## tide velocity problem

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Rocky_Wang
Posts: 45
Joined: Tue Mar 01, 2016 1:38 am
Location: the Ocean University of China

### tide velocity problem

Hello, I run the roms model with only tide forcing. We have put an ADCP into the modeled region to record the tide current velocity. When I compare the computed current velocity with observed data,I find the simulated result is smaller. which method or parameter I should adjust to increse the simulated currtrn velocity? Attachments are my H file and some paremeters about bottom boundary layer.
Attachments
bhseatide.h

lfparejar
Posts: 12
Joined: Sat Oct 05, 2013 5:21 am
Location: Rutgers University

### Re: tide velocity problem

One way could be to decrease the value of Zob in ocean.in. Zos is the surface roughness length, and you wouldn't need to tweak that here.

Another would be to decrease rdrg2, also in the ocean.in you show.

And another way could be to prescribe a constant, lower, bottom drag coefficient to increase the velocity. To do that (and if you want to keep using a quadratic drag law with the #define UV_QDRAG you have in the header file), you need to add these lines:

#define ANA_DRAG
#define UV_DRAG_GRID

Then you will need to modify and use ana_drag.h and add something like this:

# elif defined UV_QDRAG
DO j=JstrT,JendT ! based on Chezy coefficient (g/c^2)
DO i=IstrT,IendT
END DO
END DO
# endif

I'd expect quite some testing if you want to tweak rdrag2 to match your ADCP data.

Rocky_Wang
Posts: 45
Joined: Tue Mar 01, 2016 1:38 am
Location: the Ocean University of China

### Re: tide velocity problem

lfparejar wrote:One way could be to decrease the value of Zob in ocean.in. Zos is the surface roughness length, and you wouldn't need to tweak that here.

Another would be to decrease rdrg2, also in the ocean.in you show.

And another way could be to prescribe a constant, lower, bottom drag coefficient to increase the velocity. To do that (and if you want to keep using a quadratic drag law with the #define UV_QDRAG you have in the header file), you need to add these lines:

#define ANA_DRAG
#define UV_DRAG_GRID

Then you will need to modify and use ana_drag.h and add something like this:

# elif defined UV_QDRAG
DO j=JstrT,JendT ! based on Chezy coefficient (g/c^2)
DO i=IstrT,IendT
END DO
END DO
# endif

I'd expect quite some testing if you want to tweak rdrag2 to match your ADCP data.

Thanks very much, it is really helpful!
Now I want to set a constant, spatially varying bottom roughness length Z0B (m) associated with grain roughness z0N, I have the median grain size distribution data of the region that I modeled.
I know that
Z0N = 2.5 * D50 / 30
So how to modify and use ana_drag.h to achieve the goal.

# elif defined UV_LOGDRAG
DO j=JstrT,JendT ! based on Chezy coefficient (g/c^2)
DO i=IstrT,IendT
rdrag2(i,j)= *your new drag value* !Sorry I do not know how to modify there, can you give me more detaild reminder?
END DO
END DO
# endif

Chang
Posts: 20
Joined: Sun Dec 04, 2016 1:03 am
Location: ocean university of china

### Re: tide velocity problem

hello Rocky_Wang
I meet the same problem with you.so if you have figured it out,could you please show me how to do that?