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Exchange coeffecients in YSU

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New member

One question about the YSU scheme.

I have read that there are only one diagnostic variable, exch_h, which I suppose is the exchange coefficient for heat. I want the same for momentum, exch_m. In my output this is 0 everywhere, while exch_h exists.

If I run with MYNN3 instead of YSU both exists.

I have also read:

"Both MRF and YSU schemes use identical
profile functions for momentum and heat for
stable conditions, leading to a constant turbulent
Prandtl number.

Does this mean that exch_h and exch_m are equal in YSU and that Prandtl number =1 ?

Then I wonder why exch_m is zero in the output.....


Hi Martin,
I ran a quick test to output both exch_h and exch_m, using the YSU scheme. I am seeing values of zero everywhere for both variables at the bottom model level, but if I go up in the atmosphere, after the initial time, I see non-zero values. I assume you've checked other levels too? Since I'm not able to repeat your problem, can you attach the namelist.input file you're using so that I can try with your namelist? Please also let me know which version of WRF you are using. Thanks!
Hi Kelly!

I am using WRF and in this example the single column version. I have checked all model levels. Values for both variables are zero at the time of initialization. After that I get nice values out for Kh but Km is always zero. I have talked to different persons and they say that they should be equal in YSU with Prandtl-number=1.

My namelist.input is attached and for you knowledge my outpufield.txt is empty.




  • namelist.input
    4.4 KB · Views: 68
Okay, the problem is that in V3.9.1.1, the variable EXCH_M was not implemented in the YSU code. When I tested, I was using V4.1.3. I have modified the 2 files that need to be modified in order to make this work correctly. I'm attaching them here. Please put the files in your phys/ directory and then recompile the code. You don't need to clean the code, or to reconfigure. Just simply recompile, and then run a test to see if it's giving you the result you expect.


  • module_bl_ysu.F
    67.3 KB · Views: 89
  • module_pbl_driver.F
    117.8 KB · Views: 95
Hello professor,I want to output EXCH_M for YSU scheme. Following your advice,I put these two file in WRF/phys/ directory,but after I compile the code,it fails,and there are some “Error” in the compile log file. Could you please give me some help?Thank you.
What version of the WRF code are you attempting to compile? Can you please attach your configure.wrf file and your compile log so that I can see the errors? Please also attach the modified code you are using. Thanks!
Thank you for your reply. I also want to output the variable "EXCH_M" in wrfout file for YSU, MYJ, and ACM2 PBL scheme, and I use wrf v4.0.
For YSU scheme, I modify "r" to "rh" for "EXCH_M" in the Registry.EM_COMMON file, and use module_bl_ysu.F of WRFV4.1 to replace the same file of WRFV4.0, and add "EXCH_M" FOR ysu part in modle_pbl_driver.F file. But it failed when compiling WRF for some errors in log file. Because I know that in WRFV4.1, YSU scheme can directly output "EXCH_M" variable. But I use WRFV4.0, and have already done most of work.
For MYJ scheme, I modify "r" to "rh" for "EXCH_M" in the Registry.EM_COMMON file, and add the "EXCH_M" following "EXCH_H" in the module_bl_myjpbl.F and module_driver_pbl.F respectively. Then I configure and compile the wrf, but it also failed after compiling. Could you please give me some help? Could you please tell me the right steps for doing so for these 3 pbl schemes? And could you please tell me how and what to modify for these 3 pbl schemes? And I found there is differences for module_bl_ysu.F between V4.1 and V4.0. Thank you so much.
Unfortunately we don't have the resources anymore for me to provide instructions on modifying those 3 different schemes. It's possible you are doing some things correctly, but have just made a mistake. That is why I ask for your configure.wrf file, and your compile log. Please attach those, along with any modified files (e.g., Registry.EM_COMMON, and if you've modified the physics schemes or are using a version of the files attached previously in this post - for the other user) so that I can take a look.