Use of Cloud Radar Doppler Spectra to Evaluate Stratocumulus Drizzle Size Distributions in Large-Eddy Simulations with Size-Resolved Microphysics

Journal Article · Wed Dec 27 00:00:00 EST 2017 · Journal of Applied Meteorology and Climatology

DOI:https://doi.org/10.1175/JAMC-D-17-0100.1· OSTI ID:1414992

Rémillard, J. ^[1]; Fridlind, A. M. ^[2]; Ackerman, A. S. ^[2]; Tselioudis, G. ^[2]; Kollias, P. ^[3]; Mechem, D. B. ^[4]; Chandler, H. E. ^[4]; Luke, E. ^[5]; Wood, R. ^[6]; Witte, M. K. ^[7]; Chuang, P. Y. ^[7]; Ayers, J. K. ^[8]

---

1. Stony Brook University, State University of New York, Stony Brook, New York
2. NASA Goddard Institute for Space Studies, New York, New York
3. Stony Brook University, State University of New York, Stony Brook, New York, Brookhaven National Laboratory, Brookhaven, New York
4. University of Kansas, Lawrence, Kansas
5. Brookhaven National Laboratory, Brookhaven, New York
6. University of Washington, Seattle, Washington
7. University of California, Santa Cruz, Santa Cruz, California
8. Science Systems and Applications, Inc., and NASA Langley Research Center, Langley, Virginia

Here, a case study of persistent stratocumulus over the Azores is simulated using two independent large-eddy simulation (LES) models with bin microphysics, and forward-simulated cloud radar Doppler moments and spectra are compared with observations. Neither model is able to reproduce the monotonic increase of downward mean Doppler velocity with increasing reflectivity that is observed under a variety of conditions, but for differing reasons. To a varying degree, both models also exhibit a tendency to produce too many of the largest droplets, leading to excessive skewness in Doppler velocity distributions, especially below cloud base. Excessive skewness appears to be associated with an insufficiently sharp reduction in droplet number concentration at diameters larger than ~200 μm, where a pronounced shoulder is found for in situ observations and a sharp reduction in reflectivity size distribution is associated with relatively narrow observed Doppler spectra. Effectively using LES with bin microphysics to study drizzle formation and evolution in cloud Doppler radar data evidently requires reducing numerical diffusivity in the treatment of the stochastic collection equation; if that is accomplished sufficiently to reproduce typical spectra, progress toward understanding drizzle processes is likely.

• Research Organization: Brookhaven National Lab. (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: SC0006736; SC0006988; SC0013489; SC0016237; SC0012704
• OSTI ID: 1414992
• Alternate ID(s): OSTI ID: 1408700
• Report Number(s): BNL-114437-2017-JA
• Journal Information: Journal of Applied Meteorology and Climatology, Journal Name: Journal of Applied Meteorology and Climatology Vol. 56 Journal Issue: 12; ISSN 1558-8424
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES