Variations of TOA Narrowband and Broadband Radiances
with Cloud Types

By combining the ISCCP-ScaRaB DX and ScaRaB A2 datasets, instantaneous narrowband VIS and IRW radiances, broadband SW and LW radiances, SW and LW fluxes, as well as scene identifications from both the ISCCP analysis and the ERBE MLE method are available.

Figures here for one-month (May 1994), cloud-type-dependent averages of (pairwise) TOA LW and IRW, SW and VIS, VIS and IRW, SW and LW radiances, together with their standard deviations, show the radiative variability for each cloud type (this type of plot was first used by Stubenrauch et al. [1999]). Since the radiances also vary with Sun-Target-Satellite geometry, the results illustrated here are only for the near-nadir viewing pixels (separated for tropics, midlatitude and polar; land and ocean; forward- and backward-scattering conditions).

For each figure, 10 color dots label the ISCCP scene types (clear sky and 9 standard ISCCP cloud types) whereas 4 black dots label the ERBE cloud cover categories.

ISCCP Clear
ISCCP Cumulus	ISCCP Stratocumulus	ISCCP Stratus
ISCCP AltoCumulus	ISCCP Altostratus	ISCCP Nimbostratus
ISCCP Cirrus	ISCCP Cirrostratus	ISCCP Deep Convective
ERBE Clear
ERBE Partly Cloudy	ERBE Mostly Cloudy	ERBE Overcast

Tropics (30S-30N)

Land, Forward-Scattering	Land, Backward-Scattering	Ocean, Forward-Scattering	Ocean, Backward-Scattering

Midlatitude (30N-60N and 30S-60S)

Land, Forward-Scattering	Land, Backward-Scattering	Ocean, Forward-Scattering	Ocean, Backward-Scattering

Polar (60N-90N and 60S-90S)

Land, Forward-Scattering	Land, Backward-Scattering	Ocean, Forward-Scattering	Ocean, Backward-Scattering

One conclusion that can be drawn from the figures is that the ERBE MLE-derived cloud cover implicitly includes information on cloud height (Pc) and optical thickness (Tau), producing mixtures of Pc-variation and Tau-variation.

References:

Stubenrauch, C.J., W.B. Rossow, N.A. Scott, and A. Chédin, 1999: Clouds as seen by satellite sounders (3I) and imagers (ISCCP). Part III: Spatial heterogeneity and radiative effects. J. Climate, 12, 3419-3442.

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