I am modeling thermal stratification in Lake Ontario. I am facing two problems:
I am using Full Heat Balance mechanism. I am observing negative surface temperatures in February and March since air temperature is low in those months. Model produces good stratification results from April to June but I couldn’t eliminate this negative temperature problems in February and March.
I tried varying solar radiation coefficients but not much change happened.
I am reluctant to use Equilibrium Temperature (Ce-Qual-W2) because the I don’t think physics is well balanced there to take care of negative surface temperature.
What else I could do?
I am seeing some checkerboard pattern in surface temperature so I believe heat is not getting diffused thoroughly.
I increased AHD value, lowered time step but not much change happened.
What can I do to resolve this problem?
We recommend you use the Equilibrium Temperature for the Surface Heat Exchange Sub-model as it does a better job and is more robust. With this option, if ice is not switched on, then temperature at the surface layer is limited based on the freezing point of water. If salinity is being modeled then the temperature at the surface layer is a function of salinity and the freezing point of water. So for sea water the salinity is ~ 35 ppt and freezing point in -1.3 deg C. If salinity is not simulated then it is limited to 0.1 deg C.
Regarding the checkerboard pattern – this depends on what range for the color ramp that you are viewing the model. What is the actual temperature difference from cell to cell – is it in the range to be expected from the heat model? If you are seeing a large variation, eg more than 0.1 deg C from cell to cell, then you should also look at your WSEL. If this is also checkerboard then you have an unstable model.
Thank you for the suggestion about using Equilibrium Temperature for the Surface Heat Exchange Sub-model. I kind of looked at it. But is the physics balanced for this module since we are not modeling salinity? And in that case, temperature is limited to 0.1 deg C.
I am looking at the grid bathymetry for the checkerboarding problem since there are some fairly large negative temperatures in some particular cells. I am trying to modify the elevation and depth manually whenever there is a sharp jump in bathymetry. But then I get into another problem. Each time I try saving the model after the edits, I get the error message: run time error 9: subscript out of range. Then I did the depth and elevation edits on DXDY.INP file, but the model is not running with modified bathymetry.
I already posted this topic as ViewPLan Error in the forum.
Thank you for all your help. I will appreciate some more helps.
Hi Rumana, yes, the physics are still balanced for the Equilibrium Temperature if you are not modeling salinity. However, I am sorry that we are unable to provide advice on the run time error if it is for EE5. We no longer support that version. We are now at release EE7.1.
I am reading the first reply from EE_Development_Team. The sentence ’ if ice is not switched on’ catches my attention. Does EE support ice processes in the latest version?
The existing ice approach in EFDC is quite rudimentary and is not yet implemented in EE. There is input for the ice thickness in the EFDC code but it is not considered in the hydrodynamics. However, drag on the surface is accounted for in the CALTSXY subroutine. There is currently no ice blockage algorithm implementation.
Another ice issue is linking the ice formation/melt to the heat sub-model. Currently it must be specified.
We do hope to implement a more robust ice model in EFDC_DSI before too long.
Hi EFDC Team,
I was able to run my model with modified bathymtery data. There were some mismatched values, I corrected them in DXDY.INP file and the model is running now.
Also as I fine tuned bathymtery data by eliminating any sharp jump between adjacent cells and adjusting elevations, the checkerboarding problem is nearly gone now. The simulated temperature is more continuous and smooth.
Thanks for your help.