forcing agents of IPCC 20c3m type experiments?

[hwang@climate_gsfc_nasa_gov]

Dear Madam/Sir,

We are now analyzing outputs of the 20c3m type experiments performed by NCAR CCSM3 (for IPCC AR4). To help us better understand your coupled model simulation, could you provide detailed information on the external forcing agents (e.g., how many forcings are included, how each of the external forcings, such as greenhouse gases, aerosols, volcanic eruptions etc, quantitatively varies with time) that your coupled model included for the 20c3m experiments?

Thank you very much!

Hailan

 

[murphys]

H,

We have the following forcing agents:
(1. Well mixed greenhouse gases (WMGHGs): CO2, CH4, N2O, CFC-11, and CFC-12
(2. Tropospheric and stratospheric ozone
(3. Sulfate aerosol, produced by a sulfur cycle from SO2 and DMS emissions
(4. Black and organic carbonaceous aerosol
(5. Sea-salt and dust aerosols, held fixed to present-day values
(6. Solar variability
(7. Volcanic forcing
(8. No 1st or 2nd indirect effects of aerosols on clouds

Details on the forcings as follows:
(1. WMGHGs: surface concentrations = unaltered SRES scenarios A1B, A2, and B1.
Surface concentrations in 20th century = observations.
Concentrations aloft are treated prognostically included chemical loss
mechanisms detailed in Boville et al (2001).
(2. Tropospheric ozone: reference for troposphere up through 2000 is Lamar
(submitted, 2005). After 2000, we scale the troposphere using empirical
relationships between ozone and forcing from the IPCC TAR. Reference for
stratosphere is Kiehl et al 1999.
(3. Sulfate aerosol: for 21st century, we use SRES emissions + DMS climatology
in a sulfur cycle described by Barth et al and Rasch et al (2000). For
historical SO2 emissions, we use the data set of Smith, Pilcher, and Wigley
(2001).
(4. Black and organic carbonaceous aerosol: we scale a climatology for
present-day to earlier years using a global scaling for population. The
climatology is described in Collins (2005) and references therein.
(5. Sea salt and dust: held at present day climatology, described in Collins
2005 (CAM3 technote).
(6. Solar: Lean 1995
(7. Volcanic forcing: Amman 2003