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

[Wanqiu Wang]

Prajeesh,

I see your point.  Since the identification in the atmospheric side only 
changes the flag without considering the energy gain while the ocean or 
land will spend energy to melt the snow, this would introduce a spurious 
energy sink.  This spurious energy sink could be quite large, 80 
cal/g*total snow amount, another cause of the energy imbalance of the 
coupled system.

-Wanqiu

On 10/20/2014 8:16 AM, Prajeesh A.G. wrote:
> 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.)
>
> *Regards..*
>
> Prajeesh A G
>
>
>
> ------------------------------------------------------------------------
> Prajeesh,
>     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.
> Regards,
> Moorthi
> 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)
>              else
>                lprec_cc(i) = rain(i)
>                snw_cc(i) = 0.0
>              endif
>            enddo
>
>
>     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?
>
>     *Regards..*
>
>     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
> Tel:(301)683-3718

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