Calving coupling field on
CNRM-CERFACS IPCC coupled model
Why ?
For long-term runs like IPCC centenal simulations, an as-closed-as-possible water budget is mandatory to avoid dramatic drift on sea level or global salinity.
On ARPEGE model, snow falling on iced zone (mainly Greenland and Antarctic) never melts. Little by little, this implies a lack in total water cycle (about 0.1 Sv accumulates on ice sheets).
That's why this quantity must be re-directed to ocean, mimicking iceberg calving.
How ?
Solid precipitation coupling field is exchanged three times.
As “COTOSOPR”, OASIS interpolates on NEMO grid snow falling on sea and sea ice areas.
As “COCALANT” and “COCALVIN”, OASIS catches snow falling on Antarctic and Greenland land points and redirects them to NEMO grid.
Oasis process two interpolations on Antarctic and Greenland zones:
On the first one, the ocean grid points which receive calving coupled fields are located south of 60S latitude.
On the second one, accumulated water is spread all around global oceans.
For Antarctic, the interpolation simulates iceberg melting on Southern seas.
For Greenland, Cerfacs previous experiments clearly exhibits a strong effect of calving water addition around Greenland, and particularly on Labrador sea: even small, this extra fresh water volume could dramatically reduce Atlantic THC (see Dynamite FP6 project). That is the reason why this field is spread on the whole world ocean, with negligible global effect.
Oasis merges those two calving coupling fields (BLASNEW) and send it to NEMO (“ OCalving” for the new NEMO3 coupling interface)
Namcouple
#############################################################################
# Field 19 : Calving Antarctic only
#
# Warning: you must exchange antarctic calving BEFORE greenland one
#
COCALANT OCalvin2 36 _cpl_freq_ 5 atm.nc AUXILARY
a127 sne1 LAG=+_lag_atm_
P 0 P 2
#
CHECKIN BLASOLD SCRIPR CONSERV CHECKOUT
INT=1
1.1574E-5 0
DISTWGT D SCALAR LATLON 20 4
GLOBAL
INT=1
#
#############################################################################
# Field 20 : Calving Greenland only
#
COCALVIN OCalving 36 _cpl_freq_ 6 atm.nc EXPORTED
k127 tne1 LAG=+_lag_atm_
P 0 P 2
#
CHECKIN BLASOLD SCRIPR CONSERV BLASNEW CHECKOUT
INT=1
1.1574E-5 0
DISTWGT D SCALAR LATLON 20 4
GLOBAL
1. 1
OCalvin2 1.
INT=1
#
a127: ARPEGE grid. All grids points are masked except Antarctic land points
k127: ARPEGE grid. All grids points are masked except Greenland land points
sne1: NEMO grid: All grids points are masked except points south of 60S latitude
Note: tne1 is the standard NEMO grid mask.
Needed files
Special masks have to be created on ARPEGE t127 and NEMO ORCA1 grids (a127, k127 and sne1)
Thoses variables are available for those grids on masks_calving.nc files. See ftp:
ftp://ftp.cerfacs.fr/pub/globc/exchanges/maisonna/IPCC_AR5/masks_calving.nc
Warning: areas and grids files must contain variables related to those new grids. They must be identical to ARPEGE and NEMO standard variables (copy those variables and add them to areas.nc and grids.nc files)
questions: maisonna at cerfacs.fr