frequencies in TMD contist.m file

[aaretxabaleta-usgs]

We have been using the TPXO database and the TMD model code to make calculations of extreme tidal water level. We have tested the code for a location near Woods Hole, MA. When we did the prediction for a long period (1750-2120), we saw a trend in the yearly maximum water level (max_yearly_WL_woodshole_maximum_tide_1750_2100.png).

This seemed pretty weird, so we extended it to a longer time period (max_yearly_WL_woodshole_maximum_tide_1_3000.png) and we identified a pretty long (~2000-yr) modulation. We did the same calculation for other locations and some showed a trend and others didn’t.

We have identified the problem as a round-off for the frequencies of the overtides (M4,MN4, MS4). When we replace the given frequencies in the constit.m file of the TMD Matlab package with exact multiples of the main constituents, the problem goes away (max_yearly_WL_woodshole_maximum_tide_1750_2120_rightconstfreq.png).

m4: from 2.810377e-04 to 2*1.405189e-04
ms4: from 2.859630e-04 to 1.405189e-04+1.454441e-04
mn4: from 2.783984e-04 to 1.405189e-04+1.378797e-04

[fspaolo]

Hi @aaretxabaleta-usgs, did you contact Laurie (the author of TMD)? Laurie [email protected]

[aaretxabaleta-usgs]

I am in conversation with her. I have sent her the issue and the figures.