surface exchange coefficient for momentum Cd and heat Ck

Topics/questions specifically related to WRF model physics
Post Reply
ray96yelei
Posts: 45
Joined: Mon Dec 09, 2019 9:47 am

surface exchange coefficient for momentum Cd and heat Ck

Post by ray96yelei » Mon Apr 26, 2021 3:14 am

Hello professor, I want to output surface exchange coefficient for momentum Cd and heat Ck. Cd is surface drag coefficient and Ck is surface enthlpy exchange coefficient. And I know EXCH_H and EXCH_M in Registry.EM_COMMON are tubulent exchange coefficient for heat and momentum. But is there any variable in Registry.EM_COMMON represent surface exchange coefficient Cd and Ck? Thank you.

Ming Chen
Posts: 1456
Joined: Mon Apr 23, 2018 9:42 pm

Re: surface exchange coefficient for momentum Cd and heat Ck

Post by Ming Chen » Thu Apr 29, 2021 9:50 pm

Please take a look at the file WRF/Registry/Registry.EM_COMMON, in which you can find the following lines:

state real CD ij misc 1 - r "CD" "DRAG COEFF AT 10m" ""
state real CK ij misc 1 - r "CK" "ENTHALPY EXCHANGE COEFF AT 10 m" ""

Please change the 8th column of the above two lines from r to rh, then in top WRF directory, type ./clean -a and recompile the codes. With this modification, CD and CK will be included in your wrfout files.
WRF Help Desk

ray96yelei
Posts: 45
Joined: Mon Dec 09, 2019 9:47 am

Re: surface exchange coefficient for momentum Cd and heat Ck

Post by ray96yelei » Sun May 23, 2021 1:09 pm

Thank you for your reply. And in this way, I got the output CK and CD by WRF. HOWEVER, "CD" and "CK" in Registry.EM_COMMON is only available for YSU, MYNN2, MYNN3 PBL scheme, because they used same sfclay scheme Revised MM5 surface layer scheme. But for MYJ PBL scheme using MYJ sfclay, and QNSE using QNSE sfclay, wrf output "CK" and "CD" in MYJ and QNSE is always ZERO. no value. Please give me some hint and help, how to output surface exchange coefficient for heat CK and momentum CD in MYJ and QNSE these two PBL schemes. Thank you so much.

Ming Chen
Posts: 1456
Joined: Mon Apr 23, 2018 9:42 pm

Re: surface exchange coefficient for momentum Cd and heat Ck

Post by Ming Chen » Mon May 24, 2021 10:12 pm

Please take a look at phys/module_sf_myjsfc.F, in which AKHS and AKMS are the surface exchange coefficients for heat and momentum used in MYJSFC scheme. These two variables are also defined in Registry, so you can simply make them available in wrfout by adding 'h' to the 8th column of their definition line.
WRF Help Desk

ray96yelei
Posts: 45
Joined: Mon Dec 09, 2019 9:47 am

Re: surface exchange coefficient for momentum Cd and heat Ck

Post by ray96yelei » Tue May 25, 2021 2:02 am

Thank you for your reply. i follow your advice and output AKMS and AKHS in MYJ sfclay and QNSE sfclay. BUT I FOUND that the value of AKMS and AKHS value in MYJ SCFLAY and QNSE SFCLAY is much larger than CD and CK in revised MM5 sfclay scheme. AND I know In Registry.EM_COMMON, CD and CK stand for CD and CK at 10m, BUT what about AKMS and AKHS , which height level is AKMS and AKHS at? AND the value of AKMS and AKHS is much larger than CD and CK, maybe AKMS and AKHS is CD and CK mutiply a proportional coefficient, and what is the proportional coefficient?
Besides, a year ago, I can visit the website www2.mmm.ucar.edu/wrf/wrf physics survey.pdf , but now the webpage cannot found? is there anything wrong with that webpage? or is that webpage moving to other website? could you please tell me? Thank you so much.

Ming Chen
Posts: 1456
Joined: Mon Apr 23, 2018 9:42 pm

Re: surface exchange coefficient for momentum Cd and heat Ck

Post by Ming Chen » Wed May 26, 2021 3:46 am

The website is moved to https://www2.mmm.ucar.edu/wrf/users/phy ... survey.pdf. I am sorry for the inconvenience caused by this change.

For your question of AKHS and AKMS, I don't think they are modified by any factors. It is just that schemes have variations in stability functions, roughness lengths, and exchange coefficients. etc.
WRF Help Desk

ray96yelei
Posts: 45
Joined: Mon Dec 09, 2019 9:47 am

Re: surface exchange coefficient for momentum Cd and heat Ck

Post by ray96yelei » Wed May 26, 2021 8:23 am

Thank you for your reply. surface exchange coefficient Ck and Cd in Registry.EM_COMMON file as follows:

state real CD ij misc 1 - r "CD" "DRAG COEFF AT 10m" ""
state real CK ij misc 1 - r "CK" "ENTHALPY EXCHANGE COEFF AT 10 m" ""

state real AKHS ij misc 1 - r "AKHS" "SFC EXCH COEFF FOR HEAT" "m s-1"
state real AKMS ij misc 1 - r "AKMS" "SFC EXCH COEFF FOR MOMENTUM" "m s-1"

Based on them, I know "CD" and "CK" stand COEFF AT 10m, and they do not have unit. But which height level are "AKHS" and "AKMS" at? And I note that the unit of "AKHS" and "AKMS" is "m s-1"? what is that mean? "AKHS" and "AKMS" stand wind speed? I can not understand it, please give me some help.

AND Due to only sfclay1 can output "CD" and "CK", but sfclay2 and sfclay4 do not output "CD" and "CK". sfclay2 and sfclay4 can output "AKMS" and "AKHS", but the value is too large, maybe 100 times for "CD" and "CK" in sfclay1. So how can I get "CD" and "CK" at 10m for sfclay2 and sfclay4? please give me some help. Thank you so much.

Post Reply

Return to “WRF Physics”