Abstract
Optically very thin ice clouds from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and ground-based Raman lidars (RL) at the atmospheric radiation measurement (ARM) sites of the Southern Great Plains (SGP) and Tropical Western Pacific (TWP) are analyzed. The optically very thin ice clouds, with ice cloud column optical depths below 0.01, are about 23% of the transparent ice-cloudy profiles from the RL, compared to 4–7% from CALIPSO. The majority (66–76%) of optically very thin ice clouds from the RLs are found to be adjacent to ice clouds with ice cloud column optical depths greater than 0.01. The temporal structure of RL-observed optically very thin ice clouds indicates a clear sky–cloud continuum. Global cloudiness estimates from CALIPSO observations leveraged with high-sensitivity RL observations suggest that CALIPSO may underestimate the global cloud fraction when considering optically very thin ice clouds.
Highlights
Ice clouds are located globally and are recognized to be climatically important [1]
All transparent profiles from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) within a 5° latitude by 5° longitude box centered over the Southern Great Plains (SGP) and Tropical Western Pacific (TWP) sites are considered without discarding profiles when the Raman lidars (RL) is not operational
By using consistent resolutions between the RL and CALIPSO and noting a small effect of the transparent definitions, the differences in the Cumulative distribution functions (CDFs) between the RL and CALIPSO are mainly related to the differences in instrument sensitivity [8]
Summary
Ice clouds are located globally and are recognized to be climatically important [1]. Thin ice clouds are important for accurate cloud net radiative forcing estimation [6,9,10,11,12]. Many recent investigations have expanded the knowledge of the ice cloud radiative forcing for ice clouds [11,13,14,15,16], with an increased emphasis on the importance of ice clouds with small optical depths [11]. Accurate global ice cloud observations in terms of occurrence and optical depth, prove crucial to understanding the impact of ice clouds on the climate
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