Second ICAP Workshop Aerosol Modeling using the GISS modelE Sophia Zhang, Dorothy Koch, Susanna Bauer, Reha Cakmur, Ron Miller, Jan Perlwitz Nadine Bell NASA/GISS, New York

GISS Aerosol Transport Model The new GISS model version “modelE” (Schmidt et al., submitted to J. Clim.). Improved radiative treatment, including relative- humidity dependence of optical properties for sulfate, sea salt, and OC. Implementation of dissolved species budget (DSB) with stratiform cloud (Koch et al., JGR 2003, Koch et al., in prep). Closer coupling between species and the BL. Resolution: 4 o lat x 5 o long, 20 vertical layers with 10 in the troposphere. The model top is 0.1 mb.

Emissions Emission (Tg/yr) References: Industrial SO IIASA, Dentener, in prep Biomass SO 2 2.3Sprio et al., 1992 Volcanic SO GEIA (Andres and Kasgnoc, 1998) scaled by 1.5 Halmer et al., 2002; Graf et al., 1997 DMS21.2Kettle et al., 1999; Nightingale et al., 2000 Biomass Burning BC+POM Cooke and Wilson, 1996 Fossil fuel and biofuel BC+POM Bond et al., 2004 Aircraft BC0.01Baughcum et al.,1993 Dust (4 bins)1500Cakmur et al, in prep Sea Salt (2 bins)1734.4Monahan et al., 1986

Comparison with observations Remote sitesEMEP IMPROVE Implementation of DSB results in lower loadings for soluble species, especially for sulfate due to reduced aqueous-phase-produced amount. Heterogeneous processes may correct the deficient sulfate amounts.

The direct radiative forcing for anthropogenic sulfate is reduced to only W/m 2 because of a lower anthropogenic sulfate loading in this model. Direct Radiative Forcing

Ocean The Tropospheric Sulfur Cycle

SO 2 is irreversibly absorbed on the dust surface and then oxidized by ozone and forms stable sulfate on the dust surface. HET assumes 1.e -4 uptaking rate for SO 2 on dust. Heterogeneous Reaction on Dust SO4 concentrations CTR (  g/m 3 ) HET (  g/m 3 ) HET- CTR (  g/m 3 ) Sulfate surface concentrations

Comparison with observations. - CONTROL - HETERO. CHEM - CONTROL

Impact on Dust Heterogeneous reaction can change the dust loading and lifetime. In addition, sulfate, when coated on dust, can change the optical properties of dust. CTR (mg/m 2 ) HET-CTR (mg/m 2 )

BC Emissions by regions Region*Tg yr −1 % burden(Tg) % Globe Biomass S of 40 o N Biomass N of 40 o N Far East Europe North America Russia Aircraft Rest of World * Region names are not exactly correspond to their geographic labels.

Contributions to BC optical depth based on regional source experiments.

Climate effects of BC BC absorbs solar radiation and is thought to warm the climate through aerosol direct effect, and other enhancing mechanisms (semi-direct effect and snow albedo effect). The climate effect of BC is highly uncertain due the uncertainties in aerosol loading, vertical distribution, and how cloud changes due to BC.

Results of BC in each model Layer Layer Fa (w/m 2 ) Efficacy Change of Cloud Cover (%) lowmidhigh The efficacy is 0.82 for BCI and 0.60 for BCB.

Change of Low Cloud Cover When BC is put in the layer 1, the reduction of low cloud cover over land is smaller than that over ocean on average. When BC is put in the layer 4, the reduction of low cloud cover occurs mostly overland and the coastal region near source, while most of the increase of low cloud cover occurs over ocean. BC in Layer 4 (847mb)BC in Layer 1(959mb)

Correlation of anomalies of ISCCP low cloud amount and TOMS AI ( ). The TOMS AI points used for calculating anomalies are those with reflectivity ≤ 15%. The correlation for low cloud amount is slightly positive for dust and biomass burning region. Relationship between the modeled ISCCP low cloud amount and AI needs to be studied. TOMS AI vs. Low Cloud Amount TOMS AI vs. Total Cloud Amount

Optimizing Dust Emissions An optimal global value of dust emission and the aerosol load are calculated by minimizing the difference between the model and multiple observational data sets. (Cakmur et al., in prep) No single data set is sufficient to constrain the emission. The optimal value represents the influence of all data sets. The optimal dust emission ranges from 1150 to 2850 Tg/yr using different a priori sources. The result is sensitive to the a priori source, datasets, and location used

Other on-going aerosol projects at GISS Fully interactive tropospheric gas-phase coupling between sulfur and chemistry has been implemented in the GISS modelE (Bell et al., submitted to JGR). On annual and global scales, the differences of sulfate burden between the coupled and off-line simulations are small but larger deviations do occur on regional and seasonal scales. The chemistry-aerosol coupling leads increases in surface sulfate over source regions in the NH summer, with compensating decreases downwind and in the upper troposphere due to depleted SO 2.