Absorbing aerosols over Asia: A Geophysical Fluid Dynamics Laboratory general circulation model sensitivity study of model response to aerosol optical depth and aerosol absorption

Randles, C. A.; Ramaswamy, V.

doi:10.1029/2008jd010140

Cited by 109 publications

(102 citation statements)

References 64 publications

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“…Such aerosol-radiation interactions lead to large reductions of surface insolation and significant radiative heating of the atmosphere (Ramanathan and Carmichael, 2008;Johnson et al, 2008a;Malavelle et al, 2011;Milton et al, 2008). These effects may suppress the hydrological cycle by stabilizing the lower troposphere, although strong absorption can in some cases enhance precipitation regionally by increasing low-level convergence (Wu et al, 2013;Ramanathan et al, 2001;Lau et al, 2008;Randles et al, 2008). The enhancement of particulate numbers by BB can also increase the concentration of cloud condensation nuclei modifying cloud microphysical properties (Spracklen et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Evaluation of biomass burning aerosols in the HadGEM3 climate model with observations from the SAMBBA field campaign

et al. 2016

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Abstract. We present observations of biomass burning aerosol from the South American Biomass Burning Analysis (SAMBBA) and other measurement campaigns, and use these to evaluate the representation of biomass burning aerosol properties and processes in a state-of-the-art climate model. The evaluation includes detailed comparisons with aircraft and ground data, along with remote sensing observations from MODIS and AERONET. We demonstrate several improvements to aerosol properties following the implementation of the Global Model for Aerosol Processes (GLOMAP-mode) modal aerosol scheme in the HadGEM3 climate model. This predicts the particle size distribution, composition, and optical properties, giving increased accuracy in the representation of aerosol properties and physical-chemical processes over the Coupled Largescale Aerosol Scheme for Simulations in Climate Models (CLASSIC) bulk aerosol scheme previously used in HadGEM2. Although both models give similar regional distributions of carbonaceous aerosol mass and aerosol optical depth (AOD), GLOMAP-mode is better able to capture the observed size distribution, single scattering albedo, and Ångström exponent across different tropical biomass burning source regions. Both aerosol schemes overestimate the uptake of water compared to recent observations, CLAS-SIC more so than GLOMAP-mode, leading to a likely overestimation of aerosol scattering, AOD, and single scattering albedo at high relative humidity. Observed aerosol vertical distributions were well captured when biomass burning aerosol emissions were injected uniformly from the surface to 3 km. Finally, good agreement between observed and modelled AOD was gained only after scaling up GFED3 emissions by a factor of 1.6 for CLASSIC and 2.0 for GLOMAPmode. We attribute this difference in scaling factor mainly to different assumptions for the water uptake and growth of aerosol mass during ageing via oxidation and condensation of organics. We also note that similar agreement with observed AOD could have been achieved with lower scaling factors if the ratio of organic carbon to primary organic matter was increased in the models toward the upper range of observed values. Improved knowledge from measurements is required to reduce uncertainties in emission ratios for black carbon and organic carbon, and the ratio of organic carbon to primary organic matter for primary emissions from biomass burning.

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Section: Introductionmentioning

confidence: 99%

Evaluation of biomass burning aerosols in the HadGEM3 climate model with observations from the SAMBBA field campaign

et al. 2016

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“…It is important to note, however, that climate forcing by anthropogenic aerosols may not always reduce precipitation. Both Lau and Kim (2006) and Randles and Ramaswamy (1997) find substantial increases in convection over east Asia resulting from higher tropospheric concentrations of absorbing aerosols. The authors attribute precipitation increases to changes in monsoon circulation and increases in mid-troposphere stability.…”

Section: Introductionmentioning

confidence: 99%

Do biomass burning aerosols intensify drought in equatorial Asia during El Niño?

et al. 2010

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Abstract. During El Niño years, fires in tropical forests and peatlands in equatorial Asia create large regional smoke clouds. We characterized the sensitivity of these clouds to regional drought, and we investigated their effects on climate by using an atmospheric general circulation model. Satellite observations during 2000-2006 indicated that El Niño-induced regional drought led to increases in fire emissions and, consequently, increases in aerosol optical depths over Sumatra, Borneo and the surrounding ocean. Next, we used the Community Atmosphere Model (CAM) to investigate how climate responded to this forcing. We conducted two 30 year simulations in which monthly fire emissions were prescribed for either a high (El Niño, 1997) or low (La Niña, 2000) fire year using a satellite-derived time series of fire emissions. Our simulations included the direct and semi-direct effects of aerosols on the radiation budget within the model. We assessed the radiative and climate effects of anthropogenic fire by analyzing the differences between the high and low fire simulations. Fire aerosols reduced net shortwave radiation at the surface during AugustOctober by 19.1±12.9 W m −2 (10%) in a region that encompassed most of Sumatra and Borneo (90 • E-120 • E, 5 • S-5 • N). The reductions in net shortwave radiation cooled sea surface temperatures (SSTs) and land surface temperatures by 0.5±0.3 and 0.4±0.2 • C during these months. Tropospheric heating from black carbon (BC) absorption averaged 20.5±9.3 W m −2 and was balanced by a reduction in latent heating. The combination of decreased SSTs and increased atmospheric heating reduced regional precipitation by 0.9±0.6 mm d −1 (10%). The vulnerability of ecosystems to fire was enhanced because the decreases in precipitation Correspondence to: M. G. Tosca (mtosca@uci.edu) exceeded those for evapotranspiration. Together, the satellite and modeling results imply a possible positive feedback loop in which anthropogenic burning in the region intensifies drought stress during El Niño.

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“…Thus, the atmosphere becomes unstable due to the BC semi-direct effect, leading to increased cloud water and precipitation. Menon et al (2002) and Randles and Ramaswamy (2008) indicated the precipitation may increase in Asia due to the semidirect effect of BC. On the other hand, cloud water and precipitation decrease in central and southern Africa, Central America, and the Amazon during the biomass burning seasons.…”

Section: Resultsmentioning

confidence: 99%

Global Climate Modeling of Regional Changes in Cloud, Precipitation, and Radiation Budget Due to the Aerosol Semi-Direct Effect of Black Carbon

Uchida

2011

SOLA

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The aerosol semi-direct effect is generally explained as follows: aerosols, such as black carbon (BC) and mineral dust, absorb solar radiation, which warms and stabilizes the atmosphere, resulting in reduced cloudiness and cloud formation. However, the present study suggests that BC can intensify atmospheric instability and thus increase cloud water and precipitation if the BC is concentrated near the surface. Simulations using a global aerosol climate model, based on a general circulation model, show decreased cloud water over biomass-burning regions where BC is emitted to the free troposphere through the boundary layer. In contrast, increased cloud water is indicated over East and South Asia where BC from urban and industrial activities is concentrated near the surface. While the global mean change in the radiation budget at the top of the atmosphere due to the semi-direct effect of BC is estimated to be as small as +0.06 W m −2 , regional changes in cloud water, precipitation, and shortwave radiation are suggested to be large enough to modify meteorological conditions in urban and biomass-burning regions.

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Absorbing aerosols over Asia: A Geophysical Fluid Dynamics Laboratory general circulation model sensitivity study of model response to aerosol optical depth and aerosol absorption

Cited by 109 publications

References 64 publications

Evaluation of biomass burning aerosols in the HadGEM3 climate model with observations from the SAMBBA field campaign

Evaluation of biomass burning aerosols in the HadGEM3 climate model with observations from the SAMBBA field campaign

Do biomass burning aerosols intensify drought in equatorial Asia during El Niño?

Global Climate Modeling of Regional Changes in Cloud, Precipitation, and Radiation Budget Due to the Aerosol Semi-Direct Effect of Black Carbon

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