RCE world

Summary

A radiative-convective equilibrium configuration is now available as a compset in CESM2 (as of release CESM 2.1.3). It can be invoked using the short name “QPRCEMIP”.

This configuration is derived to be compatible with the RCEMIP experimental protocol. It defaults to using the spectral element dynamical core on the cubed-sphere mesh and CAM6 physics. There is no planetary rotation, insolation is uniform and constant with a reduced solar constant, and the prescribed sea-surface temperature is uniform. The default initial conditions are derived from an analytical expression.

The implementation of RCE builds upon the aquaplanet configuration. A new data ocean option was added to allow a uniform constant value (DOCN%AQPCONST). The calculation of the cosine of the solar zenith angle was modified to allow a specified angle to be used. The planetary rotation rate was modified to be a namelist parameter, which is specified as zero for the default RCE case.

Aerosols are neglected in the default case. This is accomplished by removing all emissions and setting the sea-salt emission efficiency to zero. Note that the sea-salt behavior differs from the default aquaplanet, but we recommended following this convention in both RCE and aquaplanet configurations. The microphysics scheme assumes a constant liquid drop and ice crystal number.

For details of RCEMIP, see Wing et al. (2018). Many aspects of this configuration were developed with CESM1/CAM5, and details can be found in Reed et al. (2015), Reed & Medeiros (2016), and Pendergrass et al. (2016).

Running the QPRCEMIP compset

You will need CESM 2.1.3 or later. With no modifications, follow the basic steps for creating a new case, building, and running. In this example, we will change the run length to 2 months.

$ create_newcase --case /path/to/case --compset QPRCEMIP --res ne30_ne30_g17 --project PABCDEFG --walltime 02:00:00
$ cd /path/to/case
$ ./case.setup
$ xmlchange STOP_OPTION=nmonths
$ xmlchange STOP_N=2
$ ./case.build
$ ./case.submit

NOTE: The default configuration has different output than standard CAM runs, including defaulting to timestep output frequency. This is usually not desired, so modifications (e.g., FINCL, NHTFRQ, MFILT in namelist) should be made. For example, by modifying user_nl_cam as shown here:

 avgflag_pertape = 'A'
 empty_htapes    =  .false.
 mfilt          =  1,4
 nhtfrq         =  0,-6
 fincl2         = 'T','Q','U','V','PS','PRECT','PRECC','FLUT','FSNT','SWCF','LWCF','TMQ','TGCLDLWP'
 history_amwg   = .true.
 history_budget = .true.

Modifying the default configuration

The configuration can be customized in any number of ways, and the approach follows that of standard CESM2-CAM6 modifications. Some specific RCE customizations include changing the solar zenith angle which will impact the insolation. The zenith angle can be modified with the CAM namelist parameter rad_uniform_angle with the value given in radians. Another useful modification is to change the constant SST, which can be managed by altering the data ocean namelist parameter sst_constant_value in units of Kelvin (use file user_nl_docn in the case directory). To introduce rotation, adjust the CAM namelist parameter omega (note that allows the usual calculation of Coriolis effects, and is not an idealized constant Coriolis effect as in Reed & Chavas (2015)).

REFERENCES

  • Pendergrass, A. G., K. A. Reed, and B. Medeiros (2016), The link between extreme precipitation and convective organization in a warming climate: Global radiative-convective equilibrium simulations, Geophys. Res. Lett., 43(21), 11,445–11,452, doi: 10.1002/2016GL071285, 2016GL071285.
  • Reed, K. A., B. Medeiros, J. T. Bacmeister, and P. H. Lauritzen (2015), Global radiative–convective equilibrium in the Community Atmosphere Model, Version 5, Journal of the Atmospheric Sciences, 72(5), 2183–2197, doi:10.1175/JAS-D-14-0268.1.
  • Reed, K. A., and Chavas, D. R. (2015), Uniformly rotating global radiative‐convective equilibrium in the Community Atmosphere Model, version 5, J. Adv. Model. Earth Syst., 7, 1938– 1955, doi:10.1002/2015MS000519.
  • Reed, K. A., and B. Medeiros (2016), A reduced complexity framework to bridge the gap between AGCMs and cloud-resolving models, Geophysical Research Letters, 43(2), 860–866, doi:10.1002/2015GL066713, 2015GL066713.
  • Wing, A. A., K. A. Reed, M. Satoh, B. Stevens, S. Bony, and T. Ohno (2018), Radiative–convective equilibrium model intercomparison project, Geoscientific Model Development, 11(2), 793–813, doi:10.5194/gmd-11-793-2018.

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