Confusion in interpreting the variable HFX in the wrfout file

[fpw]

Hi everyone!
I am using WRF4.5.2 to study anthropogenic heat flux. I used SLUCM and the cglc_modis_lcz map provided by WRF, and set AHOPTION=1 in URBPARM_LCZ.TBL. Then I used the visualization software panoply to view the HFX values in wrfout, and the results are provided in the attachment. The numbers 0-8 in the attached images represent the HFX distribution from 0:00 to 8:00 on July 1, 2022, but this result confuses me. I have the following questions.
1.What do negative values in HFX represent? Why do some regions have HFX exceeding 400?
2.Why is the HFX value in vegetation areas high and higher than in urban areas from time 0 to 7? Because based on the information I know, the heat flux in vegetation areas should be lower than that in urban areas.
3.How WRF calculates HFX?Where can I find more detailed information about HFX.
Thanks!

 

[Ming Chen]

Please see my answers below:

1.What do negative values in HFX represent? Why do some regions have HFX exceeding 400?
HFX is surface sensible heat flux, which is positive upward in WRF. Its value depends on several factors, including vegetation cover, land use type, climate, and time of day, etc. Negative HFX means downward sensible hear flux.
2.Why is the HFX value in vegetation areas high and higher than in urban areas from time 0 to 7? Because based on the information I know, the heat flux in vegetation areas should be lower than that in urban areas.
I agree. What are the local sun time of your model time 0-7 ? Can you plot time series of HFX over urban points and over vegetated points? I hope this can give a clear picture of model behavior.
3.How WRF calculates HFX?Where can I find more detailed information about HFX.
HFX is calculated in SFCLAY module. Depending on your option of sf_sfclay_physics, the calculation is slightly different. You can find the example in phys/module_sf_sfclayrev.F.