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This content will become publicly available on September 20, 2018

Title: Use of cloud radar Doppler spectra to evaluate stratocumulus drizzle size distributions in large-eddy simulations with size-resolved microphysics

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.
Authors:
 [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [4] ;  [4] ;  [5] ;  [6] ;  [7] ;  [7] ;  [8]
  1. Stony Brook Univ., Stony Brook, NY (United States)
  2. NASA Goddard Institute for Space Studies, New York, NY (United States)
  3. Stony Brook Univ., Stony Brook, NY (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)
  4. Univ. of Kansas, Lawrence, KS (United States)
  5. Brookhaven National Lab. (BNL), Upton, NY (United States)
  6. Univ. of Washington, Seattle, WA (United States)
  7. Univ. of California, Santa Cruz, CA (United States)
  8. NASA Langley Research Center, Langley, VA (United States)
Publication Date:
Report Number(s):
BNL-114437-2017-JA
Journal ID: ISSN 1558-8424; R&D Project: 2019‐BNL-EE630EECA-Budg; KP1701000; TRN: US1703072
Grant/Contract Number:
SC0012704; SC0006736; SC0006988; SC0013489; SC0016237
Type:
Accepted Manuscript
Journal Name:
Journal of Applied Meteorology and Climatology
Additional Journal Information:
Journal Name: Journal of Applied Meteorology and Climatology; Journal ID: ISSN 1558-8424
Publisher:
American Meteorological Society
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES
OSTI Identifier:
1408700
Alternate Identifier(s):
OSTI ID: 1414992