Changes between Version 5 and Version 6 of ticket/0663_MLF
 Timestamp:
 20100423T15:00:41+02:00 (11 years ago)
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ticket/0663_MLF
v5 v6 13 13 === Description === 14 14 15 Introduce the modified LeapFrog  RobertAsselin filter (LFRA) to fit the one presented in Leclair and Madec Ocean Modelling (2009). The scheme allows a exact conservation of the heat and salt contents when using variable volume thickness (key_vvl). The nonconservation of the standard LFRA 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. Furthermore, the scheme allows to use a much smaller Asselin filter parameter (10^4 instead of 10^1) decreasing the damping effect of the LFRA scheme, so that it is actually a quasi second order scheme.15 Introduce the modified LeapFrog  RobertAsselin filter (LFRA) to fit the one presented in Leclair and Madec Ocean Modelling (2009). The scheme allows a exact conservation of the heat and salt contents when using variable volume thickness (key_vvl). The nonconservation of the standard LFRA 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. Furthermore, the scheme allows to use a much smaller Asselin filter parameter (10^4^ instead of 10^1^) decreasing the damping effect of the LFRA scheme, so that it is actually a quasi second order scheme. 16 16 17 17 The LFRA flow chart of ''step'' is the one introduce in the trunk after the v3.1, to restore the key_vvl option. Its main characteristic is that the ''ssh'' is timestepped first, followed immediately by the computation of the ''now'' vertical velocity (see figure below). [[BR]] … … 34 34 Note that TKE equation is solved with a two level time stepping scheme : no need of a before field for its forcing term (i.e. taum) 35 35 36 sbc_oce.F90 : add "before" forcing fields (denoted by a '_b' sufix) for all ocean forcing components (utau_b, vtau_b, qns_b, qsr_b, emp_b, emps_b) 37 sbcmod.F90 : add the swap of surface fields and the read/write in the restart file. 38 Beginning of sbs routine, introduce the swap, but only for kt >= nit000+1. If no restart, the '_b' fields is known only at the end of the sbc calculation. Therefore we have choosen to regroup the setting of '_b' fields at nit000 at the end of sbc routine. CAUTION : here the swap must be done at each kt, what ever the nn_fsbc value is. Otherwise the ocean forcing will be wrong. 36 '''sbc_oce.F90 :''' add "before" forcing fields (denoted by a '_b' sufix) for all ocean forcing components (utau_b, vtau_b, qns_b, qsr_b, emp_b, emps_b) 37 38 '''sbcmod.F90 :''' add the swap of surface fields and the read/write in the restart file. 39 40 Beginning of sbs routine, introduce the swap, but only for kt >= nit000+1. If no restart, the '_b' fields is known only at the end of the sbc calculation. Therefore we have choosen to regroup the setting of '_b' fields at nit000 at the end of sbc routine. 41 42 CAUTION : here the swap must be done at each kt, what ever the nn_fsbc value is. Otherwise the ocean forcing will be wrong. 39 43 40 44 '''(2) The Asselin filter''' remove the forcing from the filter (dynnxt (?), tranxt, traqsr) 41 45 42 '''(3) The semiimplicit hpg'''. In tranxt.F90, for the semiimplicit hydrostatic pressure gradient, the coefficients are changed in order to take into account the Asselin filter parameter 46 '''(3) The semiimplicit hpg'''. 47 In tranxt.F90, for the semiimplicit hydrostatic pressure gradient, the coefficients are changed in order to take into account the Asselin filter parameter 43 48 44 49 time mean T and S for the semi implicit hpg computation was (ta+2*tn + tb) / 4 . It is now replaced by … … 53 58 54 59 Forcing evaluation : the momentum and tracers forcing are evaluated at kt+1/2, nomore at kt. This is done in the fldread routine since v3.0 60 55 61 Flow chart : general structure has changed for key_vvl (variable volume or equivalently nonlinear free surface) (v3.1). In particular the ssh equation is solved first together followed immediately by the computation of the now vertical velocity, so that wn is available to solve the tracer and the dynamics equations. 56 62