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Title: Toward low-cloud-permitting cloud superparameterization with explicit boundary layer turbulence

Systematic biases in the representation of boundary layer (BL) clouds are a leading source of uncertainty in climate projections. A variation on superparameterization (SP) called “ultraparameterization” (UP) is developed, in which the grid spacing of the cloud-resolving models (CRMs) is fine enough (250 × 20 m) to explicitly capture the BL turbulence, associated clouds, and entrainment in a global climate model capable of multiyear simulations. UP is implemented within the Community Atmosphere Model using 2° resolution (~14,000 embedded CRMs) with one-moment microphysics. By using a small domain and mean-state acceleration, UP is computationally feasible today and promising for exascale computers. Short-duration global UP hindcasts are compared with SP and satellite observations of top-of-atmosphere radiation and cloud vertical structure. The most encouraging improvement is a deeper BL and more realistic vertical structure of subtropical stratocumulus (Sc) clouds, due to stronger vertical eddy motions that promote entrainment. Results from 90 day integrations show climatological errors that are competitive with SP, with a significant improvement in the diurnal cycle of offshore Sc liquid water. Ongoing concerns with the current UP implementation include a dim bias for near-coastal Sc that also occurs less prominently in SP and a bright bias over tropical continental deepmore » convection zones. Nevertheless, UP makes global eddy-permitting simulation a feasible and interesting alternative to conventionally parameterized GCMs or SP-GCMs with turbulence parameterizations for studying BL cloud-climate and cloud-aerosol feedback.« less
Authors:
 [1] ; ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [2] ;  [3]
  1. Univ. of California, Irvine, CA (United States). Dept. of Earth System Science
  2. Univ. of Washington, Seattle, WA (United States). Dept. of Atmospheric Sciences
  3. Stony Brook Univ., NY (United States). School of Marine and Atmospheric Sciences
Publication Date:
Grant/Contract Number:
SC0012548; SC0012451; SC0012488; AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Journal of Advances in Modeling Earth Systems
Additional Journal Information:
Journal Volume: 9; Journal Issue: 3; Journal ID: ISSN 1942-2466
Publisher:
American Geophysical Union (AGU)
Research Org:
Univ. of California, Irvine, CA (United States); Univ. of Washington, Seattle, WA (United States); Stony Brook Univ., 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; ultraparameterization; superparameterization; cloud-resolving model; shallow clouds; marine boundary layer; general circulation model
OSTI Identifier:
1425466

Parishani, Hossein, Pritchard, Michael S., Bretherton, Christopher S., Wyant, Matthew C., and Khairoutdinov, Marat. Toward low-cloud-permitting cloud superparameterization with explicit boundary layer turbulence. United States: N. p., Web. doi:10.1002/2017MS000968.
Parishani, Hossein, Pritchard, Michael S., Bretherton, Christopher S., Wyant, Matthew C., & Khairoutdinov, Marat. Toward low-cloud-permitting cloud superparameterization with explicit boundary layer turbulence. United States. doi:10.1002/2017MS000968.
Parishani, Hossein, Pritchard, Michael S., Bretherton, Christopher S., Wyant, Matthew C., and Khairoutdinov, Marat. 2017. "Toward low-cloud-permitting cloud superparameterization with explicit boundary layer turbulence". United States. doi:10.1002/2017MS000968. https://www.osti.gov/servlets/purl/1425466.
@article{osti_1425466,
title = {Toward low-cloud-permitting cloud superparameterization with explicit boundary layer turbulence},
author = {Parishani, Hossein and Pritchard, Michael S. and Bretherton, Christopher S. and Wyant, Matthew C. and Khairoutdinov, Marat},
abstractNote = {Systematic biases in the representation of boundary layer (BL) clouds are a leading source of uncertainty in climate projections. A variation on superparameterization (SP) called “ultraparameterization” (UP) is developed, in which the grid spacing of the cloud-resolving models (CRMs) is fine enough (250 × 20 m) to explicitly capture the BL turbulence, associated clouds, and entrainment in a global climate model capable of multiyear simulations. UP is implemented within the Community Atmosphere Model using 2° resolution (~14,000 embedded CRMs) with one-moment microphysics. By using a small domain and mean-state acceleration, UP is computationally feasible today and promising for exascale computers. Short-duration global UP hindcasts are compared with SP and satellite observations of top-of-atmosphere radiation and cloud vertical structure. The most encouraging improvement is a deeper BL and more realistic vertical structure of subtropical stratocumulus (Sc) clouds, due to stronger vertical eddy motions that promote entrainment. Results from 90 day integrations show climatological errors that are competitive with SP, with a significant improvement in the diurnal cycle of offshore Sc liquid water. Ongoing concerns with the current UP implementation include a dim bias for near-coastal Sc that also occurs less prominently in SP and a bright bias over tropical continental deep convection zones. Nevertheless, UP makes global eddy-permitting simulation a feasible and interesting alternative to conventionally parameterized GCMs or SP-GCMs with turbulence parameterizations for studying BL cloud-climate and cloud-aerosol feedback.},
doi = {10.1002/2017MS000968},
journal = {Journal of Advances in Modeling Earth Systems},
number = 3,
volume = 9,
place = {United States},
year = {2017},
month = {6}
}