HR: 0800h
AN: A51D-0822    [Abstracts]
TI: Particle Size Distributions and Densities of Tropical Cirrus Clouds Observed by the ACE FTIR Instrument on the SciSat-1 Satellite.
AU: * Zasetsky, A Y
EM: azaset@sciborg.uwaterloo.ca
AF: University of Waterloo, Waterloo Centre for Atmospheric Sciences, Waterloo, ON N2L3G1 Canada
AU: Eremenko, M
EM: meremenk@scimail.uwaterloo.ca
AF: University of Waterloo, Waterloo Centre for Atmospheric Sciences, Waterloo, ON N2L3G1 Canada
AU: Sloan, J J
EM: sloanj@UWaterloo.CA
AF: University of Waterloo, Waterloo Centre for Atmospheric Sciences, Waterloo, ON N2L3G1 Canada
AB: The FTIR spectrometer on the SciSat-1 satellite has been providing regular occultation measurements since the completion of its commissioning phase in late February 2004. During April and May of 2004, for tangent points occurring in the tropics, several occultations contained spectra that appear to exhibit extinction signals due to tropical cirrus clouds. The spectra of atmospheric aerosols and clouds have very broad bands with locations that shift with the particle size and shape. Moreover, they are usually obscured by gas phase absorptions that can become completely opaque for observations in the mid- to upper-troposphere. To overcome this interference, it has been customary to make measurements at selected wavelengths that are relatively free from gas phase interference. Conversely, the ACE FTIR instrument produced spectra that are broad band (800 to 4000 cm$^{-1}$) and high resolution (0.02 cm$^{-1}$). Thus they contain enough information for the simultaneous retrieval of the chemical compositions, phases and size distributions of cloud and aerosol particles, without additional information. We have developed techniques to make such standalone estimates by combining occultation measurements with of pure aerosol spectra and have tested them successfully on measurements made by the ATMOS instrument of the decay of the sulfate aerosol following the Pinatubo eruption. Using these retrieval methods, we have analysed the ACE FTIR observations of tropical cirrus clouds and determined the size distributions and vertical (number, area or volume) density profiles of the ice particles in the clouds. We will report the aerosol characteristics and discuss correlations between the retrieval results and the results of equilibrium thermodynamic calculations.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0360 Transmission and scattering of radiation
DE: 0365 Troposphere--composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting