[MITgcm-support] Excess cooling at the surface layers

Mon Oct 31 10:53:03 EDT 2011

Hi, see comments below. M.
On Oct 31, 2011, at 12:13 PM, himansu pradhan wrote:

> Thank you all for your valuable suggestions. I extend my apologies for my late reply. I had to carry on some experiments as per your suggestion.  
> REPLY to Martin :
> a) ETA Values at 1st, 10 th and 15 days of model integration are as follows (Boundaries open: North South and East)
> 1 st Day: ~ 0.1m to -0.5m
> 10 th Day: ~ -14.0m
> 15 th Day: ~ -19m
So you are obviously loosing volume, too, which points to a problem along the boundaries.
> b) I have run the model as per your suggestion, closing all the boundaries :
This does not close the boundaries, but just turns off Orlanski. Close boundaries by setting useOBCS=.FALSE. and placing walls along the boundaries (requires different topography file)
> useOrlanskiNorth=.FALSE.,
> useOrlanskiSouth=.FALSE.,
> useOrlanskiEast=.FALSE.,
> useOrlanskiWest=.FALSE.,
> This resulted in ETA values as below
> 1 st Day: ~ +0.16 to -0.02m
> 10 th Day: ~ -0.24 to + 0.55m
> 15 th Day: ~ -0.3 to +0.62m
> The ETA values, I suppose, are fairly reasonable but the Circulation is practically reversed. I gave a southwestrly wind (blowing from southwest to northeast). I expect a clockwise circulation which i am getting with realistic open boundaries to my domain. (west closed and the rest open). WHEN I CLOSED ALL THE FOUR BOUNDARIES, surprisingly I AM GETTING AN ANICLOCKWISE CIRCULATION, which is not expected. 
> OUTPUT_temp_15thday.jpg : North,South and East OPENED
> Temp_CLOSED_Boundary.jpg : All boundaries CLOSED
Don't expect to get a good circulation with closed boundaries. It's about finding out, where your warm water goes. I guess it's a volume problem. Turn on balancing of obcs-velocities (see documentation)
> 
> REPLY to Dimitris Menemenlis
> 
> Still we are struggling to set the MITgcm nonhydrostatic model for the Bay of Bengal....We have not considered the heat fluxes for the time being,. To start with our main concern is to simulate the basic seasonal features corresponding to the wind forcing, which we have not yet accomplished.
> 
> REPLY to Jody
> Right now we are trying to set the model and interested to validate the model simulations on seasonal scale: e.g., Circulation, elevation and and three dimensional thermal fields etc of our model domain. Tidal forcing will be considered subsequently for the simulations of internal waves. We are not getting any reasonable simulations so far...For example, the SST is getting too cooled beyond any explicable reasoning.....Sometime we get a cyclonic circulation where we expect an anticyclonic one...etc
> We observe fairly strong temperature gradients at the open boundaries (please see the attached SST figure). That's why I wonder if this has got something to do with the open boundary conditions.
> 
> Once again I thank you all....Looking forward for more suggestions...
> 
> On Thu, Oct 27, 2011 at 9:28 PM, Jody Klymak <jklymak at uvic.ca> wrote:
> 
> The OBCS package relaxes to TRef at the boundaries by default.  Either change this in orlanski* or set your TRef to something you would like.  If you are just forcing a surface tide, I'd set TRef to your resting stratification, and then this will be a nudge to that value.
> 
> I have never done regional tidal modeling with MITGCM, but I would also consider using a sponge at the boundaries - Orlanski really won't stop any internal wave reflections beyond mode-1.  See Carter et al 2010 (I think).... 
> 
> Cheers,  Jody 
> 
> 
> 
> On Oct 27, 2011, at  7:18 AM, Martin Losch wrote: 
> 
> > 7degC in 15days corresponds to a surface heat flux of rho*cp*7K*10m/15days > 200W/m^2 for your 10m surface layer.  That's a lot. What about other parameters, such as ETAN? 
> >
> > I have no experience with Orlanski BCs. As a test you could close all boundaries and see if you still loose so much heat.
> >
> > Martin
> >
> >
> > On Oct 27, 2011, at 1:51 PM, himansu pradhan wrote:
> >
> >> Dear MITgcm users,
> >>
> >> I have run my MODEL,( configured for the Bay of Bengal ) for 15days which results in a "normal end".
> >>
> >> The input files are : a) 15 level Temperature and Salinity files b) Bathymetry file c) Wind stress files. I have used a Rectangular domain with z- cordinate. The Eastern, Northern and Southern bounderies of the domain are OPEN with Orlanski radiation boundary conditions.
> >>
> >> After a normal end, the results of
> >> 1) Velocity files have a reasonable magnitude and the circulation is satisfactory ( velocity_OUTPUT_15thday.jpg)...... this is OK.....
> >>
> >> 2) but, ??????  the sea surface temperature (OUTPUT_temp_15thday.jpg) after 15 day model integration drops almost by  4-7 degrees   from the initial surface temp (input file:- initial_temp.jpg)
> >> The drop of temperature is almost everywhere in the region .
> >>
> >> Also, at the eastern and southern open boundaries the temperature contours seems to be squeezed at some regions as seen in the figure......... i am unable to figure out what is happening here.........???????
> >>
> >> OUTPUT_vertical_temp_profile.jpg : - shows depth-time graph of temperature (at one arbitrary point in my region)...... It is seen that the contours shoots up unreasonably ............??????
> >>
> >> Do kindly help with any suggestions, hints, clues.................
> >>
> >> My data files , input plot of temperature and salinity and output velocity, temperature files are attached in this mail.
> >>
> >> Thanking You in advance
> >>
> >> Himansu Pradhan
> >> Research Scholar, IIT Delhi
> >> India. <hi.tar.gz>_______________________________________________
> >> MITgcm-support mailing list
> >> MITgcm-support at mitgcm.org
> >> http://mitgcm.org/mailman/listinfo/mitgcm-support
> >
> >
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> 
> --
> Jody Klymak
> http://web.uvic.ca/~jklymak/
> 
> 
> 
> 
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> <OUTPUT_temp_15thday.jpg><Temp_CLOSED_Boundary.jpg>_______________________________________________
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