Efficient Intersection of Distributed Meshes for use in the Community Earth System Model

• The intersection algorithm used in this paper follows the ideas from (Gander and Japhet, 2008), in which two meshes are covering the same domain. At the core is an advancing front method; For simplicity, label the two meshes red and blue, as they are covering about the same domain. • First, 2 convex cells from the red and blue meshes that are intersecting are identified, by using a search tree. This will constitute the seed of the front. Advancing in both meshes, using adjacency information, we incrementally compute all possible intersec- tions. Important for the algorithm is also a robust scheme, in which 2 intersecting cells from the different meshes are overlapped and resolved. Every edge on one of the meshes maintains a list of intersection points, and geometric tolerances are used to eliminate duplicates and ensure consistency. • The intersection of cells from different meshes is simplified and more robust if they are convex. If in the initial meshes there exist concave polygons, they are decomposed in simpler convex polygons, by simply splitting along interior diagonals. The intersec- tion between 2 convex cells will be then a convex polygon. The final result of meshes intersection will be a set of convex polygons, that cover the common domain. • All edges of cells on the sphere are considered to be great circle arcs. Using gnomonic projection, on one of the six planes, each arc becomes a straight line in the gnomonic plane, and a robust intersection is much easier to achieve.