[MITgcm-support] Model loosing salt

[Abhisek Chakraborty]

Dear Jean-Michel and Jody,

Thanks for your comments.

Jody, I have already used a sponge layer along with the obc files. Most
probably I have to increase the sponge thickness (now it is 100 km). The
option I am planning to try is to start the model few years back so that
fluxes and forcing become more stable.

regards,
Abhisek
On 28-Apr-2016 1:22 AM, "Jody Klymak" <jklymak at uvic.ca> wrote:

> In my opinion, the easiest way to deal with issues like this is to make
> your boundary far from your control region by stretching the grid so that
> you have a very large reservoir.  If the forcing in the control region is
> steady state, then the model will eventually settle into a steady state
> between the control region and the reservoir.
>
> Did you try applying a sponge layer on your southern boundary?  You can
> sponge T and S, and in your case that might add salinity to the domain
> faster than just prescribing the boundary condition at the southern most
> grid point.
>
> Cheers,   Jody
>
> > On 27 Apr 2016, at  12:43 PM, Jean-Michel Campin <jmc at mit.edu> wrote:
> >
> > Hi Abhisek and Martin,
> >
> > Just a comment on this:
> >> One can imaging prescribing fluxes,
> > Just prescribing tracer fluxes is probably not the right way to go (and
> this is why
> > it has not been implemented): any tracer anomaly that develops in the
> interior
> > should be able to be advected away when approaching an outflow OB region.
> > But prescribing tracer fluxes would prevent this, resulting in
> un-physical solution
> > (+ with potential numerical problems) with tracer anomaly being trapped
> in the
> > vicinity of OB outflow.
> >
> > Cheers,
> > Jean-Michel
> >
> > On Wed, Apr 27, 2016 at 11:41:31AM +0200, Martin Losch wrote:
> >> in the OBCS package, velocites, temperature and salinity are prescribed
> (it does not matter how they are provided, by Orlanski, Stevens or just
> from a file). There is no constraints on fluxes. One can imaging
> prescribing fluxes, but that would require a total rewrite of the code.
> Sorry ???
> >>
> >> Martin
> >>
> >>> On 26 Apr 2016, at 17:56, Abhisek Chakraborty <abhisek.sac at gmail.com>
> wrote:
> >>>
> >>> Dear Martin,
> >>> Thanks for your prompt response. Surely the atmospheric forcing is
> adding up non-zero freshwater flux. I have found the mean salinity is also
> decreasing. I am using OBCS_BALANCE with a non-zero sponge layer. I have
> tried with and without Orlanski OBC at my southern bounday but the results
> are similar. Is it always required to modify the code for balancing the
> tracers for a regional configuration of the model despite of using the
> standard OBCS package?
> >>> With best regards,
> >>> Abhisek
> >>>
> > her> > On 26-Apr-2016 4:54 PM, "Martin Losch" <Martin.Losch at awi.de>
> wrote:
> >>> Abhisek,
> >>>
> >>> as far as I can see, you have an open boundary and you use atmospheric
> surface forcing. Both of them will most likely have non-zero freshwater
> flux that will change your mean salinity (btw, does the mean salinity also
> change, or only the surface salinity as shown in your plots?). You could
> balance the surface freshwater flux with a flag (balanceEmPmR=.TRUE.) at
> each timestep, but you'd have to code balancing the freshwater flux
> (implied salinity flux, salt*vVel) through the open boundary yourself.
> >>>
> >>> Martin
> >>>
> >>> On 04/26/2016 11:53 AM, Abhisek Chakraborty wrote:
> >>> Dear All,
> >>>
> >>> I am trying to configure Mitgcm (version 65r) for Bay of Bengal with a
> >>> constant horizontal resolution of 2km. After 3 years of model runs
> >>> (2013-2015) using daily ERA forcing, I found the model is losing
> >>> salinity. The domain averaged salinity shows a decreasing trend. The
> >>> trend is more prominent for the head Bay. I am using yearly run off
> >>> climatology. A figure is attached to show my model domain and salinity
> >>> trend.
> >>>
> >>> The relevant data files are also attached.  Can anybody please help me
> >>> pointing out the possible causes of this decreasing salinity trend?
> >>>
> >>> Thanking in advance,
> >>> Abhisek
> >>>
> >>>
> >>>
> >>> _______________________________________________
> >>> MITgcm-support mailing list
> >>> MITgcm-support at mitgcm.org
> >>> http://mitgcm.org/mailman/listinfo/mitgcm-support
> >>>
> >>>
> >>> --
> >>> Martin Losch
> >>> Alfred Wegener Institute for Polar and Marine Research
> >>> Postfach 120161, 27515 Bremerhaven, Germany;
> >>> Tel./Fax: ++49(0471)4831-1872/1797
> >>>
> >>>
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> >>
> >>
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> --
> Jody Klymak
> http://web.uvic.ca/~jklymak/
>
>
>
>
>
>
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