1. Using ESMF Regridding Tools as an Observation Operator Presenter: Mathew V. Rothstein Software Engineer, NOAA/CNT Training at NRL Monterey August 5-6, 2015 Via Use of the “LocStream” Class

2. ESMF Supported Geometry Types Grid: – Structured representation of a region – A logically rectangular tile Mesh: – Unstructured representation of a region – In 2D: polygons with any number of sides including concave – In 3D: tetrahedrons & hexahedrons LocStream (Location Stream): – NEW! – Set of disconnected points E.g. locations of observations – Very flexible and efficient – Can’t be used with every regrid method

3. The LocStream Class Third in a line of geometry types supported in regridding (Grid,Mesh) Data structure is used to represent a cloud of disconnected points (often the case with observational data) Data points have no information about surrounding points There are no restrictions about how data points are arranged Support for large datasets – LocStreams can be created from file Point descriptors (location, masking) held in constructs called “keys” 3

4. The LocStream Class, continued Location keys described in Cartesian or spherical coordinates Data values at each point are stored in an ESMF Field structure LocStream-derived Fields can be used as a destination target in regridding for all non-conservative methods Using as a source in regridding requires Nearest-Neighbor method Application Program Interfaces (API’s) exist in Fortran95, C, and Python Contributed by NASA/GSFC and incorporated into ESMF 4

5. Basic Regridding Steps 1.Construct ESMF geometry structures to represent source and destination targets (for example, an ESMF_Grid for the source and ESMF_LocStream for the destination) 2.Build an ESMF_Field for both source and destination to hold the data 3.Compute the interpolation weights using the ESMF_FieldRegridStore() call and store them in a structure that describes the regridding (ESMF_RouteHandle) 4.Load source data into it’s respective Field 5.Apply the weights described in the ESMF_RouteHandle to the source data using ESMF_FieldRegrid() 6. Repeat steps 4 and 5 for each set of source data in need of regridding 5

6. LocStreams in Regridding - Fortran Example 6

7. Fortran Example, continued 7