W4_MPAS-Ocean_Langmuir_turbulence Design Document
The Design Document page provides a description of the algorithms, implementation and planned testing including unit, verification, validation and performance testing. Please read Step 1.3 Performance Expectations that explains feature documentation requirements from the performance group point of view.
Design Document
In the table below 4.Equ means Equations and Algorithms, 5.Ver means Verification, 6.Perf - Performance, 7. Val - Validation, 
- competed, 
- in progress, 
- not done
Overview table for the owner and an approver of this feature
1.Description | Langmuir turbulence parameterization |
| 2.Owner | Qing Li (Unlicensed) |
| 3.Created | |
| 4.Equ | |
| 5.Ver | |
| 6.Perf | |
| 7.Val | |
| 8.Approver | |
| 9.Approved Date |
Title: Langmuir Turbulence Parameterization
Requirements and Design
E3SM Water Cycle Group
Date:
Summary
Ocean surface waves are known to affect ocean surface boundary layer (OSBL) vertical mixing. Langmuir turbulence is one important mechanism by which ocean surface waves interact with boundary layer turbulence. This new feature includes parameterizations of two effects of Langmuir turbulence: (1) Langmuir enhanced vertical mixing within the OSBL; (2) Langmuir enhanced entrainment at the base of OSBL, via CVMix. Ocean surface wave information is required for the parameterization, which normally requires coupling with an ocean surface wave model (e.g., WAVEWATCH III). A simple solution with wave parameters approximated from surface wind using empirical wave spectrum is provided. The Langmuir turbulence parameterization generally makes the ocean surface mixed layer deeper, especially in the extratropical regions (e.g., Southern Ocean). As a result of stronger OSBL vertical mixing, subsurface layer is generally warmer.
Requirements
Requirement: Parameterizing effects of Langmuir turbulence on ocean surface vertical mixing
Date last modified:
Contributors: Qing Li (Unlicensed)
Ocean surface boundary vertical mixing should be enhanced in the presence of Langmuir turbulence.
Requirement: Wave parameters
Date last modified:
Contributors: Qing Li (Unlicensed)
The Langmuir turbulence parameterization requires wave parameters such as variants of Langmuir number, which are computed from Stokes drift profile and ocean surface friction velocity. This normally requires coupling with an ocean surface wave model such as WAVEWATCH III.
Algorithmic Formulations
Design solution: Langmuir turbulence parameterization via CVMix
Date last modified:
Contributors: Qing Li (Unlicensed)
The formulations of the Langmuir turbulence parameterization adopted here are detailed in Li et al., 2016 and Li and Fox-Kemper, 2017, which modify KPP (Large et al., 1994, Van Roekel et al., 2018) to include the effects of Langmuir turbulence. In particular, two effects of Langmuir turbulence are considered here:
- Langmuir enhanced vertical mixing within the OSBL, which is parameterized by applying an Langmuir number-dependent enhancement factor to the turbulent velocity scale in KPP following the scaling derived from large eddy simulation (LES) study by Van Roekel et al., 2012.
- Langmuir enhanced entrainment at the base of OSBL, which is parameterized by modifying the bulk Richardson number in KPP using the scaling of entrainment buoyancy flux derived from LES of Li and Fox-Kemper, 2017.
Design solution: Approximation of wave parameters from empirical wave spectrum
Date last modified:
Contributors: Qing Li (Unlicensed)
A simple solution to approximate wave parameters required by the Langmuir turbulence parameterization is provided here, which estimates the Stokes drift profile from 10-meter wind using empirical wave spectrum and some assumptions of the swell statistics following Li et al., 2017.
Design and Implementation
Implementation: Modifications to CVMix
Date last modified:
Contributors: Qing Li (Unlicensed)
The modifications to KPP to include the Langmuir turbulence parameterization are implemented in CVMix (tag v0.94b-beta or later). Additional MPAS-Ocean namelist entries to activate the options are implemented:
- config_cvmix_kpp_langmuir_mixing_opt: Options for Langmuir-enhanced vertical mixing. Valid options: 'NONE', 'LWF16'
- config_cvmix_kpp_langmuir_entrainment_opt: Options for Langmuir-enhanced entrainment. Valid options: 'NONE', 'LWF16', 'LF17'
- config_cvmix_kpp_use_theory_wave: Use empirical wave spectrum to approximate wave parameters if set to .true.
Planned Verification and Unit Testing
Verification and Unit Testing: short-desciption-of-testing-here
Date last modified:
Contributors: (add your name to this list if it does not appear)
How will XXX be tested? i.e. how will be we know when we have met requirement XXX. Will these unit tests be included in the ongoing going forward?
Planned Validation Testing
Validation Testing: short-desciption-of-testing-here
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How will XXX be tested? What observational or other dataset will be used? i.e. how will be we know when we have met requirement XXX. Will these unit tests be included in the ongoing going forward?
Planned Performance Testing
Performance Testing: short-desciption-of-testing-here
Date last modified:
Contributors: (add your name to this list if it does not appear)
How will XXX be tested? i.e. how will be we know when we have met requirement XXX. Will these unit tests be included in the ongoing going forward?