|
Possible
specifications
of external forcings From the CCM
validation activity for SPARC (CCMVal) 1st
Draft, February 2005 |
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(A) Encouraged simulations within CCMVal in the near term
(B) Reproducing the past: Forcings for a transient model simulation 1960 to present day
(C) Making predictions: Forcings for a transient model simulation from present day to 2100
(D) Model recommendations: Soon on this website
(A) Encouraged
Simulations |
Some of the key questions
that have been
addressed by the Steering Committee are: (1) How well do we understand
the past
changes in stratospheric ozone (polar and extra-polar) over the past
few
decades in an environment where stratospheric constituents (including
halogens,
nitrogen oxides, water, and methane) were changing, as was the climate
in this
region? (2) What does our best understanding of the climate and
halogens, as
well as the changing stratospheric composition, portend for the future?
(3)
Given these predictions, what would be the effect of influencing the
composition of the stratosphere?
In order to address
question (1) and (2),
we would propose the following two reference simulations:
REF 1: REPRODUCING THE
PAST, Core time period 1980
to 2000
REF 1 is designed to
reproduce the observed period and allows a more
detailed investigation of the role of natural variability and other
atmospheric
changes important for ozone balance and trends.
This transient
simulation includes all anthropogenic and natural forcings based on
changes in
trace gases, solar variability, volcanic eruptions, quasibiennial
oscillation
(QBO), and sea surface temperatures (SSTs). SSTs in this run are based
on
observations. Dependent on computer resources some model groups might
be able
to start their runs earlier, e.g. in 1950, which is why the forcings on
the
website are defined from 1950 to 2000.
Recommendation: We recommend reporting results for
REF1 between 1960 and 2004 to
examine model variability. We will be conducting detailed
model evaluation with data between 1980 and 2004 (i.e., during the
satellite measurement period). Please check the list of model
recommendations that is specified under (D). We encourage groups to run
ensembles.
REF 2 is an internally
consistent simulation from the past into the
future. The proposed transient simulation follows the IPCC model
simulation for
a given greenhouse gas scenario. REF 2, like the IPCC simulation, only
includes
anthropogenic forcings. Natural forcings like solar variability and
volcanic
activity are not considered, and the QBO is not externally forced
(neither in
the past, nor in the future). SSTs in this run are based on coupled
atmosphere
ocean model derived SSTs. Dependent on computer resources some model
groups
might be able to run longer and/or start earlier, which is why the
forcings on
the website are defined until 2050.
Recommendation: We encourage groups to run
ensembles.
Scenarios
for
sensitivity experiments to address question (3) will be defined later.
Possible
sensitivity experiments could be:
SCN 1 (REF 1 with enhanced
BrOY): An additional
simulation is being developed to represent the known
lower stratospheric deficit in modeled inorganic bromine abundance.
This
simulation will be identical to REF 1, with the exception of including
source
gases abundances that will increase the burden of BrOY.
Details of
this simulation will be made available shortly.
SCN 2 (REF 2 with natural forcings): A
sensitivity simulation defined similar to REF1, with the inclusion of
solar
variability, volcanic activity, and the QBO in the past. Future
forcings will
include a repeating solar cycle and QBO, under volcanic clean aerosol
conditions. SSTs will be based on REF2.
Scenario |
Period |
Trace Gas |
SSTs |
Volcanic Aerosol |
Solar Variability |
QBO |
Enhanced BrOY |
REF1 |
1980-2000 |
OBS |
OBS |
OBS |
OBS |
OBS |
- |
REF2 |
1980-2025 |
OBS / A1B(medium) |
Model see 5a,b,c |
- |
- |
- |
- |
|
|
|
|
|
|
|
|
SCN1 |
1980-2000 |
OBS |
OBS |
OBS |
OBS |
OBS |
Included |
SCN2 |
1980-2025 |
OBS / A1B(medium) |
Model see 5a,b,c |
OBS / bkg in future |
OBS / repeating in future |
OBS / repeating in future |
- |
(B) Reproducing the
past: Observed forcings for a transient model
simulation 1960 to present-day |
B1.
Greenhouse
Gases 1959 to present day (CO2, CH4,
N2O)
GHG used for WMO/UNEP 2002 runs. The file gives surface volume mixing ratios of CH4 (ppbv), N2O (ppbv) and CO2 (ppmv)DOWNLOAD ---> Data set 1959 to 2000 based on WMO (2003) (1.2 kB).
The
influence of the 11-year solar cycle on photolysis rates is
parameterized
according to the intensity of the 10.7 cm radiation of the sun (data
available
at: http://www.drao.nrc.ca/icarus/www/daily.html).
The
spectral distribution of changes in extra-terrestrial flux is based on
investigations presented by Lean et al. (1997).
Recommendation: Use observed flux
(column 3 in maver_1951-2000.dat)
10,7 cm solar flux from http://www.drao.nrc.ca/icarus/www/maver.txt
More explanation see http://www.drao.nrc.ca/icarus/www/sol_home.shtml
B5.
Assimilated
Quasi-Biennial
Oscillation (QBO)
The QBO has been assimilated in several studies with the aim to
study QBO effects on the dynamics and/or chemistry. Often the
assimilation procedures assume a certain idealistic
meridional structure of the QBO jets and force the model to follow the
externally given vertical zonal wind structure within the QBO domain.
Even simple relaxation methods (see for example Giorgetta et al., 1999)
can provide fairly realistic QBO structures, and the GCM will generate
the secondary meridional circulation of the QBO and the related
temperature signal. This can provide a significant improvement for
certain experiments. The method implies nearly no costs compared to the
costs of the GCM integration.
The QBO is described by zonal wind profiles measured at the equator.
QBO
data sets provided by Marco Giorgetta (Contact for questions: Marco Giorgetta
)
* Surface Area Density data (SAD)
WMO2002 SAD dataset put together by
David Considine, LaRC. This data set is based on SAGE and SAM
data.
Monthly zonal mean surface area density climatology derived from
various satellite data.
DOWNLOAD ---> SAD
data set 1979 to 1999 (1.8 MB) provided by David Considine
(Contact for
questions: David Considine)
B7.
Other
issues
(a) Impact of new HCFCs (141B, 142B, 123) (Contact for questions: Rolando Garcia and Doug Kinnison)
e.g.
instead of including HCFCs explicitly, we could instead use MCF,
HCFC22 and CH3Cl as "surrogates", as follows:
MCF --> MCF + 2/3 * HCFC141B
HCFC22 --> HCFC22 + 1.0 * HCFC142B
CH3Cl --> CH3CL + 2.0 * HCFC123
This approach was used in the WMO1998 2D model assessment. These
surrogates have similar tropospheric and stratospheric lifetimes as the
omitted HCFCs.
B8.
References
WMO, 2003: Scientific
Assessment of Ozone Depletion: 2002. Global
Ozone Research and Monitoring Project, Report No. 47,
498 pp,
(C) Making
predictions: Forcings
for a transient model
simulation from present day to 2100 |
AGREEMENT
ON SCENARIO needed. So far proposed: Scenario Ab
(best guess scenario), Scenario
B2 (Table 4B-2 of WMO2003, page 4.90)
UNEP/WMO Scientific
Assessment of Ozone Depletion: 2002
Chapter 1: Controlled substances and other trace gases
Scenarios from Archie McCulloch (Marbury Techn. Cons.), John Daniel
(NOAA/AL), Steve Montzka (NOAA/CMDL), and Guus Velders (RIVM/LLO),
September 21, 2001 (Version 3)
For the model
simulation, please use scenario -> B2
So far proposed:
The focus of the future simulation is NOT a model-model
intercomparison. Rather we would like to make the best shot at
predicting the future. REF 2 is a simulation that focuses on
consistency and that follows the IPCC simulations. Essentially we
are asking the modeling groups to
make their best prediction. Therefore, having consistent SST in
future(and past of the making prediction simulation) is not necessary.
In any case one constrait is
to make the SST data set consitstent with
the GHG scenario.
Proposal:
a.
Fully coupled atmosphere ocean CCMs with the atmosphere extending to the middle
atmosphere, with coupled chemistry, use their internally calculated
SSTs
(probably beyond the possibilities for most groups).
b.
CCMs driven by SST and sea ice of the underlying
IPCC coupled-ocean
model simulation could use
the model consistent SSTs. One constraint is to make the SST
data set consistent with the GHG scenario. However, if preferred, they
could
also decide to use the SSTs defined under (5c).
c.
All other CCM groups might wish to run with
equal SSTs: We propose to
use the modeled SSTs
of the Hadley scenario for the full time period (1980 to 2025 or
longer) based
on the chosen GHG scenario.
i.
Do
you agree? If not, why?
The
QBO is described by zonal wind profiles measured at the equator.
QBO
data sets for the future are provided by Marco Giorgetta (Contact for
questions: Marco
Giorgetta
)
Last modified: April 17, 2005 by Veronika Eyring |