Version 4 (modified by gm, 15 years ago) (diff) |
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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 4 modifications regarding the forcing evaluation, its time discretisation, the filter, and the general flowchart :
- Flow chart : general structure must be changed in a similar way to what have been done for vvl, see 2009WP/2009Stream3/VVL
- 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
Illustration of forcing integration methods. Old formulation (top) and new formulation (bottom).
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
Pending issues:
- The associated changes in TOP are still unclear. A priori, in PISCES p4zopt.F90 should be modified. Nevertheless, the TOP time stepping strategy seems to be a forward in time scheme. If yes, then the evaluation of the forcing at kt+1/2 is an improvement (if not to say a bug fix!). If not, action is required...
- Check the consistency with the change planned in the emps field (switch to fsalt, a true salt flux).
0. Flow Chart
1. Forcing evaluation
In order to evaluate the forcing at kt+1/2, all the input data in the surface module should be interpolated in time at kt+1/2.
2. Forcing time discretisation
Blah blah blah...
3. Modified filter
Blah blah blah...
Attachments (2)
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NEW_LF_RA.jpg
(53.6 KB) -
added by gm 15 years ago.
New versus old time discretisation of the forcing
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NEW_LF_RA_FlowCart.jpg
(79.1 KB) -
added by gm 15 years ago.
Flow chart of step with the new Leap-Frog + Robert-Asselin filter
Download all attachments as: .zip