An intercomparison of radar-based liquid cloud microphysics retrievals and implication for model evaluation studies
Atmospheric Measurement Techniques Discussions
This paper presents a statistical comparison of three cloud retrieval products of the Atmospheric Radiation Measurement (ARM) program at the Southern Great Plains (SGP) site from 1998 to 2006: the MICROBASE, University of Utah (UU), and University of North Dakota (UND) products. The probability density functions of the various cloud liquid water content (LWC) retrievals appear to be consistent with each other. While the mean MICROBASE and UU cloud LWC retrievals agree well in the middle of
... the middle of cloud, the discrepancy increases to about 0.03 gm -3 at cloud top and cloud base. Alarmingly large differences are found in the droplet effective radius (r e ) retrievals. The mean MICROBASE r e is more than 6 µm lower than the UU r e , whereas the discrepancy is reduced to within 1 µm if columns containing raining and/or mixed-phase layers are excluded from the comparison. A suite of stratified comparisons and retrieval experiments reveal that the LWC difference stems primarily from rain contamination, partitioning of total liquid later path (LWP) into warm and supercooled liquid, and the input cloud mask and LWP. The large discrepancy among the r e retrievals is mainly due to rain contamination and the presence of mixed-phase layers. Since rain or ice particles are likely to dominate radar backscattering over cloud droplets, the large discrepancy found in this paper can be thought as a physical limitation of single-frequency radar approaches. It is therefore suggested that data users should use the retrievals with caution when rain and/or mixed-phase layers are present in the column. ) 3 exp( 64 2 6 σ e Nr Z = (5b).