A revised hybrid bispectral threshold method is developed to improve retrievals of clear-sky and cloud-top temperatures, low-level cloud amounts, and thin cirrus clouds. These changes include the setting of constraints on the cloud albedo and the temperatures which may be included in the calculations of clear-sky temperature and cloud amount. When any of the limits are exceeded, an alternative method is used for the determination of cloud amount from the two-dimensional visible-infrared histogram. The alternate method used depends on the type of constraint violated by the results from the standard cloud amount calculation. Even though it appears that the overall average cloud amount derived with the revised method is not much different than that which would have been derived from the original technique, the new methodology produced substantial changes in about one third of the cloud amount retrievals. Low cloud retrievals were affected most often by the new constraints. Thin, high clouds were detected in many instances when they would have been missed with the original methodology.

The revised method was used to analyze a 15-day set of 3-hourly, 32-km resolution visible and infrared data taken with the GOES-West satellite over the tropical eastern Pacific for the International Satellite Cloud Climatology Project (ISCCP). Four different types of cloud regimes were prevalent over the 2.5¿¿2.5¿ regions within the study area: trade cumulus characterized by low albedo (~29%), low altitude, and low cloud amount (40%; Intertropical Convergence Zone (ITCZ) cloudiness characterized by a predominance of middle- and high-altitude clouds, with cloud albedos >35% and cloud amounts >50%; and tropical storms, with a predominance of high clouds, high albedos, and mean cloud amounts as great as 74%. Diurnally averaged albedos of 29%, 34%, and 44% were found over low, middle, and high clouds, respectively. Cloud amounts and albedos are similar to those derived from other data sets. Total and low cloud amounts in areas with trade cumulus and stratocumulus fields were usually greatest in the early morning and at a minimum in the midafternoon.

A harmonic analysis of mean 3-hourly cloudiness over the trade and stratocumulus regions revealed a very strong diurnal component over both cloud types. A regions revealed a very strong diurnal component over both cloud types. A significant semidiurnal component was found over the trade cumulus regions. Its phase corresponds to the semidiurnal tide. The semidiurnal component was much weaker over the stratocumulus regions. Over the ITCZ and the areas where the tropical storms passed, high cloud amounts generally peaked during the midafternoon. The diurnal variations of midlevel clouds were marked by early morning maxima and midday minima. ¿American Geophysical Union 1987