Liquid water path and plane-parallel albedo bias during ASTEX

Journal Article · Tue Aug 15 04:00:00 EDT 1995 · Journal of the Atmospheric Sciences

DOI:https://doi.org/10.1175/1520-0469(1995)052<3002:LWPAPP>2.0.CO;2· OSTI ID:106833

Cahalan, R F; Silberstein, D ^[1]; Snider, J B ^[2]

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1. NASA/Goddard Space Flight Center, Greenbelt, MD (United States)
2. NOAA/ERL, Boulder, CO (United States)

Inhomogeneous distributions of liquid water like those observed in real clouds generally reflect less solar radiation than idealized uniform distribution assumed in plane-parallel theory. Here the authors determine cloud reflectivity and the associated plane-parallel albedo bias from distributions of liquid water path derived from 28 days of microwave radiometer measurements obtained on Porto Santo Island in the Maderias during June 1992 as part of the atlantic Stratocumulus Transition Experiment (ASTEX). The distributions are determined for each hour of the day, both for composites of the full set of 28 days and for a subset of 8 days having a high fraction of relatively thick cloud. Both sets are compared with results obtained from California stratocumulus during FIRE [First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment]. In FIRE the albedo bias was dominated by the variability of the cloud optical depth, as measured by a fractal parameter, 0 {le} f {le} 1, while the ASTEX results are more complex. Mean cloud fraction above a 10 g m{sup -2} threshold is about 50% in the 28-day set, compared to 76% in the 8-day subset and 82% in FIRE> Cloud fraction is sensitive to the threshold for the 28 ASTEX days, probably due to a large fraction of thin cloud below the threshold, but this is not the case for the 8-day subset or for FIRE. Clear fractions during ASTEX are generally of shorter duration than those in FIRE, as are those in the 8-day subset. The diurnal mean fractal parameter is about 0.6 in ASTEX compared to 0.5 in FIRE, while the 8-day subset has nearly the same mean but a wider range. These results show that cloud fractal and radiative properties can vary considerably from one site and time to another, and at different times within the same site, as meterological conditions change. 30 refs., 7 figs.

• OSTI ID: 106833
• Journal Information: Journal of the Atmospheric Sciences, Journal Name: Journal of the Atmospheric Sciences Journal Issue: 16 Vol. 52; ISSN 0022-4928; ISSN JAHSAK
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
ALBEDO
CLOUDS
EXPERIMENTAL DATA
GREENHOUSE EFFECT
HOURLY VARIATIONS
MOISTURE
RADIANT HEAT TRANSFER
REFLECTION
REFLECTIVITY
WATER