Nudging time scales working on bry or clim

[hzh_1211]

If my bry file from daily Hycom, and clm from monthly SODA, the boundary condition gives in below, my question is

1. did these Nudging time scales work on both boundary and climatology? If I want to give a strong nudging time scale to boundary and a weak nudging time scale to climatology, how did i do?

2. many people add the climatology nudging, What is the significance? Please give me some typical cases that using clim nudging.

Code: Select all

! Shc is an update to Flather
   LBC(isFsur) ==   Che     Che     Che     Che         ! free-surface
   LBC(isUbar) ==   Shc     Shc     Shc     Shc         ! 2D U-momentum
   LBC(isVbar) ==   Shc     Shc     Shc     Shc         ! 2D V-momentum
   LBC(isUvel) ==   RadNud  RadNud  RadNud  RadNud      ! 3D U-momentum
   LBC(isVvel) ==   RadNud  RadNud  RadNud  RadNud      ! 3D V-momentum
   LBC(isMtke) ==   Clo     Clo     Clo     Clo         ! mixing TKE

   LBC(isTvar) ==   RadNud  RadNud  RadNud  RadNud \    ! temperature
                    RadNud  RadNud  RadNud  RadNud \    ! salinity


       TNUDG == 2*360.0d0                    ! days
       ZNUDG == 360.0d0                      ! days
      M2NUDG == 360.0d0                      ! days
      M3NUDG == 360.0d0                      ! days

! Factor between passive (outflow) and active (inflow) open boundary
! conditions, [1:Ngrids]. If OBCFAC > 1, nudging on inflow is stronger
! than on outflow (recommended).

      OBCFAC == 120.0d0                      ! nondimensional

! Set lateral boundary conditions keyword. Notice that a value is expected
! See glossary below for details.

     LsshCLM == T                          ! sea-surface height
      Lm2CLM == T                          ! 2D momentum
      Lm3CLM == T                          ! 3D momentum

  LtracerCLM == T T                        ! temperature, salinity, inert

! Logical switches (TRUE/FALSE) to nudge the desired climatology field(s).
! If not analytical climatology fields, users need to turn ON the logical
! switches above to process the fields from the climatology NetCDF file
! that are needed for nudging. See glossary below for details.

 LnudgeM2CLM == T                          ! 2D momentum
 LnudgeM3CLM == T                          ! 3D momentum

  LnudgeTCLM == T T                        ! temperature, salinity, inert

[kate]

Have you tried it without the climatology nudging? I would do that, then evaluate whether or not you need help along the boundaries.

You can make your own monthly climatology from the daily HYCOM fields - it would at least be consistent with your OBC values then.

Look at your code to see what nudging timescales are being used. I commented out the use of the climatology timescale for nudging in the open boundary code:

Code: Select all

                IF (LBC(iwest,isTvar(itrc),ng)%nudging) THEN
!                 IF (LnudgeTCLM(itrc,ng)) THEN
!                   obc_out=CLIMA(ng)%Tnudgcof(Istr-1,j,k,ic)
!                   obc_in =obcfac(ng)*obc_out
!                 ELSE
                    obc_out=Tobc_out(itrc,ng,iwest)
                    obc_in =Tobc_in (itrc,ng,iwest)
!                 END IF

(from t3dbc_im.F)

[hzh_1211]

Thank your very efficient reply, Kate. I maybe clear the role of nudging in clima and obc.

if activate LtracerCLM and TNUDG .ne. 0:

ANA for nudg:
reading Tnudg from roms.in; read_phypar.F
CLIMA%Tnudgcof=Tnudg; ANA_nudgcoef.F
obc_out=Tnudg; t3dbc_im.F

nc file for nudge:
get nudgcoef from nc file; get_nudgcoef.F
obc_out=CLIMA%Tnudgcof; t3dbc_im.F

That is if activate nudging for clm and obc, ROMS will give the same nudgcoef to both boundary and climatology.
Your method is a good idea to give the different time scale for clm and obc!

[isoares]

Very helpful discussion.

Can I add one question ?

Following your strategy of using a strong lateral nudging and weak nudging to climatology, if I decide to use a netcdf file to provide the nudging coefficients to the model, what would be the values in this file ?

I am trying to use 1 day at the border, decaying to 1 year in the middle of the domain. So, I prepared a netcdf file which contains M2_NudgeCoef, M3_NudgeCoef, temp_NudgeCoef, salt_NudgeCoef and tracer_NudgeCoef, and all matrices have the values, which range from 1/(86400) at the border to 1/(365*86400) in the middle of the domain.

Do you think this will result in a strong lateral nudging ?

Ivan

[kate]

Your values look like you should use 'second-1' as the units. 'day-1' is also a valid option. See get_nudgcoef.F to check that.

You say you want 1 day at the edge and one year in the middle. I think if it rather as strong (1 dayish) at the edge to infinite time (zero coefficient) over some width, say 10-20 grid points, then zero for the interior. Is that what you meant?

To answer your question, try it and see!

[isoares]

Hi Kate,

Yes, this is what I mean. I was using the wrong units. Thanks for warning me about the units. I will let you know about the new results.

Thanks

Ivan

[corvianawatie]

Your values look like you should use 'second-1' as the units. 'day-1' is also a valid option. See get_nudgcoef.F to check that.

You say you want 1 day at the edge and one year in the middle. I think if it rather as strong (1 dayish) at the edge to infinite time (zero coefficient) over some width, say 10-20 grid points, then zero for the interior. Is that what you meant?

To answer your question, try it and see!

Hi Kate, I want to ask about the nudging coefficient. I use these parameters to calculate the nudging coefficient (in d_nudgcoef.m). But the results, there is abnormal decrease/increase in temperature at the edge (please see the figure).

inner = 1/60; % 60 days at interior limit
outer = 1/5; % 5 days at boundary
width = 8; % 8 points
work = zeros(Lr,Mr);
work(:,:)= 1/10;

And this is the setting of my boundary condition

Code: Select all

   LBC(isFsur) ==   Cha     Cha     Cha     Cha         ! free-surface
   LBC(isUbar) ==   Fla     Fla     Fla     Fla         ! 2D U-momentum
   LBC(isVbar) ==   Fla     Fla     Fla     Fla         ! 2D V-momentum
   LBC(isUvel) ==   Rad     Rad     Rad     Rad         ! 3D U-momentum
   LBC(isVvel) ==   Rad     Rad     Rad     Rad         ! 3D V-momentum
   LBC(isMtke) ==   Gra     Gra     Gra     Gra         ! mixing TKE

   LBC(isTvar) ==   RadNud  RadNud  RadNud  RadNud \    ! temperature
                    RadNud  RadNud  RadNud  RadNud      ! salinity
! Factor between passive (outflow) and active (inflow) open boundary
! conditions, [1:Ngrids]. If OBCFAC > 1, nudging on inflow is stronger
! than on outflow (recommended).

      OBCFAC == 1.0d0                      ! nondimensional

Could you give me any suggestion about my nudging coefficient or my model configuration?
Thank you

[kate]

First, what is the land mask doing right there? You might want to change:

______
.........|_____

to

________________

filling in the leftmost water points with dirt. That's what I would try first. Next, look to see what the velocities are doing in that corner.