| 1 | [[PageOutline]] |
| 2 | Last edited [[Timestamp]] |
| 3 | |
| 4 | [[BR]] |
| 5 | |
| 6 | '''Author''' : Paolo Oddo |
| 7 | |
| 8 | '''ticket''' : #851 |
| 9 | |
| 10 | '''Branch''' : [http://forge.ipsl.jussieu.fr/nemo/browser/branches/2011/dev_r2802_INGV4_zdfRic dev_r2802_INGV4_zdfRic ] |
| 11 | ---- |
| 12 | |
| 13 | === Description === |
| 14 | In the current version of the Richardson number vertical turbolence scheme eddy viscosities and diffusivities are estimated based on the local gradient Richardson number Ri, using a scheme similar to that of Pacanowski and Philander (1981). |
| 15 | |
| 16 | |
| 17 | Where Ri(x, y, z, t) is ≥0, |
| 18 | |
| 19 | |
| 20 | Av=Abv+ (v0) / (1+αRi)**nn_ri |
| 21 | |
| 22 | and |
| 23 | |
| 24 | Kv=Kbv + (v0) / (1+ αRi)**(nn_ric+1). |
| 25 | |
| 26 | |
| 27 | In this shear vertical mixing scheme, the adjustable parameters are: |
| 28 | the background coefficients, Abv and Kbv; |
| 29 | |
| 30 | the shear eddy viscosity at Ri=0 denoted by v0 |
| 31 | |
| 32 | the exponent (nn_ric=2) |
| 33 | |
| 34 | the alpha parameter (5). |
| 35 | |
| 36 | |
| 37 | |
| 38 | This simple scheme has been largely used in numerical models (it is simple and robust) however it does not have any parameterization of the mixing layer. |
| 39 | |
| 40 | The basic idea is to introduce near the surface, a mixing-layer model to transfer and dissipate the atmospheric forcings (̌wind-stress and buoyancy flux). |
| 41 | |
| 42 | Following the scheme used in HOPS (Harvard Ocean Prediction System) and described in PFJ Lermusiaux (2001) we first evaluate the local depth of turbulent wind-mixing or “Ekman depth” hee(̌x, y, t). |
| 43 | |
| 44 | |
| 45 | This depth is assumed proportional to the “depth of frictional influence” that is limited by rotation: |
| 46 | |
| 47 | |
| 48 | hee=Ek u* / f0 (Rossby and Montgomery, 1935; Cushman-Roisin, 1994). |
| 49 | |
| 50 | In this similarity height relationship, the turbulent friction velocity: |
| 51 | |
| 52 | |
| 53 | u*(x,y)=SQRT(||τ|| / ρ0) |
| 54 | |
| 55 | |
| 56 | is computed from the wind stress vector τ and reference density ρ0. |
| 57 | |
| 58 | |
| 59 | The coefficient Ek is an empirical factor (tunable) and f0 is the Coriolis parameter. |
| 60 | |
| 61 | |
| 62 | The final he is further constrained by adjustable bounds hemin≤ he ≤ hemax. |
| 63 | |
| 64 | |
| 65 | Once hee is computed, the vertical eddy coefficients within hee are set to the empirical values Ae and Ke. This vertical mixing-layer model is one of the common results of more complex models (̌e.g. Mofjeld and Lavelle, 1984; Garwood et al., 1985; Stigebrandt, 1985; Large et al., 1994). |
| 66 | |
| 67 | |
| 68 | ---- |
| 69 | === Testing === |
| 70 | Testing could consider (where appropriate) other configurations in addition to NVTK]. |
| 71 | |
| 72 | ||NVTK Tested||!'''YES/NO!'''|| |
| 73 | ||Other model configurations||!'''YES/NO!'''|| |
| 74 | ||Processor configurations tested||[ Enter processor configs tested here ]|| |
| 75 | ||If adding new functionality please confirm that the [[BR]]New code doesn't change results when it is switched off [[BR]]and !''works!'' when switched on||!'''YES/NO/NA!'''|| |
| 76 | |
| 77 | (Answering UNSURE is likely to generate further questions from reviewers.) |
| 78 | |
| 79 | 'Please add further summary details here' |
| 80 | |
| 81 | * Processor configurations tested |
| 82 | * etc---- |
| 83 | |
| 84 | === Bit Comparability === |
| 85 | ||Does this change preserve answers in your tested standard configurations (to the last bit) ?||!'''YES/NO !'''|| |
| 86 | ||Does this change bit compare across various processor configurations. (1xM, Nx1 and MxN are recommended)||!'''YES/NO!'''|| |
| 87 | ||Is this change expected to preserve answers in all possible model configurations?||!'''YES/NO!'''|| |
| 88 | ||Is this change expected to preserve all diagnostics? [[BR]]!,,!''Preserving answers in model runs does not necessarily imply preserved diagnostics. !''||!'''YES/NO!'''|| |
| 89 | |
| 90 | If you answered !'''NO!''' to any of the above, please provide further details: |
| 91 | |
| 92 | * Which routine(s) are causing the difference? |
| 93 | * Why the changes are not protected by a logical switch or new section-version |
| 94 | * What is needed to achieve regression with the previous model release (e.g. a regression branch, hand-edits etc). If this is not possible, explain why not. |
| 95 | * What do you expect to see occur in the test harness jobs? |
| 96 | * Which diagnostics have you altered and why have they changed?Please add details here........ |
| 97 | |
| 98 | ---- |
| 99 | === System Changes === |
| 100 | ||Does your change alter namelists?||!'''YES !'''|| |
| 101 | ||Does your change require a change in compiler options?||!'''YES/NO !'''|| |
| 102 | |
| 103 | additional parameters must be included in the corresponding namelist. |
| 104 | |
| 105 | |
| 106 | ---- |
| 107 | === Resources === |
| 108 | !''Please !''summarize!'' any changes in runtime or memory use caused by this change......!'' |
| 109 | |
| 110 | ---- |
| 111 | === IPR issues === |
| 112 | ||Has the code been wholly (100%) produced by NEMO developers staff working exclusively on NEMO?||!'''YES/ NO !'''|| |
| 113 | |
| 114 | If No: |
| 115 | |
| 116 | * Identify the collaboration agreement details |
| 117 | * Ensure the code routine header is in accordance with the agreement, (Copyright/Redistribution etc).Add further details here if required.......... |