open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello, I have been troubleshooting a regional model for a while and would appreciate some ideas/input/expertise, if anyone is able and willing.

Aim: Regional model of Patagonian shelf

What I'm doing and why

1. Telemac-2D: have used before without issue, but not in this region.
2. I am applying the model to various palaeo-timeslices, and so it is a big computational task
3. First, I sort my domain and model out for TPXO forcing, then I calibrate it for the present-day forcing from the lower resolution global model (which I use for the palaeo-forcing). I write my own boundary conditions file for this (h,u,v) and have successfully done so in another region.

Issues

1. The tide does not propagate properly on the shelf - too much energy, and I suspect the system should be losing energy to the internal tide at the steeply-sloping shelf edge (particularly in the south).
2. A smaller on-shelf only model of the Patagonian shelf works fine with TPXO9, high resolution forcing.
3. However, when I take my boundaries off-shelf, the on-shelf tide is too energetic.
4. I have to take my boundaries off-shelf because of the relatively lower resolution palaeo-tidal forcing that I need to use, to give it time to propagate sufficiently into my region of interest.

Options + specific questions

1. Implement a baroclinic tidal dissipation parameterisation into the 2-d model (as per the work done here. It's still somewhat of a bodge job as buoyancy frequency in palaeo-timeslices unknown (but perhaps that issue would stand with Telemac-3D?). A lot of work if it might not fix the issue.
2. Move to Telemac-3d - massively computationally expensive given the task ahead. Would it deal better with the steep continental slope?
3. Try forcing the model internally and on the shelf (rather than at the boundaries) because my palaeo-tidal forcing dataset is reasonable on the shelf (but relatively low resolution, 1/8th deg). Is there a way to do this, with open boundaries at the edge of the model domain, and applying u,v,h internally?
4. Something else I've not thought of.
5. Give up and use a different model.

I'd be so grateful if anyone has any ideas or expertise they'd be willing to share. Because it's a palaeo-study it doesn't need to be perfect, it needs to be good enough (I'm working with large error bars!).

Many thanks in advance

Hello,

I am not a specialist of modelling this area at all.

Can you show the extents of the different areas you tried please? The ones which work (on shelf) and the ones which do not work (off shelf). Can you also add bottom elevation.

What about the refinement of the mesh when gradients of bathymetry are the highest? What about the size of edges at those locations?

How far are the open boundaries compared to the "steep" slopes of the shelf?

Can you upload a typical steering file you use to run TELEMAC-2D please (+ potential Fortran files)?

Have you tried with other tidal solutions? e.g.:
- Atlantic Ocean if modelling Argentinian coasts or Pacific Ocean if modelling Chilian coasts? www.tpxo.net/regional
- FES2022 global model: www.aviso.altimetry.fr/en/data/products/...global-tide-fes.html
- HAMTIDE: www.cen.uni-hamburg.de/en/icdc/data/ocean/hamtide.html

You can try using TELEMAC-3D with 2, 3 or 5 planes. CPU times will not be too much compared to TELEMAC-2D if using only a few planes.

Chi-Tuan

Hello Chi-Tuan

Thank you for the response and interest in my issues. I’ve attached various grid/bathy and boundary condition files, plus a steering file. I’ve included an example boundary forcing file (UV,H) which I generated myself (m2+s2, TPXO09), which matches this particular steering file (GridB), but this could be easily switched off of course, and the default TPXO used.

GridA = off shelf and doesn’t give me a good solution to the forcing constituents on harmonic-analysis of the output.
GridB = on shelf, works with TPXO forcing (but doesn’t work so well with my own lower-resolution palaeotidal forcing dataset, hence me wondering about going off shelf).

In response to your other thoughts:

• Although I’ve tried many different grid configurations I’ve not tried explicitly increasing the resolution at the shelf slope, as I was concentrating on the shelf itself, but I shall try this. I took the boundaries well away from the steep slopes in the off-shelf configuration.
• I don’t think that changing my modern boundary conditions is relevant here as my issue becomes particularly pertinent when I use the bespoke global palaeo- ocean tide model output as boundary forcing, so I’m stuck with that.
• I will also try a 2 or 3 plane TELEMAC-3D model, out of interest. Thanks for that info.

Looking at my files you’ll notice a somewhat unusual approach to gridding my domain: I’ve adopted the method more commonly used in flood risk modelling, whereby the land is also part of the model grid. This is because of the changes in relative sea-levels which have to be applied during the palaeo-timeslices, and allows me to make only one grid for the region (to which I'll map various palaeo-topographies). Once I’ve sorted the forcing, the aim is for 1-2 km grid resolution on-shelf.

Thanks again for your input.

Best wishes
SLR

Grid files were too big to attach so I'm using WeTransfer: we.tl/t-OMbHnRvg8y

No sign-up necessary but only available for 7 days - sorry! If that fails I'll try something else.

Hello SLR,

Have you tried to refine your mesh when bathymetry gradients are the highest?

FYI, in $HOMETEL/examples/telemac2d/tide you can find a file tid_tide-jmj.slf which was used to build a model to compute tidal constituents along the English Channel and North-East Atlantic.
It was necessary to refine the mesh around the Continental Shelf.

Hope this helps,

Chi-Tuan

Hello, a (belated!) follow-up. Thanks again Chi-Tuan for the pointers and help several months ago.

I played around with various set-ups and parameterisations, including 3-d. I managed to get the 2-d model working through a combination of bringing the problematic norther boundary further south, increasing the grid resolution at the shelf break as you suggested and crucially, I needed to change the OPTION FOR LIQUID BOUNDARIES from 2 to 1. This last point took me a while to figure out as setting '2' worked for the semi-diurnal constituents but not for the diurnal ones.

Cheers!