sensitivity.brian

Models: CAM (v3), AM (v2)

Experiments: Three APE configurations each, "control," "flat," and "qobs." I will refer to APE's "control" SST configuration as "aqua" to avoid some confusion. There are also standard runs, in the default model configuration. Each configuration is run in a +2K mode, described elsewhere, allowing us to investigate the climate sensitivity of each configuration.

To study climate sensitivity, we use the climate sensitivity and cloud feedback parameters, as defined by Cess et al. (1989, 1990, 1996). The climate sensitivity parameter is just the change in surface temperature divided by the direct radiative forcing. For these prescribed SST experiments, the direct radiative forcing is just the change in the net TOA radiative flux. The cloud feedback parameter is similar: it is just the change in cloud radiative forcing divided by the direct radiative forcing. We have calculated these quantities for each configuration of both GCMs, and we have also done it for the whole globe and the tropics separately.

Here are a few summary plots. Some of the plots also have changes in planetary and cloud albedo, and the last four figures are changes for total, high, middle, and low cloud amount for each model.

• summary:
  • global:
    • CAM [png][eps]
    • AM [png][eps]
  • tropical:
    • CAM [png][eps]
    • AM[png][eps]
• CAM v. AM, direct forcing & cloud feedback
  • global: [png][eps]
  • tropical: [png][eps]
• cloud amount:
  • global:
    • CAM [png][eps]
    • AM[png][eps]
  • tropical:
    • CAM [png][eps]
    • AM[png][eps]

More figures, and some more words, will be posted from this comparison soon.

A short work plan outlines some future directions for this project, available as a pdf.