Analysis of Cloud-Resolving Model Simulations for Scale Dependence of Convective Momentum Transport

Journal Article · Tue Jul 10 00:00:00 EDT 2018 · Journal of the Atmospheric Sciences

DOI:https://doi.org/10.1175/JAS-D-18-0019.1· OSTI ID:1459701

Liu, Yi-Chin ^[1]; Fan, Jiwen ^[2]; Xu, Kuan-Man ^[3]; Zhang, Guang J. ^[4]

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1. Pacific Northwest National Laboratory, Richland, Washington, and Air Resources Board, California Environmental Protection Agency, Sacramento, California
2. Pacific Northwest National Laboratory, Richland, Washington
3. NASA Langley Research Center, Hampton, Virginia
4. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California

Abstract We use 3D cloud-resolving model (CRM) simulations of two mesoscale convective systems at midlatitudes and a simple statistical ensemble method to diagnose the scale dependency of convective momentum transport (CMT) and CMT-related properties and evaluate a parameterization scheme for the convection-induced pressure gradient (CIPG) developed by Gregory et al. Gregory et al. relate CIPG to a constant coefficient multiplied by mass flux and vertical mean wind shear. CRM results show that mass fluxes and CMT exhibit strong scale dependency in temporal evolution and vertical structure. The upgradient–downgradient CMT characteristics for updrafts are generally similar between small and large grid spacings, which is consistent with previous understanding, but they can be different for downdrafts across wide-ranging grid spacings. For the small to medium grid spacings (4–64 km), Gregory et al. reproduce some aspects of CIPG scale dependency except for underestimating the variations of CIPG as grid spacing decreases. However, for large grid spacings (128–512 km), Gregory et al. might even less adequately parameterize CIPG because it omits the contribution from either the nonlinear-shear or the buoyancy forcings. Further diagnosis of CRM results suggests that inclusion of nonlinear-shear forcing in Gregory et al. is needed for the large grid spacings. For the small to median grid spacings, a modified Gregory et al. with the three-updraft approach help better capture the variations of CIPG as grid spacing decreases compared to the single updraft approach. Further, the optimal coefficients used in Gregory et al. seem insensitive to grid spacings, but they might be different for updrafts and downdrafts, for different MCS types, and for zonal and meridional components.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: 62201; AC05-76RL01830
• OSTI ID: 1459701
• Alternate ID(s): OSTI ID: 1492412
• Report Number(s): PNNL-SA-119826
• Journal Information: Journal of the Atmospheric Sciences, Journal Name: Journal of the Atmospheric Sciences Vol. 75 Journal Issue: 7; ISSN 0022-4928
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
Cloud parameterizations
Cloud resolving models
Convective parameterization
Cumulus clouds