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CCSM/CAM Unification Plan

- need for single executable system
  - only single executable?
  - concern that single executable in robust on all platforms
  - multiple machine runs may prefer single executable
  - performance multiple executable vs single executable

- acceptance criteria, ease of use, performance, run-time environment
- unified model has same climate as CAM stand-alone in some mode, need to determine method for moving CCSM and CAM forward

- new components, merged components
  - NO components will contain other components (for atm, ocn, ice, lnd)
    runoff is acceptable as currently implemented?
  - we need a way to instantiate components and add them easily to the system
  - hierarchy of components
  - thermo-only ice model
  - full ice model
  - data ice model
  - SOM
  - full ocean model
  - mixed layer ocean model
  - upper ocean model
  - data ocean model (SST)
  - active land (runoff, glaciers)
  - data land model 
  - aqua planet mode
  - data assimilation models
  - transport only CAM
  - CAM adjoint model
  - regional modeling
  - ensemble components

CAM internal components (some on different grids)
  - chemistry, mozart
  - single column model
  - WACCM
  - super parameterizations
  - regional modeling
  - data aerosol/prognostic aerosol models

CPL component
  - how many?

Components
  - science
  - instantiate components for testing
  - code looks better
  - is component shared program, is component visible only at main.F, is component something that meets structure at top and can be any hierarchy
  - need to start drawing diagrams
  - building blocks of components, flexibility is critical
  - should we hardwire number of top components like CCSM now (probably not)
  - is it something that talks through a coupler

- coupling strategies
  - ESMF
  - flux averaging
  - coupling every timestep, coupling frequency flexibility?
  - call and return for coupling?  
  - CAM bc/ac ordering, extra 1/2 timestep at end?
  - update bcs every timestep in CAM
  - flux computation flexibility, where do they live in components
  - model timestep and coupling frequency relationship

- serial vs concurrent execution
  - is serial required for 1 pe mode, does it have to work without MPI
    available?
  - do we need several different CCSM drivers for different applications
    of the unified model?
  - ESMF and mph work together on virtual machine, hierarchy, system needs, mediation of system resources between components and at different hierarchys
  - lightweight components for trivial coupling

- resolution support
  - all current CAM resolutions (T5-T340, FV 2,1,.5,.25, etc)
  - some ocean/ice/land configurations will need to run on the CAM grid
    (will need identity mapping in cpl)
  - should CLM be able to run at a different resolution?
  - should POP and CSIM be able to run at different resolutions?
  - land fractions?  specified land fraction vs complement of ocean,
    are both required?
  - common land fraction mechanism
  - land fractions are a critical issue
  - limited grids, regional grids
  - mesh refinement inside components
  - flexible grid at boot-up
  
- hardware support
  - CCSM platforms
  - Lahey strict compliance
  - laptop

- scientific requirements for overall system
  - WACCM impact on system?
  - BGC impact on system?
  - Chemistry impact on system?
  - support for varied coupling fields

- SE requirements/desires
  - bfb capability with different pes 
    only for certain configurations?
    as an optional capability?
  - flexibility wrt coupling frequency, coupling concurency, grids,
    number of components
  - single pe
  - error growth, validation 
  - (run time) dynamics load balance, dynamics decompositions = structures
  - flexible statically allocated load balance at initialization, automatically
  - dynamic grid refinement (probably not)
  - dynamic load balance needs to be enabled in order to test
  - science requirement for load balance, dynamic vegetation for instance

- SE infrastructure, scripts, etc.
  - common scripts in unified model, tools for building and generating
    namelist, etc.
  - common test framework, complete test framework, flexible test
    framework
  - flint, lahey strict, build checks
  - scripting practices