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README.flt
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C $Header: /u/gcmpack/MITgcm/pkg/flt/README.flt,v 1.1 2001/09/13 17:43:55 adcroft Exp $
C $Name: $
c
c ==============================
c FLOAT Package for the MITgcmUV
c ==============================
c
c
c This package allows the advection of floats during a model run.
c Although originally intended to simulate PALACE floats
c (floats that drift in at depth and to the surface at a defined
c time interval) it can also run ALACE floats (non-profiling)
c and surface drifters as well as sample moorings (simply a
c non-advective, profiling float).
c
c The stepping of the float advection is done using a second
c order Runga-Kutta scheme (Press et al., 1992, Numerical
c Recipes), whereby velocities and positions are bilinear
c interpolated between the grid points.
c
c Current version: 1.0 06-AUG-2001
c
c Please report any bugs and suggestions to:
c
c Arne Biastoch (abiastoch@ucsd.edu)
c
c
c Implementation in MITgcmUV
c --------------------------
c
c The package has only few interfaces to the model. Despite a
c general introduction of the flag useFLT and an initialization in
c packages_init_fixed.F the interfaces are in:
c
c - forward_step.F where the main float routine is called:
c
c #ifdef ALLOW_FLT
c C-- Calculate float trajectories
c if (useFLT) then
c CALL TIMER_START('FLOATS [THE_MAIN_LOOP]',myThid)
c CALL FLT_MAIN(myIter,myTime, myThid)
c CALL TIMER_STOP ('FLOATS [THE_MAIN_LOOP]',myThid)
c endif
c #endif
c
c - write_checkpoint.F where float positions are written to a restart file:
c
c #ifdef ALLOW_FLT
c if (useFLT) then
c CALL FLT_RESTART (myCurrentTime, myCurrentIter, myThid )
c endif
c #endif
c
c The rest is done in the routines residing in pkg/flt. Please make
c sure that this directory is enabled in genmake when compiling the
c Makefile.
c
c
c Settings at compilation time
c ----------------------------
c
c The main flag for switching on the float package has to be done
c in CPP_OPTIONS.h where
c #define ALLOW_FLT has to be set
c
c The package itself has its own option file called FLT_CPPOPTIONS.h.
c Currently there are only two flags available:
c #define FLT_NOISE to add white noise to the advection velocity
c #undef ALLOW_3D_FLT to allow three-dimensional float advection
c (not tested yet!) instead of drifting on a
c pre-defined (integer) vertical level.
c
c Other specifications are done in FLT.h:
c
c parameter (max_npart_tile = 300)
c is the maximum number of floats per tile. Should be smaller
c than the total number of floats when running on a parallel
c environment but as small as possible to avoid too large
c arrays. The model will stop if the number of floats per tile
c exceeds max_npart_tile at any time.
c parameter (max_npart_exch = 50)
c is the maximum number of floats per tile that can be exchanged
c with other tiles to one side (there are 4 arrays) in one
c timestep. Should be generally small because only few floats
c leave the tile exactly at the same time.
c
c
c Settings at runtime
c -------------------
c
c useFLT=.TRUE.
c has to be set in namelist PACKAGES (data.pkg) to use floats
c
c data.flt contains a namelist FLT_NML with the parameters:
c flt_int_traj is the time interval in seconds to sample
c float position and dynamic variables (T,S,U,V,Eta).
c To capture the whole profile cycle of a PALACE float
c this has to be at least as small as the
c shortest surface time
c
c flt_int_prof is the time interval in seconds to sample
c a whole profile of T,S,U,V (as well as
c positions and Eta). This has to chosen at
c least as small as the shortest profiling
c interval.
c Note: All profiling intervals have to be an integer
c multiple of this interval
c Note: The profile is always taken over the whole
c water column
c
c Example: if one would set two sets of profiling floats,
c - one with 5 days profiling interval and 24 hours surface time
c - one with 10 days profiling interval and 12 hours surface time
c one would have to set
c - flt_int_traj=43200
c - flt_int_prof=432000
c to capture all of the floats motions
c
c flt_noise If FLT_NOISE is defined this is the amplitude
c that is added to the advection velocity by the
c random number generator.
c
c flt_file the base filename of the float positions
c without tile information and ending (e.g. float_pos)
c
c
c Input
c -----
c
c The initialization is written in a way that it first looks for a
c global file (e.g. float_pos.data). A global file is mainly used
c for first-time initialization. If that not exists the routine looks
c for local files (e.g. float_pos.001.001.data, etc.) that have
c been used for storing the float positions for restart (note that
c float restarts are ALWAYS local files). The structure of the
c file is always the same:
c
c Each float contains a 9 element double precision record of a
c direct access file. The records are:
c
c - npart A unique float identifier (1,2,3,...)
c - tstart start date of integration of float (in s)
c Note: If tstart=-1 floats are integrated right from the
c beginning
c - xpart x position of float (in units of XC)
c - ypart y position of float (in units of YC)
c - kpart actual vertical level of float
c - kfloat target level of float (should be the same as kpart at
c the beginning)
c - iup flag if the float
c - should profile ( > 0 = return cycle (in s) to surface)
c - remain at depth ( = 0 )
c - is a 3D float ( = -1 ).
c - should be advected WITHOUT additional noise ( = -2 ).
c (This implies that the float is non-profiling)
c - is a mooring ( = -3 ), i.e. the float is not advected
c - itop time of float the surface (in s)
c - tend end date of integration of float (in s)
c Note: If tend=-1 floats are integrated till the end of
c the integration
c
c In addition the first line of the file contains a record with
c - the number of floats on that tile in the first record
c - the total number of floats in the sixth record
c Note: At first-time initialization in a global file both fields
c should be the same.
c
c An example how to write a float file (write_float.F) is included
c in the verification experiment (see below)
c
c
c Output/Visualization
c --------------------
c
c The output always consists of 3 series of local files:
c - files with last positions of floats that can be used for restart
c - files with trajectories of floats and actual values at depth
c - files with profiles throughout the whole water column
c
c Examples and conversion routines for the second and third series
c into NetCDF are included in verification/flt_example/aux/.
c
c
c Verification Experiment
c -----------------------
c
c The verification experiment is based on exp 4 (flow over a
c Gaussian in a channel). There are, however, two main differences
c to the original experiment:
c
c - The domain has closed boundaries. Currently the float package
c is not able to treat floats that leave the domain via open boundaries
c - There is an additional wind forcing to speed up the currents
c to get significant advection rates in time
c
c
c ToDo
c ----
c
c - testing of 3D-floats
c - allow floats to leave the domain via open boundaries
c
c
c History
c -------
c
c - first release: Arne Biastoch (abiastoch@ucsd.edu) 06-AUG-2001
c implemented and verified for checkpoint 40pre1
c - incorporated into c40p9 by adcroft@mit.edu on 11/13/01
c
c=========================================================================

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