D. Temporal__Coordination__of__the__Fluxes_________________________

      The Flux Coupler contains two nested loops.  For each outer loop iteration, the coupler
sends one message to the ocean and receives one message from the ocean model.  As part of
the initial information exchange, the ocean model passes to the coupler a positive integer,
ncpl__o, which is the number of times per day that the ocean model will exchange messages
with the coupler.  Thus, the longest interval possible at present is one day, and this is the
most  common  value  used  in  coupled  integrations  to  date.   The  ocean  model  determines
from  ncpl__o  how  many  timesteps  are  needed  between  message  passing  based  on  its  own
internal timestep.

      The  atmosphere,  land,  and  sea-ice  models  also  send  the  coupler  a  positive  integer,
which is the number of times per day that these models will exchange messages with the
coupler.  In theory,  the coupler could communicate with these models over different time
periods, but at present all three models receive and send messages over the same interval.
Thus the communication between the atmosphere, land, and sea-ice models occurs in the
inner loop in the coupler.  For each inner loop iteration, the coupler sends and receives one
message to and from the atmosphere, sea-ice, and land models.  The Flux Coupler checks
that the integers sent by the atmosphere, land, and sea-ice models are the same, and then
calculates the number of inner loop iterations per outer loop iteration as ncpl__a / ncpl__o,
which  must  be  an  integer.   ncpl__a  is  the  number  of  times  per  day  that  the  atmosphere
will communicate with the coupler and is passed to the coupler in the initial information
exchange.  The atmosphere model determines from ncpl__a how many timesteps are needed
between message passing based on its own internal timestep.  The land and sea-ice models
also do this based on their own internal timesteps.

      Input  flux  means  fluxes  given  by  the  coupler  to  a  model.  Output  flux  means  fluxes
computed  within  a  model  and  given  to  the  coupler.  All  input  fluxes  for  one  model  were
either  computed  by  the  coupler  or  were  the  output  flux  of  another  model.  In  general,  a
given  flux  field  between  any  two  component  models  may  have  been  computed  in  one  of
three places:  within either of the two models or within the coupler.

      One function of the coupler is to gather, merge, sum, and/or time-average various flux
fields  from  various  sources  and  form  a  complete  set  of  input  fluxes  for  each  component
model.   This  gathering  and  merging  process  will  generally  involve  mapping  flux  fields
between various model grids and combining like fields from several grids onto one grid.  A
summation might be required, e:g:, net heat flux = solar + latent + sensible + longwave
(see  encircled  crosses  in  Fig.  1).  Also,  for  some  flux  fields  the  coupler  might  be  required
to form time-averaged quantities.  Thus component fluxes are mapped, merged, summed,
and/or time-averaged by the coupler in order to form complete input fluxes for the models.
Component fluxes that are gathered, merged, summed, and/or time-averaged to form the
complete input fluxes are:



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                                                                                                                   (Section C)
   o  F aid = atm/ice flux, computed by the drv                                                  (F1 d)
   o  F aia = atm/ice flux, computed by the atm model (an atm output flux)       (F1 a)
   o  F ald = atm/lnd flux, computed by the drv                                                 (F2 d)
   o  F ala = atm/lnd flux, computed by the atm model (an atm output flux)      (F2 a)
   o  F all = atm/lnd flux, computed by the lnd model (a lnd output flux)         (F2 l)
   o  F aod = atm/ocn flux, computed by the drv                                               (F3 d)
   o  F aoa = atm/ocn flux, computed by the atm model (an atm output flux)     (F3 a)
   o  F iod = ice/ocn flux, computed by the drv                                                   (F4 d)
   o  F ioo = ice/ocn flux, computed by the ocn model (an ocn output flux)         (F4 o)
   o  F ioi = ice/ocn flux, computed by the ice model (an ice output flux)             (F4 l)
   o  F lol = lnd/ocn flux, computed by the lnd model (a lnd output flux)          (F5 l)


Examples:                                                                         (Section C)
   o  F aid:  momentum flux between the atm and ice                  ("o1)
   o  F aia:  net shortwave radiation between the atm and ice       (S1 )
   o  F ald:  momentum flux between the atm and lnd                  ("o2)
   o  F ala:  net shortwave radiation between the atm and lnd       (S2 )
   o  F aod:  momentum flux between the atm and ocn                 ("o3)
   o  F aoa:  net shortwave radiation between the atm and ocn      (S3 )
   o  F iod:  momentum flux between the ocn and ice                    ("o4)
   o  F ioi:  net shortwave radiation between the ocn and ice         (S4 )
   o  F ioo:  ice formed within the ocn                                          (QH  )
   o  F lol:  ocean runoff formed within the lnd                            (FS )


Complete input fluxes (an overbar denotes a daily average):
   o  F axx = all atm model input fluxes:  a mapping/merging/summation of:  F aod, F aid,
      F ald, F all
   o  F lxx = all lnd model input fluxes:  a mapping/merging/summation of:  F ald, F ala
   o  F oxx__=__all_ ocn__model__input_ fluxes:_ a__mapping/merging/summation/time-averaging_
      of:  F aod   , F aoa   , F ioi  , F iod   , F lol
   o  F ixx = all ice_model_input fluxes:  a mapping/merging/summation/time-averaging of:
      F aid, F aia, F ioo  , F iod


These time-average_fluxes will need to be formed:
   o  F_aid___ = atm/ice fluxes, computed by the driver, time averaged by the driver
   o  F_aia___ = atm/ice fluxes, computed by the atm model, time averaged by the driver
   o  F_aoa___ = atm/ocn fluxes, computed by the atm model, time averaged by the driver
   o  F_aod___ = atm/ocn fluxes, computed by the driver, time averaged by the driver
   o  F_ioo__  = ice/ocn fluxes, computed by the ocn model, time averaged by the ocn
   o  F ioi   = ice/ocn fluxes, computed by the ice model, time averaged by the ice



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