Help about boundaries sponge layer

[lalvarez]

Hello to All

I have got some results from my modeling in the California Current, but as you may see (attached figures are monthly mean surface velocities for january and may 1996), I still have some problems with my north, south & west boundaries, so i'm looking for help in order to reduce this problems and get more involved about how to set an sponge layer or boundary.

I attach also my *.in & *.h files

Thanks in advance & have a nice day

[kate]

I see that you are using clamped boundaries. What is it that you are clamping to? Is it such a good match that you don't want your model to have wiggle room? I have been using the RadNud boundary condition since it came out with timescales somewhat similar to your TNUDG and OBCFAC values. You would have to change M3NUDG and so forth from zero if you switch to RadNud.

A sponge layer is a band of increased horizontal friction and diffusivity. It's not obvious that it would improve your solution.

[lalvarez]

Hello Kate

Thanks a lot for your answer, please let me understand it slowly; this is how i have my LBC now

Code: Select all

!                   W       S       E       N
!                   e       o       a       o
!                   s       u       s       r
!                   t       t       t       t
!                           h               h
!
!                   1       2       3       4

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

   LBC(isTvar) ==   Cla     Cla     Clo     Cla \       ! temperature
                    Cla     Cla     Clo     Cla         ! salinity

What you are suggesting me to do is to change the clamped ones, these are:

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LBC(isUvel) ==   Cla     Cla     Clo     Cla         ! 3D U-momentum
LBC(isVvel) ==   Cla     Cla     Clo     Cla         ! 3D V-momentum
and
C(isTvar) ==   Cla     Cla     Clo     Cla \       ! temperature
               Cla     Cla     Clo     Cla         ! salinity

for the RadNud mode (correct me if i'm wrong), so that would be:

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LBC(isUvel) ==   Sch     Sch     Clo     Sch         ! 3D U-momentum
LBC(isVvel) ==   Sch     Sch     Clo     Sch         ! 3D V-momentum
and
LBC(isTvar) ==   Sch     Sch     Clo     Sch \       ! temperature
                 Sch     Sch     Clo     Sch         ! salinity

Another question, What are values you use for the:

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! Nudging/relaxation time scales, inverse scales will be computed
! internally, [1:Ngrids].

       TNUDG == 100.0d0  100.0d0           ! days
       ZNUDG == 0.0d0                      ! days
      M2NUDG == 0.0d0                      ! days
      M3NUDG == 0.0d0                      ! days

Thanks in advance & have a nice weekend

[kate]

Close, but this is what I typically use:

Code: Select all

   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

and

Code: Select all

       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

Now, there are domains in which I still have boundary currents. I think it depends on the quality of the fields being used for boundary conditions. Daily ROMS fields from a larger domain are a better match than weekly SODA fields. Sometimes I use daily HYCOM fields. What do you have?

[Ahumada]

Hi Leo,

The following are good references for this topic:

Marchesiello et al. (2001) Open boundary conditions for long-term integration of regional oceanic models. Ocean Modelling, 3, 1-20.

Mason et al. (2010) Procedures for offline grid nesting in regional ocean models. Ocean Modelling, 35, 1-15.

Cheers!

Miguel Angel

[lalvarez]

Hola Miguel

Thanks a lot for those referencies i´m reading them.

Have a nice day my Friend

[lalvarez]

Hello Kate

Thanks a lot for your guiding, i´m running my domain with values you posted for the LBC´s.

I still have some wierd things happening on my boundaries, specially on the west one, I hope tomorrow will post some graphic results about daily salinity, temperature and velocities.

Well i´m forcing with:
Tides are TPOX 7
Surface and LBC (monthly T°c,Sal, Rad, etc) are WOA 2005
Bathymetry is ETOPO1
Surface wind is CCMP (6 hours)

I hope this is what you refer to.

Have a nice day

[kate]

Yes, that's what I meant.

Surface and LBC (monthly T°c,Sal, Rad, etc) are WOA 2005

Many, many years ago we used monthly T,S climatologies on the boundary and didn't get very good results. Is there some reason you can't use something better? HYCOM, perhaps? Anyone else have good luck with a climatology?

[lalvarez]

Hello Kate

We have not try the HYCOM info, I'm sure it must have better results as you say.

By now we are facing another problem, we expand our domain fron 500km to 1000km offshore and when making the climatological files, it seems the _clim.nc file gets too big (>3 G) and can't be handeled.

My question is: Can the _clim.nc file be divided in 2 (such as _clim1.nc & _clim2.nc) with succesive ending-starting dates? I saw something alike here in the forum, but cannot remember well where it was.

Any hint will be heplful

Have a nice day

[kate]

Yes, you can split the climatology files in time, as long as they are not using cyclic time.

Modern 64-bit systems can handle files larger than 2 GB, though, so cyclic time should be possible. Just make sure your netcdf files are created in 64-bit mode, or maybe compressed netcdf4 mode.

[lalvarez]

Hello Kate

Thanks for your answer and Yes we are working on 64 bits.

I will try making my files smaller, i'll make a 1 year sequence and try making a 6, 4 and 3 months files and see what happen

Have a nice day

[lalvarez]

Hello Kate

We have finally change to HYCOM daily data for the forcing and OBC´s, but I still have one question about a suggestion of yours.

We are doing a 455 days run and my question is, How do I must handle the TNUDG, ZNUDG, M2NUDG, M3NUDG and OBCFAC parameters in order to adjust them to my 455 day run?

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

Thanks in advance and have a nice day

[kate]

Is there some reason you want to change those values? Are you unhappy with the solution? They are simply time-scales of nudging and shouldn't change with the length of your run.

[lalvarez]

Hello Kate

Actually there´s no reason I just had the doubt

Thanks a lot