High albedos of cirrus in the tropical Pacific warm pool: Microphysical interpretation from CEPEX and from Kwajalein, Marshall Islands
- National Center for Atmospheric Research, Boulder, CO (United States)
Recent studies suggest that extensive shields of cirrus clouds over the equatorial Pacific {open_quotes}warm pool{close_quotes} may have a significant influence on the global climate, yet details of the links between cloud microphysical properties, upper-tropospheric latent and radiative beating rates, and climate are poorly understood. This study addresses whether relatively reflective ice crystals with dimensions smaller than about 100 {mu}m near the tops of tropical cirrus clouds, produced by deep convection when the sea surface temperature exceeds 300 K, are principally responsible for the high albedos observed in this region. In situ measurements of ice crystal size distributions and shapes, acquired during the Central Equatorial Pacific Experiment (CEPEX), are used to derive cloud ice water content (IWC), particle cross-sectional area (A), and other microphysical and optical properties from particles with sizes down to 5 {mu}m. These measurements are needed to ascertain the microphysical properties primarily responsible for determining cloud optical depth and albedo in visible wavelengths. Analysis shows that IWC, A, and various measures of particle size all tend to decrease with decreasing temperature and increasing altitude, although considerable scatter is observed. Small ice crystals make up more than half the mass and cause more than half the extinction on average in the upper, colder parts of the cirrus; however, the predominantly large particles in the lower, warmer parts of the cirrus contain at least an order of magnitude greater mass and are dominant in producing the high observed albedos. An examination of the lidar and radiometer data acquired onboard the NASA ER-2, which overflew the Learjet during CEPEX, supports the conclusion that the higher, colder regions of the cirrus typically have volume extinction coefficients that are only about 10% of those in the lower, warmer regions. 36 refs., 25 figs., 4 tabs.
- OSTI ID:
- 513345
- Journal Information:
- Journal of the Atmospheric Sciences, Vol. 53, Issue 17; Other Information: PBD: 1 Sep 1996
- Country of Publication:
- United States
- Language:
- English
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