Conservative Leap-Frog + Asselin filter

Last edited Timestamp?

Object:
Introduce in the trunk the modified Leap-Frog + Robert-Asselin filter time stepping scheme (thereafter LF-RA) described in (Leclair and Madec Ocean Modelling 2009, in press). The scheme allows a exact conservation of the heat and salt contents when using variable volume thickness (key_vvl). The non-conservation of the standard LF-RA due to the time diffusion of the forcing through the filter. In the modified scheme the exact conservation is achieved by removing the forcing from the filter. This requires 3 modifications regarding the forcing evaluation, its time discretisation, and the filter :

• Forcing evaluation : the momentum and tracers forcing are evaluated at kt+1/2, no-more at kt.
  
• Forcing time discretisation : 0.5 * ( Q(k+1/2) + Q(kt-1/2) ), instead of simply Q(kt).
  
• Filter : the RA filter no-more act on the forcing, i.e. -afp * rdt * ( Q(kt+1/2) - Q(kt-1/2) ) is removed from the filter
  

Status:

ongoing work (NEMO-Paris).

Module involved:

fldread.F90
sbcmod.F90 ; trasbc.F90 , traqsr.F90 , dynzdf_exp.F90 , dynzdf_imp.F90
sshnxt.F90 , tranxt.F90 , dynnxt.F90

---

1. Forcing evaluation

Blah blah blah...

---

2. Forcing time discretisation

Illustration of forcing integration methods. Old formulation (top) and new formulation (bottom).

Blah blah blah...

---

3. Modified filter

Blah blah blah...