where can I find snow cover fraction?

[yuzuoing]

Hi,
I found many research papers state the snow cover fraction, but I could not find it in nc files (geo.nc,metgrid.nc,wrfinput,wrfout). Where can I find this variable.
It is an important factor which is used to calculate the actual snow albedo while snowing. I find landusef and greenfac in nc files, dose that mean snow cover fraction can be calculated through static geographic data? If true, how can I incorporate or update snow relatived static geographic data?
In addition, can snow cover be updated in geog folder? If true, how can I deal with Vtable? Noah MP may be relative to snow cover, should I use this scheme?

Fu
23 Oct, 2019

 

[Ming Chen]

fractional snow cover is not a variable included in met_em files. The variable "FGSN" is a diagnostic variable that can be included in wrfout files.

I don't think snow cover is a variable included in static data.

 

[yuzuoing]

Mr Chen,

Thanks for you reply!

I want to know how dose SNOWC(FLAG INDICATING SNOW COVERAGE) in wrfout come from? This variable is absent in geo.nc and metgrid.nc. I am wondering whether it is calculted by Noah LSM, because Noah LSM has many variables related to snow physics such as "snow cover fraction", "SNOW WATER EQUIVALENT", "MAXIMUM SNOW ALBEDO ".

Fu
2019.12.12

 

[Ming Chen]

Hi Fu,

"SNOWC" is initialized in dyn_em/module_initialize_real.F, i.e.:
DO j = jts, MIN(jte,jde-1)
DO i = its, MIN(ite,ide-1)
IF ( skip_middle_points_t ( ids , ide , jds , jde , i , j , em_width , hold_ups ) ) CYCLE
IF ( grid%snow(i,j) .GE. 10. ) then
grid%snowc(i,j) = 1.
ELSE
grid%snowc(i,j) = 0.0
END IF
END DO
END DO


This variable is later diagnosed in phys/module_sf_noahlsm. Note that it is renamed as SNCOVER in this code. Please see the following piece of code:
2836 ! ----------------------------------------------------------------------
2837 ! SNUP IS VEG-CLASS DEPENDENT SNOWDEPTH THRESHHOLD (SET IN ROUTINE
2838 ! REDPRM) ABOVE WHICH SNOCVR=1.
2839 ! ----------------------------------------------------------------------
2840 IF (SNEQV < SNUP) THEN
2841 RSNOW = SNEQV / SNUP
2842 SNCOVR = 1. - ( EXP ( - SALP * RSNOW) - RSNOW * EXP ( - SALP))
2843 ELSE
2844 SNCOVR = 1.0
2845 END IF
2846

After the call of LSM scheme, In driver (phys/module_sf_noahdrv.F), the value of SNCOVER is given to SNOWC again, i.e.,
SNOWC(I,J)=SNCOVR

Hope this is helpful for you to understand the general flowchart for the calculation of snowc.

 

[yuzuoing]

Mr Chen,

Thank you for your guidance. I have found the .F script, and I probably know WRF snow process.

Fu