Multiple Factors Explaining the Deficiency of Cloud Profiling Radar on Detecting Oceanic Warm Clouds

Abstract

The Cloud Profiling Radar (CPR) detecting efficiency on low-level clouds is affected by many situations, including surface clutter, spatial resolution, and radar sensitivity. These factors can uniquely or jointly result in missed detections of oceanic single-layer warm clouds. Fifty-seven percent of missed detections are attributed to a single factor, and the rest are attributed to two or more factors that are indistinguishable. For missed warm clouds above 1 km, 30% result from the nonovercast effect, while the CPR range resolution is the major cause for the overcast ones. In particular, 18.4% are attributed exclusively to specific cloud microphysics, which is characterized by droplet effective radius (DER) and cloud optical thickness (COT). Compared to COT, the CPR detection is more dependent on DER, with a critical value standing around 10 μm. It is only for larger DER that the effects from COT turn to arise. Given liquid water path, clouds with larger DER and smaller COT are more likely to generate sufficient reflectivity and be detected than their counterpart. For clouds with the same DER and COT, opposite detecting results are primarily determined by the different droplet size distributions that lead to a variable reflectivity across the CPR detecting limit. Over global oceans, total miss rate of cloud occurrences approaches 0.73, while the loss rate of cloud water mass is 0.42 due to the smaller liquid water path of CPR-missed clouds. The CPR-missed detections also lead to uncertainties in cloud radiative forcing estimations. A notable overestimation of shortwave cloud forcing at 160% is found at bottom and top of atmosphere.The 94-GHz Cloud Profiling Radar (CPR) aboard CloudSat is the first spaceborne millimeter-wavelength radar, which began operational data collection since 2006. It is able to detect shallow convective clouds and drizzle that centimeter-wavelength radar remains insensitive. By virtue of its À28 dBZ sensitivity and the resulting cloud water resolving capability, CPR's observations have been involved in considerable investigations as an important data source for cloud and precipitation studies (Behrangi et al., 2012; Haynes et al., 2013; Key Points: • CPR-missed detections that are uniquely or jointly caused by different factors are identified and examined over global oceans • CPR cloud detection is more dependent on DER, with a critical value around 10 μm, and the effects from COT arise for only larger DER • Opposite detection for clouds with the same DER and COT results from variable reflectivity across the CPR detecting limit Supporting Information: • Supporting Information S1 . (2018). Multiple factors explaining the deficiency of cloud profiling radar on detecting oceanic warm clouds.Figure 5. (a) Zonal distribution of each missing type and (b) the respective fractions from south to north. Histogram of the pixel amount of all missing types in (a) and the averaged frozen layer height in (b).

Characteristics of Warm Clouds and Precipitation in South China during the Pre-Flood Season Using Datasets from a Cloud Radar, a Ceilometer, and a Disdrometer

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Characteristics of Oceanic Warm Cloud Layers within Multilevel Cloud Systems Derived by Satellite Measurements

“…There are exceptionally low values over the narrow regions adjacent to west coast of continents. These should be attributed to the deficiency of CPR for detecting clouds at very low levels, which are mostly coastal stratus and they occur very frequently in these regions [24,28,29]. Furthermore, Figure 2c shows the ratios of profiles with only warm cloud layers to those with warm cloud layers.…”

Mind the gap – Part 1: Accurately locating warm marine boundary layer clouds and precipitation using spaceborne radars

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