[MITgcm-devel] horiVertRatio in forcing

[Chris Hill]

I don't get it :-)

When r->p we define our coordinate system as (m,m,pa) so volume has units
m*m*pa
When r->m we define our coordinate system as (m,m,m ) so volume has units
m*m*m

So it is the mass per unit volume in our coordinate system - isn't it?

Chris



 

> -----Original Message-----
> From: mitgcm-devel-bounces at mitgcm.org 
> [mailto:mitgcm-devel-bounces at mitgcm.org] On Behalf Of Alistair Adcroft
> Sent: Friday, December 05, 2003 9:00 AM
> To: MITgcm-devel at mitgcm.org
> Subject: RE: [MITgcm-devel] horiVertRatio in forcing
> 
> The "r" are in the names because it is the "density" in "r" 
> coordinates as opposed to mass per unit physical volume.
> 
> A.
> --
> Dr Alistair Adcroft            http://www.mit.edu/~adcroft
> MIT Climate Modeling Initiative        tel: (617) 253-5938
> EAPS 54-1523,  77 Massachusetts Ave,  Cambridge,  MA,  USA
> 
> -----Original Message-----
> From: mitgcm-devel-bounces at mitgcm.org
> [mailto:mitgcm-devel-bounces at mitgcm.org] On Behalf Of Chris Hill
> Sent: Friday, December 05, 2003 8:41 AM
> To: MITgcm-devel at mitgcm.org
> Subject: RE: [MITgcm-devel] horiVertRatio in forcing
> 
> 
> J-M
> 
> Do we need the r in the names. Why not m2v(k) and v2m(k)? I 
> always think of the volume as dx*dy*dr and letting the units 
> be whatever they are. Is that bad? 
> 
> In general it would be really nice to tidy this up everywhere 
> into a form we all agree on. 
> I've never liked horiVertRatio either (even though I created 
> it!) but I've never seen a better suggestion for how to 
> encode what we need. I would prefer something that we can 
> apply consistently everywhere. Not sure what it will be but I 
> know it will make Alistair's blood pressure rise to discuss 
> it, which is always fun. 
> 
> Chris
> 
> > -----Original Message-----
> > From: mitgcm-devel-bounces at mitgcm.org 
> > [mailto:mitgcm-devel-bounces at mitgcm.org] On Behalf Of Jean-Michel 
> > Campin
> > Sent: Thursday, December 04, 2003 11:02 PM
> > To: MITgcm-devel at mitgcm.org
> > Subject: [MITgcm-devel] horiVertRatio in forcing
> > 
> > Hi,
> > 
> > I have a suggestion regarding horiVertRatio:
> > 
> > right now we have :
> > 
> > horiVertRatio = 1 (if r=z)
> > horiVertRatio = gravity*rhoConst (if r=p)
> > 
> > Since non-boussinesq (p-coordinate) does not need any constant
> > (reference) density, it's a litle curious to see rhoConst in the 
> > P-coordinate model, although, since horiVertRatio is 
> (almost) always 
> > used as horiVertRatio/rhoConst or 
> rhoConst*recip_horiVertRatio, this 
> > is not a real problem.
> > 
> > I propose (in a first step in external_forcing_surf only) to use:
> > 
> > mass2rVolum :: convert mass unit (kg) to "model" volume unit ( 
> > 1/"model density")
> >                so that: (dx*dy*dr)_unit = mass2rVolum * dMass_unit
> >                mass2rVolum = 1 / rhoConst (if r=z) ; = gravity (if 
> > r=p) ; rVolum2mass :: convert "model" volume unit to mass 
> unit (kg) (= 
> > "model density")
> >                so that: dMass_unit = rVolum2mass * (dx*dy*dr)_unit
> >                = rhoConst (if r=z) ; = 1/gravity (if r=p) ;
> > 
> > The name for those 2 constants can change (althougth not too long 
> > would be better). But I think it could help to clarify the 
> forcing and 
> > diagnostic units.
> > 
> > I looked to other places where horiVertRatio is used, and 
> seems to be 
> > only in NonHydrostatic parts:  ini_cg3d.F  cg3d.F  
> > solve_for_pressure.F (NH part)  mom_u_coriolis_nh.F  
> mom_u_metric_nh.F 
> > mom_v_metric_nh.F
> > 
> > I think that we can leave those S/R as they are, because
> > a) in z coordinate, it's easy to remember that horiVertRatio=1.
> > b) it does not matter too much since P-coordinate cannot
> >    really be used with NonHydrostatic. horiVertRatio is just there 
> >    to make the units right, no more.
> > 
> > Any comment ?
> > 
> > Jean-Michel
> > _______________________________________________
> > MITgcm-devel mailing list
> > MITgcm-devel at mitgcm.org
> > http://dev.mitgcm.org/mailman/listinfo/mitgcm-devel
> > 
> 
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