Add user and developer documentation

components/omega/doc/devGuide/HorzMesh.md

@@ -1,3 +1,29 @@
 (omega-dev-horz-mesh)=
 
 ## Horizontal Mesh
+
+The OMEGA horizontal mesh uses the [MPAS Mesh
+Specification](https://mpas-dev.github.io/files/documents/MPAS-MeshSpec.pdf).
+A mesh object is created by using the constructor, which requires a Decomp object:
+```c++
+Err = OMEGA::Decomp::init();
+OMEGA::Decomp *DefDecomp = OMEGA::Decomp::getDefault();
+OMEGA::HorzMesh Mesh(DefDecomp);
+```
+The constructor replicates the subdomain mesh cell/edge/vertex counts and
+connectivity information from Decomp so this information can be passed among the
+computational rountines.  It then creates several parallel I/O decompositions
+and reads in the remaining subdomain mesh information.  Finally, any mesh
+information needed on the device to a device YAKL array from the host.  These
+tasks are orgainzed into several private methods.  The variable names for host
+arrays hare appended with in `H`, array variable names not ending in `H` are
+device arrays.  The copy from host to device array is performed via: 
+```c++
+AreaCell = AreaCellH.createDeviceCopy();
+```
+The device arrays are deallocated by the `HorzMesh::clear()` method, which is
+necessary before calling `yakl::finalize`.
+
+
+
+

components/omega/doc/userGuide/HorzMesh.md

@@ -1,3 +1,44 @@
 (omega-user-horz-mesh)=
 
 ## Horizontal Mesh
+
+OMEGA uses the MPAS mesh specification found
+[here](https://mpas-dev.github.io/files/documents/MPAS-MeshSpec.pdf). 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](#omega-user-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](#omega-dev-decomp). 
+This 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 |
+| BottomDepth | Depth of the bottom of the ocean at cell centers | 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 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).
+