friedemann
New member
Hi!
Short version of my question:
The WRF-Chem user guide recommends to set diff_6th_opt=0, but I think diff_6th_opt=2 would improve the wind fields in my simulation. So I would like to know why the user guide recommends this, and whether it's safe to turn it on in my case.
And here is the long version:
I'm using WRF-Chem (version 4.1) to simulate transport of passive trace gases (chem_opt=17, and I define the tracers in the registry myself). The WRF-Chem user guide (https://ruc.noaa.gov/wrf/wrf-chem/Users_guide.pdf) recommends the following advection options in namelist.input. Quote from the user guide:
It's not clear to me why the recommendation is to turn diff_6th_opt off. I have the impression that, on the contrary, turning it on can be important for making wind fields (and thus tracer transport) more realistic. See this report: https://www.researchgate.net/publication/241648605, where they show how diff_6th_opt corrects an oscillating up- and downdraft pattern. I see something similar in my simulations. Furthermore, it's recommended to set diff_6th_opt=2 when using sf_urban_physics, which I do, "in order to avoid oscillations that may arise at the border of the city where a strong change in roughness is present" (https://ral.ucar.edu/sites/default/files/public/product-tool/Multi_layer_UCM.pdf).
For these reasons I would like to set diff_6th_opt=2, while sticking to the other recommendations from the user guide quoted above. But why does the user guide recommend diff_6th_opt=0? Does diff_6th_opt=2 negatively affect tracer transport? In my case, mass conservation and realistic dispersion of the tracer are important.
Thanks!
Short version of my question:
The WRF-Chem user guide recommends to set diff_6th_opt=0, but I think diff_6th_opt=2 would improve the wind fields in my simulation. So I would like to know why the user guide recommends this, and whether it's safe to turn it on in my case.
And here is the long version:
I'm using WRF-Chem (version 4.1) to simulate transport of passive trace gases (chem_opt=17, and I define the tracers in the registry myself). The WRF-Chem user guide (https://ruc.noaa.gov/wrf/wrf-chem/Users_guide.pdf) recommends the following advection options in namelist.input. Quote from the user guide:
It's not clear to me why the recommendation is to turn diff_6th_opt off. I have the impression that, on the contrary, turning it on can be important for making wind fields (and thus tracer transport) more realistic. See this report: https://www.researchgate.net/publication/241648605, where they show how diff_6th_opt corrects an oscillating up- and downdraft pattern. I see something similar in my simulations. Furthermore, it's recommended to set diff_6th_opt=2 when using sf_urban_physics, which I do, "in order to avoid oscillations that may arise at the border of the city where a strong change in roughness is present" (https://ral.ucar.edu/sites/default/files/public/product-tool/Multi_layer_UCM.pdf).
For these reasons I would like to set diff_6th_opt=2, while sticking to the other recommendations from the user guide quoted above. But why does the user guide recommend diff_6th_opt=0? Does diff_6th_opt=2 negatively affect tracer transport? In my case, mass conservation and realistic dispersion of the tracer are important.
Thanks!