1. First analysis of existing conservative
interpolation schemes : SCRIP, ESMF
(coupling between climate models)
Joël Chavas
Joël Chavas, WP8 face-to-face meeting 11 june 2012

2. Interpolating between two grids
Source grid Destination grid
Fsi
Fdj
Joël Chavas, WP8 face-to-face meeting 11 june 2012

3. The interpolator
interpolator
Grid Compute area Regridding
Compute edges
vertices intersections coefficients
Joël Chavas, WP8 face-to-face meeting 11 june 2012

4. Why computing edges in the
interpolator? Why a false area ?
● Software engineering
● Computational cost
● Grid cell areas used by the models don't necessarily
form a disjoint set (NEMO/OPA, LMDZ,...)
Joël Chavas, WP8 face-to-face meeting 11 june 2012

5. Compute edges
● SCRIP : linear in lat-lon coordinates
● ESMF : great circles
Joël Chavas, WP8 face-to-face meeting 11 june 2012

6. Programming
● SCRIP : serial
● ESMF :
– C++
– Regridding : a separate API
– Parallel (MPI)
Joël Chavas, WP8 face-to-face meeting 11 june 2012

7. Conservative interpolation
interpolator
Grid
vertices
Compute area Regridding
Compute edges
intersections coefficients
True grid
cell areas
Joël Chavas, WP8 face-to-face meeting 11 june 2012

8. What has been done in the first three
months
● Discussions with CERFACS
● Contacts with LSCE
● Technical report containing the mathematics that
renders SCRIP truly conservative. This applies
whenever grid cell areas of the interpolator don't
match true grid cell areas
Joël Chavas, WP8 face-to-face meeting 11 june 2012

9. What comes
● Put done this result
● Evaluate the ESMF regridding for the coupler
OASIS3-MCT
● Discussions about the need of a parallel
interpolation library
Joël Chavas, WP8 face-to-face meeting 11 june 2012

10. Acknowledgments
● Sophie Valcke, Laure Coquart (CERFACS,
Toulouse)
● Martial Mancip, Edouard Audit (Maison de la
Simulation, Paris)
● Olivier Marti, Yann Meurdesoif (LSCE, Paris)
● Thomas Dubos (LMD, Paris)
Joël Chavas, WP8 face-to-face meeting 11 june 2012