Is there anyone who use Romstools to create tidal forcing?

[chenyf]

Hi, all,

Im wondering is there anyone whos using Romstools to create tides to ROMS forcing file for tidal forcing by the boundary conditions?

Im testing two cases but get different results which i expected to be the same.

BTW, Im using TPXO data for the tidal data which I believe should be tidal harmony constituents.

The 1st case:

I set parameters in Romstools as following and get the tidal forcing input file:

Yorig = 1900;
Ymin = 2005;
Yman = 2005;
Min = 5;
Max = 5;
Dmin = 22;
Hmin = 0;
Min_min = 0;
Smin =0;

While I set in ROMS input file:

DSTART = 0.0d0
TIDE_START = 0.0d0
TIME_REF = 20050522.0d0

***************************

The 2nd case:

I set parameters in Romstools as:

Yorig = 1900;
Ymin = 1900;
Yman = 1900;
Min = 1;
Max = 1;
Dmin = 1;
Hmin = 0;
Min_min = 0;
Smin =0;

While I set in ROMS input file:

DSTART = 38492d0 ----which is the days between 1900/01/01 and 2005/05/22
TIDE_START = 0.0d0
TIME_REF = 19000101.0d0

*******************************

Im expecting both case should be running the case with tidal input from 2005/05/22 and get the same results. Am I wrong?

Not sure whether I explain it clearly enough or not....

Thanks in advance:)

[kate]

I can't say anything about ROMStools, but I know that ROMS should perhaps be changed so that TIDE_START of zero means year zero, the time origin for TPXO. The way it is now, TIDE_START of zero means that the tides have the same time origin as the physics, or TIME_REF.

[chenyf]

Hi,Kate,

Thanks for your kind reply.

But im confused. I thought if I set TIDE_START = 0, that means it has the same time of TIME_REF. Isnt it?

Thats why I set TIDE_START to be zero in both case because in the 1st case, I already used romstools to compute tide to be 2005/05/22 which is the same of TIME_REF. While in the 2nd case, I was thinking Im using romstools to compute tide to be 1900/01/01 which is also the same of TIME_REF.

BTW, as for TPXO, I thought it was harmony constituent and the time original was 1900/01/01? Am I wrong?

Thanks a lot

[kate]

You need to find out of ROMStools is changing the phase of the tides so as to match your time origin. The tool I use does not and I therefore need to set a TIDE_START of -693962.0d0. This is the number of days between my time origin in 1900 and the year zero (I hope).

You still will not exactly match a tide gauge record for 2005 unless you account for the long-period tides somehow.

[chenyf]

I guess I still need to think about it...

But anyway, thank you so much

[wilkin]

There is some documentation authored by Eli Hunter at Rutgers on the ROMS Wiki regarding Matlab code to create tidal forcing files from either the ADCIRC EastCoast 2001 database (Mukai et al. 2002) or the Oregon State OTPS (TPX0) database (Egbert and Erofeeva 2002). See https://www.myroms.org/wiki/index.php/Tidal_Forcing or search "Tidal Forcing" in the Wiki.

The documentation explains the requirements for making the time keeping consistent within your ROMS 3.0 application and its associated tides forcing file. Basically, the issues are that the whatever the base date is for your ROMS time (i.e. the notion that ROMS ocean_time is "days since..." or "seconds since" some base date) the tides file needs to share the same base date. If not, the the tides base date needs to be shifted with TIDE_START. The wiki explains how to apply the shift.

HOWEVER: Some caution is in order. Students of tides will appreciate that the "nodal correction" accounts for long time scale (18.6 year) modulation in the orbital forcing of the lunar tides, and therefore a set of tidal harmonic coefficients are typically computed as being valid for a relatively short time period (say, 2 years) from a given base date. Thus, if you choose a base date when t=0 in ROMS (say, 1-Jan-2005) you might request that your harmonic be valid, to the best approximation, to 2 years (i.e. centered on 1-Jan-2006 +/- 1 year). The wiki post explains this.

In the event you have constructed a tides forcing file (valid from a base date of e.g. 1-Jan-2005 and valid for 2 years) but wish to start a model run starting from t=0 at, e.g. 1-Jan-2006, then you can shift the tides harmonic forcing with parameter TIDE_START. If you enter TIDE_START in the ROMS Wiki search you will reach https://www.myroms.org/wiki/index.php/tide_start which explains how this works. Note that if your new base date (when t=0) for ocean_time is after the base date of your tides forcing file, your tide-start will be < 0.

My understanding of the tidal harmonic forcing literature indicates that if you use a shift of TIDE_START > a few years then you are neglecting the whole notion of the long-time-scale (18.6 year) modulation of the harmonic forcing. Setting TIDE_START to shift to a set of harmonics valid for e.g. 1-Jan-1900 is simply wrong. The whole nodal factor business is lost.

If all you want to do is to introduce the qualitative role of tidal mixing into your simulation, the phase hardly matters. If you seek some faithful reproduction of the timing of ebb and flood on an hourly basis, you must use a set of harmonics computed for the time period of interest.

In closing I will also note that ROMS TIME_REF does not specify the reference time the model uses on input. In specifies the attribute of the ocean_time variable written to netcdf output. If you change TIME_REF in the form of yyyymmdd in ocean*.in it makes no difference to the model execution. It is up the user to make sure that the notion of ocean_time in initial, boundary and forcing conditions in consistent (i.e. they all refer to the same "days since..." or "seconds since..." base date.

Mukai, A. Y., J. J. Westerink, R. A. Luettich, and D. J. Mark, 2002: Eastcoast 2001, A tidal constituent database for the western North Atlantic, Gulf of Mexico and Caribbean SeaTech. Rep. TR-02-24, 196 pp.

Egbert, G. D. and S. Y. Erofeeva, 2002: Efficient Inverse Modeling of Barotropic Ocean Tides. Journal of Atmospheric and Oceanic Technology, 19, 183-204.

[johnluick]

If you just want to check if you are understanding the phase correctly, use a single purely solar constituent like S2 that is not affected by the nodal modulation. Then worry about the nodal modulation later. It modulates the amplitude and phase of the lunar constituents. You can write yourself a little script to compute the modulations quite easily using Table 4:3, p 107 in David Pugh's Tides, Surges, and Mean Sea Level then apply it to the TPXO data.

[chenyf]

Thanks, wilkin and johnluick. I will try to test it:)

[viviocean]

I encounter the similar problem. I would consult, Would you like to connect with me, My MSN is ocean8102@yahoo.com.cn