cc: jma@ncar.ucar.edu, wmw@ncar.ucar.edu date: Tue, 26 Jan 1999 10:44:57 -0700 (MST) from: meehl@meeker.ucar.EDU (Jerry Meehl) subject: DDC questions to: m.hulme@uea.ac.uk Mike, Julie forwarded your questions about the NCAR model run to me, and I will see if I can answer them for you. If you have any other questions, let us know. Cheers, Jerry ------------------------------------------------------------ 1. The runs cease in 2036 (actually the target was 2035 with one year over-run) for a variety of reasons. At the time we were running the model at Livermore and we were coming up against resource limitations, so we ran the CO2-only and CO2+sulfates for 45 years past present day (1990) to compare to a set of sensitivity experiments performed with idealized scenarios of CO2 and sulfates for nominally 1960-1990, and then extended 45 years into the future for a total of 75 year experiments (Meehl et al., 1996). We would have liked to extend the scenario experiments past 2035 later when we got more resources, but by then the operating system had changed, and that version of the model was retired. (the subsequent versions of coupled models at NCAR, the Climate System Model (CSM) and Parallel Climate Model (PCM) will have submissions to the DDC in the next couple months) 2. The NCAR model version is what we call the NCAR DOE global coupled model, sometimes referred to as the Washington-Meehl coupled model. See references below. 3. short summary (absract from Meehl et al., 1999, submitted to J. Climate): ANTHROPOGENIC FORCING AND CLIMATE SYSTEM RESPONSE IN SIMULATIONS OF 20TH AND 21ST CENTURY CLIMATE Gerald A. Meehl, Warren M. Washington, Julie M. Arblaster, Thomas W. Bettge, and Warren G. Strand Jr. Simulations of 20th century climate and projections of climate into the 21st century are conducted with a global coupled climate model without flux adjustment. The global coupled climate model used in these experiments has an atmospheric component with rhomboidal 15 (R15) resolution (roughly 4.5 degrees latitude by 7.5 degrees longitude) with 9 levels, mass flux convection and a cloud albedo feedback scheme; a global 1 degree by 1 degree 20 level ocean; and dynamic and thermodynamic sea ice (Meehl and Washington, 1995; Washington and Meehl, 1996). Characteristics of this model are described by Meehl and Washington (1995) for sensitivity aspects of the cloud albedo feedback scheme, Meehl (1997) for details on the spin-up and systematic errors, Washington and Meehl (1996) for basic description of a 1% per year CO2 increase experiment and features of the high latitude response in the northern Hemisphere, Meehl and Washington (1996) for description of the ``El Nino-like" pattern in the 1% CO2 increase sensitivity experiment, and Meehl et al. (1996) for results from a set of sensitivity experiments including the 1% per year CO2 increase experiment compared to experiments that include direct and indirect effects of sulfate aerosols. Two climate change experiments are performed, both starting in the year 1900. The first uses greenhouse gas radiative forcing (represented by equivalent CO2) observed during the 20th century, and extends greenhouse gas forcing to the year 2035 by increasing CO2 1% per year compound after 1990 (CO2-only experiment). The second includes the same greenhouse gas (equivalent CO2) forcing as the first, but adds the effects of time-varying geographic distributions of monthly sulfate aerosol radiative forcing (CO2+sulfates experiment). These are compared to a 135 year control experiment with no change in external forcing. Climate system responses in the CO2-only and CO2+sulfates experiments are marked not only by greater warming at high latitudes in the winter hemisphere, but also by a global ``El Nino-like" pattern in surface temperature, precipitation, and sea level pressure. This is characterized by relatively greater increase of SST in the central and eastern equatorial Pacific compared to the west, a shift of precipitation maxima from the western Pacific to the central Pacific, mostly decreases of Asian-Australian monsoon strength, lower pressure over the eastern tropical Pacific, deeper midlatitude troughs in the north and south Pacific, and higher pressure over Australasia. An EOF analysis of surface temperature indicates that the ``El Nino-like" pattern in the model characterizes not only CO2-only and CO2+sulfates climate system response to time-varying external forcing, but also internally-generated climate variability at the El Nino and decadal (9-20 year) timescales. These results indicate that the ``El Nino-like" pattern is an ubiquitous response in the climate system that occurs at different timescales due to different forcings. The coupled model climate change experiments show that time-evolving external forcing can introduce this same low frequency response pattern into the coupled climate system.