Measurement-based Aerosol Radiative Effects within the Context of CCSP and IPCC

Hongbin Yu, Yoram KaufmanFebruary 10, 2006

Background Presently the IPCC assessments are largely model-based (the models are evaluated using satellite and surface measurements).

In recent years, a great deal of effort has gone into improving measurements and data sets:

It is feasible to shift the estimate of aerosol radiative effects from largely model-based to increasingly measurement-based.

MISR

CCSP• CCSP, an interagency program, was established

to coordinate and integrate scientific research on global change & climate change.

• CCSP is generating 21 synthesis & assessment products to (1) support policymaking & adaptive management; and (2) contribute to IPCC FAR.– Product 2.3: Aerosol Properties and Their Aerosol Properties and Their

Impacts on Climate Impacts on Climate (lead by NASA, Phil DeCola)(lead by NASA, Phil DeCola)

• In-situ measurements of aerosol properties and In-situ measurements of aerosol properties and direct forcing direct forcing (Bates et al.)(Bates et al.)

• Satellite measurements of aerosol direct Satellite measurements of aerosol direct effecteffect (Kaufman, Chin, Feingold)(Kaufman, Chin, Feingold)

• Aerosol indirect effects Aerosol indirect effects (Penner et al.)(Penner et al.)

Specific Goals• Assess the global aerosol distribution and Assess the global aerosol distribution and

direct radiative effect using satellites direct radiative effect using satellites supplemented by chemical transport supplemented by chemical transport models.models.

• Assess the anthropogenic component, using satellite data and models.

• Evaluate these assessments against surface network data and field experiments; and compare them to model estimates.“A review of measurement-based assessments of the aerosol direct effect and forcing”, accepted to Atmospheric Chemistry and Physics

Possible reasons for the discrepancies:

Optical depth (cloud contamination in satellites; low biases of models --- sources, humidification, …...)

Large discrepancies exist in Forcing Efficiency (forcing normalized by optical depth), which may result from model biases, such as high absorption, weak backscattering (large size), too bright surface.

11 observations (MODIS, CERES, MISR, POLDER, SeaWiFS, MO_MI_GO, ……)

5 models (GOCART, GISS, ……)

M/O=0.64 M/O=0.58

natural + anthrop.

Regional Assessments

Measurements Models

Remer & Kaufman, Atmos. Chem. Phys., 6, 237-253, 2006OCEAN, TOA

Over ocean, the anthropogenic contribution to MODIS AOD is about 21%. MODIS and models are consistent in anthropogenic AOD. (Kaufman et al., GRL, 2005)

Natural +

Anthropogenic

Anthropogenic

MODIS measured aerosol size parameters can be used to distinguish anthropogenic aerosols from natural aerosols

Kaufman Y. J., O. Boucher, D. Tanrˇ , M. Chin, L. A. Remer & T. Takemura, Aerosol anthropogenic component estimated from satellite data, Geoph. Res. Lett., VOL. 32, L178 04, doi:10.1029/2005 GL 023125, 2005

total

Anthrop.

Clear-sky DCF = x ff x faf x Ea

Using as many measurements as possible, we estimate the TOA forcing of -1.3 ± 0.8 W/m2 for cloud-free conditions (LAND + OCEAN).

9 models give -0.6 W/m2 (Michael Schulz)

Fine-mode fraction

Anthrop. fraction in fine- mode

Forcing efficiency

Estimating the DIRECT FORCING in the presence of clouds:

We need GLAS and Calipso!!!! And to know aerosol absorption better!!

Aerosol-Cloud Interactions as Inferred from MODIS Measurements

• Kaufman, Y. J., I. Koren, L. A. Remer, D. Rosenfeld, and Y. Rudich, 2005: The Effect of Smoke, Dust and Pollution Aerosol on Shallow Cloud Development Over the Atlantic Ocean, Proc. Nat. Acad. Sci.,102(32), pp.11207-11212.

• Koren, I., Y. J. Kaufman, D. Rosenfeld, L. A. Remer, and Y. Rudich, 2005: Aerosol Invigoration and Restructuring of Atlantic Convective Clouds. Geophys. Res. Lett., 32, LI4828, doi: 10.1029/2005GL023187. adding new observational evidence for aerosol impacts on clouds in IPCC FAR.

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Kaufman et al., 2005, Proc. Nat. Acad. Sci.

Total TOA Solar Forcing

= Cloud modifications (fraction, Nc, LWP)

+ Direct effect