AeroCom/Recommendations

AeroCom wiki discussion entry

See also AeroCom/Working group structure

Recommendations for AeroCom phase II

Version 1.0 - summarising discussions during the 5th AeroCom workshop in Virginia Beach, 17-19 October 2006

Michael Schulz / LSCE

Goals

• Evaluate and compare global aerosol models
• Compare aersol observations and models
• Improve the global aerosol models
• Derive useful products

Organisational

It is suggested to establish working groups for major problems associated to the modelling of the aerosol life cycle and aerosol properties. Each working group is asked to establish a work plan by December 2006, which indicates proposed diagnostics, experiments and analysis tasks.

The definition of the AeroCom working groups and their coordination is planned to be done via an interactive, transparent AeroCom wiki page.

The workshop recommends a coordinating committee to be formed from the lead persons of the working groups. (See list of working groups)

As overall coordinator are proposed Michael Schulz, Mian Chin and Stefan Kinne

The AeroCom initiative shall be further developed such, that it may contribute as the aerosol component to the « Atmospheric Chemistry and Climate » initiative of WCRP and IGAC.

A cooperation with the HTAP initiative on joint analysis of aerosol experiments performed under HTAP is pursued.

Subgoals

To improve the analysis of the aerosol anthropogenic forcing in effect for the 4th AR IPCC simualtion, it is suggested that AeroCom coordinates an a-posteriori analysis by asking model groups to calculate the radiative forcing for two years (present and preindustrial) of the total aerosol, long lived greenhouse gases and other short-lived anthropogenic species.

It is suggested to develop comparable diagnostics of aerosol effects in coupled aerosol-climate simulations. Among these is a proposition to keep track of the evolution of aerosol radiative forcing in 20th century.

Interested groups may coordinate work on efficient ways to integrate complex aerosol models in coupled climate simulations. Of interest would be to Investigate how complex an aerosol model needs to be to study aerosol climate feedbacks. The use of an aerosol climatology from AeroCom as input to climate models may be proposed.

Deviating from former IPCC scenarios an updated publicly available emission scenario for all aerosol species and precursors is needed for three time periods :

• preindustrial to present
• satellite observation period (1979-2005)
• preindustrial to the near future (2030 and 2100)

Unless other propositions become a priority it is suggested to use a median, a minimum and maximum scenario to explore uncertainty with respect to emissions. Sector related emissions are needed to differentiate anthropogenic emissions and reconstruction of different pathways.

A preliminary AeroCom version is required to be available for the year 2007 to be used to produce at an early stage an aerosol climatology of concentrations for realistic aerosol-climate runs.

AeroCom recognizes the important role of other initiatives ( such as GEIA, EMF, EDGAR, IPCC WG2) to establish emission scenarios and strongly proposes open cooperation among these to allow for independent testing of different scenarios by different transport modelling groups. The AeroCom emission working group is asked to elaborate practical suggestions for harmonized, widely available emission scenarios. Its role would be to express the interest of the AeroCom community in emissions, to recommend ways to implement emissions consistently in different models and to propose diagnostics to document microphysical properties of emitted primary aerosols.

The needs of AeroCom are best met by progress on the automatization of model documentation, the longterm maintenance of tha AeroCom database and the application of formatting standards as suggested under Air_Quality/Chemistry_Naming_Conventions in the framework of HTAP. AutoMod (developed for OCMIP) is expected to be a suitable tool for this automatization task. Furthermore data and diagnostics need to be integrated into benchmark tests to make full use of such an automated model analysis tool.

AeroCom acknowledges the specific need to prepare and discuss the use of satellite products for model evaluation. A working group could prepare ways on how to interface measurements and datasets with model input and how to get proper datasets prepared for use in models. The discrepancy between the basic modelled quantity of mass concentrations and the observation of optical properties from satellites is put to the attention of the working group. An explicit link is recommended with the ongoing GEWEX Global Aerosol Products Assessment.

The importance of the aerosol indirect effect requires a continuation of the existing working group and a redesign of the first set of indirect experilents. It is proposed to prepare a data inventory and to determine associated diagnostics. Of special value may be to attempt for CCN closure, to look for combined aircraft/field experiments, to extend to in situ datasets, to investigate droplet closure, observed drizzle rate, effective radius, cloud top temperature. Single column model experiments may be useful, when field data are available. It is suggested to coordinate with the DOE ARM MPACE SCM experiments. To harmonize the diagnostics of the first and second indirect effects, to separate the various indirect and semidirect effects it is recommended to include diagnostics as suggested in the literature by Hansen et al JGR 2005 and Kristjannson. Data to look at: AMSR, CERES, A train data subset from Langley ASDC, CALIPSO aerosol-cloud subset, ARM sites, CMDL sites.

Additional indirect effect intercomparison experiments require a revisit of the diagnostics.

It is recommended to put emphasis on regional and event specific analyses for specific aerosol components and collect airborne and other data sets (in situ, lidar, etc.) to address specific modeling issue. Although difficulties are expected when matching and comparing small data sets and models it is thought that it is now necessary to move beyond AERONET and satellite AOT comparisons. Basic aerosol properties need to be incorporated in the AeroCom analysis such as size distribution, absorption, vertical distribution, deposition, horizontal transport, the anthropogenic fraction, dust properties, the link between surface and column properties and hygroscopic growth of the aerosol.

Of special value are super sites where a co-location of surface measurements (e.g. IMPROVE, AERONET, MPLnet, GAW, EUSAAR etc ) exist, which allow to look also in extensive aerosol properties such as BC/SU ratios, forcing efficiency, mass and absorption coefficients, eventually under known or controlled humidity.

It is advocated to have a specific working group to address absorption.

To initiate the preparation of benchmark tests for the purpose of aerosol model evaluation it is proposed to establish a diagnostic table, following the example of the ccmVAL initiative. This tanle shall link important Processes, Diagnostics, Variables, Data and available references.

Joint Experiments

The recommendations for additional diagnostics and experiments shall be co-ordinated after the initial discussion in the working groups has concluded in December 2006. The goal would be to initiate a revised set of some few joint AeroCom experiments. The list below is an initial input for consideration of the different working groups.

• AeroCom D

(as AeroCom A but revised model versions and diagnostics for purpose of further analysis of problems found earlier in AeroCom)

• AeroCom-Calipso

An initial reanalysis of two early months of the Calipso mission could provide early on important insight into the capability of models to simulate the vertical profile of aerosols. Suggested: August and September 2006, including Texas campaign, AMMA, boreal fire periods.

• HTAP experiments SR1 and SR6 and SR7

Hemispheric transport of air pollution analysis of source receptor relationships Diagnostics PM and AOD (and gases), Reduction by 20% of anthropogenic Emissions in Asia, Europe and N-America, CO passive tracer experiment.

• AeroCom F

Fixed monthly 3d removal rates (and emissions) prescribed, to eliminate diversity due to differing removal process parameterisations

• Reanalysis of 4th AR IPCC experiments

Radiative forcing calculation for coupled model versions used for AR4. Rerun of a characteristic pre-industrial and present year with full RF diagnostics Coherent diagnostics with AeroCom database

• AeroCom Indirect II

Follow up of Penner et al. 2006 experiment suite. Re-designed diagnostics.

• Reanalysis of aerosol (and climate) evolution in 20th century

Compute all or segments of 20th century until 2005 with analysed meteorology or transient climate model

• Future median/high/low aerosol emission scenarios with aerosol-climate interactions

In preparation of the 5th AR IPCC;