[MITgcm-support] Guide to output variables?

[Baylor Fox-Kemper]

Hi Chris:
Dmitris is right, check out model/inc/GRID.h, but here goes my take:
> XC.*
X coordinate a centered (e.g., temp, salt, pressure) points
> XG.*
X coordinate on grid (i.e., where U velocities and zonal fluxes are)
> PH.*
PhiHyd: Flow Potential::: Different depending on whether you're  
atmospheric or oceanic:::
C     phiHydC    :: hydrostatic potential anomaly at cell center
C                   In z coords phiHyd is the hydrostatic potential
C                      (=pressure/rho0) anomaly
C                   In p coords phiHyd is the geopotential height  
anomaly.
> PHL.*
PhiHydLow: different estimate of PhiHyd
> RAC.*
area of cell center:  1/diff(XC)/diff(YC)
> RAS.*
area of 'south' point: 1/diff(XC)/diff(YG)
> RAW.*
area of 'west' point: 1/diff(XG)/diff(YC)
> RAZ.*
area of vorticity (zeta) point: 1/diff(XG)/diff(YG)

The notation is crummy, I agree.  But, Ed is right, mnc does give you  
some hints.  Here is an ncdump from a typical grid.001.nc file, which  
gives you 'long names' for these variables.

	double Z(Z) ;
	double RC(Z) ;
		RC:description = "R coordinate of cell center" ;
		RC:units = "m" ;
	double Zp1(Zp1) ;
	double RF(Zp1) ;
		RF:description = "R coordinate of cell interface" ;
		RF:units = "m" ;
	double Zu(Zu) ;
	double RU(Zu) ;
		RU:description = "R coordinate of upper interface" ;
		RU:units = "m" ;
	double Zl(Zl) ;
	double RL(Zl) ;
		RL:description = "R coordinate of lower interface" ;
		RL:units = "m" ;
	double drC(Z) ;
		drC:description = "r cell center separation" ;
	double drF(Z) ;
		drF:description = "r cell face separation" ;
	double X(X) ;
	double Y(Y) ;
	double XC(Y, X) ;
		XC:description = "X coordinate of cell center (T-P point)" ;
		XC:units = "degree_east" ;
	double YC(Y, X) ;
		YC:description = "Y coordinate of cell center (T-P point)" ;
		YC:units = "degree_north" ;
	double Xp1(Xp1) ;
	double Yp1(Yp1) ;
	double XG(Yp1, Xp1) ;
		XG:description = "X coordinate of cell corner (Vorticity point)" ;
		XG:units = "degree_east" ;
	double YG(Yp1, Xp1) ;
		YG:description = "Y coordinate of cell corner (Vorticity point)" ;
		YG:units = "degree_north" ;
	double dxC(Y, Xp1) ;
		dxC:description = "x cell center separation" ;
	double dyC(Yp1, X) ;
		dyC:description = "y cell center separation" ;
	double dxF(Y, X) ;
		dxF:description = "x cell face separation" ;
	double dyF(Y, X) ;
		dyF:description = "y cell face separation" ;
	double dxG(Yp1, X) ;
		dxG:description = "x cell corner separation" ;
	double dyG(Y, Xp1) ;
		dyG:description = "y cell corner separation" ;
	double dxV(Yp1, Xp1) ;
		dxV:description = "x v-velocity separation" ;
	double dyU(Yp1, Xp1) ;
		dyU:description = "y u-velocity separation" ;
	double rA(Y, X) ;
		rA:description = "r-face area at cell center" ;
	double rAw(Y, Xp1) ;
		rAw:description = "r-face area at U point" ;
	double rAs(Yp1, X) ;
		rAs:description = "r-face area at V point" ;
	double rAz(Yp1, Xp1) ;
		rAz:description = "r-face area at cell corner" ;
	double fCori(Y, X) ;
		fCori:description = "Coriolis f at cell center" ;
	double fCoriG(Yp1, Xp1) ;
		fCoriG:description = "Coriolis f at cell corner" ;
	double R_low(Y, X) ;
		R_low:description = "base of fluid in r-units" ;
	double Ro_surf(Y, X) ;
		Ro_surf:description = "surface reference (at rest) position" ;
	double Depth(Y, X) ;
		Depth:description = "fluid thickness in r coordinates (at rest)" ;
	double HFacC(Z, Y, X) ;
		HFacC:description = "vertical fraction of open cell at cell center" ;
	double HFacW(Z, Y, Xp1) ;
		HFacW:description = "vertical fraction of open cell at West face" ;
	double HFacS(Z, Yp1, X) ;
		HFacS:description = "vertical fraction of open cell at South face" ;

Hope that helps.  -Baylor
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