Upcoming ROMS Algorithms

An overview of the upcoming ROMS algorithms will be presented. Several new algorithms have been developed and are currently under extensive testing before they are released. These include Phase III (final phase) of multiple grid nesting, a Reduced Preconditoned Conjugate Gradient (RPCG) algorithm for 4D-Var, data assimilation observations quality control, and Objective Analysis (OA) packages for Fortran and Matlab.

Three types of nesting capabilities have been designed and coded in ROMS: (i) refinement grids which provide increased resolution (3:1, 5:1, or 7:1) in a specific region; (ii) mosaics which connect several grids along their edges, and (iii) composite grids which allow overlap regions of aligned and non-aligned grids. The mosaic and composite grid code infrastructures are identical. The differences are geometrical and primarily based on the alignment between adjacent grids. All the mosaic grids are exactly aligned with the adjacent grid. In general, the mosaic grids are a special case of the composite grids.

The nesting development in ROMS was divided into three phases due to its complexity. Phase I included substantial modifications of the numerical kernels to allow a generic treatment of the spatial horizontal operators in the nesting contact regions. Phase II included an overhaul of ROMS lateral boundary conditions to facilitate, in a generic way, their processing or not in applications with nested grids. Phase III included the data managing and time-stepping infrastructure for one or more nesting layers. Phase I was released to the community as ROMS 3.5 on April 25, 2011 whereas Phase II was released as ROMS 3.6 on September 23, 2011. The coding of Phase III has been completed and is currently under extensive testing.

The ROMS nested grid design includes three Super-Classes and several Sub-Classes:

  1. Composite Grids Super-Class:
  2. Refinement Grids Super-Class:
  3. Composite and Refinement Combination Super-Class:


Hence, there are several possibilities and combinations. The design is flexible enough to allow complex nested grid configurations in coastal applications. An extensive library of Matlab scripts (https://www.myroms.org/wiki/index.php/Matlab_Scripts) was released to process the contact points in the nesting grids contact regions. The information is quite technical but it provides a good guideline for building nested grid applications. The exchange of information is always two-way.