1. Nesting Milestone Materials Nesting design document Updated NUOPC Layer software prototype bundled with ESMF Updated NUOPC Layer reference manual Nesting prototype examples under SVN, esmfcontrib:  Single nested domain within a parent domain  Two nested domains within the same parent domain  Two nested domains within the same parent domain, where one of the child domains becomes the parent domain of yet another child generation (telescoping)

2. Functions of prototype Extended the architecture in which major components (ATM, OCN, ICE, LND, WAV) are siblings to where multiple instances of the same component can represent nested domains. A single component definition (Fortran module) is instantiated multiple times to create nested domains. (→ No need to introduce multiple component definitions.) Two additional component Attributes were introduced to identify the nesting level and sibling order for each instance. The NUOPC_RunSequence type, introduced as part of the implicit coupling milestone, is leveraged to implement a “flat” representation of domain nesting. The nested case is driven by the same generic NUOPC_Driver as the explicit and implicit coupling cases before.

3. Interoperability impact The nesting problem is addressed by the same familiar data structures used for implicit and explicit coupling. The same NUOPC rules that apply to mediate between different model components also apply to instances of the same component that represent nested domains. The same component code (Fortran module) is used to implement multiple nests. This promotes maximum code reuse. Encoding the interaction of the nested domains through the NUOPC_RunSequence data structure inside a NUOPC_Driver holds the potential to fully encapsulate and hide the nested nature of a model once Driver-in-Driver support is implemented.

4. More information See: http://www.earthsystemmodeling.org/plans/milestone_ 1209_nuopc.shtml For additional information on this milestone, including links to NUOPC Layer code, documentation, and supporting design documents.