CCMVal

Possible specifications of external forcings for transient model simulations

From the CCM validation activity for SPARC (CCMVal)

1st Draft, February 2005

Open for Discussion
SPARC

WCRP

This draft has been prepared by V. Eyring, D. Kinnison, T. Shepherd, B. Boville, C. Bruehl, M. Chipperfield, M. Dameris, R. Garcia, M. Giorgetta, E. Manzini, and R. Salawitch

General questions regarding the specifications of external forcings can be directed to Veronika Eyring, Doug Kinnison, and Ted Shepherd.
Please directly contact the appropriate scientists for questions regarding specific data sets (see below).
 
BACK to CCMVal website
(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: MAKING PREDICTIONS, Core time period 1980 to 2025

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.

 Table 1: Summary of proposed WMO / CCMVal scenarios.

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).

Surely it would be better  to use observations up to present day.
Can anybody update these numbers to present day, based on observations?

B2.   Halogens (1950 to present day)

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)

DOWNLOAD ---> Data set (1950 to 2000) based on WMO (2003) (5.9 kB).

Can anybody update these numbers to present day, based on observations?



B3.   Sea Surface Temperatures 1950 to present day

AGREEMENT ON OBSERVED SSTs needed. So far two data sets proposed (HadISST1 or blend of HADISST (prior to 1979) and Reynolds).

Sea Surface Temperature prescribed as monthly means following the global sea ice and sea surface temperature (HadISST1) data set provided by UK Met Office Hadley Center (Rayner et al., 2003).

The data is available without charge, but please read the terms and conditions before using it. The UK Met Office Hadley Center also asks you to register before downloading the data.
Web site to download  Sea Hadley Centre Sea Ice and SST data set (HadISST): follow the link Marine Data HadISST - Globally complete sea-ice and sea-surface temperature.

OR

Blend of HADISST (prior to 1979) and Reynolds, assembled by Jim Hurrell, very similar to what is used in ERA40. The data set is update monthly, but the standard input files, available at many resolutions, are for Jan 1949 - Oct 2001 (Contact: Byron Boville).
The climatological files are available on the web, through the initial and boundary files for specific resolutions at http://www.ccsm.ucar.edu/models/atm-cam/download/index.html
If we agree on this data set monthly time series files will be made available.


B4.   Solar Cycle 1951-2000

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).

DOWNLOAD --->  Data Set for transient model simulations (maver_1951-2000.dat) (25.2 kB).   (Contact for questions: Christoph Brühl)

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.

Care must be taken with regard to the effect of the QBO on vertical momentum fluxes, as provided by resolved vertically propagating waves or parameterized gravity waves, and the resulting vertical dynamical coupling between the QBO and the semiannual oscillation ( SAO). If the QBO is assimilated, then its shear layers will act immediately as a filter on vertically propagating waves, resolved or parameterized. Hence wave mean-flow interaction will be intensified in the QBO domain and reduced at higher levels. This may lead to a substantial reduction of the zonal momentum fluxes passing the stratopause towards the mesosphere, with consequences for instance for the circulation above the QBO domain. This may cause changes for example in the SAO compared to the SAO in a simulation without QBO assimilation.

The QBO is described by zonal wind profiles measured at the equator.

QBO data sets provided by Marco Giorgetta (Contact for questions: Marco Giorgetta )


B6.   Volcanic eruptions and aerosol loading

Some groups might wish to include the impact of volcanic eruptions on the aerosol distribution, both in the chemistry and radiative packages.
Contact for questions: Rolando Garcia and Doug Kinnison)

* 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)

* Heating from volcanic aerosols: If you need help, please contact Doug Kinnison or Martin Dameris


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

Rayner, N. A.; Parker, D. E.; Horton, E. B.; Folland, C. K.; Alexander, L. V.; Rowell, D. P.; Kent, E. C.; Kaplan, A.  Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century J. Geophys. Res.Vol. 108, No. D14, 4407 10.1029/2002JD002670.

WMO, 2003: Scientific Assessment of Ozone Depletion: 2002. Global Ozone Research and Monitoring Project, Report No. 47, 498 pp, Geneva.
 



(C) Making predictions: Forcings for a transient model simulation from present day to 2100


C1. Greenhouse Gases 2001-2100 (CO2, CH4, N2O)
COMMENT: The chapter of the next IPCC assessment (AR4) that includes the greenhouse gases will use the scenarios B1 (low case), A1b (medium), and A2 (high)

Since the IPCC AR4 results will be aligned with these selected scenarios, we suggest to use the medium A1b scenario.
The file gives surface volume mixing ratios of CH4 (ppbv), N2O (ppbv) and CO2 (ppmv).
For the model simulation, please use scenario A1b (medium).

DOWNLOAD --->     IPCC GHG scenarios B1 (low case), A1b (medium), and A2 (high), dataset 1990 to 2100.   (59 kB)

C2.   Halogens  2001-2100

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

DOWNLOAD ---> Data set (1950 to 2050) based on WMO (2003), Table 4B-2. Halocarbon scenario used in the 2-D model calculations. This scenario is essentially the same
(except for a few small deviations) as the baseline scenario Ab described in Tables 1-13 and 1-16 of Chapter 1 of the WMO 2003 report.




C3.   Sea Surface Temperatures 1980 to 2100 for the "Making Prediction" simulation

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?



C4.   Solar Cycle 2001-2085

Not included in reference simulation REF 2.

DOWNLOAD ---> Data Set for transient model simulations (maver_2001-2085.dat) (Contact for questions: Christoph Brühl)

Recommendation: Use observed flux (column 3 in maver_2001-2080.dat), which is a continuation of observed 11-year cycle.


C5.   Assimilated Quasi-Biennial Oscillation (QBO)

Not included in reference simulation REF 2.
Soon on this web site

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 )



C6.   Volcanic Eruptions and aerosol loading

Volcanic eruptions are not included in reference simulation REF 2.

For aerosol loading, please use 1999 from the
WMO2002 SAD dataset put together by David Considine, specified under B6.


C7.   Other issues


C8.   References

WMO, 2003: Scientific Assessment of Ozone Depletion: 2002. Global Ozone Research and Monitoring Project, Report No. 47, 498 pp, Geneva.



Last modified:  April 17, 2005
by Veronika Eyring


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