Idealized single-forcing GCM simulations with GFDL CM2.1

This repository contains a set of single-forcing general circulation model (GCM) simulations run with the Geophysical Fluid Dynamics Laboratory (GFDL) Climate Model 2.1 (CM2.1).  In each of these equilibrium simulations, one climate forcing was altered while all others were held constant at preindustrial levels, modeling the climate response to individual climate forcings.  Simulations were run for obliquity (low and high obliquity), precession (four phases of the precession cycle with high eccentricity, and one simulation with eccentricity set to zero), half CO₂, and LGM-sized ice sheets.  The values chosen for the orbital simulations represent the extreme values of the past 900 thousand years.

Simulations were run for at least 500 years, and forcings do not change from year to year.  The uploaded files are 100 year annual-means and monthly climatologies.  Variables are presented for the atmosphere, ocean, sea ice, and land.  Monthly ocean files are not currently available; please contact Michael Erb at michael.p.erb@gmail.com if you are interested in those results.

=== FORCINGS ===

Preindustrial climate forcings were set to the following values:

 - Obliquity: 23.439°

 - Longitude of perihelion: 102.93°

 - Eccentricity: 0.0167

 - CO₂: 286 ppm

 - Ice sheets: 0 ka BP

The remaining simulations explore the climate response to a change in one of these forcings, with all other forcings set to preindustrial levels.  Forcings are specified as follows:

 - lo_obliq and hi_obliq: Obliquity is set to 22.079° or 24.480°, respectively.

 - 0_AEQ, 90_WSOL, 180_VEQ, and 270_SSOL: Perihelion occurs at the NH autumnal equinox, winter solstice, vernal equinox, or summer solstice, respectively, with eccentricity set to 0.0493.  This corresponds to a longitude of perihelion of 0°, 90°, 180°, or 270°, respectively.

 - ECC_0: Eccentricity is set to 0.

 - half_CO2: CO₂ is set to 143 ppm.

 - ice_sheets: Ice sheets and sea level are set to Last Glacial Maximum (LGM) levels.  Ice sheets come from the ICE-5G reconstruction.

A note about preindustrial simulations: The single-forcing simulations were not all run at the same time, and some details of the model or setup changed.  Because of this, if a preindustrial control simulation is wanted for analysis, it is recommended that you use certain preindustrial simulations for certain comparisons, as follows:

- preind_exp1: Control simulation for obliquity simulations.

- preind_exp2: Control simulation for precession, eccentricity, and half CO₂ simulations.

- preind_exp3: Control simulation for ice sheets simulation.

=== NOTES ===

More detailed description of these simulations, as well as results, can be found in the following papers:

Mantsis, D. F., A. C. Clement, A. J. Broccoli, and M. P. Erb, 2011: Climate feedbacks in response to changes in obliquity. J. Climate, 24, 2830-2845, doi:10.1175/2010CJLI3986.1.

Erb, M. P., A. J. Broccoli, and A. C. Clement, 2013: The contribution of radiative feedbacks to obliquity driven climate change. J. Climate, 26, 5897-5914, doi:10.1175/JCLI-D-12-00419.1.

Mantsis, D. F., B. R. Lintner, A. J. Broccoli, M. P. Erb, A. C. Clement, and H.-S. Park, 2014: The response of large-scale circulation to obliquity-induced changes in meridional heating gradients. J. Climate, 27, 5504-5516, doi:10.1175/JCLI-D-13-00526.1.

Erb, M. P., A. J. Broccoli, N. T. Graham, A. C. Clement, A. T. Wittenberg, and G. A. Vecchi, 2015: Response of the equatorial Pacific seasonal cycle to orbital forcing. J. Climate, 28, 9258-9276, doi:10.1175/JCLI-D-15-0242.1.

Erb, M. P., C. S. Jackson, and A. J. Broccoli, 2015: Using single-forcing GCM simulations to reconstruct and interpret Quaternary climate change. J. Climate, 28, 9746-9767, doi:10.1175/JCLI-D-15-0329.1.

Erb, M. P., C. S. Jackson, A. J. Broccoli, D. W. Lea, P. J. Valdes, M. Crucifix, and P. N. DiNezio, in press: Model evidence for a seasonal bias in Antarctic ice cores. Nature Communications.

Bosmans, J. H. C., M. P. Erb, A. M. Dolan, S. S. Drijfhout, E. Tuenter, F. J. Hilgen, D. Edge, J. O. Pope, and L. J. Lourens, in press: Response of the Asian summer monsoons to idealized precession and obliquity forcing in a set of GCMs. Quat. Sci. Rev.

Note that the monthly data analyzed in some of these papers has been converted to a common fixed-angular calendar in which every "month" corresponds to a 30° arc of Earth's orbit.  This was done because changes in precession affect the speed at which Earth travels through different parts of its orbit according to Kepler's second law, complicating the comparison of months in different precession experiments.  However, the results provided in this repository use the model's original fixed-day calendar.

The half_CO2, ice_sheets, and preind_exp3 simulations were run by Bryan Raney (braney@envsci.rutgers.edu).  Most of the remaining experiments were run by Michael Erb.  If you use these simulations for research, please let us know.

For a similar set of experiments using another model (NCAR CESM), see doi:10.5281/zenodo.1194490.

Contact:
Michael Erb
Postdoctoral Scholar at Northern Arizona University
michael.p.erb@gmail.com