Bibliography - Paul Ginoux

1. Ganguly, D, Paul Ginoux, and V Ramaswamy, et al., in press: Retrieving the composition and concentration of aerosols over the Indo-Gangetic basin using CALIOP and AERONET data. Geophysical Research Letters. 3/09.
2. Ginoux, Paul, D Garbuzov, and N C Hsu, in press: Anthropogenic and natural attribution of dust sources using MODIS Deep Blue Level 2 data. Journal of Geophysical Research. 5/09.
   [ Abstract ]

   Mineral dust interacts with radiation, and it impacts on regional to global climate. But the natural or anthropogenic attribution of dust sources is largely uncertain. Although human activities disturb soils and subsequently enhance wind erosion, their contribution to global dust emission has never been directly evaluated by lack of data. The retrieval of aerosol properties over land, including deserts, from MODIS Deep Blue algorithm allows for the first time to attribute directly anthropogenic or natural origin to dust sources, and quantify their relative importance. To separate freshly emitted dust from other aerosol types and aged dust particles, the spectral dependence of the single scattering albedo and the Angstrom wavelength exponent are used. Furthermore, to obtain adequate spatial resolution, the geolocated level 2 data are interpolated on a 0.1º resolution grid. Four years of data are processed in the eastern part of West Africa, which includes one of the most active natural dust source and the highest population density in Africa. The sources are identified from the persistence of significant aerosol optical depth of freshly emitted dust. The natural or anthropogenic attribution of dust sources is established from land use dataset. Our results indicate that, in that region, anthropogenic dust, essentially by roaming cattle herds, is less frequent with lower optical depth than dust from natural sources, but they cover nearly 50% of dusty area at least 20% of the time. Although they appear weaker than natural sources, their contribution in that region is not negligible. Furthermore, they occupy the tropical region between the Gulf of Guinea and the southern limit of the dust belt (15º N) used by models, which may have significant effect on long range transport, in particular to the Amazon basin in boreal winter.

3. Li, F, Paul Ginoux, and V Ramaswamy, in press: Transport of South American dust to East Antarctica. Journal of Geophysical Research. 5/09.
   [ Abstract ]

   The transport of South American dust to East Antarctica is investigated by using the Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model in combination with satellite products. The mechanisms of dust transport to Antarctica are studied by analyzing the transport pathways and their relationship to main meteorological factors. The study shows that the transport to Antarctica is an intermittent process, occurring mainly through two pathways. A south-eastern corridor across southern Atlantic Ocean is the principal transport pathway. The dust transport is determined by the positions of the anomalous dipole of low and high sea level pressure systems over the southern Atlantic Ocean and the Antarctic Peninsula. South American dust goes through the south-eastern pathway when the dipole is located east of the Antarctic Peninsula, while a southward transport occurs when the two pressure anomaly systems are located on different side of the peninsula. Demonstrating these by following the journeys of specific dust plumes from the South American sources to East Antarctica, this study clarifies how climatic factors affect the amount of dust deposited in Antarctic ice cores.

4. Dubovik, O, Y Lapyonok, Y J Kaufman, M Chin, Paul Ginoux, R A Kahn, and A Sinyuk, 2008: Retrieving global aerosol sources from satellites using inverse modeling. Atmospheric Chemistry and Physics, 8(2), 209-250.
   [ Abstract PDF ]

   Understanding aerosol effects on global climate requires knowing the global distribution of tropospheric aerosols. By accounting for aerosol sources, transports, and removal processes, chemical transport models simulate the global aerosol distribution using archived meteorological fields. We develop an algorithm for retrieving global aerosol sources from satellite observations of aerosol distribution by inverting the GOCART aerosol transport model. The inversion is based on a generalized, multi-term least-squares-type fitting, allowing flexible selection and refinement of a priori algorithm constraints. For example, limitations can be placed on retrieved quantity partial derivatives, to constrain global aerosol emission space and time variability in the results. Similarities and differences between commonly used inverse modeling and remote sensing techniques are analyzed. To retain the high space and time resolution of long-period, global observational records, the algorithm is expressed using adjoint operators. Successful global aerosol emission retrievals at 2°×2.5 resolution were obtained by inverting GOCART aerosol transport model output, assuming constant emissions over the diurnal cycle, and neglecting aerosol compositional differences. In addition, fine and coarse mode aerosol emission sources were inverted separately from MODIS fine and coarse mode aerosol optical thickness data, respectively. These assumptions are justified, based on observational coverage and accuracy limitations, producing valuable aerosol source locations and emission strengths. From two weeks of daily MODIS observations during August 2000, the global placement of fine mode aerosol sources agreed with available independent knowledge, even though the inverse method did not use any a priori information about aerosol sources, and was initialized with a "zero aerosol emission" assumption. Retrieving coarse mode aerosol emissions was less successful, mainly because MODIS aerosol data over highly reflecting desert dust sources is lacking.

5. Ganguly, D, Paul Ginoux, and V Ramaswamy, et al., in press: Inferring the composition and concentration of aerosols by combining AERONET and MPLNET data: comparison with measurements and GCM output. Journal of Geophysical Research. 9/08.
6. Li, F, Paul Ginoux, and V Ramaswamy, May 2008: Distribution, transport, and deposition of mineral dust in the Southern Ocean and Antarctica: Contribution of major sources. Journal of Geophysical Research, 113, D10207, doi:10.1029/2007JD009190.
   [ Abstract ]

   A model-based investigation of the transport, distribution and deposition of mineral dust in the Southern Hemisphere (SH) is performed by using the GFDL Atmospheric Model (AM2). The study represents an attempt to quantify the contribution of the major sources by tagging dust based on its origin. We evaluate the contribution of each source to the emission, distribution, mass burden and deposition of dust in the Southern Ocean and Antarctica, and show that each source produces distinctive meridional transport, vertical distribution, and deposition patterns. The dust in SH originates primarily from Australia (120 Tg a⁻¹), Patagonia (38 Tg a⁻¹) and the inter-hemispheric transport from Northern Hemisphere (31 Tg a⁻¹). A small fraction of it (7 Tg a⁻¹) is transported and deposited in the Southern Ocean and Antarctica, where dust from South America, Australia, and Northern Hemisphere are essentially located in the boundary layer, mid-troposphere, and upper-troposphere, respectively. These three sources contribute to nearly all the dust burden in the Southern Ocean and Antarctica. South America and Australia are the main sources of the dust deposition, but they differ zonally, with each one dominating half of a hemisphere along 120°E–60°W: the half comprising the Atlantic and Indian oceans in the case of the South American dust and the Pacific half in the case of the Australian dust. Our study also indicates a potentially important role of Northern Hemisphere dust, as it appears to be a significant part of the dust burden but contributing little to the dust deposition in Antarctica.

7. Magi, B I., Paul Ginoux, Yi Ming, and V Ramaswamy, in press: Evaluation of tropical and extratropical Southern Hemisphere African aerosol properties simulated by a climate model. Journal of Geophysical Research. 9/08.
   [ Abstract ]

   We compare aerosol optical depth (AOD) and single scattering albedo (SSA) simulated by updated configurations of a version of the atmospheric model (AM2) component of the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) general circulation model (GCM) over Southern Hemisphere Africa with AOD and SSA derived from research aircraft measurements and NASA Aerosol Robotic Network (AERONET) stations, and with regional AOD from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) satellite. The results of the comparisons suggest that AM2 simulates AOD seasonality reasonably well, but that compared to available observations, AM2 AOD is biased low by 30-40% in the tropics and 0-20% in the extratropics, while AM2 SSA is biased high by 3-8%. The AM2 SSA bias is higher during the biomass burning season, and the monthly variations in AM2 SSA are poorly correlated with AERONET. There are no significant improvements in the comparisons when an internally-mixed aerosol is used. Based on a comparison of aerosol mass in the models with available measurements from southern Africa, we suggest that the low bias in AOD and high bias in SSA are related to an underestimate of carbon aerosol mass in the inventories used by AM2. We estimate that the AM2 biases in AOD and SSA imply that top of the atmosphere radiative forcing over southern Africa is overestimated by ~8%, while surface radiative forcing is underestimated by ~20% throughout the year.

8. Ming, Yi, Paul Ginoux, Leo J Donner, Stuart Freidenreich, Larry Horowitz, Ming Zhao, J-C Golaz, and Shian-Jiann Lin, in press: Transport of European Air Pollution influences Arctic climate. Science. 8/08.
   [ Abstract ]

   Arctic climate is changing at a pace faster than the global average in the recent decades (1, 2). Arctic haze (3) - an accumulation of long-range transported aerosols - enhances longwave emissivity of liquid water clouds both by reducing droplet size (4–6) and by increasing liquid condensate, thus exerting substantial surface warming in winter. The formation of Arctic haze and its influence on local climate are poorly understood, and constitutes an important missing piece of the Arctic climate puzzle. Here we find, with the help of a state-of-the-art global climate model with explicit treatment of pollutant transport and aerosol-cloud interactions, that the poleward transport of European air pollution is controlled strongly by the fluctuation in the second climate mode of the North Atlantic - European region. Though accounting for a smaller fraction of the region’s overall climate variability than the first mode (namely the North Atlantic Oscillation), the second mode has its impacts on Arctic climate amplified through modulating the amount of aerosols reaching the Arctic. This is supported by the fact that the surface aerosol concentrations and longwave downward radiative flux measured at locations lying in the model-projected transport pathway show strong correlation with the second mode. A shift of the mode from negative to positive phases doubles the abundance of Arctic haze, and the resulting increase in cloud liquid condensate alone is estimated to warm the surface by 1.8 K or to reduce the wintertime sea ice by 0.16 m. This finding is essential for understanding Arctic climate variability and change.

9. Chin, M, T Diehl, Paul Ginoux, and W Malm, 2007: Intercontinental transport of pollution and dust aerosols: implications for regional air quality. Atmospheric Chemistry and Physics, 7(21), 5501-5517.
   [ Abstract PDF ]

   We use the global model GOCART to examine the impact of pollution and dust aerosols emitted from their major sources on surface fine particulate matter concentrations at regional and hemispheric scales. Focusing on the North America region in 2001, we use measurements from the IMPROVE network in the United States to evaluate the model-simulated surface concentrations of the "reconstructed fine mass" (RCFM) and its components of ammonium sulfate, black carbon (BC), organic matter (OM), and fine mode dust. We then quantify the RCFM budget in terms of the RCFM chemical composition, source type, and region of origin to find that in the eastern U.S., ammonium sulfate is the dominant RCFM component (~60%) whereas in the western U.S., dust and OM are just as important as sulfate but have considerable seasonal variations, especially in the NW. On an annual average, pollution aerosol (defined as aerosols from fuel combustion for industrial and transportation uses) from North America accounts for 65–70% of the surface RCFM in the eastern U.S. and for a lower proportion of 30–40% in the western U.S.; by contrast, pollution from outside of North America contributes to just 2–6% (~0.2 μg m−3) of the total RCFM over the U.S. In comparison, long-range transport of dust brings 3 to 4 times more fine particles than the transport of pollution to the U.S. (0.5–0.8 μg m−3 on an annual average) with a maximum influence in spring and over the NW. Of the major pollution regions, Europe has the largest potential to affect the surface aerosol concentrations in other continents due to its shorter distance from receptor continents and its larger fraction of sulfate-producing precursor gas in the outflow. With the IPCC emission scenario for the year 2000, we find that European emissions increase levels of ammonium sulfate by 1–5 μg m−3 over the surface of northern Africa and western Asia, and its contribution to eastern Asia (≥0.2 μg m−3) is twice as much as the Asian contribution to North America. Asia and North America pollution emissions exert strong impacts on their neighboring oceans, but their influences over other continents are relatively small (≤10%) due to long traveling distances across the oceans and efficient removal during transport. Among the major dust source regions, Asia displays a significant influence over large areas in the northern hemisphere except over the North Atlantic and the tropics, where African dust dominates. We also notice that the African dust and European pollution can travel eastward through a pathway spanning across Asia and North Pacific to western North America; such a pathway is difficult to detect because these aerosols usually merge and travel together with Asian dust and pollution labeled as "Asian outflow".

10. Ming, Yi, V Ramaswamy, Leo J Donner, V T J Phillips, Stephen A Klein, Paul Ginoux, and Larry Horowitz, February 2007: Modeling the interactions between aerosols and liquid water clouds with a self-consistent cloud scheme in a general circulation model. Journal of the Atmospheric Sciences, 64(4), doi:10.1175/JAS3874.1.
    [ Abstract ]

    To model aerosol-cloud interactions in general circulation models (GCMs), a prognostic cloud scheme of cloud liquid water and amount is expanded to include droplet number concentration (N_d) in a way that allows them to be calculated using the same large-scale and convective updraft velocity field. In the scheme, the evolution of droplets fully interacts with the model meteorology. An explicit treatment of cloud condensation nuclei (CCN) activation enables the scheme to take into account the contributions to N_d of multiple aerosol species (i.e., sulfate, organic, and sea-salt aerosols) and to consider kinetic limitations of the activation process. An implementation of the prognostic scheme in the Geophysical Fluid Dynamics Laboratory (GFDL) AM2 GCM yields a vertical distribution of N_d with a characteristic maximum in the lower troposphere; this feature differs from the profile that would be obtained if N_dis diagnosed from the sulfate mass concentration based on an often-used empirical relationship. Prognosticated N_d exhibits large variations with respect to the sulfate mass concentration. The mean values are generally consistent with the empirical relationship over ocean, but show negative biases over the Northern Hemisphere midlatitude land, perhaps owing to the neglect of subgrid variations of large-scale ascents and inadequate convective sources. The prognostic scheme leads to a substantial improvement in the agreement of model-predicted present-day liquid water path (LWP) and cloud forcing with satellite measurements compared to using the empirical relationship. The simulations with preindustrial and present-day aerosols show that the combined first and second indirect effects of anthropogenic sulfate and organic aerosols give rise to a steady-state global annual mean flux change of -1.8 W m^-2, consisting of -2.0 W m^-2 in shortwave and 0.2 W m^-2 in longwave. The ratios of the flux changes in the Northern Hemisphere (NH) to that in Southern Hemisphere (SH) and of the flux changes over ocean to that over land are 2.9 and 0.73, respectively. These estimates are consistent with the averages of values from previous studies stated in a recent review. The model response to higher Nd alters the cloud field; LWP and total cloud amount increase by 19% and 0.6%, respectively. Largely owing to high sulfate concentrations from fossil fuel burning, the NH midlatitude land and oceans experience strong radiative cooling. So does the tropical land, which is dominated by biomass burning-derived organic aerosol. The computed annual, zonal-mean flux changes are determined to be statistically significant, exceeding the model's natural variations in the NH low and midlatitudes and in the SH low latitudes. This study reaffirms the major role of sulfate in providing CCN for cloud formation.

11. Rotstayn, L D., W Cai, M R Dix, G D Farquhar, Y Feng, Paul Ginoux, M Herzog, A Ito, J Penner, M L Roderick, and M Wang, 2007: Have Australian rainfall and cloudiness increased due to the remote effects of Asian anthropogenic aerosols? Journal of Geophysical Research, 112(D09202), doi:10.1029/2006JD007712.
    [ Abstract ]

    There is ample evidence that anthropogenic aerosols have important effects on climate in the Northern Hemisphere but little such evidence in the Southern Hemisphere. Observations of Australian rainfall and cloudiness since 1950 show increases over much of the continent. We show that including anthropogenic aerosol changes in 20th century simulations of a global climate model gives increasing rainfall and cloudiness over Australia during 1951–1996, whereas omitting this forcing gives decreasing rainfall and cloudiness. The pattern of increasing rainfall when aerosols are included is strongest over northwestern Australia, in agreement with the observed trends. The strong impact of aerosols is primarily due to the massive Asian aerosol haze, as confirmed by a sensitivity test in which only Asian anthropogenic aerosols are included. The Asian haze alters the meridional temperature and pressure gradients over the tropical Indian Ocean, thereby increasing the tendency of monsoonal winds to flow toward Australia. Anthropogenic aerosols also make the simulated pattern of surface-temperature change in the tropical Pacific more like La Niña, since they induce a cooling of the surface waters in the extratropical North Pacific, which are then transported to the tropical eastern Pacific via the deep ocean. Transient climate model simulations forced only by increased greenhouse gases have generally not reproduced the observed rainfall increase over northwestern and central Australia. Our results suggest that a possible reason for this failure was the omission of forcing by Asian aerosols. Further research is essential to more accurately quantify the role of Asian aerosols in forcing Australian climate change.

12. Textor, C, M Schulz, S Guibert, S Kinne, Y Balkanski, S E Bauer, T Berntsen, T F Berglen, O Boucher, M Chin, F Dentener, T Diehl, J Feichter, D W Fillmore, and Paul Ginoux, et al., 2007: The effect of harmonized emissions on aerosol properties in global models – an AeroCom experiment. Atmospheric Chemistry and Physics, 7, 4489-4501.
    [ Abstract PDF ]

    The effects of unified aerosol sources on global aerosol fields simulated by different models are examined in this paper. We compare results from two AeroCom experiments, one with different (ExpA) and one with unified emissions, injection heights, and particle sizes at the source (ExpB). Surprisingly, harmonization of aerosol sources has only a small impact on the simulated inter-model diversity of the global aerosol burden, and consequently global optical properties, as the results are largely controlled by model-specific transport, removal, chemistry (leading to the formation of secondary aerosols) and parameterizations of aerosol microphysics (e.g., the split between deposition pathways) and to a lesser extent by the spatial and temporal distributions of the (precursor) emissions. The burdens of black carbon and especially sea salt become more coherent in ExpB only, because the large ExpA diversities for these two species were caused by a few outliers. The experiment also showed that despite prescribing emission fluxes and size distributions, ambiguities in the implementation in individual models can lead to substantial differences. These results indicate the need for a better understanding of aerosol life cycles at process level (including spatial dispersal and interaction with meteorological parameters) in order to obtain more reliable results from global aerosol simulations. This is particularly important as such model results are used to assess the consequences of specific air pollution abatement strategies.

13. Weaver, C, A Da Silva, M Chin, Paul Ginoux, O Dubovik, D Flittner, A Zia, L Remer, B Holben, and W Gregg, 2007: Direct insertion of MODIS radiances in a Global Aerosol Transport Model. Journal of the Atmospheric Sciences, 64(3), doi:10.1175/JAS3838.1.
    [ Abstract ]

    In this paper results are presented from a simple offline assimilation system that uses radiances from the Moderate Resolution Imaging Spectroradiometer (MODIS) channels that sense atmospheric aerosols over land and ocean. The MODIS information is directly inserted into the Goddard Chemistry and Aerosol Radiation Transport model (GOCART), which simulates the following five aerosol types: dust, sea salt, black carbon, organic carbon, and sulfate. The goal is to produce three-dimensional fields of these aerosol types for radiative forcing calculations. Products from this assimilation system are compared with ground-based measurements of aerosol optical depth (AOD) from the Aerosol Robotic Network (AERONET). Insertion of MODIS radiances draws the GOCART model closer to the AERONET AOD. However, there are still uncertainties with surface reflectivity over moderately bright surfaces and with the amount of absorbing aerosol. Also described is the assimilation cycle. The forward model takes the aerosol information from the GOCART model and calculates radiances based on optical parameters of the aerosol type, satellite viewing angle, and the particle growth from relative humidity. Because the GOCART model is driven by previously assimilated meteorology, these forward model radiances can be directly compared with the observed MODIS level-2 radiances. The offline assimilation system simply adjusts the aerosol loading in the GOCART model so that the observed minus forward model radiances agree. Minimal change is made to the GOCART aerosol vertical distribution, size distribution, and the ratio of the five different aerosol types. The loading in the GOCART model is updated with new MODIS observations every 6 h. Since the previously assimilated meteorology provides surface wind speed, radiance sensitivity to wind speed over rough ocean is taken into account. Over land the dark target approach, also used by the MODIS–atmosphere group retrieval, is used. If the underlying land surface is deemed dark enough, the surface reflectances at the 0.47- and 0.66-µm wavelengths are constant multiples of the observed 2.13-µm reflectance. Over ocean the assimilation AOD compares well with AERONET, over land less so. The results herein are also compared with AERONET-retrieved single-scattering albedo. This research is part of an ongoing effort at NASA Goddard to integrate aerosols into the Goddard Modeling and Assimilation Office (GMAO) products.

14. Cakmur, R V., R L Miller, J Perlwitz, I V Geogdzhayev, Paul Ginoux, D Koch, K E Kohfeld, I Tegen, and C S Zender, March 2006: Constraining the magnitude of the global dust cycle by minimizing the difference between a model and observations. Journal of Geophysical Research, 111, D06207, doi:10.1029/2005JD005791.
    [ Abstract ]

    Current estimates of global dust emission vary by over a factor of two. Here, we use multiple data types and a worldwide array of stations combined with a dust model to constrain the magnitude of the global dust cycle for particles with radii between 0.1 and 8 ìm. An optimal value of global emission is calculated by minimizing the difference between the model dust distribution and observations. The optimal global emission is most sensitive to the prescription of the dust source region. Depending upon the assumed source, the agreement with observations is greatest for global, annual emission ranging from 1500 to 2600 Tg. However, global annual emission between 1000 and 3000 Tg remains in agreement with the observations, given small changes in the method of optimization. Both ranges include values that are substantially larger than calculated by current dust models. In contrast, the optimal fraction of clay particles (whose radii are less than 1 ìm) is lower than current model estimates. The optimal solution identified by a combination of data sets is different from that identified by any single data set and is more robust. Uncertainty is introduced into the optimal emission by model biases and the uncertain contribution of other aerosol species to the observations.

15. Delworth, Thomas L., Anthony J Broccoli, Anthony Rosati, Ronald J Stouffer, Ventakramani Balaji, J A Beesley, W F Cooke, Keith W Dixon, John Dunne, Krista A Dunne, J W Durachta, Kirsten L Findell, Paul Ginoux, Anand Gnanadesikan, C Tony Gordon, Stephen Griffies, Rich Gudgel, Matthew J Harrison, Isaac Held, Richard S Hemler, Larry Horowitz, Stephen A Klein, Thomas R Knutson, P J Kushner, A R Langenhorst, H C Lee, Shian-Jiann Lin, Jian Lu, S Malyshev, P C D Milly, V Ramaswamy, J L Russell, M Daniel Schwarzkopf, Elena Shevliakova, Joseph J Sirutis, Michael J Spelman, William F Stern, Michael Winton, Andrew T Wittenberg, Bruce Wyman, Fanrong Zeng, and Rong Zhang, 2006: GFDL's CM2 Global Coupled Climate Models. Part I: Formulation and Simulation Characteristics. Journal of Climate, 19(5), doi:10.1175/JCLI3629.1.
    [ Abstract ]

    The formulation and simulation characteristics of two new global coupled climate models developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL) are described. The models were designed to simulate atmospheric and oceanic climate and variability from the diurnal time scale through multicentury climate change, given our computational constraints. In particular, an important goal was to use the same model for both experimental seasonal to interannual forecasting and the study of multicentury global climate change, and this goal has been achieved. Two versions of the coupled model are described, called CM2.0 and CM2.1. The versions differ primarily in the dynamical core used in the atmospheric component, along with the cloud tuning and some details of the land and ocean components. For both coupled models, the resolution of the land and atmospheric components is 2° latitude × 2.5° longitude; the atmospheric model has 24 vertical levels. The ocean resolution is 1° in latitude and longitude, with meridional resolution equatorward of 30° becoming progressively finer, such that the meridional resolution is 1/3° at the equator. There are 50 vertical levels in the ocean, with 22 evenly spaced levels within the top 220 m. The ocean component has poles over North America and Eurasia to avoid polar filtering. Neither coupled model employs flux adjustments. The control simulations have stable, realistic climates when integrated over multiple centuries. Both models have simulations of ENSO that are substantially improved relative to previous GFDL coupled models. The CM2.0 model has been further evaluated as an ENSO forecast model and has good skill (CM2.1 has not been evaluated as an ENSO forecast model). Generally reduced temperature and salinity biases exist in CM2.1 relative to CM2.0. These reductions are associated with 1) improved simulations of surface wind stress in CM2.1 and associated changes in oceanic gyre circulations; 2) changes in cloud tuning and the land model, both of which act to increase the net surface shortwave radiation in CM2.1, thereby reducing an overall cold bias present in CM2.0; and 3) a reduction of ocean lateral viscosity in the extratropics in CM2.1, which reduces sea ice biases in the North Atlantic. Both models have been used to conduct a suite of climate change simulations for the 2007 Intergovernmental Panel on Climate Change (IPCC) assessment report and are able to simulate the main features of the observed warming of the twentieth century. The climate sensitivities of the CM2.0 and CM2.1 models are 2.9 and 3.4 K, respectively. These sensitivities are defined by coupling the atmospheric components of CM2.0 and CM2.1 to a slab ocean model and allowing the model to come into equilibrium with a doubling of atmospheric CO2. The output from a suite of integrations conducted with these models is freely available online (see http://nomads.gfdl.noaa.gov/). Manuscript received 8 December 2004, in final form 18 March 2005

16. Dentener, F, S Kinne, T Bond, O Boucher, J Cofala, S Generoso, Paul Ginoux, S Gong, J J Hoelzemann, A Ito, L Marelli, J Penner, J-P Putaud, C Textor, M Schulz, G R van der Werf, and R John Wilson, 2006: Emissions of primary aerosol and precursor gases in the years 2000 and 1750, prescribed data-sets for AeroCom. Atmospheric Chemistry and Physics, 6, 4321-4344.
    [ Abstract PDF ]

    Inventories for global aerosol and aerosol precursor emissions, and auxiliary information, have been collected, assessed and prepared for the year 2000 (present-day conditions) and for the year 1750 (pre-industrial conditions). These global datasets establish a reference for input in global modeling, when simulating the aerosol impact on climate with state-of-the-art aerosol component modules. These modules stratify aerosol by type, distinguishing among dust, seasalt, sulfate, organic matter and soot. The datasets are also intented to serve as systematic constraints in sensitivity studies of the AeroCom initiative, which aims to evaluate uncertainties in aerosol global modeling. The datasets comprise daily size-resolved emissions of sea-salt and dust and monthly-to-yearly emissions for all other currently known emissions of natural and anthropogenic aerosol (precursors). The emissions are a reference dataset for aerosol modeling in the coming years and benchmark the emissions according to our knowledge in the year 2004.

17. Ginoux, Paul, Larry Horowitz, V Ramaswamy, I V Geogdzhayev, B Holben, G Stenchikov, and X Tie, 2006: Evaluation of aerosol distribution and optical depth in the Geophysical Fluid Dynamics Laboratory coupled model CM2.1 for present climate. Journal of Geophysical Research, 111, D22210, doi:10.1029/2005JD006707.
    [ Abstract ]

    This study evaluates the strengths and weaknesses of aerosol distributions and optical depths that are used to force the GFDL coupled climate model CM2.1. The concentrations of sulfate, organic carbon, black carbon, and dust are simulated using the MOZART model (Horowitz, 2006), while sea-salt concentrations are obtained from a previous study by Haywood et al. (1999). These aerosol distributions and precalculated relative-humidity-dependent specific extinction are utilized in the CM2.1 radiative scheme to calculate the aerosol optical depth. Our evaluation of the mean values (1996–2000) of simulated aerosols is based on comparisons with long-term mean climatological data from ground-based and remote sensing observations as well as previous modeling studies. Overall, the predicted concentrations of aerosol are within a factor 2 of the observed values and have a tendency to be overestimated. Comparison with satellite data shows an agreement within 10% of global mean optical depth. This agreement masks regional differences of opposite signs in the optical depth. Essentially, the excessive optical depth from sulfate aerosols compensates for the underestimated contribution from organic and sea-salt aerosols. The largest discrepancies are over the northeastern United States (predicted optical depths are too high) and over biomass burning regions and southern oceans (predicted optical depths are too low). This analysis indicates that the aerosol properties are very sensitive to humidity, and major improvements could be achieved by properly taking into account their hygroscopic growth together with corresponding modifications of their optical properties.

18. Kinne, S, M Schulz, C Textor, S Guibert, Y Balkanski, S E Bauer, Paul Ginoux, M Herzog, and Larry Horowitz, et al., 2006: An AeroCom initial assessment – optical properties in aerosol component modules of global models. Atmospheric Chemistry and Physics, 6, 1815-1834.
    [ Abstract PDF ]

    The AeroCom exercise diagnoses multi-component aerosol modules in global modeling. In an initial assessment simulated global distributions for mass and mid-visible aerosol optical thickness (aot) were compared among 20 different modules. Model diversity was also explored in the context of previous comparisons. For the component combined aot general agreement has improved for the annual global mean. At 0.11 to 0.14, simulated aot values are at the lower end of global averages suggested by remote sensing from ground (AERONET ca. 0.135) and space (satellite composite ca. 0.15). More detailed comparisons, however, reveal that larger differences in regional distribution and significant differences in compositional mixture remain. Of particular concern are large model diversities for contributions by dust and carbonaceous aerosol, because they lead to significant uncertainty in aerosol absorption (aab). Since aot and aab, both, influence the aerosol impact on the radiative energy-balance, the aerosol (direct) forcing uncertainty in modeling is larger than differences in aot might suggest. New diagnostic approaches are proposed to trace model differences in terms of aerosol processing and transport: These include the prescription of common input (e.g. amount, size and injection of aerosol component emissions) and the use of observational capabilities from ground (e.g. measurements networks) or space (e.g. correlations between aerosol and clouds).

19. Miller, R L., R V Cakmur, J Perlwitz, I V Geogdzhayev, Paul Ginoux, D Koch, K E Kohfeld, C Prigent, R Ruedy, G A Schmidt, and I Tegen, 2006: Mineral dust aerosols in the NASA Goddard Institute for Space Sciences ModelE atmospheric general circulation model. Journal of Geophysical Research, 111, D06208, doi:10.1029/2005JD005796.
    [ Abstract ]

    We describe an updated model of the dust aerosol cycle embedded within the NASA Goddard Institute for Space Studies ‘ModelE’ atmospheric general circulation model (AGCM). The model dust distribution is compared to observations ranging from aerosol optical thickness and surface concentration to deposition and size distribution. The agreement with observations is improved compared to previous distributions computed by either an older version of the GISS AGCM or an offline tracer transport model. The largest improvement is in dust transport over the Atlantic due to increased emission over the Sahara. This increase comes from subgrid wind fluctuations associated with dry convective eddies driven by intense summertime heating. Representation of ‘preferred sources’ of soil dust particles is also fundamental to the improvement. The observations suggest that deposition is too efficient in the model, partly due to AGCM rainfall errors.

20. Textor, C, M Schulz, S Guibert, S Kinne, Y Balkanski, S E Bauer, T F Berglen, Paul Ginoux, and Larry Horowitz, et al., 2006: Analysis and quantification of the diversities of aerosol life cycles within AeroCom. Atmospheric Chemistry and Physics, 6(7), 1777-1813.
    [ Abstract PDF ]

    Simulation results of global aerosol models have been assembled in the framework of the AeroCom intercomparison exercise. In this paper, we analyze the life cycles of dust, sea salt, sulfate, black carbon and particulate organic matter as simulated by sixteen global aerosol models. The differences among the results (model diversities) for sources and sinks, burdens, particle sizes, water uptakes, and spatial dispersals have been established. These diversities have large consequences for the calculated radiative forcing and the aerosol concentrations at the surface. Processes and parameters are identified which deserve further research. The AeroCom all-models-average emissions are dominated by the mass of sea salt (SS), followed by dust (DU), sulfate (SO4), particulate organic matter (POM), and finally black carbon (BC). Interactive parameterizations of the emissions and contrasting particles sizes of SS and DU lead generally to higher diversities of these species, and for total aerosol. The lower diversity of the emissions of the fine aerosols, BC, POM, and SO4, is due to the use of similar emission inventories, and does therefore not necessarily indicate a better understanding of their sources. The diversity of SO4-sources is mainly caused by the disagreement on depositional loss of precursor gases and on chemical production. The diversities of the emissions are passed on to the burdens, but the latter are also strongly affected by the model-specific treatments of transport and aerosol processes. The burdens of dry masses decrease from largest to smallest: DU, SS, SO4, POM, and BC. The all-models-average residence time is shortest for SS with about half a day, followed by SO4 and DU with four days, and POM and BC with six and seven days, respectively. The wet deposition rate is controlled by the solubility and increases from DU, BC, POM to SO4 and SS. It is the dominant sink for SO4, BC, and POM, and contributes about one third to the total removal of SS and DU species. For SS and DU we find high diversities for the removal rate coefficients and deposition pathways. Models do neither agree on the split between wet and dry deposition, nor on that between sedimentation and other dry deposition processes. We diagnose an extremely high diversity for the uptake of ambient water vapor that influences the particle size and thus the sink rate coefficients. Furthermore, we find little agreement among the model results for the partitioning of wet removal into scavenging by convective and stratiform rain. Large differences exist for aerosol dispersal both in the vertical and in the horizontal direction. In some models, a minimum of total aerosol concentration is simulated at the surface. Aerosol dispersal is most pronounced for SO4 and BC and lowest for SS. Diversities are higher for meridional than for vertical dispersal, they are similar for the individual species and highest for SS and DU. For these two components we do not find a correlation between vertical and meridional aerosol dispersal. In addition the degree of dispersals of SS and DU is not related to their residence times. SO4, BC, and POM, however, show increased meridional dispersal in models with larger vertical dispersal, and dispersal is larger for longer simulated residence times.

21. Washington, R, M C Todd, G Lizcano, I Tegen, C Flamant, I Koren, Paul Ginoux, S Engelstaedter, C S Bristow, C S Zender, A S Goudie, A Warren, and J M Prospero, 2006: Links between topography, wind, deflation, lakes and dust: The case of the Bodélé Depression, Chad. Geophysical Research Letters, 33, L09401, doi:10.1029/2006GL025827.
    [ Abstract ]

    The Bodélé Depression, Chad is the planet's largest single source of dust. Deflation from the Bodélé could be seen as a simple coincidence of two key prerequisites: strong surface winds and a large source of suitable sediment. But here we hypothesise that long term links between topography, winds, deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land-atmosphere processes with topography acting as the overall controlling agent. We use a variety of observational and numerical techniques, including a regional climate model, to show that: 1) contemporary deflation from the Bodélé is delineated by topography and a surface wind stress maximum; 2) the Tibesti and Ennedi mountains play a key role in the generation of the erosive winds in the form of the Bodélé Low Level Jet (LLJ); 3) enhanced deflation from a stronger Bodélé LLJ during drier phases, for example, the Last Glacial Maximum, was probably sufficient to create the shallow lake in which diatoms lived during wetter phases, such as the Holocene pluvial. Winds may therefore have helped to create the depression in which erodible diatom material accumulated. Instead of a simple coincidence of nature, dust from the world's largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world's largest dust source. Similar processes plausibly operate in other dust hotspots in topographic depressions.

22. Kaufman, Y J., I Koren, L Remer, D Tanré, Paul Ginoux, and Song-Miao Fan, 2005: Dust transport and deposition observed from the Terra-Moderate Resolution Imaging Spectroradiometer (MODIS) spacecraft over the Atlantic Ocean. Journal of Geophysical Research, 110, D10S12, doi:10.1029/2003JD004436.
    [ Abstract ]

    Meteorological observations, in situ data, and satellite images of dust episodes were used already in the 1970s to estimate that 100 Tg of dust are transported from Africa over the Atlantic Ocean every year between June and August and are deposited in the Atlantic Ocean and the Americas. Desert dust is a main source of nutrients to oceanic biota and the Amazon forest, but it deteriorates air quality, as shown for Florida. Dust affects the Earth radiation budget, thus participating in climate change and feedback mechanisms. There is an urgent need for new tools for quantitative evaluation of the dust distribution, transport, and deposition. The Terra spacecraft, launched at the dawn of the last millennium, provides the first systematic well-calibrated multispectral measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument for daily global analysis of aerosol. MODIS data are used here to distinguish dust from smoke and maritime aerosols and to evaluate the African dust column concentration, transport, and deposition. We found that 240 ± 80 Tg of dust are transported annually from Africa to the Atlantic Ocean, 140 ± 40 Tg are deposited in the Atlantic Ocean, 50 Tg fertilize the Amazon Basin (four times as previous estimates, thus explaining a paradox regarding the source of nutrition to the Amazon forest), 50 Tg reach the Caribbean, and 20 Tg return to Africa and Europe. The results are compared favorably with dust transport models for maximum particle diameter between 6 and 12 ìm. This study is a first example of quantitative use of MODIS aerosol for a geophysical research.

23. Lamarque, J F., J T Kiehl, P G Hess, W D Collins, L K Emmons, Paul Ginoux, C Luo, and X Tie, 2005: Response of a coupled chemistry-climate model to changes in aerosol emissions: Global impact on the hydrological cycle and the tropospheric burdens of OH, ozone, and NOx. Geophysical Research Letters, 32, L16809, doi:10.1029/2005GL023419.
    [ Abstract ]

    In this study, we analyze the response of the coupled chemistry-climate system to changes in aerosol emissions in fully coupled atmospheric chemistry-climate-slab ocean model simulations; only the direct radiative effect of aerosols and their uptake of chemical species are considered in this study. We show that, at the global scale, a decrease in emissions of the considered aerosols (or their precursors) produces a warmer and moister climate. In addition, the tropospheric burdens of OH and ozone increase when aerosol emissions are decreased. The ozone response is a combination of the impact of reduced heterogeneous uptake of N₂O₅ and increased ozone loss in a moister atmosphere. Under reduced aerosol emissions, the tropospheric burden of NOx (NO + NO₂) is strongly reduced by an increase in nitric acid formation but also increased by the reduced N₂O₅ uptake. Finally, we discuss the significant difference found between the combined impact of all aerosols emissions and the sum of their individual contributions.

24. Ming, Yi, V Ramaswamy, Paul Ginoux, and Larry Horowitz, 2005: Direct radiative forcing of anthropogenic organic aerosol. Journal of Geophysical Research, 110, D20208, doi:10.1029/2004JD005573.
    [ Abstract ]

    This study simulates the direct radiative forcing of organic aerosol using the GFDL AM2 GCM. The aerosol climatology is provided by the MOZART chemical transport model (CTM). The approach to calculating aerosol optical properties explicitly considers relative humidity–dependent hygroscopic growth by employing a functional group–based thermodynamic model, and makes use of the size distribution derived from AERONET measurements. The preindustrial (PI) and present-day (PD) global burdens of organic carbon are 0.17 and 1.36 Tg OC, respectively. The annual global mean total-sky and clear-sky top-of-the atmosphere (TOA) forcings (PI to PD) are estimated as −0.34 and −0.71 W m⁻², respectively. Geographically the radiative cooling largely lies over the source regions, namely part of South America, Central Africa, Europe and South and East Asia. The annual global mean total-sky and clear-sky surface forcings are −0.63 and −0.98 W m⁻², respectively. A series of sensitivity analyses shows that the treatments of hygroscopic growth and optical properties of organic aerosol are intertwined in the determination of the global organic aerosol forcing. For example, complete deprivation of water uptake by hydrophilic organic particles reduces the standard (total-sky) and clear-sky TOA forcing estimates by 18% and 20%, respectively, while the uptake by a highly soluble organic compound (malonic acid) enhances them by 18% and 32%, respectively. Treating particles as non-absorbing enhances aerosol reflection and increases the total-sky and clear-sky TOA forcing by 47% and 18%, respectively, while neglecting the scattering brought about by the water associated with particles reduces them by 24% and 7%, respectively.

25. Ming, Yi, V Ramaswamy, Paul Ginoux, Larry Horowitz, and L M Russell, 2005: Geophysical Fluid Dynamics Laboratory general circulation model investigation of the indirect radiative effects of anthropogenic sulfate aerosol. Journal of Geophysical Research, 110, D22206, doi:10.1029/2005JD006161.
    [ Abstract ]

    The Geophysical Fluid Dynamics Laboratory (GFDL) atmosphere general circulation model, with its new cloud scheme, is employed to study the indirect radiative effect of anthropogenic sulfate aerosol during the industrial period. The preindustrial and present-day monthly mean aerosol climatologies are generated from running the Model for Ozone And Related chemical Tracers (MOZART) chemistry-transport model. The respective global annual mean sulfate burdens are 0.22 and 0.81 Tg S. Cloud droplet number concentrations are related to sulfate mass concentrations using an empirical relationship (Boucher and Lohmann, 1995). A distinction is made between "forcing" and flux change at the top of the atmosphere in this study. The simulations, performed with prescribed sea surface temperature, show that the first indirect "forcing" ("Twomey" effect) amounts to an annual mean of -1.5 W m^-2, concentrated largely over the oceans in the Northern Hemisphere (NH). The annual mean flux change owing to the response of the model to the first indirect effect is -1.4 W m^-2, similar to the annual mean forcing. However, the model's response causes a rearrangement of cloud distribution as well as changes in longwave flux (smaller than solar flux changes). There is thus a differing geographical nature of the radiation field than for the forcing even though the global means are similar. The second indirect effect, which is necessarily an estimate made in terms of the model's response, amounts to -0.9 W m^-2, but the statistical significance of the simulated geographical distribution of this effect is relatively low owing to the model's natural variability. Both the first and second effects are approximately linearly additive, giving rise to a combined annual mean flux change of -2.3 W m^-2, with the NH responsible for 77% of the total flux change. Statistically significant model responses are obtained for the zonal mean total indirect effect in the entire NH and in the Southern Hemisphere low latitudes and midlatitudes (north of 45°S). The area of significance extends more than for the first and second effects considered separately. A comparison with a number of previous studies based on the same sulfate-droplet relationship shows that, after distinguishing between forcing and flux change, the global mean change in watts per square meter for the total effect computed in this study is comparable to existing studies in spite of the differences in cloud schemes.

26. Tie, X, S Madronich, S Walters, D P Edwards, Paul Ginoux, N Mahowald, R-Y Zhang, C Lou, and G P Brasseur, 2005: Assessment of the global impact of aerosols on tropospheric oxidants. Journal of Geophysical Research, 110, D03204, doi:10.1029/2004JD005359.
    [ Abstract ]

    We present here a fully coupled global aerosol and chemistry model for the troposphere. The model is used to assess the interactions between aerosols and chemical oxidants in the troposphere, including (1) the conversion from gas-phase oxidants into the condensed phase during the formation of aerosols, (2) the heterogeneous reactions occurring on the surface of aerosols, and (3) the effect of aerosols on ultraviolet radiation and photolysis rates. The present study uses the global three-dimensional chemical/transport model, Model for Ozone and Related Chemical Tracers, version 2 (MOZART-2), in which aerosols are coupled with the model. The model accounts for the presence of sulfate, soot, primary organic carbon, ammonium nitrate, secondary organic carbon, sea salt, and mineral dust particles. The simulated global distributions of the aerosols are analyzed and evaluated using satellite measurements (Moderate-Resolution Imaging Spectroradiometer (MODIS)) and surface measurements. The results suggest that in northern continental regions the tropospheric aerosol loading is highest in Europe, North America, and east Asia. Sulfate, organic carbon, black carbon, and ammonium nitrate are major contributions for the high aerosol loading in these regions. Aerosol loading is also high in the Amazon and in Africa. In these areas the aerosols consist primarily of organic carbon and black carbon. Over the southern high-latitude ocean (around 60°S), high concentrations of sea-salt aerosol are predicted. The concentration of mineral dust is highest over the Sahara and, as a result of transport, spread out into adjacent regions. The model and MODIS show similar geographical distributions of aerosol particles. However, the model overestimates the sulfate and carbonaceous aerosol in the eastern United States, Europe, and east Asia. In the region where aerosol loading is high, aerosols have important impacts on tropospheric ozone and other oxidants. The model suggests that heterogeneous reactions of HO₂ and CH₂O on sulfate have an important impact on HO_x (OH + HO₂) concentrations, while the heterogeneous reaction of O₃ on soot has a minor effect on O₃ concentrations in the lower troposphere. The heterogeneous reactions on dust have very important impacts on HO_x and O₃ in the region of dust mobilization, where the reduction of HO_x and O₃concentrations can reach a maximum of 30% and 20%, respectively, over the Sahara desert. Dust, organic carbon, black carbon, and sulfate aerosols have important impacts on photolysis rates. For example, the photodissociation frequencies of ozone and nitrogen dioxide are reduced by 20% at the surface in the Sahara, in the Amazon, and in eastern Asia, leading to 5–20% reduction in the concentration of HO_x and to a few percent change in the O₃ abundance in these regions.

27. Barnum, B H., N S Winstead, J Wesely, A Hakola, P R Colarco, O B Toon, Paul Ginoux, G Brooks, L Hasselbarth, and B Toth, 2004: Forecasting dust storms using the CARMA-dust model and MM5 weather data. Environmental Modelling and Software, 19(2), doi:10.1016/S1364-8152(03)00115-4.
    [ Abstract ]

    An operational model for the forecast of dust storms in Northern Africa, the Middle East and Southwest Asia has been developed for the United States Air Force Weather Agency (AFWA). The dust forecast model uses the 5th generation Penn State Mesoscale Meteorology Model (MM5) as input to the University of Colorado CARMA dust transport model. AFWA undertook a 60 day evaluation of the effectiveness of the dust model to make short, medium and long- range (72 h) forecasts of dust storms. The study is unique in using satellite and ground observations of dust storms to score the model’s effectiveness using standard meteorological statistics. Each of the main forecast regions was broken down into smaller areas for more detailed analysis. The study found the forecast model is an effective forecast tool with Probability of Detection of dust storm occurrence exceeding 68 percent over Northern Africa, with a 16 percent False Alarm Rate. Southwest Asia forecasts had average Probability of Detection values of 61 percent with False Alarm Rates averaging 10 percent.

28. Chin, M, A Chu, R Levy, L Remer, Y J Kaufman, B Holben, T Eck, Paul Ginoux, and Q Gao, 2004: Aerosol distribution in the Northern Hemisphere during ACE-Asia: Results from global model, satellite observations, and Sun photometer measurements. Journal of Geophysical Research, 109, D23S90, doi:10.1029/2004JD004829.
    [ Abstract ]

    We analyze the aerosol distribution and composition in the Northern Hemisphere during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) field experiment in spring 2001. We use the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model in this study, in conjunction with satellite retrieval from the Moderate-Resolution Imaging Spectroradiometer (MODIS) on EOS-Terra satellite and Sun photometer measurements from the worldwide Aerosol Robotic Network (AERONET). Statistical analysis methods including histograms, mean bias, root-mean-square error, correlation coefficients, and skill scores are applied to quantify the differences between the MODIS 1° × 1° gridded data, the daytime average AERONET data, and the daily mean 2° × 2.5° resolution model results. Both MODIS and the model show relatively high aerosol optical thickness (τ) near the source regions of Asia, Europe, and northern Africa, and they agree on major features of the long-range transport of aerosols from their source regions to the neighboring oceans. The τ values from MODIS and from the model have similar probability distributions in the extratropical oceans and in Europe, but MODIS is approximately 2–3 times as high as the model in North/Central America and nearly twice as high in Asia and over the tropical/subtropical oceans. Comparisons with the AERONET measurements in the Northern Hemisphere demonstrate that in general the model and the AERONET data have comparable values and similar probability distributions of τ, whereas MODIS tends to report higher values of τ over land, particularly North/Central America. The MODIS high bias is primarily attributed to the difficulties in land algorithm dealing with surface reflectance over inhomogeneous and bright land surfaces, including mountaintops, arid areas, and areas of snow/ice melting and with land/water mixed pixels. The model estimates that on average, sulfate, carbon, dust, and sea salt comprise 30%, 25%, 32%, and 13%, respectively, of the 550-nm τ in April 2001 in the Northern Hemisphere, with ∼46% of the total τ from anthropogenic activities and 66% from fine mode aerosols.

29. Ginoux, Paul, J M Prospero, O Torres, and M Chin, 2004: Long-term simulation of global dust distribution with the GOCART model: Correlation with North Atlantic Oscillation. Environmental Modelling and Software, 19(2), doi:10.1016/S1364-8152(03)00114-2.
    [ Abstract ]

    Global distribution of aeolian dust is simulated from 1981 to 1996 with the Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model. The results are compared with in situ measurements and satellite data. An index is calculated from the model results and the satellite viewing angles to allow quantitative comparison with the Total ozone mapping spectrometer (TOMS) absorbing aerosol index. The annual budget over the different continents and oceans are analyzed. The simulated annual emission varies from a minimum of 1950 Tg in 1996 to a maximum of 2400 Tg in 1988. Of these emissions, 65% is from North Africa and 25% from Asia. It is found that North America received twice as much dust from other continents than it emits per year. There is no significant trend over the 16-year simulation. The inter-annual variability of dust distribution is analyzed over the North Atlantic and Africa. It is found that in winter a large fraction of the North Atlantic and Africa dust loading is correlated with the North Atlantic Oscillation (NAO) index. It is shown that a controlling factor of such correlation can be attributed to dust emission from the Sahel. The Bodele depression is the major dust source in winter and its inter-annual variability is highly correlated with the NAO. However, the long record of dust concentration measured at Barbados indicates that there is no correlation with the NAO index and surface concentration in winter. Longer simulation should provide the information needed to understand if the effects of the NAO on dust distribution is rather limited or Barbados is at the edge of the affected region.

30. Ansmann, A, J Bösenberg, A Chaikovsky, A Comerón, S Eckhardt, R Eixmann, V Freudenthaler, Paul Ginoux, L Komguem, H Linné, P Marquet, I Mattis, V Mitev, D Müller, S Music, S Nickovic, J Pelon, L Sauvage, P Sobolewsky, M K Srivastava, A Stohl, O Torres, G Vaughan, U Wandinger, and M Wiegner, 2003: Long-range transport of Saharan dust to northern Europe: The 11-16 October 2001 outbreak observed with EARLINET. Journal of Geophysical Research, 108(D24), 4783, doi:10.1029/2003JD003757.
    [ Abstract ]

    The spread of mineral particles over southwestern, western, and central Europe resulting from a strong Saharan dust outbreak in October 2001 was observed at 10 stations of the European Aerosol Research Lidar Network (EARLINET). For the first time, an optically dense desert dust plume over Europe was characterized coherently with high vertical resolution on a continental scale. The main layer was located above the boundary layer (above 1-km height above sea level (asl)) up to 3–5-km height, and traces of dust particles reached heights of 7–8 km. The particle optical depth typically ranged from 0.1 to 0.5 above 1-km height asl at the wavelength of 532 nm, and maximum values close to 0.8 were found over northern Germany. The lidar observations are in qualitative agreement with values of optical depth derived from Total Ozone Mapping Spectrometer (TOMS) data. Ten-day backward trajectories clearly indicated the Sahara as the source region of the particles and revealed that the dust layer observed, e.g., over Belsk, Poland, crossed the EARLINET site Aberystwyth, UK, and southern Scandinavia 24–48 hours before. Lidar-derived particle depolarization ratios, backscatter- and extinction-related Ångström exponents, and extinction-to-backscatter ratios mainly ranged from 15 to 25%, -0.5 to 0.5, and 40–80 sr, respectively, within the lofted dust plumes. A few atmospheric model calculations are presented showing the dust concentration over Europe. The simulations were found to be consistent with the network observations.

31. Chin, M, Paul Ginoux, R Lucchesi, B Huebert, R J Weber, Jeffrey L Anderson, S Masonis, B Blomquist, A Bandy, and D Thornton, 2003: A global aerosol model forecast for the ACE-Asia field experiment. Journal of Geophysical Research, 108(D23), 8654, doi:10.1029/2003JD003642.
    [ Abstract ]

    We present the results of aerosol forecast during the ACE-Asia field experiment in spring 2001, using the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model and the meteorological forecast fields from the Goddard Earth Observing System Data Assimilation System (GEOS DAS). The model provides direct information on aerosol optical thickness and concentrations for effective flight planning, while feedbacks from measurements constantly evaluate the model for successful model improvements. We verify the model forecast skill by comparing model-predicted aerosol quantities and meteorological variables with those measured by the C-130 aircraft. The GEOS DAS meteorological forecast system shows excellent skills in predicting winds, relative humidity, and temperature, with skill scores usually in the range of 0.7-0.99. The model is also skillful in forecasting pollution aerosols, with most scores above 0.5. The model correctly predicted the dust outbreak events and their trans-Pacific transport, but it constantly missed the high dust concentrations observed in the boundary layer. We attribute this "missing" dust source to desertification regions in the Inner Mongolia Province in China, which have developed in recent years but were not included in the model during forecasting. After incorporating the desertification sources, the model is able to reproduce the observed boundary layer high dust concentrations over the Yellow Sea. We demonstrate that our global model can not only account for the large-scale intercontinental transport but also produce the small-scale spatial and temporal variations that are adequate for aircraft measurements planning.

32. Ginoux, Paul, 2003: Effects of nonsphericity on mineral dust modeling. Journal of Geophysical Research, 108(D2), 4052, doi:10.1029/2002JD002516.
    [ Abstract PDF ]

    The dependency of nonsphericity on gravitational settling of mineral dust particles is parameterized for prolate ellipsoids and Reynolds number lower than 2. The settling speed is numerically solved from the momentum equation as a function of particle diameter and aspect ratio. The reduction of settling speed due to nonsphericity is included in the Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model to simulate dust size distribution for April 2001. Two numerical schemes for solving sedimentation are compared. For particles of diameter greater than 5 mum, the simulated size distribution is sensitive to the numerical sedimentation scheme. Changing the particle shape from spherical to nonspherical with lambda = 2 makes little difference to the simulated surface concentration and size distribution except at the periphery of the dust sources. However, when very elongated particles ( lambda = 5) are simulated, the differences between nonspherical and spherical particles are significant. With limited in situ measurements reporting most frequent lambda around 1.5, the overall effects on global modeling is rather negligible and the essential benefit is to relax the CFL condition of Eulerian settling schemes.

33. Ginoux, Paul, and O Torres, 2003: Empirical TOMS index for dust aerosol: Applications to model validation and source characterization. Journal of Geophysical Research, 108(D17), 4534, doi:10.1029/2003JD003470.
    [ Abstract ]

    An empirical relation is developed to express the Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) for the case of dust plumes, as an explicit function of four physical quantities: the single scattering albedo, optical thickness, altitude of the plume and surface pressure. This relation allows sensitivity analysis of the TOMS AI with physical properties, quantitative comparison with dust model results and physical analysis of dust sources, without the necessity of cumbersome radiative calculation. Two applications are presented: (1) the case study of a dust storm over the North Atlantic in March 1988, and (2) the characterization of 13 major dust sources. The first application shows that simulated dust distribution can be quantitatively compared to TOMS AI on a daily basis and over regions where dust is the dominant aerosol. The second application necessitates to further parameterize the relation by replacing the optical thickness and the altitude of the plume by meteorological variables. The advantage is that surface meteorological fields are easily available globally and for decades but the formulation only applies to dust sources. The daily, seasonal and interannual variability of the parameterized index over major dust sources reproduces correctly the variability of the observed TOMS AI. The correlation between these two indices is used to determine the surface characteristics and physical properties of dust aerosol over the sources.

34. Gregg, W, M E Conkright, Paul Ginoux, J E O'Reilly, and N W Casey, 2003: Ocean primary production and climate: Global decadal changes. Geophysical Research Letters, 30(15), 1809, doi:10.1029/2003GL016889.
    [ Abstract ]

    Satellite-in situ blended ocean chlorophyll records indicate that global ocean annual primary production has declined more than 6% since the early 1980's. Nearly 70% of the global decadal decline occurred in the high latitudes. In the northern high latitudes, these reductions in primary production corresponded with increases in sea surface temperature and decreases in atmospheric iron deposition to the oceans. In the Antarctic, the reductions were accompanied by increased wind stress. Three of four low latitude basins exhibited decadal increases in annual primary production. These results indicate that ocean photosynthetic uptake of carbon may be changing as a result of climatic changes and suggest major implications for the global carbon cycle.

35. Gregg, W, Paul Ginoux, P S Schopf, and N W Casey, 2003: Phytoplankton and iron: validation of a global three-dimensional ocean biogeochemical model. Deep-Sea Research, Part II, 50, 3143-3169.
    [ Abstract PDF ]

    The JGOFS program and NASA ocean-color satellites have provided a wealth of data that can be used to test and validate models of ocean biogeochemistry. A coupled three-dimensional general circulation, biogeochemical, and radiative model of the global oceans was validated using these in situ data sources and satellite data sets. Biogeochemical processes in the model were determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among four phytoplankton functional groups (diatoms, chlorophytes, cyanobacteria, and coccolithophores) and four nutrients (nitrate, ammonium, silica, and dissolved iron). Annual mean log-transformed dissolved iron concentrations in the model were statistically positively correlated on basin scale with observations (P<0.05) over the eight (out of 12) major oceanographic basins where data were available. The model tended to overestimate in situ observations, except in the Antarctic where a large underestimate occurred. Inadequate scavenging and excessive remineralization and/or regeneration were possible reasons for the overestimation. Basin scale model chlorophyll seasonal distributions were positively correlated with SeaWiFS chlorophyll in each of the 12 oceanographic basins (P<0.05). The global mean difference was 3.9% (model higher than SeaWiFS). The four phytoplankton groups were initialized as homogeneous and equal distributions throughout the model domain. After 26 years of simulation, they arrived at reasonable distributions throughout the global oceans: diatoms predominated high latitudes, coastal, and equatorial upwelling areas, cyanobacteria predominated the mid-ocean gyres, and chlorophytes and coccolithophores represented transitional assemblages. Seasonal patterns exhibited a range of relative responses: from a seasonal succession in the North Atlantic with coccolithophores replacing diatoms as the dominant group in mid-summer, to successional patterns with cyanobacteria replacing diatoms in mid-summer in the central North Pacific. Diatoms were associated with regions where nutrient availability was high. Cyanobacteria predominated in quiescent regions with low nutrients. While the overall patterns of phytoplankton functional group distributions exhibited broad qualitative agreement with in situ data, quantitative comparisons were mixed. Three of the four phytoplankton groups exhibited statistically significant correspondence across basins. Diatoms did not. Some basins exhibited excellent correspondence, while most showed moderate agreement, with two functional groups in agreement with data and the other two in disagreement. The results are encouraging for a first attempt at simulating functional groups in a global coupled three-dimensional model but many issues remain.

36. Kinne, S, Ü Lohmann, J Feichter, M Schulz, C Timmreck, S Ghan, R Easter, M Chin, Paul Ginoux, T Takemura, I Tegen, D Koch, M Herzog, J Penner, G Pitari, B Holben, T Eck, A Smirnov, O Dubovik, I Slutsker, D Tanré, O Torres, M Mishchenko, I V Geogdzhayev, D A Chu, and Y J Kaufman, 2003: Monthly averages of aerosol properties: a global comparison among models, satellite data, and AERONET ground data. Journal of Geophysical Research, 108(D20), 4634, doi:10.1029/2001JD001253.
    [ Abstract ]

    New aerosol modules of global (circulation and chemical transport) models are evaluated. These new modules distinguish among at least five aerosol components: sulfate, organic carbon, black carbon, sea salt, and dust. Monthly and regionally averaged predictions for aerosol mass and aerosol optical depth are compared. Differences among models are significant for all aerosol types. The largest differences were found near expected source regions of biomass burning (carbon) and dust. Assumptions for the permitted water uptake also contribute to optical depth differences (of sulfate, organic carbon, and sea salt) at higher latitudes. The decline of mass or optical depth away from recognized sources reveals strong differences in aerosol transport or removal among models. These differences are also a function of altitude, as transport biases of dust do not always extend to other aerosol types. Ratios of optical depth and mass demonstrate large differences in the mass extinction efficiency, even for hydrophobic aerosol. This suggests that efforts of good mass simulations could be wasted or that conversions are misused to cover for poor mass simulations. In an attempt to provide an absolute measure for model skill, simulated total optical depths (when adding contributions from all five aerosol types) are compared to measurements from ground and space. Comparisons to the Aerosol Robotic Network (AERONET) suggest a source strength underestimate in many models, most frequently for (subtropical) tropical biomass or dust. Comparisons to the combined best of Moderate-Resolution Imaging Spectroradiometer (MODIS) and Total Ozone Mapping Spectrometer (TOMS) indicate that away from sources, model simulations are usually smaller. Particularly large are discrepancies over tropical oceans and oceans of the Southern Hemisphere, raising issues on the treatment of sea salt in models. Totals for mass or optical depth in many models are defined by the absence or dominance of only one aerosol component. With appropriate corrections to that component (e.g., to removal, to source strength, or to seasonality) a much better model performance can be expected. Still, many important modeling issues remain inconclusive as the combined result of poor coordination (different emissions and meteorology), insufficient model output (vertical distributions, water uptake by aerosol type), and unresolved measurement issues (retrieval assumptions and temporal or spatial sampling biases).

37. Martin, R V., D J Jacob, R M Yantosca, M Chin, and Paul Ginoux, 2003: Global and regional decreases in tropospheric oxidants from photochemical effects of aerosols. Journal of Geophysical Research, 108(D3), 4097, doi:10.1029/2002JD002622.
    [ Abstract ]

    We evaluate the sensitivity of tropospheric OH, O₃, and O₃ precursors to photochemical effects of aerosols not usually included in global models: (1) aerosol scattering and absorption of ultraviolet radiation and (2) reactive uptake of HO, NO, and NO₃. Our approach is to couple a global 3-D model of tropospheric chemistry (GEOS-CHEM) with aerosol fields from a global 3-D aerosol model (GOCART). Reactive uptake by aerosols is computed using reaction probabilities from a recent review ((HO = 0.2, (NO = 10^-4, (NO₃ = 10^-3). Aerosols decrease the O₃ ® O(¹D) photolysis frequency by 5–20% at the surface throughout the Northern Hemisphere (largely due to mineral dust) and by a factor of 2 in biomass burning regions (largely due to black carbon). Aerosol uptake of HO accounts for 10–40% of total HOx radical (= OH + peroxy) loss in the boundary layer over polluted continental regions (largely due to sulfate and organic carbon) and for more than 70% over tropical biomass burning regions (largely due to organic carbon). Uptake of NO and NO₃ accounts for 10–20% of total HNO₃ production over biomass burning regions and less elsewhere. Annual mean OH concentrations decrease by 9% globally and by 5–35% in the boundary layer over the Northern Hemisphere. Simulated CO increases by 5–15 ppbv in the remote Northern Hemisphere, improving agreement with observations. Simulated boundary layer O₃ decreases by 15–45 ppbv over India during the biomass burning season in March and by 5–9 ppbv over northern Europe in August, again improving comparison with observations. We find that particulate matter controls would increase surface O₃ over Europe and other industrial regions.

38. Weaver, C, J Joiner, and Paul Ginoux, 2003: Mineral aerosol contamination of TIROS Operational Vertical Sounder (TOVS) temperature and moisture retrievals. Journal of Geophysical Research, 108(D8), 4246, doi:10.1029/2002JD002571.
    [ Abstract PDF ]

    Since mineral aerosols absorb significant amounts of infrared radiation, they may contribute to errors in the retrievals of atmospheric and surface parameters from the TIROS Operational Vertical Sounder (TOVS) High-Resolution Infrared Radiation Sounder (HIRS) if the atmosphere is assumed clear. TOVS is an operational sounder on NOAA polar satellites. To see if observed brightness temperatures are reduced by mineral aerosol, we analyzed results from the Data Assimilation Office (DAO) Finite Volume Data Assimilation System (fvDAS). Every 6 hours the assimilated temperature and moisture profiles are used as a first guess in the DAO interactive cloud-clearing TOVS retrieval system. The observed minus the forecast (O–F) brightness temperature, which is a measure of the accuracy of the first guess and radiative transfer parameters, becomes more negative with increasing dust concentrations. Dust concentrations are from the Goddard Ozone Chemistry Aerosol Radiation Transport (GOCART) model. Since there was no account of dust during this fvDAS run, the dependence of O–F on the estimated atmospheric dust concentrations from GOCART indicates that the dust is affecting the TOVS brightness temperatures. HIRS channels that are sensitive to the surface temperature, lower tropospheric temperature, and moisture are subject to a 0.5 K or more reduction in the brightness temperature during heavy dust loading conditions. The radiative transfer module used in the TOVS retrieval system was modified to account for dust assuming a composition of illite, and the fvDAS run was repeated. Accounting for dust absorption in the retrieval system yields warmer surface temperatures (0.4 K) and warmer lower tropospheric temperatures in regions of moderate dust loading over the tropical Atlantic.

39. Chin, M, Paul Ginoux, S Kinne, O Torres, B Holben, B N Duncan, R V Martin, J Logan, A Higurashi, and T Nakajima, 2002: Tropospheric aerosol optical thickness from the GOCART model and comparisons with satellite and Sun photometer measurements. Journal of the Atmospheric Sciences, 59(3), 461-483.
    [ Abstract PDF ]

    The Georgia Institute of Technology–Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model is used to simulate the aerosol optical thickness τ for major types of tropospheric aerosols including sulfate, dust, organic carbon (OC), black carbon (BC), and sea salt. The GOCART model uses a dust emission algorithm that quantifies the dust source as a function of the degree of topographic depression, and a biomass burning emission source that includes seasonal and interannual variability based on satellite observations. Results presented here show that on global average, dust aerosol has the highest τ at 500 nm (0.051), followed by sulfate (0.040), sea salt (0.027), OC (0.017), and BC (0.007). There are large geographical and seasonal variations of τ, controlled mainly by emission, transport, and hygroscopic properties of aerosols. The model calculated total τs at 500 nm have been compared with the satellite retrieval products from the Total Ozone Mapping Spectrometer (TOMS) over both land and ocean and from the Advanced Very High Resolution Radiometer (AVHRR) over the ocean. The model reproduces most of the prominent features in the satellite data, with an overall agreement within a factor of 2 over the aerosol source areas and outflow regions. While there are clear differences among the satellite products, a major discrepancy between the model and the satellite data is that the model shows a stronger variation of τ from source to remote regions. Quantitative comparison of model and satellite data is still difficult, due to the large uncertainties involved in deriving the τ values by both the model and satellite retrieval, and by the inconsistency in physical and optical parameters used between the model and the satellite retrieval. The comparison of monthly averaged model results with the sun photometer network [Aerosol Robotics Network (AERONET)] measurements shows that the model reproduces the seasonal variations at most of the sites, especially the places where biomass burning or dust aerosol dominates.

40. Penner, J, S Zhang, M Chin, C C Chuang, J Feichter, Y Feng, I V Geogdzhayev, Paul Ginoux, M Herzog, and Brian J Soden, et al., 2002: A comparison of model- and satellite-derived aerosol optical depth and reflectivity. Journal of the Atmospheric Sciences, 59(3), 441-460.
    [ Abstract PDF ]

    The determination of an accurate quantitative understanding of the role of tropospheric aerosols in the earth's radiation budget is extremely important because forcing by anthropogenic aerosols presently represents one of the most uncertain aspects of climate models. Here the authors present a systematic comparison of three different analyses of satellite-retrieved aerosol optical depth based on the Advanced Very High Resolution Radiometer (AVHRR)-measured radiances with optical depths derived from six different models. Also compared are the model-derived clear-sky reflected shortwave radiation with satellite-measured reflectivities derived from the Earth Radiation Budget Experiment (ERBE) satellite. The three different satellite-derived optical depths differ by between -0.10 and 0.07 optical depth units in comparison to the average of the three analyses depending on latitude and month, but the general features of the retrievals are similar. The models differ by between -0.09 and +0.16 optical depth units from the average of the models. Differences between the average of the models and the average of the satellite analyses range over -0.11 to +0.05 optical depth units. These differences are significant since the annual average clear-sky radiative forcing associated with the difference between the average of the models and the average of the satellite analyses ranges between -3.9 and 0.7 W m-2 depending on latitude and is -1.7 W m-2 on a global average annual basis. Variations in the source strengths of dimethylsulfide-derived aerosols and sea salt aerosols can explain differences between the models, and between the models and satellite retrievals of up to 0.2 optical depth units. The comparison of model-generated reflected shortwave radiation and ERBE-measured shortwave radiation is similar in character as a function of latitude to the analysis of modeled and satellite-retrieved optical depths, but the differences between the modeled clear-sky reflected flux and the ERBE clear-sky reflected flux is generally larger than that inferred from the difference between the models and the AVHRR optical depths, especially at high latitudes. The difference between the mean of the models and the ERBE-analyzed clear-sky flux is 1.6 W m-2. The overall comparison indicates that the model-generated aerosol optical depth is systematically lower than that inferred from measurements between the latitudes of 10° and 30°S. It is not likely that the shortfall is due to small values of the sea salt optical depth because increases in this component would create modeled optical depths that are larger than those from satellites in the region north of 30°N and near 50°S. Instead, the source strengths for DMS and biomass aerosols in the models may be too low. Firm conclusions, however, will require better retrieval procedures for the satellites, including better cloud screening procedures, further improvement of the model's treatment of aerosol transport and removal, and a better determination of aerosol source strengths.

41. Prospero, J M., Paul Ginoux, O Torres, S E Nicholson, and T E Gill, 2002: Environmental characterization of global sources of atmospheric soil dust identified with the NIMBUS 7 Total Ozone Mapping Spectrometer (TOMS) absorbing aerosol product. Reviews of Geophysics, 40(1), 1002, doi:10.1029/2000RG000095.
    [ Abstract PDF ]

    We use the Total Ozone Mapping Spectrometer (TOMS) sensor on the Nimbus 7 satellite to map the global distribution of major atmospheric dust sources with the goal of identifying common environmental characteristics. The largest and most persistent sources are located in the Northern Hemisphere, mainly in a broad "dust belt" that extends from the west coast of North Africa, over the Middle East, Central and South Asia, to China. There is remarkably little large-scale dust activity outside this region. In particular, the Southern Hemisphere is devoid of major dust activity. Dust sources, regardless of size or strength, can usually be associated with topographical lows located in arid regions with annual rainfall under 200-250 mm. Although the source regions themselves are arid or hyperarid, the action of water is evident from the presence of ephemeral streams, rivers, lakes, and playas. Most major sources have been intermittently flooded through the Quaternary as evidenced by deep alluvial deposits. Many sources are associated with areas where human impacts are well documented, e. g., the Caspian and Aral Seas, Tigris-Euphrates River Basin, southwestern North America, and the loess lands in China. Nonetheless, the largest and most active sources are located in truly remote areas where there is little or no human activity. Thus, on a global scale, dust mobilization appears to be dominated by natural sources. Dust activity is extremely sensitive to many environmental parameters. The identification of major sources will enable us to focus on critical regions and to characterize emission rates in response to environmental conditions. With such knowledge we will be better able to improve global dust models and to assess the effects of climate change on emissions in the future. It will also facilitate the interpretation of the paleoclimate record based on dust contained in ocean sediments and ice cores.

42. Torres, O, P K Bhartia, J R Herman, A Sinyuk, Paul Ginoux, and B Holben, 2002: A long-term record of aerosol optical depth from TOMS observations and comparison to AERONET measurements. Journal of the Atmospheric Sciences, 59(3), 398-413.
    [ Abstract PDF ]

    Observations of backscattered near-ultraviolet radiation from the Total Ozone Mapping Spectrometer (TOMS) on board the Nimbus-7 (1979-92) and the Earth Probe (mid-1996 to present) satellites have been used to derive a long-term record of aerosol optical depth over oceans and continents. The retrieval technique applied to the TOMS data makes use of two unique advantages of near-UV remote sensing not available in the visible or near-IR: 1) low reflectivity of all land surface types (including the normally bright deserts in the visible), which makes possible aerosol retrieval over the continents; and 2) large sensitivity to aerosol types that absorb in the UV, allowing the clear separation of carbonaceous and mineral aerosols from purely scattering particles such as sulfate and sea salt aerosols. The near-UV method of aerosol characterization is validated by comparison with Aerosol Robotic Network (AERONET) ground-based observations. TOMS retrievals of aerosol optical depth over land areas (1996-2000) are shown to agree reasonably well with AERONET sun photometer observations for a variety of environments characterized by different aerosol types, such as carbonaceous aerosols from biomass burning, desert dust aerosols, and sulfate aerosols. In most cases the TOMS-derived optical depths of UV-absorbing aerosols are within 30% of the AERONET observations, while nonabsorbing optical depths agree to within 20%. The results presented here constitute the first long-term nearly global climatology of aerosol optical depth over both land and water surfaces, extending the observations of aerosol optical depth to regions and times (1979 to present) not accessible to ground-based observations.

43. Weaver, C, Paul Ginoux, N C Hsu, M-D Chou, and J Joiner, 2002: Radiative forcing of Saharan dust: GOCART model simulations compared with ERBE data. Journal of the Association for Computing Machinery, 59(3), 736-747.
    [ Abstract PDF ]

    This study uses information on Saharan aerosol from a dust transport model to calculate radiative forcing values. The transport model is driven by assimilated meteorological fields from the Goddard Earth Observing System Data Assimilation System. The model produces global three-dimensional dust spatial information for four different mineral aerosol sizes. These dust fields are input to an offline radiative transfer calculation to obtain the direct radiative forcing due to the dust fields. These estimates of the shortwave reduction of radiation at the top of the atmosphere (TOA) compare reasonably well with the TOA reductions derived from Earth Radiation Budget Experiment (ERBE) and Total Ozone Mapping Spectrometer (TOMS) satellite data. The longwave radiation also agrees with the observations; however, potential errors in the assimilated temperatures complicate the comparison. Depending on the assumptions used in the calculation and the dust loading, the summertime forcing ranges from 0 to -18 W m-2 over ocean and from 0 to +20 W m-2 over land. Increments are terms in the assimilation general circulation model (GCM) equations that force the model toward observations. They are differences between the observed analyses and the GCM forecasts. Off west Africa the analysis temperature increments produced by the assimilation system show patterns that are consistent with the dust spatial distribution. It is not believed that radiative heating of dust is influencing the increments. Instead, it is suspected that dust is affecting the Television Infrared Observational Satellite (TIROS) Operational Vertical Sounder (TOVS) satellite temperature retrievals that provide the basis of the assimilated temperatures used by the model.

44. Ginoux, Paul, M Chin, I Tegen, J M Prospero, B Holben, O Dubovik, and Shian-Jiann Lin, 2001: Sources and distributions of dust aerosols simulated with the GOCART model. Journal of Geophysical Research, 106(D17), 20,255-20,273.
    [ Abstract PDF ]

    The global distribution of dust aerosol is simulated with the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model. In, this model all topographic lows with bare ground surface are assumed to have accumulated sediments which are potential dust sources. The uplifting of dust particles is expressed as a function of surface wind speed and wetness. The GOCART model is driven by the assimilated meteorological fields from the Goddard Earth Observing System Data Assimilation System (GEOS DAS) which facilitates direct comparison with observations. The model includes seven size classes of mineral dust ranging from 0.1-6 mum radius. The total annual emission is estimated to be between 1604 and 1960 Tg yr(-1) in a 5-year simulation. The model has been evaluated by comparing simulation results with ground-based measurements and satellite data. The evaluation has been performed by comparing surface concentrations, vertical distributions, deposition rates, optical thickness, and size distributions. The comparisons show that the model results generally agree with the observations without the necessity of invoking any contribution from anthropogenic disturbances to soils. However, the model overpredicts the transport of dust from the Asian sources to the North Pacific. This discrepancy is attributed to an overestimate of small particle emission from the Asian sources.

Direct link to page: http://www.gfdl.noaa.gov/bibliography/resultstest.php?author=1043