Dear WRF Support Team,
I am using WRF v4.8.0 with the Noah-MP land surface model (sf_surface_physics = 4) for a winter simulation, and I would like to replace the default/model-calculated surface albedo with satellite-derived MODIS albedo.
My initial idea is to download MODIS albedo for my simulation period, regrid it to each WRF domain, and directly replace the ALBEDO field in the wrfinput_d0* files with the corresponding MODIS values.
However, I am not sure whether this is the correct approach for Noah-MP. My understanding is that Noah-MP calculates surface/snow albedo internally using the opt_alb option (opt_alb = 1 for BATS or opt_alb = 2 for CLASS). Therefore, I am concerned that even if I replace ALBEDO in wrfinput_d0*, Noah-MP may only use this value during initialization and then recalculate/overwrite it during the subsequent model time steps.
Could you please clarify the recommended approach?
If directly replacing ALBEDO in wrfinput_d0* with MODIS albedo is appropriate, which Noah-MP and/or WRF namelist options should I use to ensure that Noah-MP actually uses the input MODIS albedo during the simulation? In particular, should I modify opt_alb, usemonalb, sst_update, or any other option?
If directly modifying ALBEDO in wrfinput_d0* is not appropriate for Noah-MP, what is the recommended method for prescribing time-specific MODIS albedo? Should I instead modify ALBBCK or ALBEDO12M, or provide the MODIS albedo as a time-varying field such as ALBEDO_NEW through wrflowinp_d0*?
I would also appreciate clarification on how externally prescribed MODIS albedo interacts with the Noah-MP opt_alb calculation. If MODIS albedo is supplied externally, will opt_alb still recalculate the effective surface albedo, particularly over snow-covered grid cells?
My main objective is to ensure that the MODIS albedo is actually used by Noah-MP during the simulation rather than only appearing in the initial wrfinput file and then being replaced by the model-calculated albedo.
Thank you very much for your guidance.
Best regards,
I am using WRF v4.8.0 with the Noah-MP land surface model (sf_surface_physics = 4) for a winter simulation, and I would like to replace the default/model-calculated surface albedo with satellite-derived MODIS albedo.
My initial idea is to download MODIS albedo for my simulation period, regrid it to each WRF domain, and directly replace the ALBEDO field in the wrfinput_d0* files with the corresponding MODIS values.
However, I am not sure whether this is the correct approach for Noah-MP. My understanding is that Noah-MP calculates surface/snow albedo internally using the opt_alb option (opt_alb = 1 for BATS or opt_alb = 2 for CLASS). Therefore, I am concerned that even if I replace ALBEDO in wrfinput_d0*, Noah-MP may only use this value during initialization and then recalculate/overwrite it during the subsequent model time steps.
Could you please clarify the recommended approach?
If directly replacing ALBEDO in wrfinput_d0* with MODIS albedo is appropriate, which Noah-MP and/or WRF namelist options should I use to ensure that Noah-MP actually uses the input MODIS albedo during the simulation? In particular, should I modify opt_alb, usemonalb, sst_update, or any other option?
If directly modifying ALBEDO in wrfinput_d0* is not appropriate for Noah-MP, what is the recommended method for prescribing time-specific MODIS albedo? Should I instead modify ALBBCK or ALBEDO12M, or provide the MODIS albedo as a time-varying field such as ALBEDO_NEW through wrflowinp_d0*?
I would also appreciate clarification on how externally prescribed MODIS albedo interacts with the Noah-MP opt_alb calculation. If MODIS albedo is supplied externally, will opt_alb still recalculate the effective surface albedo, particularly over snow-covered grid cells?
My main objective is to ensure that the MODIS albedo is actually used by Noah-MP during the simulation rather than only appearing in the initial wrfinput file and then being replaced by the model-calculated albedo.
Thank you very much for your guidance.
Best regards,