An intercomparison of radar-based liquid cloud microphysics retrievals and implications for model evaluation studies

[摘要] This paper presents a statistical comparison of three cloud retrievalproducts of the Atmospheric Radiation Measurement (ARM) program at theSouthern Great Plains (SGP) site from 1998 to 2006: MICROBASE,University of Utah (UU), and University of North Dakota (UND) products. Theprobability density functions of the various cloud liquid water content(LWC) retrievals appear to be consistent with each other. While the meanMICROBASE and UU cloud LWC retrievals agree well in the middle of cloud, thediscrepancy 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 thanthe UU r_e, whereas the discrepancy is reduced to within 1 μm if columnscontaining raining and/or mixed-phase layers are excluded from thecomparison. A suite of stratified comparisons and retrieval experimentsreveal that the LWC difference stems primarily from rain contamination,partitioning of total liquid later path (LWP) into warm and supercooledliquid, and the input cloud mask and LWP. The large discrepancy among ther_e retrievals is mainly due to rain contamination and the presence ofmixed-phase layers. Since rain or ice particles are likely to dominate radarbackscattering over cloud droplets, the large discrepancy found in thispaper can be thought of as a physical limitation of single-frequency radarapproaches. It is therefore suggested that data users should use theretrievals with caution when rain and/or mixed-phase layers are present inthe column.

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