[MITgcm-support] Understanding the shortwave radiation

Marcello Gatimu Magaldi Marcello.Magaldi at jhu.edu
Fri Jan 8 16:03:53 EST 2010

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 
rads, air temperature, rel humidity and winds. Since KPP is used, I am 
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 
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
5) Third confusing thing: there is another place in external_forcing.F 
where Qsw is added this time directly to gT always if

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

Marcello Gatimu Magaldi,
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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