20C3M experiments

CCSM case names: b30.030a b30.030b b30.030c b30.030d b30.030e b30.030b.ES01 b30.030f.ES01 b30.030g.ES01 b30.030h.ES01 b30.030h

Description

The 20C3M simulations run in the United States (all runs without "ES" in the case name) were started from different times in the PIcntrl run separated by 20 yr with the first ensemble member branching from the control run at year 360 (these experiments started branching 60 yr after the PIcntrl run showed a stable surface climate). The runs in Japan (the "ES" runs) branched at 30- and 50-yr intervals from the PIcntrl run there, so chosen to have different Atlantic meridional overturning initial states than the other ensemble members. The forcings included in the 20C3M simulation are as follows:

Sulfate: direct effect from sulfur cycle model using time- and space-varying SO2 emissions (Smith et al. 2001, 2004).
Solar: Lean et al. (1995).
Volcanoes: Ammann et al. (2003; volcanic effects included as aerosol optical depths).
Ozone: twentieth-century tropospheric ozone (up to tropopause defined by temperature gradient) spatially varying as computed from the Model for Ozone and Related Chemical Tracers (MOZART) model, snapshot runs every 20 yr: 1890, 1910, 1930, 1950, 1970, 1990 on T42 18L resolution with meteorology from PCM all-forcings twentieth-century run (Meehl et al. 2004a) for those years using spatially varying emissions of ozone precursors (Lamarque et al. 2005). Interpolation was then performed in space and time to the Community Atmospheric Model version 3 (CAM3) T85 26L. Time-varying zonal mean stratospheric ozone was prescribed from a National Oceanic and Atmospheric Administration (NOAA) dataset to 1990 (Kiehl et al. 1999). The top two model levels have exactly the zonal mean values. Levels to the tropopause are weighted and interpolated, and therefore contain some imprint from the tropopause (i.e., those levels are not purely zonal means). From 1990 to 2000, 1990 column tropospheric ozone has no appreciable trend so 1990 values were filled in to 2000. Time-evolving stratospheric ozone for 1990 to 2000 was scaled by NOAA ozone dataset.
GHGs (C02, CH4 , N20): From the IPCC Third Assessment Report [TAR; C02 from the Integrated Science Assessment Model (ISAM)].
Halocarbons (including SF6): (Dai et al. 2001). We use direct CFC11 and equivalent CFC12 where equivalent is based on forcing, not on global warming potentials (GWPs).
Other aerosols: A present-day estimate of the spatial distribution and magnitude of black carbon was scaled by population so there are time-evolving values of black carbon over the twentieth century with a fixed pattern; sea salt and dust spatial distributions are held fixed throughout the twentieth century at year 2000 values (Collins et al. 2006b). Land surface characteristics are fixed at presentday values.

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Well-mixed
greenhouse gases
Sulfate emissions Ozone concentration Solar forcing Volcanic forcing Other aerosols
(black and organic carbon,
sea salt, dust)
scaling factor