Coupling for multiple and moving domain cases

[janahaddad]

Problem to be solved:

• users have complicated regional applications with mult. regions (e.g. telescoping/nested domains with increasing resolutions; HAFS has hurricane-tracking moving domains)
• a coupling application needs a way to handle this

Potential solutions:

1. Multiple instantiations

• Mult instantiations of the NUOPC Cap for each model, and they are coupled together and with the other model components.
• customizable but lots of Cons ... mediator may not support, sharing of resources is a problem, a ton of connectors needed, may cause downstream issues

2. Coupling sets

• for coupling multiple nested or regional domains: domain 1 in model 1 only exchanges data with domain 1 in model 2
• NCAR has built some of this out already for telescoping nests in the NUOPC Layer
• NUOPC only creates the route handle at the time of initialization for the connector, and that's what's used going forward. that makes moving grids a problem.

3. Consolidate regions/domains into one

• this is what HAFS is doing... consolidate all domains into single static "parent" domain, and couple moving regions to the static parent (using FMS)
• only a single static state is exchanged between models
• the model component is where the region to region coupling happens as needed
• the model you're coupling to has no access to the higher-res "children" domains
• but pretty straightforward in the coupling interface

4. Consolidate the regions onto an XGrid

• all models would have access to the high-res domain data
• but creating and maintaining XGrid is difficult esp. for moving regions