[Ncep.list.emc.monsoondesk] Regarding the Snow-Rain conversion in CFS

Prajeesh A.G. prajeesh.cat at tropmet.res.in
Mon Oct 20 12:16:29 UTC 2014

Yes sir, 

I got your point. 

However, my concern is again about the heat flux. Because, as I mentioned, the snw_cc goes to Ocean model and there it takes heat from the ocean surface to melt this amount of snow. So, if there is snow fall over the ocean, the ocean looses heat (cools the ocean) and in reality this heat lost by the ocean should have been gained by the atmosphere in terms of latent heat release. But this release of latent heat is missing. 

(From a quick look of the Noah land model, I guess similar process is also been done in the land surface too.) 


Prajeesh A G 

Admittedly, it is a simple scheme to identify whether the rainfall is snow or water based on T850. 
However, this is not a conversion; it is just an identification. Latent heat is considered in the microphysics. 
More advanced microphysics will provide rain and snow rates directly. 
I hope this helps. 
On 10/20/2014 05:45 AM, Prajeesh A.G. wrote: 

I have a doubt regarding the snow-rain conversion in CFS. 
In the model, the total precipitation is considered as snow fall if the temperature at 850hpa is below 0C. 

See the below code from gbphys_v.f 
!  --- ...  lu: snow-rain detection is performed in land/sice module
!           factor=weighted mean tep.

      do i = 1, im
        tprcp(i) = rain(i)               ! clu: rain -> tprcp
        srflag(i) = 0.0                  ! clu: default srflag as 'rain'
        if ( t850(i) <= 273.16 ) then
          srflag(i) = 1.0                ! clu: set srflag to 'snow'


      do i = 1, im
!       if ( t850(i)<=273.16 .and. slmsk(i)/=0.0 ) then
        if ( t850(i) <= 273.16 ) then
          lprec_cc(i) = 0.0
          snw_cc(i) = rain(i)
          lprec_cc(i) = rain(i)
          snw_cc(i) = 0.0
Here the 'srflag' is used in the sfc_drv (Land model) to detect whether the falling precipitation is snow or not. Similarly snw_cc goes to ocean model. 

My doubt is, where is the latent heat of fusion released during this conversion? 


Prajeesh A G 

Dr. Shrinivas Moorthi
Research Meteorologist
Global Climate and Weather Modeling Branch
Environmental Modeling Center / National Centers for Environmental Prediction
5830 University Research Court - (W/NP23), College Park MD 20740 USA
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