How does WRF calculate the underlying surface albedo？

[rubyyuki]

Hello all,

Greetings!


I used MODIS land surface data in my simulation, and there was a desert within the study area. During a 1.5-day weak precipitation simulation, I noticed that the albedo values in the geo_em.d03.nc and wrf_inputd03 data were not fixed, but when I used the WRF simulation output as wrfout data, the albedo of the bare soil part in the first time step was output as 0.25, and in the second time step and later it was output as 0.38. I would like to ask why this is the case? Is it because the parameterization scheme I set needs to calculate the albedo?


In addition, my research requires fixing the albedo of the bare soil land surface to a specific fixed value. Should I change it to a fixed value at the beginning and let it be calculated later, or should I keep it at that value throughout the model's run?


For the latter idea, I tried modifying the albedo part in module_sf_noahlsm.F, but there was no change in the albedo output, is it because I didn't modify the critical code?


Here's my namelist.input &physics section：


&physics

mp_physics = 3, 3, 3,

ra_lw_physics = 1, 1, 1,

ra_sw_physics = 1, 1, 1,

radt = 30, 30, 30,

sf_sfclay_physics = 1, 1, 1,

sf_surface_physics = 2, 2, 2,

bl_pbl_physics = 1, 1, 1,

bldt = 0, 0, 0,

cu_physics = 1, 1, 0,

cudt = 5, 5, 5,

isfflx = 1,

ifsnow = 1,

icloud = 1,

surface_input_source = 1,

num_soil_layers = 4,

num_land_cat = 21,

sf_urban_physics = 0, 0, 0,

Thank you very much for your help!

Kind regards,
Yuki Wang

 

[Ming Chen]

At the beginning of model run, ALBEDO is determined from LANDUSE.TBL based on land use type.

In LANDUSE.TBL, alb = 0.25 for barren land.

Once wrf.exe starts , albedo is re-determined from VEGPARM.TBL, which gives alb = 0.38 for barren land.

For your specific case, You can modify VEGPARM.TBL, setting alb to the value you want for barren land. I suppose this is enough and you don't need to change anything else.

 

[rubyyuki]

At the beginning of model run, ALBEDO is determined from LANDUSE.TBL based on land use type. In LANDUSE.TBL, alb = 0.25 for barren land.

Once wrf.exe starts , albedo is re-determined from VEGPARM.TBL, which gives alb = 0.38 for barren land.

For your specific case, You can modify VEGPARM.TBL, setting alb to the value you want for barren land. I suppose this is enough and you don't need to change anything else.

Thank you very much for your reply. After modifying VEGPARM.TBL, I conducted a simulation and successfully changed the barren land albedo. Thank you very much for your help to me.