Wednesday, May 9, 2012

4029.txt

cc: jma@ncar.ucar.edu, wmwatXYZxyzr.ucar.edu
date: Tue, 26 Jan 1999 10:44:57 -0700 (MST)
from: meehlatXYZxyzker.ucar.EDU (Jerry Meehl)
subject: DDC questions
to: m.hulmeatXYZxyz.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.

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