[Mitgcm-support] Sign Conventions for Ocean-Atmosphere Fluxes

[mitgcm-support at dev.mitgcm.org]

All, sorry to bring-up the boring and unpopular issue of
signs and units, once again ...

Alistair, what is latest fashion regarding flux forcing these days?
Specifically, the release1 sign convention definitions for fu and fv in
FFIELDS.h are reversed relative to what the code actually expects.

Patrick, what are the sign convetion expected by pkg/exf bulk formulae?
Also, I am assuming that "lwflux" is "downward" as opposed to "net" longwave
radiation (see earlier message to Tom Haine) and that "swflux" is "net"
shortwave when used with option "ALLOW_KPP" and "downward" shortwave when used
with option "ALLOW_ATM_TEMP" (these are not the same).  Is this correct?


To minimize present headaches and future confusion I venture to make
following suggestions:


1) leave ocean model convention as is, even if it is ocean-centric for
   wind-stress and atmosphere-centric for heat fluxes, but
   clarify/fix FFIELDS.h definitions in following way:

C     fu     - Zonal surface wind stress
C                Units are           N/m^2 (>0 from West to East)
C
C     fv     - Meridional surface wind stress
C                Units are           N/m^2 (>0 from South to North))
C
C     Qnet   - Net upward surface heat flux
C                Units are           W/m^2=kg/s^3 (>0 for ocean cooling)
C
C     Qsw    - Net upward short-wave radiation
C                Units are           W/m^2=kg/s^3 (>0 for ocean cooling)


2) pkg/exf and pkg/seaice should use same sign conventions
   for radiative fluxes.  Without prejudice ;-), I suggest the
   following:

C     lwflux - Downward longwave radiation in W/m^2
C              at North-East B-grid tracer point
C              >0 for ocean warming
C     swflux - Downward shortwave radiation in W/m^2
C              at North-East B-grid tracer point
C              >0 for ocean warming


3) To avoid confusion, add a separate variable to pkg/exf for "net shortwave
   radiation".  This will also permit a mode of integration, where both "net"
   and "downward" shortwave radiation fields are specified externally.


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