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(RESOLVED) WRF Single-layer, UCM crashed

tslin2

New member
I ran a case in WRFv4.4.2, which was a 15 km run using Noah-MP land surface model.
Simulation for SF_URBAN_PHYSICS = 1, Single-layer UCM in the Southeast United States.
Simulation started from 2015-08-02 00Z and plan to end at 2015-08-10 00Z

The run crashed at 2015-08-03_14:30:00Z due to NaN values for air density and vertical water mixing ratio in the non-urban grid. A huge negative (-1450 W/m2) sensible heat flux was found in an urban grid at 2015-08-02 22Z (see figure), and urban fraction at this grid is around 30%. The default TS_SCHEME is 1 (4-layer model) in the URBPARM.TBL, changing TS_SCHEME from 1 (4-layer model) to 2 (force_restore) in the URBPARM.TBL file can fix this issue and the results look good.

A further diagnosis in the 4-layer model (TS_SCHEME is 1) found that the road temperature dropped too much after rainfall due to increasing latent heat flux in the impervious surface when precipitation is larger than 1mm/hr, and create imbalance of energy budgets. The non-linear energy equation solved by Newton-Rapson method for road and wall temperature is unstable, creating very bad road, urban canopy air, and wall temperature after numerical iteration.

The force restore method (TS_SCHEME is 2) works because it assumes the energy balance by ground heat flux. The ground heat fluxes is residual of net radiation, sensible, and latent flux.

Another solution may assume no latent heat flux in the impervious road after rainfall or changing BETG (minimum moisture availability of road) to 0.1 from 0.7 (rainfall >1mm/hr) in the code. Or assuming the ground heat fluxes is residual of net radiation, sensible, and latent flux before solving energy equation. However, for a quick repair, altering TS_SCHEME in the URBPARM.TBL from 1 (4-layer model) to 2 (force_restore) may be the best temporary option.

Picture1.jpg

Tzu-Shun
 
Last edited:

tslin2

New member
I did some tests trying to improve the 4-layer scheme by revising the Non-Linear Simultaneous Equation for wall and road using Newton-Rapson in SLUCM.

In SLUCM, the codes

Iterate 20 times or meet all five thresholds
1. ABS(F) < 0.000001
Net radiation fluxes for wall
2. ABS(DTB) < 0.000001
Wall temperature change
3. ABS(GF) < 0.000001
Net radiation fluxes for road
4. ABS(DTG) < 0.000001
Road temperature change
5. ABS(DTC) < 0.000001
Urban canopy air temperature change

There are five tests here, the 4th and 5th one can resolve the issue.

1. Default (20 times iteration or less than 0.000001 change for iteration)
Run crashed at 2015-08-02_16:49:30

2. Changing threshold from 0.000001 to 0.0001 (default used for green roof)
Run crashed at 2015-08-02_23:10:00

3. Increasing iteration from 20 times to 100 times (default used for green roof)
Run crashed at 2015-08-02_17:45:00

4. DTG/6 and DTB/6 (default used for green roof)
Run successfully

5. all changes in 2., 3., and 4. together
Run successfully
 
Last edited:

Ming Chen

Moderator
Staff member
Many thanks for the update. I will talk to our expert regarding your changes. We will keep you updated if we have any concerns/ideas.
 

tslin2

New member
Many thanks for the update. I will talk to our expert regarding your changes. We will keep you updated if we have any concerns/ideas.
Thank you. A quick update, I had a run with WRFv4.3.3 and it ran successfully without any changes.
 

Donte18

New member
@Ming Chen Any ideas if the problem of WRF-Urban crushing when SLUCM is activated that was also in v4.5.1 has been solved in v4.5.2 or we should still use v4.3.3?
 

Ming Chen

Moderator
Staff member
@ Donte18

Since these changes are not included in WRFv4.5.x, if you have the same issues, you may
(1) stay with WRFV4.3.3
or
(2) add these changes to WRFV4.5.x if you wnat to run WRFV4.5.x
 
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