNAM Universidad Nacional Aut¢noma de M‚xico Circuito Exterior s/n, Ciudad Universitaria, Mexico City, DF 04510 Mexico
AU: Kok, G
EM: glkok@dropletmeasurement.com
AF: Droplet Measurement Technologies, 5710B Flatiron Parkway, Boulder, CO 80301 United States
AU: Anderson, B
EM: B.E.Anderson@LaRC.NASA.GOV
AF: NASA Langley Research Center, Mail Stop 483, Hampton, VA 23681-0001 United States
AU: Garrett, T
EM: tgarrett@met.utah.edu
AF: University of Utah, 135 S 1460 E, Rm 819, Salt Lake City, UT 84112-0110 United States
AU: Weinstock, E
EM: weinstock@huarp.harvard.edu
AF: Harvard University, 40 Oxford Street, Cambridge, MA 02138 United States
AU: Smith, J
EM: jsmith@huarp.harvard.edu
AF: Harvard University, 40 Oxford Street, Cambridge, MA 02138 United States
AB: The bulk density, surface area, asphericity and fractal dimensions of crystals in tropical cirrus clouds are derived by combining complementary measurement techniques that were employed during the CRYSTAL/FACE experiment in July, 2002. The instruments that are used in this derivation are the Cloud, Aerosol and Precipitation Spectrometer (CAPS) that measures single particle properties, the cloud integrating nephelometer (CIN) that measures ensemble light scattering and the Harvard Total Water (HTW) sensor that measures the vapor concentration of evaporated cloud particles. The asphericity of particles smaller than 50 $\mu$m is determined by comparing the forward and backward scattering light spectra that is measured with the CAPS. The ratio of the areas under the forward and back scattering spectra is proportional to the asymmetry factor and can be used in radiative transfer calculations for evaluating the flux of radiation through the cirrus layers. The fractal dimension of ice crystals larger than 200 $\mu$m is also derived from the CAPS measurements and is a measure of the crystal "roughness", related to the surface area and bulk density. The bulk density is estimated from CAPS and HTW measurements by calculating the volume of particles from the measured size distribution and then deriving the bulk density that would give an ice water content comparable to that measured by the HTW. The evaluation produces a family of curves relating ice crystal effective diameter and bulk density to ice water content. The behavior of these curves under different temperature conditions provides information on the type and age of ice crystals. The ice crystal surface areas are derived in a similar fashion by comparing the scattering coefficient calculated from the size distributions and direct measurements with the CIN. As with the derivation of bulk density, the surface area computed by this technique depends on the assumed shapes of the crystals. The average fractal dimension, asphericity factor, surface area and bulk density are sensitive to cloud temperature, distance from cloud top and cloud age. Contrail crystals are clearly distinguishable from natural cirrus by much lower fractal dimensions and smaller asphericity.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting