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Title: RACORO continental boundary layer cloud investigations. Part I: Case study development and ensemble large-scale forcings

Observation-based modeling case studies of continental boundary layer clouds have been developed to study cloudy boundary layers, aerosol influences upon them, and their representation in cloud- and global-scale models. Three 60-hour case study periods span the temporal evolution of cumulus, stratiform, and drizzling boundary layer cloud systems, representing mixed and transitional states rather than idealized or canonical cases. Based on in-situ measurements from the RACORO field campaign and remote-sensing observations, the cases are designed with a modular configuration to simplify use in large-eddy simulations (LES) and single-column models. Aircraft measurements of aerosol number size distribution are fit to lognormal functions for concise representation in models. Values of the aerosol hygroscopicity parameter, κ, are derived from observations to be ~0.10, which are lower than the 0.3 typical over continents and suggestive of a large aerosol organic fraction. Ensemble large-scale forcing datasets are derived from the ARM variational analysis, ECMWF forecasts, and a multi-scale data assimilation system. The forcings are assessed through comparison of measured bulk atmospheric and cloud properties to those computed in 'trial' large-eddy simulations, where more efficient run times are enabled through modest reductions in grid resolution and domain size compared to the full-sized LES grid. Simulations capture manymore » of the general features observed, but the state-of-the-art forcings were limited at representing details of cloud onset, and tight gradients and high-resolution transients of importance. Methods for improving the initial conditions and forcings are discussed. The cases developed are available to the general modeling community for studying continental boundary clouds.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [1] ;  [3] ;  [4] ;  [5] ;  [1] ;  [3] ;  [4] ;  [2] ;  [6] ;  [6]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. NASA Goddard Inst. for Space Studies (GISS), New York, NY (United States)
  3. UCLA Joint Institute for Regional Earth System and Engineering (JIFRESSE), Los Angeles, CA (United States); California Institute of Technology, Pasadena, CA (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  5. NOAA National Severe Storms Lab., Norman, OK (United States)
  6. Stony Brook Univ., NY (United States)
Publication Date:
OSTI Identifier:
1188220
Report Number(s):
BNL--107839-2015-JA
Journal ID: ISSN 2169-897X; R&D Project: 2016-BNL-EE630EECA-Budg; KP1701000
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research: Atmospheres
Additional Journal Information:
Journal Volume: 90; Journal Issue: 12; Journal ID: ISSN 2169-897X
Publisher:
American Geophysical Union
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