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RBCS Package

Introduction

A package which provides the flexibility to relax fields (temperature, salinity, ptracers, horizontal velocities) in any 3-D location: so could be used as a sponge layer, or as a “source” anywhere in the domain.

For a field (T) at every grid point the tendency is modified so that:

\frac{dT}{dt}=\frac{dT}{dt} - \frac{M_{rbc}}{\tau_T} (T-T_{rbc})

where M_{rbc} is a 3-D mask (no time dependence) with values between 0 and 1. Where M_{rbc} is 1, relaxing timescale is 1/\tau_T. Where it is 0 there is no relaxing. The value relaxed to is a 3-D (potentially varying in time) field given by T_{rbc}.

A seperate mask can be used for T,S and ptracers and each of these can be relaxed or not and can have its own timescale \tau_T. These are set in data.rbcs (see below).

Key subroutines and parameters

The only compile-time parameter you are likely to have to change is in :filelink:`RBCS_SIZE.h <pkg/rbcs/RBCS_SIZE.h>`, the number of masks, PARAMETER(maskLEN = 3 ), see below.

:numref:`tab_phys_pkg_rbcs_runtime_flags` summarizes the runtime flags that are set in data.rbcs, and their default values.

.. tabularcolumns:: |\Y{.285}|\Y{.09}|\Y{.105}|\Y{.545}|
RBCS runtime parameters
Flag/Parameter Group Default Description
:varlink:`rbcsForcingPeriod` PARM01 0.0 Time interval between forcing fields (in seconds), zero means constant-in-time forcing.
:varlink:`rbcsForcingCycle` PARM01 0.0 Repeat cycle of forcing fields (in seconds), zero means non-cyclic forcing.
:varlink:`rbcsForcingOffset` PARM01 0.0 Time offset of forcing fields (in seconds, default 0); this is relative to time averages starting at t=0, i.e., the first forcing record/file is placed at (:varlink:`rbcsForcingOffset` + :varlink:`rbcsForcingPeriod` )/2 ; see below for examples.
:varlink:`rbcsSingleTimeFiles` PARM01 FALSE If .TRUE., forcing fields are given 1 file per :varlink:`rbcsForcingPeriod`.
:varlink:`deltaTrbcs` PARM01 :varlink:`deltaTclock` Time step used to compute the iteration numbers for :varlink:`rbcsSingleTimeFiles` = .TRUE..
:varlink:`rbcsVanishingTime` PARM01 0.0 If :varlink:`rbcsVanishingTime` > 0, the relaxation strength reduces linearly to vanish at :varlink:`myTime` == :varlink:`rbcsVanishingTime`.
:varlink:`rbcsIter0` PARM01 0 Shift in iteration numbers used to label files if :varlink:`rbcsSingleTimeFiles` = .TRUE. (see below for examples).
:varlink:`useRBCtemp`, :varlink:`useRBCsalt`, :varlink:`useRBCuVel`, :varlink:`useRCvVel` PARM01 FALSE Whether to use RBCS for T/S/U/V.
:varlink:`tauRelaxT`, :varlink:`tauRelaxT`, :varlink:`tauRelaxT`, :varlink:`tauRelaxT` PARM01 0.0 Timescales in seconds of relaxing in T/S/U/V (\tau_T in equation above). Where mask is 1, relax rate will be 1/tauRelaxT. Must be set if the corresponding useRBCxxx is TRUE.
:varlink:`relaxMaskFile` (irbc) PARM01 ' ' Filename of 3-D file with mask (M_{rbc} in equation above). Need a file for each irbc (1=temperature, 2=salinity, 3=ptracer1, 4=ptracer2, etc). If :varlink:`maskLEN` is les than the number of tracers, then relaxMaskFile(maskLEN) is used for all remaining tracers.
:varlink:`relaxMaskUFile`, :varlink:`relaxMaskVFile` PARM01 ' ' Filename of 3-D file with mask for U/V.
:varlink:`relaxTFile`, :varlink:`relaxSFile`, :varlink:`relaxUFile`, :varlink:`relaxVFile` PARM01 ' ' Name of file where the field that need to be relaxed to (T_{rbc} in equation above) is stored. The file must contain 3-D records to match the model domain. If :varlink:`rbcsSingleTimeFiles` = .FALSE., it must have one record for each forcing period. Otherwise there must be a separate file for each period and a 10-digit iteration number is appended to the file name (see Table [:ref:`tab_phys_pkg_rbcs_timing`] and examples below).
:varlink:`useRBCptracers` PARM02 FALSE DEPRECATED Use one :varlink:`useRBCpTrNum` per tracer instead.
:varlink:`useRBCpTrNum` (iTrc) PARM02 FALSE Whether to use RBCS for the corresponding passive tracer.
:varlink:`tauRelaxPTR` (iTrc) PARM02 0.0 Relaxing timescale for the corresponding ptracer.
:varlink:`relaxPtracerFile` (iTrc) PARM02 ' ' File with relax fields for the corresponding ptracer.

Timing of relaxation forcing fields

For constant-in-time relaxation, set :varlink:`rbcsForcingPeriod` =0. For time-varying relaxation, Table :numref:`tab_phys_pkg_rbcs_timing` illustrates the relation between model time and forcing fields (either records in one big file or, for :varlink:`rbcsSingleTimeFiles` = .TRUE. , individual files labeled with an iteration number). With :varlink:`rbcsSingleTimeFiles` = .TRUE. , this is the same as in the offline package, except that the forcing offset is in seconds.

.. tabularcolumns:: |l|l|l|c|
Timing of RBCS relaxation fields
  rbcsSingleTimeFiles = T F
  c=0 c\ne0 c\ne0
model time file number file number record
t_0 - p/2 i_0 i_0 + c/{\Delta t_{\text{rbcs}}} c/p
t_0 + p/2 i_0 + p/{\Delta t_{\text{rbcs}}} i_0 + p/{\Delta t_{\text{rbcs}}} 1
t_0+p+p/2 i_0 + 2p/{\Delta t_{\text{rbcs}}} i_0 + 2p/{\Delta t_{\text{rbcs}}} 2
... ... ... ...
t_0+c-p/2 ... i_0 + c/{\Delta t_{\text{rbcs}}} c/p
... ... ... ...

where

p = :varlink:`rbcsForcingPeriod`

c = :varlink:`rbcsForcingCycle`

t_0 = :varlink:`rbcsForcingOffset`

i_0 = :varlink:`rbcsIter0`

{\Delta t_{\text{rbcs}}} = :varlink:`deltaTrbcs`

Example 1: forcing with time averages starting at t=0

Cyclic data in a single file

Set :varlink:`rbcsSingleTimeFiles` = .FALSE. and :varlink:`rbcsForcingOffset` = 0, and the model will start by interpolating the last and first records of rbcs data, placed at -p/2 and p/2, resp., as appropriate for fields averaged over the time intervals [-p, 0] and [0, p].

Non-cyclic data, multiple files

Set :varlink:`rbcsForcingCycle` = 0 and :varlink:`rbcsSingleTimeFiles` = .TRUE. . With :varlink:`rbcsForcingOffset` = 0, :varlink:`rbcsIter0` = 0 and :varlink:`deltaTrbcs` = :varlink:`rbcsForcingPeriod`, the model would then start by interpolating data from files relax\*File.0000000000.data and relax\*File.0000000001.data, ... , again placed at -p/2 and p/2.

Example 2: forcing with snapshots starting at t=0

Cyclic data in a single file

Set :varlink:`rbcsSingleTimeFiles` = .FALSE. and :varlink:`rbcsForcingOffset` =-p/2, and the model will start forcing with the first record at t=0.

Non-cyclic data, multiple files

Set :varlink:`rbcsForcingCycle` = 0 and :varlink:`rbcsSingleTimeFiles` = .TRUE.. In this case, it is more natural to set :varlink:`rbcsForcingOffset` =+p/2. With :varlink:`rbcsIter0` = 0 and :varlink:`deltaTrbcs` = :varlink:`rbcsForcingPeriod`, the model would then start with data from files relax\*File.0000000000.data at t=0. It would then proceed to interpolate between this file and files relax\*File.0000000001.data at t={}:varlink:`rbcsForcingPeriod`.

Do’s and Don’ts

Reference Material

Experiments and tutorials that use rbcs

In the directory, the following experiments use rbcs: