[Mitgcm-support] Re: pkg/seaice and pkg/exf

[mitgcm-support at dev.mitgcm.org]

Which NCEP field do I use for evaporation?  I don't see the relevant field
at either cdc.noaa.gov or on ingrid.ldgo.columbia.edu. Do you figure it
out from latent heat flux?

I think I'll wait for you guys to iron out these issues. 
Tom.

On Mon, 6 Jan 2003, Dimitris Menemenlis wrote:

> 
> >> (i) Which shortwave flux should I use if both ALLOW_KPP and ALLOW_ATM_TEMP
> >> are defined?  It would help if these subtleties were documented somewhere.
> 
> I agree this is confusing.  I have sent a message to Patrick about this and
> hope to make some changes to pkg/exf, which will simplify and clarify things a
> bit in near future.  Your feedback really helps for this.  In the meantime the
> situation is as follows:
> 
> 1) KPP package requires net shortwave, that which actually penetrates
>    into the ocean.
> 
> 2) Sea-ice bulk formulae require the downward shortwave, that which arrives at
>    the surface of the ocean.  Part of it will be reflected due to albedo.
>    pkg/seaice will then generate the correct shortwave flux, which is passed
>    on to the KPP package.
> 
> 3) I am not sure what pkg/exf bulk formulae require or do.  I am waiting to
>    hear from Patrick about this.
> 
> In the meantime, if you use pkg/exf and pkg/seaice with
> SEAICE_EXTERNAL_FORCING defined and SEAICE_EXTERNAL_FLUXES undefined, that is,
> if you use pkg/exf to read-in atmospheric state but pkg/seaice bulk formulae,
> as you are, then you need to provide "downward", not "net" shortwave flux.
> 
> >> (ii) I get a compile-time error in growth.F if ALLOW_RUNOFF is undef'ed,
> >> not a runtime warning.
> 
> OK thanks.  I'll fix that.
> 
> >> (iii) I'm using SEAICE_EXTERNAL_FORCING and EXF_NO_BULK_COMPUTATIONS so as
> >> to use the pkg/seaice bulk formulae code. My evaporation field looks wrong,
> >> however (it's O(10^-5) m/s and has both signs - I expect O(10^-8), and only
> >> positive values). With EXF_READ_EVAP undef'ed and no evaporation file
> >> defined I was expecting pkg/seaice to calculate the evap. In fact,
> >> exf_getffields.F seems to be used to get it. I'm confused!
> 
> Oops!  You are really giving the seaice package a run for its money!
> pkg/seaice does not compute evaporation.  It expects evaporation to be
> provided.  With EXF_READ_EVAP undefined you are relying on the evaporation
> field computed by exf_getffields.F, which from the sounds of it is not working
> too well.  Problem is probably one of units/sign incosistency between pkg/exf
> and pkg/seaice, which I need to sort out with Patrick and will be easy to fix.
> But even beyond that, there will be some question mark regarding application
> of exf_getffields.F evaporation fields over ice-covered areas.  This requires
> a little more thought and hacking.  In the meantime, your best option is to
> explicitly provide evaporation files from the NCEP reanalysis.
> 
> Dimitris
> 
> -- 
> Dimitris Menemenlis                      menemenlis at jpl.nasa.gov
> Jet Propulsion Lab, MS 300-323           tel: 818-354-1656
> 4800 Oak Grove Dr, Pasadena CA 91109     fax: 818-393-6720
>