Abstract
Abstract. This study attempted to explain why deep convective clouds (DCCs) over the western Pacific are generally darker than those found over tropical African and South American land regions. The western Pacific domain was further divided into its land and ocean regions to deduce the general differences in DCC characteristics between convectively active tropical land and ocean regions. DCC in this study is defined as a single-layer cloud whose thickness is greater than 15 km, and it is determined from CloudSat-measured reflectivity profiles. Corresponding MODIS-measured reflectivities at 0.645 μm were examined, along with the analysis of cloud products from Cloud Aerosol Lidar Infrared Pathfinder Satellite Observation (CALIPSO) measurements. From an analysis of the four January months of 2007–2010, a distinct difference in ice water path (IWP) between the ocean region of the western Pacific and the three tropical land regions was revealed. Distinct differences in the effective radius between land and ocean were also found. The findings lead to a conclusion that smaller IWP over the western Pacific ocean region than over the tropical land regions, which should be caused by different cloud microphysics between land and ocean, is the main cause of smaller reflectivity there.
Highlights
Deep convective clouds (DCCs) associated with strong convection play an important role in the global climate because DCCs can alter the radiation balance due to changes in solar reflectivity or infrared emission level and due to changes in water vapor and hydrometeor profiles associated with deep convection
It has been reported that DCCs over the tropical western Pacific are generally darker compared with the reflectivities of DCCs over tropical Africa and South America
In order to examine the main cause of the lower reflectivity over the western Pacific, we examined the regional differences in cloud optical properties observed in satellite measurements of Moderate Resolution Imaging Spectroradiometer (MODIS) (Aqua), CloudSat, and Cloud Aerosol Lidar Infrared Pathfinder Satellite Observation (CALIPSO), with a further separation of the western Pacific domain into its land and oceanic areas
Summary
Deep convective clouds (DCCs) associated with strong convection play an important role in the global climate because DCCs can alter the radiation balance due to changes in solar reflectivity or infrared emission level and due to changes in water vapor and hydrometeor profiles associated with deep convection. A recent study by Doelling et al (2013), based on an analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) solar channel measurements, reported that DCCs over the tropical western Pacific have lower reflectivity (or are darker) than DCCs over continental tropical regions such as Africa and South America. This phenomenon is quite interesting and an immediate attempt to explain the reason for it may be related to different cloud microphysics between land and ocean. The results obtained from this study will lead to a better understanding of the role of tropical DCCs in influencing radiation budgets and climate feedback and may improve the performance in the use of DCC targets for solar channel calibration
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