CESM/ESMF Progress Report Mariana Vertenstein NCAR Earth System Laboratory CESM Software Engineering Group (CSEG) NCAR is sponsored by the National Science Foundation

CESM Community Registered CESM Release Users 4240 Total registered users 1110 New users in past 12 months DiscussCESM Forums Bulletin Board Total Registered users 14 Top level forums with 77 sub-forums 5229 Total posts (topics + comments) 800 posts since March 2014 Registered CESM Developers 290 Total registered users – vetted annually

CESM Architecture (CPL7) Single executable 7 geophysical components / 1 coupler (hub) – atm, land, river, land-ice, sea-ice, ocean, wave – run on potentially different grids – exchange boundary data with each other Hub and Spoke architecture – components communicate with each other ONLY a coupler (hub and spoke architecture) – components/hub can run on unique PES concurrently) or overlapping PES (sequentially) or hybrid layout – components can be prognostic or prescribed -data Model Driver – runs on union of all component/hub PES – coordinates time evolution of system

CESM Architecture (cont) processors time CPL (regridding, merging) CAM CLM CICE Driver (controls time evolution) POP Sequential Layout processors Hybrid Sequential/Concurrent Layout CAM CLM CICE POP Driver CPL Driver (controls time evolution) Concurrent Layout CAMCLMCICEPOP processors time

CESM/ESMF Offline Regridding ESMF offline regridding has – completely changed the ability of CESM to run on new grids – both structured and unstructured – Enabled new science! CESM has now introduced new tool chain based on the ESMF offline regridding – capability has been introduced as part of the CESM releases in top level directory What took days (even weeks) now takes hours to create

Recent Example Problem: With CAM spectral element dycore, ocean is having problems spinning up from Levitus (much slower compared to using CAM finite volume dycore)

Want to examine this further by creating new polar refined grid Created new atm/land grid and mapping files and was able to obtain new coupled model run on this grid in < 2 weeks! Result showed that grid was not not problem

ESMF online regridding - why? As more regionally refined grids are introduced (e.g. MPAS, SE) – need to – minimize the number of mapping files that are needed – simplify and streamline workflow for generating new user grid configurations Will be a requirement for run-time adaptive mesh refinement ESMF is the only tool that currently delivers this capability Status: Prototype implementation has been done and is being updated for newest coupler

NUOPC/HYCOM in ESMF Goal – Introduce HYCOM into CESM as an alternate ocean component via the NUOPC Layer. Initial work – Redesigned the CESM driver so that it easily accommodate both NUOPC-based components and components that use native CESM datatypes, from the Model Coupling Toolkit (MCT)

Why Redesign Driver/Hub Implementation? driver code hard-coded to contain MCT types one large routine (~6K lines) with functionality often repeated difficult to understand and MODIFY flow through system difficult to implement use of alternative coupling architecture (e.g. ESMF) at the driver/hub

Redesign Details Introduced a new abstraction layer between driver and components - driver now has no references to either MCT or ESMF types – Driver LOC reduced from 6k -> 3k and much easier to understand and modify flow Much easier to incorporate ESMF/NUOPC driver components Permits ESMF and MCT data structures to share memory where possible - allows significant backwards compatibility Redesign work has been brought into CESM trunk (development code base) with both ESMF and MCT data types