Observations of the macrophysical properties of cumulus cloud fields over the tropical western Pacific and their connection to meteorological variables
Abstract. The poor representation of the macrophysical properties of shallow oceanic cumuli in climate models contributes to the large uncertainty in cloud feedback. These properties are also difficult to measure because it requires high-resolution satellite imagery that are seldomly collected over ocean. Here, we examine cumulus cloud macrophysical properties, their size, shape, and spatial distributions, over the tropical western Pacific using 170 15-m resolution scenes from Terra’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) collected during the 2019 Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) mission. The average cloud fraction (CF) was 0.12, half of which was contributed by clouds less than 1.6 km in area-equivalent diameter. This compared well to Terra’s Multiangle Imaging Spectroradiometer (MISR) resolution-corrected CF of 0.13, but less than the 0.19 measured by Terra’s Moderate Resolution Imaging Spectroradiometer (MODIS). The cloud size distribution exhibited a power law form with exponent of 2.93 and an area-perimeter power law with dimension of 1.24. ASTER, MISR, and CAMP2Ex aircraft lidar showed excellent agreement in the cloud top height (CTH) distribution peak altitude of ~750 m. We examined cumulus properties in relation to meteorological variables and found that the variation in mean CTH is most controlled by the total column water vapor, lower-tropospheric stability (LTS), and estimated inversion strength (EIS). The variation in CF is most controlled by surface wind speed and near-cloud relative humidity instead of LTS/EIS, suggesting the need to improve low cloud parameterizations in climate models that use LTS/EIS based on stratocumulus studies.
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