The diurnal cycle of entrainment and detrainment in LES of the Southern Ocean driven by observed surface fluxes and waves

Journal Article · Fri Oct 01 00:00:00 EDT 2021 · Journal of Physical Oceanography

DOI:https://doi.org/10.1175/jpo-d-20-0308.1· OSTI ID:1983023

Large, William G. ^[1]; Patton, Edward G. ^[1]; Sullivan, Peter P. ^[1]

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1. National Center for Atmospheric Research (NCAR), Boulder, CO (United States)

Empirical rules for both entrainment and detrainment are developed from LES of the Southern Ocean boundary layer when the turbulence, stratification, and shear cannot be assumed to be in equilibrium with diurnal variability in surface flux and wave (Stokes drift) forcing. A major consequence is the failure of downgradient eddy viscosity, which becomes more serious with Stokes drift and is overcome by relating the angle between the stress and shear vectors to the orientations of Lagrangian shear to the surface and of local Eulerian shear over 5 m. Thus, the momentum flux can be parameterized as a stress magnitude and this empirical direction. In addition, the response of a deep boundary layer to sufficiently strong diurnal heating includes boundary layer collapse and the subsequent growth of a morning boundary layer, whose depth is empirically related to the time history of the forcing, as are both morning detrainment and afternoon entrainment into weak diurnal stratification. Below the boundary layer, detrainment rules give the maximum buoyancy flux and its depth, as well a specific stress direction. Another rule relates both afternoon and nighttime entrainment depth and buoyancy flux to surface layer turbulent kinetic energy production integrals. These empirical relationships are combined with rules for boundary layer transport to formulate two parameterizations; one based on eddy diffusivity and viscosity profiles and another on flux profiles of buoyancy and of stress magnitude. Evaluations against LES fluxes show the flux profiles to be more representative of the diurnal cycle, especially with Stokes drift.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
• Sponsoring Organization: National Collaborative Research Infrastructure Strategy (NCRIS); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); e National Science Foundation (NSF)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1983023
• Journal Information: Journal of Physical Oceanography, Journal Name: Journal of Physical Oceanography Journal Issue: 10 Vol. 51; ISSN 0022-3670
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
Boundary layer
Langmuir circulation
Large eddy simulations
Oceanic mixed layer
Oceanography
Parameterization