MITgcm

b29547f131 Oliv*0001 Package longstep
                0002 ================
                0003
                0004 This package allows the passive tracer time step to be longer than that for
                0005 dynamical fields: the ptracers are updated only every LS_nIter time step.
                0006 Dynamical fields are averaged over LS_nIter time steps and are available as
                0007 fields LS_* (declared in LONGSTEP.h):
                0008
                0009 original fld.  averaged fld.
                0010 ------------------------------
                0011 UVEL           LS_uVel
                0012 VVEL           LS_vVel
                0013 WVEL           LS_wVel
                0014 THETA          LS_theta
                0015 SALT           LS_salt
                0016 IVDConvCount   LS_IVDConvCount
                0017 Qsw            LS_Qsw
                0018
                0019 Kwx            LS_Kwx
                0020 Kwy            LS_Kwy
                0021 Kwz            LS_Kwz
                0022
                0023 KPPdiffKzS     LS_KPPdiffKzS
                0024 KPPghat        LS_KPPghat
                0025
                0026 The T and S time step remains the same as that for u,v,...
                0027
                0028
                0029 Packages that use ptracers (like DIC) need to be adapted:
                0030
                0031 1. replace dtTracerLev by PTRACERS_dTLev
                0032 2. replace THETA, SALT, etc. by their longstep averages from the table above.
                0033    This should be made between #ifdef ALLOW_LONGSTEP ... #endif.
                0034    (You need to #include "LONGSTEP.h")
                0035
                0036 The package is activated by including "longstep" in packages.conf.  There is
                0037 no "use_LONGSTEP", the package is always on when compiled.
                0038
                0039
                0040 The run-time parameters are set in data.longstep.  The default is:
                0041
                0042  &LONGSTEP_PARM01
                0043  LS_nIter=1,
fda3710353 Oliv*0044  LS_whenToSample=0,
b29547f131 Oliv*0045  &
                0046
fda3710353 Oliv*0047 LS_nIter        :: number of dynamical time steps between ptracer time steps.
                0048 LS_whenToSample :: when to sample dynamical fields for the longstep average
                0049                    0 - at beginning of timestep (reproduces offline results)
                0050                    1 - after first THERMODYNAMICS but before DYNAMICS
                0051                        (use use old U,V,W for advection, but new T,S for GCHEM if
                0052                        staggerTimeStep=.FALSE.; reproduces online with
                0053                        staggerTimeStep=.FALSE. for LS_nIter=1)
                0054                    2 - after DYNAMICS and second THERMODYNAMICS
                0055                        (use new U,V,W and T,S; reproduces online with
                0056                        staggerTimeStep=.TRUE. for LS_nIter=1)
b29547f131 Oliv*0057
                0058 Default is to sample dynamical fields at the beginning of the time step.  This
fda3710353 Oliv*0059 reproduces results from offline runs with unshifted time averages used for the
                0060 dynamical fields.
                0061
                0062 To have a time stepping closer to the online model (and reproduce results
                0063 for LS_nIter=1), use
                0064
                0065 LS_whenToSample=1 if staggerTimeStep=.FALSE.
                0066 LS_whenToSample=2 if staggerTimeStep=.TRUE.
b29547f131 Oliv*0067