[Ncep.list.emc.monsoondesk] Why Climatological Sea-Ice fraction send to GFS, but not the one computed by MOM-SIS

[Xingren Wu]

Prajeesh,

Firstly, let me explain why we used data_overide for sea ice climatology 
in CFSv2 (over *Land only*, as you saw, it passed into *Land%fice*)*:*

Because of the mismatch of the masks between MOM and GFS grids, i.e. 
when MOM indicates Land but GFS requires Ocean/Sea-Ice, this is done 
(i.e. using the climatological values). This occurs because of the 
difference in MOM/GFS masks. If the Ocean masks match each other in GFS 
and in MOM there is no need to do this.

Now come to the point why we do not pass Ice%part_size directly to GFS 
(but use fice_atm instead):

In the GFS there is only one category of sea ice, but in MOM there are 
multiple categories of sea ice, e.g., without loss of generality, MOM 
may have sea ice (with thickness >0) distribution with fractions of 
0.11, 0.12, 0.15, 0.18, 0.19; GFS would only need the sum of them, i.e., 
0.75 for sea ice fraction (with 0.25 for open water fraction in this 
case). Certainly one can send all those categories of sea ice (e.g. 
0.11, 0.12, 0.15, 0.18, 0.19) to GFS and sum them later; however, what 
we did is sum them in MOM (e.g. 0.75) and then send the total, here is 
how we did it:

scatter the following numbers first (Ice%fice):
0          1          1          1          1          1

then sum them over

0.25   0.11   0.12    0.15     0.18    0.19

we get 0.75 (for fice_atm). _The key is that the first part is open 
water_ with the rest for different categories of sea ice (in MOM). if 
over an area without sea ice, i.e.,

1.0       0.0      0.0      0.0     0.0      0.0

one then gets 0 (for fice_atm), or ice free.

That is why you saw "*fice_atm* get data from *ex_fice*. *ex_fice* get 
data from *Ice%fice* and *Land%fice*. *Ice%fice* is initialized every 
time to 1 and 0 just before its been put to *ex_fice*. and *Land%fice* 
get data from *Atm%fice* in the subroutine sfc_boundary_layer, which in 
turn get data from data_override call."

Hope this helps!

Best regards,
Xingren

On 2/19/2014 11:39 AM, Prajeesh A.G CAT wrote:
> Dear Wu,
>
> Thank you for the reply,
>
> Actually, I am sorry, the following change in the code was made by me 
> for testing purpose.
> But, what actually I was mentioning was about *fice_atm* only, it is 
> not about Atmos%fice.
>
> *!  call mpp_send(fice_atm,size(fice_atm,1)*size(fice_atm,2), 
> Atmos%coupler_rank)*
> **call mpp_send(Atmos%fice,size(fice_atm,1)*size(fice_atm,2), 
> Atmos%coupler_rank).
> ***
> fice_atm* get data from *ex_fice*. *ex_fice* get data from *Ice%fice* 
> and *Land%fice*. *Ice%fice* is initialized every time to 1 and 0 just 
> before its been put to *ex_fice*. and *Land%fice* get data from 
> *Atm%fice* in the subroutine sfc_boundary_layer, which in turn get 
> data from data_override call.
>
> Moreover, as far as I know, the computed Ice fraction from the Ice 
> model is in the variable *Ice%part_size, *which is not at all used here*.
> *
>
> *Regards..*
> Prajeesh A G
> Scientist 'B'
> CCCR, IITM
> Pune, India
>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://lstsrv.ncep.noaa.gov/pipermail/ncep.list.emc.monsoondesk/attachments/20140219/2f53d4de/attachment-0001.html