flfall in atmdrvMod.F90

[cory_pettijohn@oregonstate_edu]

Hi, I'm worried there may be a bug in how CLM3.5's atmdrvMod.F90 calculates the fraction of total precip. falling as liquid, or 'flfall', using the 1956 'Snow Hydrology'. I don't have this publication on hand, but I am assuming that flfall is simply a linear trend from 0 to 1 between freezing air temp. and air temp + tcrit (273.16 K + 2.5 K). The code reads:

%%%%%% START COPY FROM atmdrvMod.F90 %%%%%%

! Snow and Rain
! Set upper limit of air temperature for snowfall at 275.65K.
! This cut-off was selected based on Fig. 1, Plate 3-1, of Snow
! Hydrology (1956).

if (aV_atm_d2a%rAttr(iprcxy,g1) + aV_atm_d2a%rAttr(iprlxy,g1) > 0._r8) then
if (atm_a2l%forc_t(g) > (SHR_CONST_TKFRZ + tcrit)) then
atm_a2l%forc_rain(g) = aV_atm_d2a%rAttr(iprcxy,g1) + aV_atm_d2a%rAttr(iprlxy,g1)
atm_a2l%forc_snow(g) = 0._r8
atm_a2l%flfall(g) = 1._r8
else
atm_a2l%forc_rain(g) = 0._r8
atm_a2l%forc_snow(g) = aV_atm_d2a%rAttr(iprcxy,g1) + aV_atm_d2a%rAttr(iprlxy,g1)
if (atm_a2l%forc_t(g)

 

[cory_pettijohn@oregonstate_edu]

or is it simply that, if a precip. event occurs when air temp.

 

[slevis]

I suggest diagnosing the situation by putting write statements in the code to find out if it works the way you think. If you become sure that there's a bug, pls let us know.

Thanks,
Sam