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 Model 6 Aerosol modes Advection, convection, mixing, as well as wet and dry deposition AGCM NCAR CCM3/CAM + CLM Circulation and State of Atmosphere Clouds and Precipitation Radiation MIT EPPA + Emission Processor NCAR DMS emissions Concentrations of Aerosols Winds, T, H 2 O, Precipitation & Vertical Fluxes Emissions OGCM or SST Data A-O Exchanges

SO 4 ait SO 4 nuc SO 4 acc H 2 SO 4 (g)OCpure BC BC/SO 4 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 S Size distributions of various modes

a)Air-rich fresh methane soot b)Air-rich fresh propane soot c)Fuel-rich propane soot after exposure to H 2 SO 4 vapor d)Kerosene soot after exposure to H 2 SO 4 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size and BC/acid volume ratio (Toon and Ackerman, 1981; revised by W. Wiscombe) (Courtesy by R. Zhang, Texas A&M; unpublished; 2006) An Example for the BC-Core Model: TEM images of various soot-containing aerosols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 Concentration Seasonal means; Const. emissions; observations are from EPA monitoring stations; Model results = accumulation sulfate + sulfate in mixed mode

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 SSA Calculated 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/m 2 ) Internal mixing scheme, size- and BC/acid volume ratio dependent, BC core model 0.05

Atmospheric Forcing of Mixed Aerosols (W/m 2 ) Internal mixing scheme, size- and BC/acid volume ratio dependent, BC core model Atmospheric Forcing of Black Carbon (W/m 2 ) Mass based, external mixing scheme BC mass = external BC + mixed mode BC

Challenges in connecting aerosol processes with global models Redistribution of Various Aerosols in CRM Simulations (Ekman et al., 2006) Aitken Sulfate Accumulate Sulfate BC BC3D: 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.)