Is there difference between fsnow 'snow flag' and snow+ice land use classification?

[PaulHamer]

I am asking this question in the context of looking at the non-stomatal deposition resistances for SO2. Looking in the descriptions in the ACP paper (Simpson et al. 2012 The EMEP MSC-W chemical transport model – technical description) and the supplment for that paper (table S19), I see that RgsSO2 for snow and ice is 1000. Looking in the most recent version of the code rv4_36, I see that there is a calculation for RsnowS and the calculations in the code bound it between a possible range of 70-700 depending on temperature.

My question is whether the value of RgsSO2 for snow and ice listed in table S19 is used at all in the model or is the value of RsnowS used in its place?

My current assumption is that RgsSO2 (snow+ice, S19: 1000) is used for land surface types listed as permanent snow and ice and that RsnowS is being used when there is some fraction of a vegetated land use type that has a fraction of non-permanent snow cover. I just want to double check my understanding is correct.

Thank you in advance for your time.

[mifads]

Hi Paul, Looks like that value of 1000 is never used. As you point out, if the underlying local land-cover is ice/snow, the values are constrained to be between 70-700 depending on temperature. Tbe key lines in the code in Rsurface_mod are:

  RsnowS = 70.0*(2.0 -L%t2C)
  ...
  if (L%is_ice) fsnow=1.0 !ice_nwp in Landuse
                            !to ensure it is treated
                            !same way as met input
                            !and not Ggs from table
...
   GnsS = (1.-fsnow)/(RnsS * lowTcorr) + fsnow/RsnowS

so if fsnow is one only the last term is used, which is the 70--700 version. (We are working on a new documentation paper (it is about time!); I'll modify that entry in the table.)

[PaulHamer]

Thanks for the explanation!