CESM2 Configurations (CESM2.2)

The CESM2 system can be configured a number of different ways from both a science and technical perspective. CESM2 supports numerous resolutions, and component sets. In addition, each model component has input options to configure specific model settings and parameterizations.

CESM2 Components

CESM2 consists of seven geophysical model components:

and an external system processing component

  • external system processing (esp)

In addition CESM2 is accompanied by a driver/coupler (cpl7) that coordinates the time evolution of geophysical components and periodically permits the components to exchange data. Each component is represented in one of several modes: “active,” “data,” “dead,” or “stub” that permits the whole system to activate and deactive component feedbacks by allowing for a variety of “plug and play” combinations.

During the course of a CESM2 run, the model components integrate forward in time, periodically exchanging information with the coupler. The coupler meanwhile receives fields from the component models, computes, maps, and merges this information, then sends the fields back to the component models. The coupler brokers this sequence of communication interchanges and manages the overall time progression of the coupled system. A CESM2 component set is comprised of eight components: one component from each model (atm, lnd, rof, ocn, ice, glc, wav, and esp) plus the coupler. Model components are written primarily in Fortran.

The active (dynamical) components are generally fully prognostic, and they are state-of-the-art climate prediction and analysis tools. Because the active models are relatively expensive to run, data models that cycle input data are included for testing, spin-up, and model parameterization development. The dead components generate scientifically invalid data and exist only to support technical system testing. The dead components must all be run together and should never be combined with any active or data versions of models. Stub components exist only to satisfy interface requirements when the component is not needed for the model configuration (e.g., the active land component forced with atmospheric data does not need ice, ocn, or glc components, so ice, ocn, and glc stubs are used).

The CESM2 components can be summarized as follows:

“CESM2 model components”

Component Generic Type

Component Generic Name

Component Name

Component Type

Description

atmosphere

atm

cam

active

The Community Atmosphere Model (CAM) is a global atmospheric general circulation model developed from the NCAR CCM3.

atmosphere

atm

datm

data

The data atmosphere component is a pure data component that reads in atmospheric forcing data

atmosphere

atm

xatm

dead

Used only for testing the driver/coupler

atmosphere

atm

satm

stub

Used only to satisy the interface requirements

land

lnd

clm

active

The Community Land Model (CLM) is the result of a collaborative project between scientists in the Terrestrial Sciences Section of the Climate and Global Dynamics Division (CGD) at NCAR and the CESM Land Model Working Group. Other principal working groups that also contribute to the CLM are Biogeochemistry, Paleoclimate, and Climate Change and Assessment.

land

lnd

dlnd

data

The data land component is a purely data-land component (reading in coupler history data for atm/land fluxes and land albedos produced by a previous run, or snow surface mass balance fields) or both.

land

lnd

xlnd

dead

Used only for testing the driver/coupler

land

lnd

slnd

stub

Used only to satisy the interface requirements

river

rof

rtm

active

The river transport model (RTM) was previously part of CLM and was developed to route total runoff from the land surface model to either the active ocean or marginal seas which enables the hydrologic cycle to be closed (Branstetter 2001, Branstetter and Famiglietti 1999). This is needed to model ocean convection and circulation, which is affected by freshwater input.

river

rof

mosart

active

MOdel for Scale Adaptive River Transport (MOSART) , a new large-scale river routing model. MOSART improves the magnitude and timing of river flow simulations.

river

rof

drof

data

The data runoff model was previously part of the data land model and functions as a purely data-runoff model (reading in runoff data).

river

rof

xrof

dead

Used only for testing the driver/coupler

river

rof

srof

stub

Used only to satisy the interface requirements

ocean

ocn

pop

active

The ocean model is an extension of the Parallel Ocean Program (POP) Version 2 from Los Alamos National Laboratory (LANL).

ocean

ocn

mom6

active

Based on the Modular Ocean Model version 6; an early functional release is available starting in CESM2.2. Note that MOM6 is not obtained by default; for instructions on obtaining it, see https://github.com/ESCOMP/MOM_interface/wiki/Detailed-Instructions.

ocean

ocn

docn

data

The data ocean component has two distinct modes of operation. It can run as a pure data model, reading ocean SSTs (normally climatological) from input datasets, interpolating in space and time, and then passing these to the coupler. Alternatively, docn can compute updated SSTs based on a slab ocean model where bottom ocean heat flux convergence and boundary layer depths are read in and used with the atmosphere/ocean and ice/ocean fluxes obtained from the coupler.

ocean

ocn

xocn

dead

ocean

ocn

socn

stub

sea-ice

ice

cice

active

The sea-ice component (CICE) is an extension of the Los Alamos National Laboratory (LANL) sea-ice model and was developed though collaboration within the CESM Polar Climate Working Group (PCWG). In CESM, CICE can run as a fully prognostic component or in prescribed mode where ice coverage (normally climatological) is read in.

sea-ice

ice

dice

data

The data ice component is a partially prognostic model. The model reads in ice coverage and receives atmospheric forcing from the coupler, and then it calculates the ice/atmosphere and ice/ocean fluxes. The data ice component acts very similarly to CICE running in prescribed mode.

sea-ice

ice

xice

dead

Used only for testing the driver/coupler

sea-ice

ice

sice

stub

land-ice

glc

cism

active

The CISM component is an extension of the Glimmer ice sheet model.

land-ice

glc

sglc

stub

Used only to satisy the interface requirements

ocean-wave

wav

wav

ww3

The ww3 component adds prognostic ocean waves to the system

ocean-wave

wav

xwav

dead

Used only for testing the driver/coupler

ocean-wave

wav

swav

stub

Used only to satisy the interface requirements

coupler

cpl

cpl

active

The CESM coupler was built primarily through a collaboration of the NCAR CESM Software Engineering Group and the Argonne National Laboratory (ANL). The MCT coupling library provides much of the infrastructure.

CESM2 Component Sets

The CESM2 components can be combined in numerous ways to carry out various scientific or software experiments. A particular mix of components, along with component-specific configuration and/or namelist settings is called a component set or compset. CESM has a shorthand naming convention for component sets that are supported out-of-the-box.

The compset name usually has a well defined first letter followed by some characters that are indicative of the configuration setup. Each compset name has a corresponding short name.

See supported component sets for a complete list of supported compset options. Running query_config with the --compsets option will also provide a listing of the supported out-of-the-box component sets for the local version of CESM2.

CESM2 Grids

The supported grid resolutions are specified in CESM2 by setting an overall model resolution. Once the overall model resolution is set, components will read in appropriate grid files and the coupler will read in appropriate mapping weights files. Coupler mapping weights are always generated externally in CESM2. The components will send the grid data to the coupler at initialization, and the coupler will check that the component grids are consistent with each other and with the mapping weights files.

In CESM2, the ocean and ice must be on the same grid, but the atmosphere, land, river runoff and land ice can each be on different grids. Each component determines its own unique grid decomposition based upon the total number of pes or processing elements assigned to that component.

CESM2 supports several types of grids out-of-the-box including single point, finite volume, cubed sphere, displaced pole, and tripole. These grids are used internally by the models. Input datasets are usually on the same grid but in some cases, they can be interpolated from regular lon/lat grids in the data models. The finite volume is generally associated with atmosphere and land models but the data ocean and data ice models are also supported on that grid. The cubed sphere grid is used only by the active atmosphere model, cam. The displaced pole and tripole grids are used by the ocean and ice models. Not every grid can be run by every component. The ocean and ice models run on either a Greenland dipole or a tripole grid. The Greenland Pole grid is a latitude/longitude grid, with the North Pole displaced over Greenland to avoid singularity problems in the ocn and ice models. The low-resolution Greenland pole mesh from CCSM3 is illustrated in Yeager et al., “The Low-Resolution CCSM3”, AMS (2006), Figure 1b., Web. Similarly, the Poseidon tripole grid is a latitude/longitude grid with three poles that are all centered over land.

CESM2 Machines

Scripts for supported machines and userdefined machines are provided with the CESM2 release. Supported machines have machine specific files and settings added to the CESM2 scripts and are machines that should run CESM2 cases out-of-the-box. Machines are supported in CESM2 on an individual basis and are usually listed by their common site-specific name. To get a machine ported and functionally supported in CESM2, local batch, run, environment, and compiler information must be configured in the CESM2 scripts. The machine name “userdefined” machines refer to any machine that the user defines and requires that a user edit the resulting xml files to fill in information required for the target platform. This functionality is handy in accelerating the porting process and quickly getting a case running on a new platform. For more information on porting, see the CIME porting guide. The list of available machines are documented in CESM2 supported machines. Running query_config with the --machines option will also show the list of all machines for the current local version of CESM. Supported machines have undergone the full CESM2 porting process. The machines available in each of these categories changes as access to machines change over time.

CESM2 Validation

Although CESM2 can be run out-of-the-box for a variety of resolutions, component combinations, and machines, MOST combinations of component sets, resolutions, and machines have not undergone rigorous scientific climate validation. Control runs accompany scientifically supported component sets and resolutions and are documented on the release page. These control runs should be scientifically reproducible on the original platform or other platforms. Bit-for-bit reproducibility cannot be guaranteed due to variations in compiler or system versions. Users should carry out their own port validations on any platform prior to doing scientific runs or scientific analysis and documentation.