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This study uses measurements of radiation and cloud properties taken between January and August 1998 by three Tropical Rainfall Measuring Mission (TRMM) instruments, the Clouds and the Earth's Radiant Energy System (CERES) scanner, the TRMM Microwave Imager (TMI), and the Visible and InfraRed Scanner (VIRS), to evaluate the variations of tropical deep convective systems (DCS) with sea surface temperature (SST) and precipitation.This study finds that DCS precipitation efficiency increases with SST at a rate of ~2%/K.Despite increasing rainfall efficiency, the cloud areal coverage rises with SST at a rate of about 7%/K in the warm tropical seas. There, the boundary layer moisture supply for deep convection and the moisture transported to the upper troposphere for cirrus-anvil cloud formation increase by ~6.3%/K and ~4.0%/K, respectively. The changes in cloud formation efficiency, along with the increased transport of moisture available for cloud formation, likely contribute to the large rate of increasing DCS areal coverage. Although no direct observations are available, the increase of cloud formation efficiency with rising SST is deduced indirectly from measurements of changes in the ratio of DCS ice water path and boundary layer water vapor amount with SST.Besides the cloud areal coverage, DCS cluster effective sizes also increase with precipitation.Furthermore, other cloud properties, such as cloud total water and ice water paths, increase with SST. These changes in DCS properties will produce a negative radiative feedback for the earth's climate system due to strong reflection of shortwave radiation by the DCS. These results significantly differ from some previous hypothesized dehydration scenarios for warmer climates, and have great potential in testing current cloud-system resolving models and convective parameterizations of general circulation models.

. The random error decreases as the averaging scale increases, but error due to inhomogeneity remains. At the 60 km scale the average •rror is about 6% for high Sun, 2% for low Sun. Individual scenes, however, have retrieved optical depth errors as high as 45% due to horizontal radiative transport. The ability to retrieve higher statistical moments of the frequency distribution of optical depth is also assessed. Sigma, (a), the standard deviation of 7-, is retrieved quite well up to a point, then is underestimated due to the smoothing effect of horizontal radiative transport. The gamma function parameter another measure of the width of the 7-frequency distribution, is retrieved quite well over a wide range but with a systematic bias which varies with solar zenith angle, again due to horizontal radiative transport. A method is sought to reduce the optical depth retrieval error using a simple correction based on remotely sensed cloud properties. Of those considered, cloud physical aspect ratio (computed here from one possible relation which depends on properties obtainable from remote sensing) is tbund to be the most effective correction parameter. The aspect ratio correction reduces the retrieved optical depth bias error by 50 to 100% and the RMS error by 20 to 50%. Correction coefficients are presented at three solar zenith angles. This work is limited by its consideration of only single-level marine boundary layer clouds, assumptions of conservative scattering, constant cloud droplet size, no gas absorption or surface reflectance, and restriction to two-dimensional radiative transport. Future work will attempt to remove some of these limitations. The Landsat data used are also limited due to radiative smoothing.

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W ater vapor is the constituent of the atmosphere that is most responsible for weather, the hydrological cycle, and the maintenance of Earth's temperature within a range that supports life as we know it (Mockler 1995). Furthermore, water vapor condensed on sulfate and other hygroscopic aerosols can significantly increase the aerosol optical thickness of the atmosphere (Tang 1996).The direct and indirect influence of water vapor on weather, climate, and the environment is so important that there is significant interest in techniques for inferring its vertical distribution and its total abundance in a vertical column through the atmosphere. The latter parameter, the measurement of which is the central subject of this paper, is variously described as  A $20 infrared thermometer pointed at the cloud-free zenith sky can measure precipitable water vapor about as well as a sun photometer, and it can do so during the day or night.Readings from this infrared thermometer (foreground) were compared with total water vapor measured by the nearby NOAA GPS receiver at Hawaii's Mauna Loa Observatory.

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