the mit/ncar three-dimensional interactive aerosol-climate model
DESCRIPTION
An Interactive Aerosol-Climate Model based on CAM/CCSM: Progress and challenging issues Chien Wang and Dongchul Kim (MIT) Annica Ekman (U. Stockholm) Mary Barth and Phil Rasch (NCAR) Acknowledgments: NSF, NASA, Ford-MIT alliance, and MIT Global Change Joint Program. Concentrations of Aerosols. - PowerPoint PPT PresentationTRANSCRIPT
An Interactive Aerosol-Climate Model based on CAM/CCSM: Progress and challenging issues
Chien Wang and Dongchul Kim (MIT) Annica Ekman (U. Stockholm)Mary Barth and Phil Rasch (NCAR)
Acknowledgments: NSF, NASA, Ford-MIT alliance, and MIT Global Change Joint Program
The MIT/NCAR Three-Dimensional Interactive Aerosol-Climate Model
References: Kim et al., 2006; Wang 2004; Ekman et al., 2005, 2006; Wilson et al., 2001; Barth et al., 2000; Mayer et al., 2000; Wang et al., 1998; Kiehl et al., 1998; Boville and Gent, 1998
Atmospheric Aerosol ModelAtmospheric Aerosol Model
6 Aerosol modes6 Aerosol modesAdvection, convection, mixing,Advection, convection, mixing,
as well as wet and dry depositionas well as wet and dry deposition
AGCMAGCM
NCAR CCM3/CAM + CLM NCAR CCM3/CAM + CLM
Circulation and State of AtmosphereCirculation and State of AtmosphereClouds and PrecipitationClouds and Precipitation
RadiationRadiation
MIT EPPA + Emission ProcessorMIT EPPA + Emission ProcessorNCAR DMS emissionsNCAR DMS emissions
Concentrations Concentrations of Aerosolsof Aerosols
Winds, T, HWinds, T, H22O,O,
Precipitation Precipitation & Vertical Fluxes& Vertical Fluxes
EmissionsEmissions
OGCM or SSTOGCM or SST DataData
A-O ExchangesA-O Exchanges
SO4 ait
SO4 nuc
SO4 acc
H2SO4(g) OC pure BC
BC/SO4 mixed
coagulation
condensation
dry deposition
wet deposition
emission
nucleation
growth
A Size-Resolving Aerosol Model Prognostic variables: Q and N for each mode + Qbc in mixed mode
WANG 12.806 05S
Size distributions of various modes
(a) (b)
(d)(c)
a) Air-rich fresh methane soot b) Air-rich fresh propane sootc) Fuel-rich propane soot after
exposure to H2SO4 vapord) Kerosene soot after exposure
to H2SO4 vapor.
Modeling the Mixed Aerosol:The “black carbon core” model; diffusive growth and coagulation are allowed;
radiative properties are calculated based on particle size and BC/acid volume ratio (Toon and Ackerman, 1981; revised by W. Wiscombe)
(Courtesy by R. Zhang, Texas A&M; unpublished; 2006)
An Example for the BC-Core Model:
TEM images of various soot-containing
aerosols
Modeled vs. Observed Surface Sulfate ConcentrationSeasonal means; Const. emissions; observations are from EPA monitoring stations;
Model results = accumulation sulfate + sulfate in mixed mode
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
OBS
MODEL
Model vs. Observations: Vertical Sulfate Profile
Obs: ACE Asia, south Japan flights, late April; see Bahreini et al., 2003
Model: April-May mean; Kim et al., 2006
Model vs. Observations: Aerosol Optical Depth
(From selected AERONET stations; all are annual means)
Critical SSACalculated based on a
simple reflection model(Seinfeld and Pandis, 1998)
For: = 0.15; ocean = 0.06;20-yr mean surface albedo
TOA Forcing of Mixed Aerosols
Clear sky, no-feedback (W/m2)
Internal mixing scheme, size- and BC/acid volume
ratio dependent,BC core model
0.05
Atmospheric Forcing of Mixed Aerosols (W/m2)
Internal mixing scheme, size- and BC/acid volume
ratio dependent,BC core model
Atmospheric Forcing of Black Carbon (W/m2)
Mass based, external mixing scheme
BC mass = external BC + mixed mode BC
Challenges in connecting aerosol processes with global modelsRedistribution of Various Aerosols in CRM Simulations (Ekman et al., 2006)
Aitken Sulfate Accumulate Sulfate
BCBC3D: 3h
Nucleation scavenging of aerosols One of the major sinks of aerosols and the connecting point to the
indirect forcing Required information: supersaturation, aerosol size distribution Current assumption: assuming a given “typical supersaturation” to
calculate the minimum size of droplet activation
Recycling of aqueous S(VI) Determines a significant supply of sulfuric acids in the air for aerosol
nucleation and diffusive growth Required information: stored aqueous concentration of S(VI) and the
model (not net) evaporation measure of liquid particles Current assumption: assuming an arbitrary evaporation ratio of total
aqueous S(VI) based on CRM results
Conversion of cloud droplet to rain Critical process in simulating aerosol’s role in hydrological cycle Required information: precipitation efficiency in various clouds Current assumption: ?
Summary
Model is “functioning”; aerosol-forced integrations are undergoing Including size distribution and chemical composition in calculation
brings some interesting effects and would provide useful information for aerosol-rainfall and indirect forcing projects
Atmospheric forcing of BC/acid mixed mode aerosol is ~ 2x of that of BC estimated using external mixing scheme; Note their TOA forcings could differ significantly (SSA and surface albedo).
Interesting Issues
The role of aerosol in precipitation and more generally in hydrological cycle
How to use CRM and aerosol process models to derive parameterization of aerosol processes for the global models
Coupling with tropospheric chemistry model (oxidation; heterogeneous reactions, etc.)