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BOM 4.1:
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BOM 3.2:
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2005-05-06: Internal pressure and rotated grids
A recent work on internal pressure gradient errors in the well known seamount case, has shown that it is possible to reduce the error significantly by computing the gradient as a linear combination of the standard stencil and a stencil rotated 45 degrees with respcect to the model grid.This new algorithm can easily be implemented in the BOM 4.1 version by following the below steps:
In the file state.f90 add the following line
REAL, DIMENSION(IM,JM) :: DCORNER
REAL, DIMENSION(IM,JM,KB) :: DELTAUROT, DELTAVROT
In the BOM source file Main.f90, glue in the below
lines around each call to the INTERNAL subroutine:
...
CALL INTERNALROT
DELTAUROT = DELTAU
DELTAVROT = DELTAV
CALL INTERNAL
DELTAU = (2.5*DELTAU+DELTAUROT)/3.5
DELTAV = (2.5*DELTAV+DELTAVROT)/3.5
...
Download the file
at this link
into your BOM source directory, call it
e.g. internalrot.f90. Then, in the Makefile add
internalrot.o to the OBJECTS variable and recompile.
2004-09-01: BOM 4.1 released
While experimenting with non hydrostatic extensions, a typo bug in the predictor part of the time stepping for momentum were found and corrected with this release.It is very hard to see differences in the results after rerunning experiements and comparing with version 4.0, but this may be case dependant. The 2D solution seems to be non-affected, while e.g. the stratification seems somewhat improved. Generally the bug has lead to a damping of the solution, so it will generally be necessary to increase the viscosity up to levels corresponding to 3.x, likewise reduce the time step, in order to get stable results.
2003-11-18: BOM 4.0 released
New predictor corrector time stepping scheme with better stability properties and higher numerical order. The barotropic part of the equations is advanced in time with the leapfrog scheme for the predictor, and the Crank-Nicholson scheme for the corrector. The baroclinic part uses leapfrog for the predictor step and the Adams-Moulton scheme for the corrector step. In some experiments it is now possible to increase the 3d time step with a factor of three relative to version 3.X.The alternative internal pressures scheme (due to McCalpin) with fourth order discretization along sigma layers has been made a runtime option. By applying the integration by parts rule to the internal pressure term it is possible to do the vertical integral in a more robust way. This scheme has been proven effective to reduce internal pressure error in the infamous Seamount case. It is not, however, clear how beneficial the effects are in more realistic cases.
The numerical kernel of BOM seems to stabilize, so it is not expected that there will be major changes to the core in the future. A non-hydrostatic version of the modesplit routine is under testing, and may be added soon, and depending on funding there may come a separate MPI version of 4.0 next year.
New animations of the contintental shelf on the examplespage
2003-03-03: BOM 3.2 released
This release contains a bugfix for the routine ADVECT.f90, which was by accident hardcoded for advecting density only. It can now advect a general field.Also updated Makefile with flags for Intel Fortran and Pentium4.
2002-09-06: Small bug in 3.0 fixed
Two 3D arrays that should have been globally defined in state.f90, were only declared locally. This is fixed in version 3.0.1.2002-08-20: BOM 3.0 released
Finally BOM 3.0 is released, seems to work robustly.New features:
- Predictor/corrector time-stepping scheme, with the theta-method on the corrector step. Hopefully this approach will be useful for studies with low viscosity, and prevent/reduce unphysical grovth of certain modes, e.g. from errors in internal pressure calculations.
- Additional recent advection scheme due to Shchepetkin. Gives sharp fronts, but may have some overshoot.
