Custom Query (964 matches)

• A bug was corrected in obs_write.F when computing the final misfit in I4D-Var. The TLmodVal is included and we need only to have:

          IF (wrtMisfit(ng)) THEN
            DO iobs=Mstr,Mend
  #  if defined IS4DVAR
              misfit(iobs)=ObsScale(iobs)*SQRT(ObsErr(iobs))*             &
       &                   (NLmodVal(iobs)-ObsVal(iobs))
  

  This is just a diagnostic quantity for output and doesn't affect the I4D-Var computations. Many thanks to Ha Joon Song for nicely ​reporting this bug.

• Updated the makefile to add version 3.82 of gmake to the NEED_VERSION macro. The gmake 3.82 was released earlier in the summer.

• Updated the documentation in build.sh and build.bash. Notice that it is possible to compile with a serial NetCDF-4/HDF5 library in distributed-memory (MPI). The parallel version of these libraries is only required for parallel I/O when the C-preprocessing option PARALLEL_IO is activated in ROMS. Many thanks to David Robertson for bringing this to my attention.

• Updated the UPWELLING test case so we can use either EW_PERIODIC or NS_PERIODIC. We just needed to reformulate the bathymetry (ana_grid.h) and wind stress (ana_smflux.h) forcing to the opposite direction in NS_PERIODIC applications. Still the EW_PERIODIC is the default configuration.

• Updated documentation in distribute.F about why we cannot USE mod_netcdf in mp_ncread and mp_ncwrite because cyclic dependencies.

Correted routine slevels.F in the plotting package. The variable tindx was already declared in common block (ncinfo.h).

Many thanks to David Robertson for bringing this to my attention. The was also reported by Robert Bauer in the ​forum.

There are a couple of significant problems with the operation of the FLOAT_VWALK option:

1) the nudging velocity that forces the vertical random walk is not scaled correctly before it is applied in interp_floats, leading to the vertical diffusion being too large by a factor equal to the layer thickness, Hz;

2) with this problem fixed, the vertical diffusion applied to the floats is the correct magnitude with VWALK_FORWARD defined, but too small a factor of 0.71 (suspiciously close to 1/sqrt(2)) when the predictor-corrector scheme is in operation.

I investigated these problems with a simple case: fluid at rest with uniform diffusivity at 10^-5 m2/s, doubly periodic domain 50 m deep, 5 uniformly spaced levels, 300 floats released at 25 m depth and followed for 0.5 days. The standard deviation of the float vertical position should increase with time as sqrt(2 K t) so at 0.5 days should be 0.93 m. However in the simulation it is 9.3 m (VWALK_FORWARD defined) or 6.6 m (not defined).

The scaling problem arises because the nudging velocity (nudg) is calculated in vwalk_floats.F in m/s and is then applied in interp_floats.F to calculate the rhs term track(izrhs,...) without further scaling. It should be scaled by the layer depth Hz.

I have applied the correct (I think) scaling in a copy of interp_floats.F on my branch on the developers' repository

​https://www.myroms.org/svn/omlab/branches/hadfield/trunk/ROMS/Nonlinear/interp_floats.F

I haven't yet looked into the situation where VWALK_FORWARD is undefined, but presumably it arises from the predictor-corrector scheme trying to cope with impulsive perturbations and can be fixed by multiplying the perturbations by sqrt(2).