[MITgcm-support] Understanding the shortwave radiation

[Marcello Gatimu Magaldi]

Hi folks,

sorry for the clutter, I am a little bit confused by how the shortwave 
flux is handled in the model.

Ok, first my relevant configuration. I am providing downward short and 
longwave
rads, air temperature, rel humidity and winds. Since KPP is used, I am 
defining SHORTWAVE_HEATING too.
I tracked the code and I ended up with:
1) downward short and longwave rads are converted respectively in upward 
net short and longwave
rad in exf_radiation.F.
2) sensible and latent heat fluxes are calculated using model fields in 
exf_bulkformulae.F
3) the total upward net heat flux is calculated in exf_getforcing.F 
summing these contributions. Here the first
confusing thing: if SHORTWAVE_HEATING is defined the shortwave flux is 
not added with the other fluxes
but few lines later. Anyway, exiting exf_getforcing.F the total upward 
net heat flux (which it seems to me that ALWAYS includes the shortwaves)
is assigned to the variable qnet via exf_mapfields.F. Similarly the 
upward net shortwave flux is assigned to qsw.
4) the heat flux is used in external_forcing_surf.F (which is called by 
do_oceanic_phys.F) to change surfaceForcingT.
surfaceForcingT is ultimately the variable by which the fluxes enter the 
theta-equation since it affects gT (via subroutine
external_forcing_T.F called by calc_gt.F which is in turn called by 
thermodynamics.F... uff... complicated! A beer will help!).
However, here the second confusing thing: if SHORTWAVE_HEATING is 
defined the model adds Qnet (ok!) but again
Qsw! But Qnet already contains shortwaves, why is Qsw added a second 
time? I am sure the code is right. I am just not
understanding.
5) Third confusing thing: there is another place in external_forcing.F 
where Qsw is added this time directly to gT always if
SHORTWAVE_HEATING is defined.

I am sure I am missing something. Can somebody explain the rationale 
behind this multiple addition?
Thanks in advance,
m.


-- 
Marcello Gatimu Magaldi,
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The Johns Hopkins University
Department of Earth and Planetary Sciences
328 Olin Hall
34th and North Charles Streets
Baltimore, Maryland 21218, USA
e-mail: < Marcello.Magaldi at jhu.edu >
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