help~really confused about the so called add tidal forcing~

[leon]

Dear all,
After learning ROMS for several months, I'm really confused about the so called 'add tidal forcing.
Q1: I have run a model with OBCs, which the OBC data are getted from some global ocean model such as HYCOM. There's no tidal forcing here. The result is good. If I want to simulate sediment transport, it's better to add tide here, right? The tidal forcing can be added as what is said by wikiROMS. But how to change the *.h file? I mean the tidal part. What I did is as follows:
*.h file:

Code: Select all

#define SSH_TIDES
#define UV_TIDES 

#ifdef SSH_TIDES
#define ADD_FSOBC
#endif

#ifdef UV_TIDES
#undef FSOBC_REDUCED
#define ADD_M2OBC
#endif
 
#define SOUTH_FSCHAPMAN 
#define SOUTH_M2FLATHER
#define SOUTH_M2NUDGING  
#define SOUTH_M3GARDIENT
#define SOUTH_M3NUDGING  
#define SOUTH_TRADIATION  
#define SOUTH_TNUDGING   

The bounday file is still the file used in the no tide simulation.

The model still can run, but the results are really different.

Is what I did right? Should I define ADD_FSOBC and ADD_UVOBC or not?

Shoul I still give the boundary file used in the no tide simulation or not?

Q2: I saw the latte_c case in https://www.myroms.org/wiki/index.php/ROMS_UNSW2008 . In the latte case, the obc is given by tide. I mean there is no BRYNAME file in *.in file.
If the *.h defined as follows, there is no need for BRYNAME file.

Code: Select all

#define SOUTH_FSCHAPMAN
#define SOUTH_M2FLATHER
#define SOUTH_M3GRADIENT
#define SOUTH_TGRADIENT


#define ANA_FSOBC
#define ANA_M2OBC

#define SSH_TIDES       /* read tidal SSH     from file */
#define UV_TIDES        /* read tidal U and V from file */

#ifdef  SSH_TIDES
# define ADD_FSOBC
#endif

#ifdef UV_TIDES
# undef  FSOBC_REDUCED   /* boundary pg is calculated using bounday zeta */
# define ADD_M2OBC
#endif

So what is the difference between Q2 setting ans Q1 setting? If I want to simulate sediment transport, which one should I choose?

Q3: How to check the tidal right or not? I mean how to put out tidal information such as amplitude. I didn't find any settings about this.

I'm really confused about this. I hope some experts can sovle the probleom for me.

Thancks a lot~

[wilkin]

In the LaTTE example we specify the external slowly varying sea level and depth average (M2) velocity though analytical subroutines, hence the:

Code: Select all

#define ANA_FSOBC
#define ANA_M2OBC 

In your case, evidently you have the slowly varying subtidal variability available in a boundary file. So you do not want to define ANA_{FS.M2}OBC. With these undefined, ROMS will go looking for the data in a netcdf file. Check your standard output (a.k.a. logfile) to be sure ROMS read those data.

Assuming the data was read, you DO want:

Code: Select all

#define ADD_FSOBC
#define ADD_M2OBC

because this adds the subtidal variability (read from input) to the tide harmonics.

I would suggest that you DO NOT want:

Code: Select all

#define SOUTH_M2NUDGING 

because this nudges the boundary M2 to the subtidal velocity, which works against the tide.

I also notice your posting says you have:

Code: Select all

#define SOUTH_M3GARDIENT

which is misspelled. Perhaps this typo is just in your Forum posting, but be aware that a misspelled CPP option in your application *.h will not trigger any error at compilation. But the option you thought you have defined will be undefined. You can check what options are active by reviewing the information sent to stdout and written to the netcdf files.

Whatever options you think you requested of ROMS, the options written out are the ones that were actually active.

[leon]

Thank you very much. You really do me a favor. In my case, I use add_fsobc and add_m2obc. One more question,

If I add tide using SSH_TIDE UV_TIDE ADD_FSOBC ADD_M2OBC, the model will generate tidal information such as amplitude, right? But how to output the tidal information?
I didn't find settings about output of tidal in the *.in file.

Thanks a lot~

[wilkin]

You have to specify the tidal boundary conditions - ROMS does not create these itself.
See the wiki entry on tidal forcing: https://www.myroms.org/wiki/index.php/Tidal_Forcing

I'm not sure what you mean about outputs of tidal information. Tidal variability is part of the model response to the tide forcing - it's in all the output variables.

[mathieu]

Some remarks: The code in set_tides.F has the code

Code: Select all

#  if defined WEST_FSOBC || defined WEST_M2OBC

in the section for adding the tidal variability to zeta_west, but zeta_west exist only if WEST_FSOBC is triggered. Thus this simplifies to the clearer

Code: Select all

#ifdef WEST_FSOBC

In this case, SOUTH_M2NUDGING has no effect because this option is used only by SOUTH_M2RADIATION.

[leon]

Dear all, I'm still confused about the tidal forcing. Actually, my model domain is East China Sea. At first, I get the OBC data--zeta,u,v, from OCCAM ( a global ocean model). And there is no tidal forcing. The model rusult is fine. But when I add tidal force, the currents just become disorderly. I'm not sure the way I add tidal force. You know, my OBC data is zeta,u,v,ubaar,vbar from a global model. I just keep the OBC data. And add #define SSH_TIDES #define UV_TIDES #define ADD_FSOBC #define ADD_M2OBC to the *.h file. Then add the tidal forc and run. Am I right?
Or Shoul I just define SSH_TIDES ADD_FSOBC in the *.h file when the boundary file exist zeta u v ubar vbar from a global model? Or set the OBC zeta to be zeros?
Which is right?
By the way, I run the climatological simulation, that is time perid is 360.

Thank you~

[wilkin]

You know, my OBC data is zeta,u,v,ubaar,vbar from a global model. I just keep the OBC data. And add #define SSH_TIDES #define UV_TIDES #define ADD_FSOBC #define ADD_M2OBC to the *.h file. Then add the tidal forc and run. Am I right?

This is right, but how do you add the tidal forcing? You need to give harmonics on the ROMS 2-D rho points grid in a forcing file. The CDL template for the file is in the code, but you can browse it at https://www.myroms.org/projects/src/bro ... a/ROMS/CDL

The wiki describes some options for obtaining tide data from global tide models:
https://www.myroms.org/wiki/index.php/Tidal_Forcing

[leon]

Thank you very much~
I made the tidal forcing file before, I'm just not sure the way I define the tidal options in *.h file. Because when I add tidal forcing, the current just go disorderly, I mean not so good as the no tidal case. Maybe there are some problem with the tidal harmonics, I'll check it. Thank you very much~~