Parameterizations of INDOEX microphysical measurements and calculations of cloud susceptibility: Applications for climate studies

Greg M. McFarquhar, Andrew J. Heymsfield

Research output: Contribution to journalArticlepeer-review


This study develops parameterizations of cloud microphysical properties in terms of bulk variables, provides new calculations of cloud susceptibility, and explores applications for climate studies. On the basis of cloud microphysical properties acquired during the Indian Ocean Experiment (INDOEX), the cloud effective radius re is observed to be proportional to the cube root of the ratio of cloud liquid water content (LWC) to total cloud droplet concentration Nt. A shape parameter k, depending on the skewness and dispersion of the cloud droplet size distribution, determines the proportionality constant and is highly dependent on the number of aerosols Na observed; k values range from 0.83 ± 0.07 in pristine clouds (Na < 500 cm-3) to 0.73 ± 0.08 in polluted clouds (Na > 1500 cm-3). Further, Nt is parameterized as a function of Na and cloud vertical velocity or LWC. Although the parameterization coefficients vary between pristine and polluted clouds, the parameterization equations are similar to those developed for other geographic locations and other cloud types, suggesting that they might be applied in climate models with varying coefficients. Using an empirically derived relation between Nt and the projected area of the cloud droplet distributions ac, the cloud susceptibilities are 2.16 times larger than those calculated using the original definition of susceptibility which does not take into account changes in cloud spectral width. Because susceptibility is shown to not vary significantly with wavelength in the solar regime, the average visible susceptibilities of 1.4×10-3 cm3 and 0.4×10-3 cm3 for pristine and polluted clouds are representative of the albedo effect. Observed susceptibilities and re agree with those calculated from the parameterization mostly within 30%, suggesting the parameterization can be applied in models to predict indirect radiative forcing.

Original languageEnglish (US)
Article number2000JD900777
Pages (from-to)28675-28698
Number of pages24
JournalJournal of Geophysical Research Atmospheres
Issue numberD22
StatePublished - Nov 27 2001
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology


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