Gb. Raga et Pr. Jonas, MICROPHYSICAL AND RADIATIVE PROPERTIES OF SMALL CUMULUS CLOUDS OVER THE SEA, Quarterly Journal of the Royal Meteorological Society, 119(514), 1993, pp. 1399-1417
Microphysical and radiative data obtained in fields of cumulus clouds
over the sea around the United Kingdom are presented. The Meteorologic
al Research Flight C-130 aircraft was used to make radiation and cloud
microphysical measurements in situ on four different occasions. The s
ub-cloud aerosol concentrations ranged from 100 to 5000 cm-3, from fai
rly maritime to heavily polluted. Vertical profiles of microphysical v
ariables indicate that small cumuli over the sea have some properties
that are more similar to marine stratocumuli than to continental cumul
i. Nonetheless, variables, such as liquid-water content and droplet-nu
mber concentration, exhibit a larger variability than in stratocumuli,
owing to more vigorous entrainment in cumuli. Mie theory was used to
compute extinction cross-sections, single scattering albedo, back-scat
tering cross-sections, and asymmetry parameters for all in-cloud sampl
es. The average vertical profiles are in agreement with values compute
d by previous authors for trade-wind cumuli. Our results show that the
se properties depend upon the background aerosol concentrations. A sim
ple two-stream radiative-transfer model, using the back-scattering cro
ss-section, is presented and shows good agreement with run-averaged ra
diometric observations.