Retrieving Liquid Water Content Profiles Using ARM Dual-frequency Cloud Radars

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Description

Retrieving Liquid Water Content Profiles Using ARM Dual-frequency Cloud Radars Cloud microphysical properties, including liquid water content, greatly impact the Earth’s radiation budget but have high uncertainties in global climate models. Although Today’s most trusted liquid water path measurements are from the three-channel microwave radiometer provides today’s most trusted liquid water path measurements, and new efforts are underway to extend these retrievals to those for liquid water contents. One such method that derives liquid water content using a dual-frequency radar approach is presented. This dual-frequency method depends on reflectivity measurements from Ka- (35-GHz) and W-band (94-GHz) radars. One benefit of this method is its dependence on differences in absorption between the two frequencies so there is no need for the radars to be calibrated. Differences in absorption are proportional to path-integrated liquid in the cloud and therefore used to retrieve liquid water contents at every height inside the cloud. This method is limited to clouds consisting of liquid water drops small compared to the radar wavelengths. Accuracies of retrieved liquid water content profiles depend on precision of the reflectivity measurements, overlap of the sample volumes of the radars, accurate temperature profiles, and the validity of the small drop scattering assumption. To decrease sensitivity due to errors in the reflectivity measurements, regularization techniques are used. We find that liquid water paths calculated from liquid water contents retrieved from four different Atmospheric Radiation Measurement program Climate Research Facility sites using this approach track microwave radiometer-derived liquid water paths greater than approximately 0.04 mm of precipitable cloud liquid water.