[MITgcm-support] Mellor-Yamada in MITgcm

[Olivier Marchal]

Hello All,

I would appreciate input on the following two questions which arose when looking at how Mellor-Yamada is implemented in MITgcm:

1. The following statements appear one lines 161-162 of my82_calc.F:

MYviscAr(I,J,K,bi,bj) = MYhbl(I,J,bi,bj)*tkel*SM(I,J,K)
MYdiffKr (I,J,K,bi,bj) = MYbhl(I,J,bi,bj)*tkel*SH(I,J,K)

where tkel is calculated one line 159 from

tkel =  MYhbl(I,J,bi,bj)*tke(I,J,K)

and tke is calculated on line 113 from

tke(I,J,K) = sqrt(tkesquare)

The coded equations for MYviscAr and MYdiffKr can easily be related to equations (32a)-(32b) of Mellor and Yamada (1982). However, assuming MYhbl is in [m], tke = sqrt(tkesquare) is in [m/s] so that tkel is in [m^2/s], and SM and SH are dimensionless, then MYviscAr and MYdiffKr would be in [m^3/s] and so would not have units of viscosities and diffusivities. Shouldn't tkel on line 161-162 be replaced by tke(I,J,K)?

2. At which depths of the C grid do the values in the diagnostic files KPPviscAz.* and KPPdiffKz(T,S).* correspond to? To the depths of the U,V-carrier points, or to the depths of the W-carrier points? Viscosities/diffusivities are often defined at W-carrier points since vertical turbulent flux divergences are often discretized using central-difference schemes, but it is unclear to me whether these are the values in the diagnostic files.

Any input about (1)-(2) would be deeply appreciated.

Thank you!

Olivier.


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