8.3.2. RBCS Package¶
8.3.2.1. Introduction¶
pkg/rbcs provides the flexibility to relax fields (temperature, salinity, ptracers, horizontal velocities) in any 3-D location, thus can be used to implement a sponge layer, or a “source” anywhere in the domain, among other uses.
For a field (\(T\)) at every grid point the tendency is modified so that:
where \(M_{rbc}\) is a 3-D mask (no time dependence) between 0 and 1. Values are relaxed to a field given by \(T_{rbc}\), which can be set to vary in time. Where \(M_{rbc}(x,y,z) = 1.0\), the relaxing timescale is \(\tau_T\); where \(M_{rbc}(x,y,z) = 0.0\), there is no relaxing. If \(M_{rbc}(x,y,z) = 0.5\) then relaxation occurs but at a timescale of \(2\,\tau_T\).
A separate mask can be used for \(\theta, S\) 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).
8.3.2.2. Key subroutines and parameters¶
The only compile-time parameter you are likely to have to change is in RBCS_SIZE.h, the number of masks, PARAMETER( maskLEN = 3 ) by default, see below.
Table 8.3 summarizes the runtime flags that are
set in data.rbcs, and their default values.
Flag/Parameter |
Group |
Default |
Description |
|---|---|---|---|
PARM01 |
0.0 |
time interval between forcing fields (in seconds), zero means constant-in-time forcing |
|
PARM01 |
0.0 |
repeat cycle of forcing fields (in seconds), zero means non-cyclic forcing |
|
PARM01 |
0.0 |
time offset of forcing fields (in seconds), relative to time averages starting at \(t=0\), i.e., the first forcing record/file is placed at (rbcsForcingOffset + rbcsForcingPeriod)/2; see below for examples |
|
PARM01 |
FALSE |
if |
|
PARM01 |
time step used to compute the iteration numbers for rbcsSingleTimeFiles = |
||
PARM01 |
0.0 |
if rbcsVanishingTime > 0, the relaxation strength reduces linearly to vanish at myTime == rbcsVanishingTime |
|
PARM01 |
0 |
shift in iteration numbers used to label files if rbcsSingleTimeFiles = |
|
PARM01 |
FALSE |
whether to use RBCS for T/S/U/V |
|
PARM01 |
0.0 |
timescales (in seconds) for relaxing T/S/U/V (\(\tau_T\) in equation above); required if the corresponding |
|
relaxMaskFile (irbc) |
PARM01 |
' ' |
filename of 3-D file with mask (\(M_{rbc}\) above), requires a file for each irbc (1=temperature, 2=salinity, 3=ptracer1, 4=ptracer2, etc);
if maskLEN is less than the number of tracers, then |
PARM01 |
' ' |
filename of 3-D file with mask for U/V. |
|
PARM01 |
' ' |
name of file with 3-D relaxation field values (\(T_{rbc}\) in equation above);
if rbcsSingleTimeFiles = |
|
useRBCpTrNum (iTrc) |
PARM02 |
FALSE |
if |
tauRelaxPTR (iTrc) |
PARM02 |
0.0 |
relaxing timescale (seconds) for the corresponding ptracer |
relaxPtracerFile (iTrc) |
PARM02 |
' ' |
file with relaxation field for the corresponding ptracer |
8.3.2.3. Timing of relaxation forcing fields¶
For constant-in-time relaxation, set rbcsForcingPeriod =0. For
time-varying relaxation, Table 8.4 illustrates the
relation between model time and forcing fields (either records in one big file
or, for rbcsSingleTimeFiles = .TRUE. , individual files labeled
with an iteration number). With rbcsSingleTimeFiles = .TRUE. ,
this is the same as in the offline package, except that the forcing offset is
in seconds.
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
\(p\) = rbcsForcingPeriod
\(c\) = rbcsForcingCycle
\(t_0\) = rbcsForcingOffset
\(i_0\) = rbcsIter0
\({\Delta t_{\text{rbcs}}}\) = deltaTrbcs
8.3.2.4. Example 1: forcing with time averages starting at \(t=0\)¶
8.3.2.4.1. Cyclic data in a single file¶
Set rbcsSingleTimeFiles = .FALSE. and
rbcsForcingOffset = 0, and the model will start by interpolating the
last and first records of rbcs data, placed at \(-p/2\) and \(p/2\),
respectively, as appropriate for fields averaged over the time intervals
\([-p, 0]\) and \([0, p]\).
8.3.2.4.2. Non-cyclic data, multiple files¶
Set rbcsForcingCycle = 0 and rbcsSingleTimeFiles =
.TRUE. . With rbcsForcingOffset = 0, rbcsIter0 =
0 and deltaTrbcs = 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
\(p/2\).
8.3.2.5. Example 2: forcing with snapshots starting at \(t=0\)¶
8.3.2.5.1. Cyclic data in a single file¶
Set rbcsSingleTimeFiles = .FALSE. and
rbcsForcingOffset =\(-p/2\), and the model will start forcing
with the first record at \(t=0\).
8.3.2.5.2. Non-cyclic data, multiple files¶
Set rbcsForcingCycle = 0 and rbcsSingleTimeFiles =
.TRUE.. In this case, it is more natural to set
rbcsForcingOffset =\(+p/2\). With rbcsIter0 = 0 and
deltaTrbcs = 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 \(t={}\)rbcsForcingPeriod.
8.3.2.6. Do’s and Don’ts¶
8.3.2.7. Reference Material¶
8.3.2.8. Experiments and tutorials that use rbcs¶
In the directory, the following experiments use pkg/rbcs:
tutorial Southern Ocean Reentrant Channel makes use of pkg/rbcs at its northern boundary as a sponge layer;
exp4 simulating flow over a Gaussian bump based on [AHM97], demonstrating relaxation of a ptracer field.