[MITgcm-support] Tidal input at open boundary

Martin Losch Martin.Losch at awi.de
Mon Jun 8 09:54:15 EDT 2020

Hi Weiyang,

it’s totally safe to implement your obcs forcing inside of obcs_calc.F. That’s what this file is for. Reading the from files is added convenience. 


> On 5. Jun 2020, at 18:36, Weiyang Bao <wbao at udel.edu> wrote:
> Dear MITgcm users,
> I encountered a problem when trying to apply a barotropic tide (u=u0*sin(wt)) at the only open boundary (east side) of my model domain. Firstly I used the script /seaice_obcs/input.tide/mk_tide.m to generate input files and keep the M2 constituent only:
> % specify (0.1 m/s, 1 hr) for East boundary tidal component 1
> if strcmp(ob,'E')
>         tmp(:,2:end) = 0;      %Set dummy components
>    if strcmp(fld,'am')
>       tmp(:,1) = tmp(:,1) + 0.1;
>    else
>       tmp(:,1) = tmp(:,1) + 1 * 3600;
>    end
> end
> However, this generated really small velocity (close to zero) at the boundary. Even if I cranked up the amplitude, the output velocity increased but still much smaller than the prescribed magnitude. Then instead of generating the tidal input files, I made a direct modification of the eastern boundary velocity as OBEu = u0*sin(wt) in the “obcs_calc.F” file, which gave the expected results. So I’m wondering if anyone could share some experience of generating the example tidal input files, and is it a safe way to modify the boundary velocity in obcs_calc.F directly? Thanks for your time!
> Best, Weiyang
> Weiyang Bao
> Ph.D. Student, Physical Ocean Science and Engineering
> School of Marine Science and Policy
> University of Delaware
> wbao at udel.edu
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