WRF surface energy budget (ALBEDO and EMISS)

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hongcheq
Posts: 2
Joined: Fri Apr 09, 2021 9:53 pm

WRF surface energy budget (ALBEDO and EMISS)

Post by hongcheq » Fri Apr 09, 2021 10:49 pm

Hello all,

Greetings!

This is a researcher currently working with a raft of WRF (version3.61) output files with hourly output frequency in a previously conducted WRF simulation (Feng et al. 2018). The simulation was done with 4-km horizontal resolution and 65 vertical layers. Simulation period is from 1 May 2011 to 31 August 2011. Other setup configurations are as follows:
The lateral and surface forcing: Global Forecast System Reanalysis.
PBL scheme: YSU.
Surface scheme: MM5.
Land surface model: Noah Land Surface model.
Longwave radiation scheme: RRTMG.
Shortwave radiation scheme: Goddard shortwave scheme.
MIcrophysics: Morrison 2-moment; Thompson.

I was following some posts on alternative ways to reconstruct surface energy budget and found the following posts to be enlightening!
viewtopic.php?f=43&t=10014&p=20146&hilit=ALBEDO#p20146
viewtopic.php?f=43&t=5674&p=13582&hilit ... get#p13582
viewtopic.php?f=57&t=5532&p=10650&hilit=ALBBCK#p10650

In short, the WRF output files I have did not have enough variables to directly calculate various terms of the surface energy balance. However, I’m hoping to do it indirectly by following an approach suggested by Kelly in one of the posts as follows:

gsw = (1-ALBEDO) * SWDOWN
glw = GLW
lwupflux = np.power(TSK,4) * STBOLT
netlw = EMISS*(glw-lwupflux)
netrad = gsw + netlw
seb = netrad + GRDFLX -HFX -LH

I found a portion of variables required in this framework are available in the current WRF outputs I possess, including surface skin temp (TSK), downward SW flux at ground (SWDOWN), downward LW flux at ground (GLW), and ground heat flux (GRDFLX). Some other variables required in this framework but are not in the WRF output files are ALBEDO and surface emissivity (EMISS).

With respect to ALBEDO, the WRF outputs do have background albedo "ALBBCK". Given that the ALBEDO is missing, it's tantalizing to use ALBBCK as a proxy. However, from previous post in the forum and some sniff tests suggest that these two variables (ALBBCK, ALBEDO) are different and their values differ. From the third posts mentioned above. Kelly posted:
"ALBBCK is the monthly albedo map that comes from the geogrid program, and ALBEDO is based on the surface model, and comes from the table values that model uses. If usemonalb = .true. the model uses ALBBCK instead of ALBEDO. After running, you would still want to look at the variable ALBEDO because the model will fill the ALBEDO array with the values from ALBBCK."

With respect to EMISS, in the user guide of a more recent version WRF AWR [version 4, Jan 2019], the following piece of information might be relevant.
Chapter "6. WRF Data Assimilation"
Section of "Radiance Data Assimilation in WRFDA"
"c. Radiative Transfer Models"
"The RTTOV package is not distributed with WRFDA, due to licensing restrictions. Users need to follow the instructions at http://nwpsaf.eu/site/software/rttov/ to download the RTTOV source code and supplement coefficient files and the emissivity atlas dataset."

It seems to suggest there's some kind of emissivition atlas datasets.

In short, the questions are:
(1) Are these two variables (EMISS, ALBEDO) obtained from external or intermediate files somewhere under the hood in the WRF runs?
(2) Are there certain ways one could obtain or derive the EMISS and/or ALBEDO information offline with hourly frequency in a previously conducted WRF (v3.61) simulation? (please see the beginning of the post for setup configurations)
(4) Are the two variables interactively calculated by the WRF model (so that they're difficult to get offline)? What additional information is needed to reproduce or retrieve the EMISS and ALBEDO information?

Thank you very much for your help!


Kind regards,
Hongchen

Reference
Feng, Z., Leung, L. R., Houze, R. A., Hagos, S., Hardin, J., Yang, Q., et al. (2018). Structure and Evolution of Mesoscale Convective Systems: Sensitivity to Cloud Microphysics in Convection‐Permitting Simulations Over the United States. Journal of Advances in Modeling Earth Systems, 10(7), 1470–1494. https://doi.org/10.1029/2018MS001305

Ming Chen
Posts: 1444
Joined: Mon Apr 23, 2018 9:42 pm

Re: WRF surface energy budget (ALBEDO and EMISS)

Post by Ming Chen » Fri Apr 23, 2021 12:45 am

Hi Hong Chen,
Again, I apologize for answering late. You raised a hard question for us to address.
Surface albedo in Noah is determined either from monthly mean climatic values (usemonalb = .true.) or based on parameters related to landuse type (VEGPARM.TBL). However, albedo is also adjusted based on snow cover, vegetation fraction, etc. In phys/module_sf_noahlsm.F, you can find all the codes related to albedo calculation. Unless you have all the information used in this code for albedo calculation, you cannot reproduce albedo solely based on variables in wrfout. Note that there exist large differences between climatological albedo and albedo derived from landuse type. Similar to albedo, Emissivity is also determined based on landuse type, snow cover, vegetation fraction. etc. To answer your questions:

(1) Are these two variables (EMISS, ALBEDO) obtained from external or intermediate files somewhere under the hood in the WRF runs?

No. They are not available in intermediate files.

(2) Are there certain ways one could obtain or derive the EMISS and/or ALBEDO information offline with hourly frequency in a previously conducted WRF (v3.61) simulation? (please see the beginning of the post for setup configurations)

It is possible if you have all the data required for ALBEDO/EMISSI calculation, although the results may not be that accurate since you only have hourly wrfout files.

(4) Are the two variables interactively calculated by the WRF model (so that they're difficult to get offline)? What additional information is needed to reproduce or retrieve the EMISS and ALBEDO information?

Yes it is kind of difficult to obtain these two variables offline. Please take a look at the code phys/module_sf_noahlsm.F, in which you will find the details related to albedo and emissi calculation. Unfortunately I don't know all the details and our expert in this field left a few month ago. He basically no longer answer our questions.

I hope the above information is helpful for you. Good luck!

Ming
WRF Help Desk

hongcheq
Posts: 2
Joined: Fri Apr 09, 2021 9:53 pm

Re: WRF surface energy budget (ALBEDO and EMISS)

Post by hongcheq » Tue Apr 27, 2021 9:19 pm

Ming, thank you very much for your reply!

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