Numerical Blow up in ROMS after Adding Tides and the Impact of WET_DRY on the Kuroshio Structure

[jc_Sun]

Hello everyone,

I am encountering a numerical stability issue related to tides during my ROMS simulation and would like to ask about possible causes.

Without tidal forcing, the model runs stably; however, after adding TPXO8 tidal forcing (e.g., M2 constituent), a blow up error occurs at approximately timestep 3600. The blow up is concentrated primarily in the waters west of the Korean Peninsula. I examined the tidal amplitude in this region (tide_Eamp and tide_Cmax) and found that the values are indeed relatively high there.

My model configuration is as follows:
Vertical coordinates: N=35, t_cline=30, theta_s=4, theta_b=0.1
Minimum depth: h_min=10 m
Horizontal resolution: approximately 6–7 km
DT=60s

After enabling WET_DRY, the model runs stably without overflow. However, I noticed the following:
With tidal forcing + WET_DRY enabled, temperatures in the waters west of the Korean Peninsula are significantly lower compared to simulations without tides;
Meridional cross-sections show stronger upwelling in this region;
Previous discussions on the forum have indicated that WET_DRY may affect the Kuroshio Current structure, and my results appear to exhibit similar issues.

My core questions are:
Is the overflow after adding tidal forcing primarily caused by the combination of large tidal amplitude in this region + insufficient grid resolution/terrain processing?
Although WET_DRY resolves the stability issue, does it significantly alter the regional dynamical structure (such as the Kuroshio Current or local upwelling)?

Under these circumstances, what would be a more reasonable approach:
Optimize the grid/bathymetry (e.g., smoothing, increasing resolution), OR
Adjust the tidal forcing, OR
Continue using WET_DRY but accept its impacts?

Code: Select all

      3031 2015-07-03 14:31:00.00  2.095785E-02  1.883366E+04  1.883368E+04  4.379472E+15
                     (165,308,35)  5.606840E-02  4.601120E-02  6.118530E-01  7.047417E+00
      3032 2015-07-03 14:32:00.00  2.095898E-02  1.883365E+04  1.883367E+04  4.379464E+15
                     (165,308,35)  5.628090E-02  4.594417E-02  6.166848E-01  7.072564E+00
      3033 2015-07-03 14:33:00.00  2.096008E-02  1.883364E+04  1.883366E+04  4.379456E+15
                     (165,308,35)  5.649082E-02  4.587781E-02  6.213160E-01  7.096841E+00
      3034 2015-07-03 14:34:00.00  2.096117E-02  1.883363E+04  1.883365E+04  4.379448E+15
                     (165,308,35)  5.669703E-02  4.581247E-02  6.257710E-01  7.119643E+00
      3035 2015-07-03 14:35:00.00  2.096963E-02  1.883362E+04  1.883364E+04  4.379439E+15
                     (165,308,35)  5.689978E-02  4.574830E-02  6.300684E-01  5.999783E+01
 Found Error: 1    Line: 362      Source: ROMS/Nonlinear/main3d.F
 Found Error: 1    Line: 312      Source: ROMS/Drivers/nl_roms.h, ROMS_run

 Blowing-up: Saving latest model state into  RESTART file
     REASON: MaxSpeed =  6.0E+01

Thank you for your insights.

[jcwarner]

with a "Horizontal resolution: approximately 6–7 km" there is absolutely no need for wet/dry. This option is somehow covering up a different problem.
What is your minimum depth in the whole grid? not just the wet points, but in the whole grid?

[jc_Sun]

with a "Horizontal resolution: approximately 6–7 km" there is absolutely no need for wet/dry. This option is somehow covering up a different problem.
What is your minimum depth in the whole grid? not just the wet points, but in the whole grid?

Hi Warner,

Thanks for your comment.

I checked the bathymetry carefully. The minimum depth over the entire grid is 10 m, and the minimum over wet points is also 10 m. This indicates that there are no zero or negative depths anywhere in the grid.

The model blow-up only occurs after adding tidal forcing (TPXO8, e.g., M2), and is localized mainly in the region west of the Korean Peninsula, where tidal amplitudes are relatively large. Without tides, the model remains stable.

Given this, I am wondering whether the instability could instead be related to other factors, such as:
– strong tidal currents interacting with bathymetry gradients,
– insufficient smoothing of the topography,
– time-stepping constraints

Do you think this type of instability is more likely caused by these factors rather than the bathymetry itself?

I would appreciate any suggestions on how to further diagnose or isolate the source of the instability.

[arango]

Repeatedly posting about your application issues without addressing the provided recommendations is unproductive. The ROMS development team, with extensive experience and published expertise, has offered guidance. It may be advisable to seek alternative support channels if current advice is not being followed.

[jc_Sun]

Dear Dr. Warner and Dr. Arango,

I sincerely apologize for my previous reply. I realize now that I misunderstood the underlying point of Dr. Warner's question regarding the bathymetry, and I did not provide the necessary diagnostic information. I appreciate your patience and the time you take to support the community.

Based on your comments, I will stop focusing on WET_DRY itself and instead diagnose the instability more systematically.

Thank you again for pointing me in the right direction. I will not use WET_DRY to bypass this, and I will stop speculating and instead focus on systematically testing the other potential factors. I will report back only when I have isolated the specific cause based on the diagnostics.

Best regards