Horizontal Mesh

Omega uses the MPAS mesh specification found here. The names of the mesh variables have been retained, with the caveat that they now begin with a capital letter.

The Mesh class is meant to be a container for all mesh variables local to a decomposed sub-domain that can be easily passed among the dycore routines. It depends on a given Decomp and reproduces the cell/edge/vertex totals and connectivity information from that class. The Mesh class also creates parallel I/O decompositions that are used to read in the additional mesh variables, which are not required for Decomp.

Currently, the Mesh class reads in all variables from the MPAS mesh specification except those read by Decomp. These are all read using the input IOStream HorzMeshIn

  IOStreams:
    HorzMeshIn:
      UsePointerFile: false
      Filename: OmegaMesh.nc
      Mode: read
      Precision: double
      Freq: 1
      FreqUnits: OnStartup
      UseStartEnd: false
      Contents:
        - HorzMeshIn

Only the Filename should be changed by the user to point to the relevant input mesh file. The mesh Filename is sometimes overridden by the driver routine in the case of unit tests using an optional argument to the decomposition. The input contents are defined by the HorzMeshIn FieldGroup that currently includes the following variables:

Variable Name	Description	Units
XCell, YCell, ZCell	Cartesian coordinates of cell centers	m
XEdge, YEdge, ZEdge	Cartesian coordinates of edge centers	m
XVertex, YVertex, ZVertex	Cartesian coordinates of vertices	m
FCell, FEdge, FVertex	Coriolis parameter at cell centers/edges/vertices	radians/s
LonCell, LatCell	Longitude/latitude coordinates of cell centers	radians
LonEdge, LatEdge	Longitude/latitude coordinates of edge centers	radians
LonVertex, LatVertex	Longitude/latitude coordinates of vertices	radians
AreaCell	Area of each cell	m^2
AreaTriangle	Area of each triangle in the dual grid	m^2
KiteAreasOnVertex	Area of the portions of each dual cell that are part of each cellsOnVertex	m^2
DvEdge	Length of each edge, computed as the distance between verticesOnEdge	m
DcEdge	Length of each edge, computed as the distance between CellsOnEdge	m
AngleEdge	Angle the edge normal makes with local eastward direction	radians
MeshDensity	Value of density function used to generate a particular mesh at cell centers	-
WeightsOnEdge	Reconstruction weights associated with each of the edgesOnEdge	-

In addition, some mesh metadata are read from the file and stored as mesh variables. These include OnSphere (or on_a_sphere for backcompatibility), IsPeriodic (is_periodic), SphereRadius (sphere_radius), XPeriod (x_period), and YPeriod (y_period). The two flags OnSphere and IsPeriodic are stored as YES/NO strings in the metadata but as boolean flags in the code.

In the future, the Mesh class will optionally compute the mesh variables that are dependent on the Cartesian mesh coordinates internally. This includes the various areas, lengths, angles, and weights needed for the TRiSK discretization (e.g. rows 5-11 in the table above).