Atmospheric responses to the redistributionof anthropogenic aerosolsYuan Wang1, Jonathan H. Jiang1, and Hui Su1
1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
Abstract The geographical shift of global anthropogenic aerosols from the developed countries to the Asiancontinent since the 1980s could potentially perturb the regional and global climate due to aerosol-cloud-radiationinteractions. We use an atmospheric general circulation model with different aerosol scenarios to investigatethe radiative and microphysical effects of anthropogenic aerosols from different regions on the radiationbudget, precipitation, and large-scale circulations. An experiment contrasting anthropogenic aerosol scenariosin 1970 and 2010 shows that the altered cloud reflectivity and solar extinction by aerosols results in regionalsurface temperature cooling in East and South Asia, and warming in the US and Europe, respectively. Theseaerosol-induced temperature changes are consistent with the relative temperature trends from 1980 to 2010over different regions in the reanalysis data. A reduced meridional streamfunction and zonal winds overthe tropics as well as a poleward shift of the jet stream suggest weakened and expanded tropical circulations,which are induced by the redistributed aerosols through a relaxing of the meridional temperature gradient.Consequently, precipitation is suppressed in the deep tropics and enhanced in the subtropics. Our assessmentsof the aerosol effects over the different regions suggest that the increasing Asian pollution accounts for theweakening of the tropics circulation, while the decreasing pollution in Europe and US tends to shift thecirculation systems southward. Moreover, the aerosol indirect forcing is predominant over the total aerosolforcing in magnitude, while aerosol radiative and microphysical effects jointly shape the meridional energydistributions and modulate the circulation systems.
1. Introduction
Atmospheric aerosols from natural or anthropogenic sources have profound impacts on the regional andglobal climate [Andreae and Rosenfeld, 2008]. Currently, the radiative forcing of aerosols in the climate systemremains highly uncertain, representing the largest uncertainty in climate predictions [Myhre et al., 2013]. Inaddition to the complicated chemical and physical properties of aerosols [Zhang et al., 2015; Wang et al.,2013] and the various mechanisms of aerosol-cloud-precipitation interactions [Rosenfeld et al., 2014;Altaratz et al., 2014], the inhomogeneous and fast varying distribution of aerosols in space substantiallycontributes to the uncertainties of the aerosol forcing assessment. In particular, the anthropogenic emissionsof aerosols and precursor gases have undergone dramatic changes during the past few decades. As theworld’s most populous continent, Asia has experienced a quasi-exponential growth in industrialization,which has led to a rapid increase in emissions of gas-phase and particulate pollutants to the atmosphere.Conversely, emission levels have been stabilized or substantially reduced in the traditionally developedcountries of North America and Europe since the 1960s [Smith et al., 2011], due to stricter governmentenvironmental policies. This global redistribution of anthropogenic aerosols could potentially emerge as acritical player in global climate change due to its significant effects on regional radiative budget, as well as thedynamical and microphysical evolution of cloud systems.
The impacts of changes in anthropogenic emissions from preindustrial (PI) to present-day (PD) conditions onthe global climate and on large-scale circulations have been extensively investigated by previous modelingstudies. For instance, Ming and Ramaswamy [2011] employed an atmosphere-ocean coupled generalcirculation model (AOGCM) to study the responses of the tropical circulation and hydrological cycle to theinter-hemispherically asymmetrical aerosol forcings by contrasting the PD and PI aerosol scenarios. Theyfound a weakened (enhanced) Hadley circulation in the Northern (Southern) Hemisphere due to the elevatedaerosol levels and the associated radiative cooling in the Northern Hemisphere since the 1850s. Such amodulation results in northward energy fluxes across the equator and a southward shift in tropical rainfall.Similar climate responses in the form of a southward shift of the Intertropical Convergence Zone (ITCZ) to
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9625
PUBLICATIONSJournal of Geophysical Research: Atmospheres
RESEARCH ARTICLE10.1002/2015JD023665
Key Points:• The emission shift contributes to the“dimming” in Asia and “brightening”in the US and Europe
• Atmospheric meridional circulationsare weakened by the redistributedaerosols
• Aerosol effects from different regionscontribute distinctively to thecirculation modification
Citation:Wang, Y., J. H. Jiang, and H. Su (2015),Atmospheric responses to theredistribution of anthropogenicaerosols, J. Geophys. Res. Atmos., 120,9625–9641, doi:10.1002/2015JD023665.
Received 13 MAY 2015Accepted 24 AUG 2015Accepted article online 27 AUG 2015Published online 30 SEP 2015
the aerosol forcings since the preindustrial days were reported by Xie et al. [2013] which analyzed the simula-tion results from the Coupled Model Intercomparison Project Phase 5 (CMIP5). They also suggested thatthrough the ocean-atmosphere feedbacks in the coupled models, the aerosol forcing in the NorthernHemisphere caused a reduction of surface temperature and wind speed over the Southern Ocean. In subtro-pics and extratropics, Ming et al. [2011] simulated a wintertime equatorward shift of the subtropical jet andmidlatitude storm tracks in the Northern Hemisphere, particularly in the North Pacific, due to the pronouncedcooling effect of aerosols. Rotstayn et al. [2013] further argued that anthropogenic aerosol effects in theNorthern Hemisphere tend to weaken the subtropical jet in the Southern Hemisphere by decreasing themidtropospheric temperature gradient between low and middle latitudes.
In recent decades, especially since 1980, the regional and global climate has experienced dramatic changes.Numerous studies linked the recent climate change to the variation of the aerosols in the different regions. Atthe global scale, Allen and Sherwood [2010] and Allen et al. [2012] attributed the observed tropical expansionin recent decades to the increases in heterogeneous warming caused by the elevated absorbing aerosolssuch as black carbon as well as tropospheric ozone based on global climate simulations. Murphy [2013]showed little net clear-sky radiative forcing from the recent (2000–2012) regional redistribution of aerosolsusing satellite observation and a radiative transfer model, while the modeling study by Yang et al. [2014] sug-gested a global cooling (�0.015 K/decade) driven by the Asian aerosols since the 1970s. The influence of localchanges in aerosol amount and types on the regional radiation budget and hydrological cycle is expected tobe more prominent than that on global mean. Over South Asia, Bollasina et al. [2011] used a series of climatemodel experiments to investigate the responses of the South Asian monsoon to enhanced aerosol forcing.They concluded that the recent widespread drought in South Asia is an outcome of a slowdown of thetropical meridional overturning circulation, which can be attributed mainly to anthropogenic aerosol emis-sions. Over East Asia, long-term in situ measurements and regional cloud-resolving simulations suggestedthat the increases in anthropogenic aerosols serving as cloud condensation nuclei (CCN) can suppress lightprecipitation, enhance heavy precipitation, invigorate the convective system, and elevate lightning activitiesin China [Qian et al., 2009;Wang et al., 2011; Fan et al., 2012]. Moreover, modeling studies suggested that theobserved tendency of “southern flood and northern drought” during the weakened East Asian summer mon-soon was caused by the reduction in the land-sea thermal contrast due to the aerosol forcing over northernChina [Wu et al., 2013; Song et al., 2014]. Over the North Pacific, multiscale modeling studies suggested Asianpollution outflow accounts for an enhanced amount of deep convective clouds, increased precipitation, andinvigorated storms during the wintertime [Wang et al., 2014a, 2014b]. Over Central Europe, regional model-ing simulations constrained by reanalysis data showed that aerosol reduction and the associated radiativeeffects are responsible for about 80% of the atmospheric brightening and 23% of the surface warming sincethe 1980s [Nabat et al., 2014, Cherian et al., 2014].
Most of the previous modeling studies focused on the regional changes in cloud systems and atmosphericstates due to local aerosol perturbations using regional climate modeling systems. Hence, there is a funda-mental need to comprehensively assess the impacts of the observed shift of global anthropogenic aerosoldistributions on the global radiation budget, hydrological cycle, and circulation systems. However, it ischallenging to achieve this assessment by analyzing all of the CMIP5 simulation results. In the currentCMIP5 GCMs, the representations of aerosols and parameterizations of aerosol-cloud interactions varysubstantially in the degree of complexity, which profoundly affects quantifications of aerosol effects[Ekman, 2014]. NCAR-DOE Community Earth System Model (CESM) employs sophisticated parameterizationsof aerosol effects in terms of an online prognostic aerosol module and an explicit aerosol activation scheme,but its simulation results are not included in some recent CMIP5 analyses [i.e., Song et al., 2014]. As a first stepin a series of research efforts, we employ the atmospheric component of CESM in this study to illustrate fastresponses in the climate system, without consideration of ocean feedbacks, due to dramatic changes inaerosol distributions over the globe. Serving as important references, the fast responses to aerosol perturba-tions reported in this study will be systematically compared with ocean-mediated responses from slab oceanconfigurations like Ganguly et al. [2012a, 2012b] as well as fully coupled transient simulations like Bollasinaet al. [2011] in our future studies. Such comparisons can facilitate the attribution of the aerosol-inducedchanges to fast atmospheric responses or slow feedbacks from air-sea interactions. In this study, the possibleglobal impacts of the aerosol changes over particular regions will be assessed individually, and we will alsoseparate and compare the aerosol indirect (microphysical) effects from the aerosol direct (radiative) effects.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9626
This paper is structured as follows: theexperiment design and the importantaspects of the aerosol effects pertainingto our numerical model are provided insection 2, the simulated impacts of theredistributed aerosols from 1970 to2010 from a suite of sensitivity experi-ments are discussed in section 3, and aconclusion and discussions on themeritand the limitation of this modelingstudy are provided in section 4.
2. Model Description
The atmospheric component of theCESM version 1.0.4, i.e., CAM5.1, isadopted in this study. It includes sub-
stantial improvements and updates for the dynamics and the physical parameterizations compared to pre-vious versions. For example, a new moist turbulence scheme [Bretherton and Park, 2009] explicitlysimulates cloud-radiation-turbulence interactions in planetary boundary layer as well as the aerosol effectson stratus. Large-scale cloud and precipitation processes are parameterized with a prognostic two-momentbulk stratiform cloud microphysics scheme [Morrison and Gettelman, 2008]. Deep convection is parameter-ized by the Zhang and McFarlane [1995] scheme with modifications of Neale et al. [2008] to use dilute con-vective available potential energy for closure. Note that aerosol indirect effects on deep convective cloudsare still not explicitly considered in CAM5.1. In addition, parameterizations of homogeneous ice nucleationand heterogeneous immersion nucleation in cirrus clouds [Liu and Penner, 2005] are implemented in themicrophysics scheme, making it possible to explicitly simulate the effects of sulfate and dust aerosol servingas ice nuclei on cold clouds. Aerosol radiative effects in shortwave and longwave are taken into account bythe Rapid Radiative Transfer Method for GCMs (RRTMG) radiative transfer scheme [Iacono et al., 2008]
The modal aerosol module with three modes (MAM3) is available in CAM5.1, which provides internallymixed representations of number concentrations and mass for Aitken, accumulation, and coarse aerosolmodes [Liu et al., 2012]. Various types of aerosol with different hygroscopicities and optical propertiesare considered in MAM3, including sulfate, black carbon (BC), primary organic matter, secondary organicaerosol, dust, and sea salt. The aerosol module accounts for most of the important processes associatedwith atmospheric aerosols, including emission, nucleation, coagulation, condensational growth, gas- andaqueous-phase chemistry, dry deposition, in-cloud and below-cloud scavenging, and reproductionfrom evaporated cloud droplets. The multicomponent aerosol activation parameterization is based onthe scheme of Abdul-Razzak and Ghan [2000]. Anthropogenic emissions are adopted from theIntergovernmental Panel on Climate Change (IPCC) AR5 historic emission data set developed for theCMIP5 [Lamarque et al., 2010], which covers the time period of 1850–2010. Production of sea salt fromocean and mineral dust aerosols from desert will be online calculated following the parameterizationsby Mårtensson, 2003 and Yoshioka et al. [2007], respectively.
To illustrate the overall magnitude of emission shift, the historic and projected temporal evolutions of the SO2
emission from 1950 to 2050 are shown in Figure 1 based on the IPCC AR5 anthropogenic emission data set incombination with the representative concentration pathways (RCP 8.5) [Riahi et al., 2011]. As the most impor-tant precursor gas for sulfate aerosol, evolutions of SO2 emission reflect that anthropogenic emissions overEurope and North America have been sharply reduced since 1970 by 73% and 63%, respectively, due tothe energy usage transformation in Central Europe like the “Black Triangle” region (Germany-Porland-Czech Republic) and the legislative controls, such as the Clean Air Act in the US. Meanwhile, SO2 emissionsgrew fast over developing Asian counties like China and India along with the booming local economy. Bythe end of 2010, SO2 emissions have been elevated by four and eight times over East Asia and South Asia,respectively, compared to the emission levels in 1970. As projected by the RCP 8.5, such an emission shiftfrom developed countries to developing ones is expected to last for another 10–20 years. Therefore, it is a
Figure 1. Temporal evolutions of the SO2 emissions from anthropogenicsectors (such as energy and industry) over South/East Asia, Europe, andNorth America.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9627
critical moment now to investigate the regional aerosol-cloud interactions and the atmospheric responses tothe unique inhomogeneous aerosol forcings.
In this study, the emission scenarios at the years 1970 and 2010 are chosen to represent the historical day(HD) and the present-day (PD) aerosol conditions, respectively. The model’s resolution is 1.25° in longitudeand 0.9° in latitude with 30 vertical levels from surface to 3 hPa. The sea surface temperature and sea iceare prescribed by the year 1982–2001 climatology for both PD and HD experiments. The modeling experimentfor each anthropogenic emission scenario consists of seven ensemble simulations starting from randomlyperturbed initial meteorological fields. Only aerosols forcings are different between PD and HD, while all otherforcings like greenhouse gases are identical. For each ensemble member, the model ran for 10 years, and theresults from the last 5 years in each run are analyzed. Four regions (countries) are targeted in this study,including East Asia (China), South Asia (India), Europe, and North America (US).
3. Results3.1. Model Evaluation
Before sensitivity experiments, CAM5 PD simulations of aerosol, cloud properties, and top-of-atmosphere(TOA) radiation fluxes are evaluated with available satellite measurements. At the global scale, CAM5captures the major hot spots of AOD around the world in comparison of the Moderate Resolution ImagingSpectroradiometer (MODIS) measurements, including the mineral dust over Sahara, sea salt over SouthernOcean, and the anthropogenic pollution over East and South Asia, as shown in Figures 2a and 2b. The overallcorrelation coefficient between the AOD spatial patterns from model and satellite is 0.4. The global mean inAOD is 0.13 in CAM5, which is comparable to 0.15 averaged from 6 year MODIS measurements from 2005 to2010. However, at finer scales, the magnitude of AOD in CAM5 is lower than MODIS for most of the nondustregions. This is consistent with the previous study by Shindell et al. [2013] that systematically evaluated AODsimulations in CMIP5 models. The underestimated AOD over remote maritime areas in CAM5 was discussedin Wang et al. [2013] and was attributed to the unrealistic wet removal processes in convective clouds ofCAM5. Over continents, biases on AOD could stem from underestimations in the emissions inventory andunresolved subgrid variations of relative humidity due to the model’s coarse resolution. Better than theAOD simulations, spatial patterns of total cloud fraction in CAM5 are comparable to the MODIS retrievals witha correlation coefficient of 0.7. The model reproduces the distributions of tropical convective clouds, cloudswith midlatitude storm tracks, and nimbostratus clouds over Southern Ocean (Figures 2c and 2d). The model-simulated cloud properties such as liquid water path (LWP) and ice water content have been validated bysatellite measurements [Jiang et al., 2012]. Precipitation in CAM5 is evaluated by the Tropical RainfallMeasuring Mission (TRMM) measurements which have spatial coverage from 50°S to 50°N (Figures 2e and2f). Globally, the rainfall patterns show a good agreement between CAM5 and TRMM. Precipitation rate isbiased high over a narrow belt along the Central Pacific ITCZ and underestimated over the Western Pacificwarm pool. The precipitation patterns and the magnitude with midlatitude cyclones are well captured byCAM5. The TOA shortwave radiation fluxes simulated by CAM5 also show a good agreement with theClouds and the Earth’s Radiant Energy System (CERES) measurements in terms of the spatial patterns(correlation coefficient of 0.8) and magnitude. The overall performance of CAM5 is reasonable as suggestedby the previous inter-model comparison study [Jiang et al., 2012], which makes it eligible to assessatmospheric equilibrium and transient responses to aerosol changes.
3.2. Responses to Aerosol Forcings from 1970 to 2010
Under the influence of the shifted anthropogenic emissions, the differences and fractional changes in aerosoloptical depth (AOD) between PD and HD are pronouncedmainly over the Northern Hemisphere. As shown inFigures 3a and 3b, the significant AOD increases occur in East China, India, and Southeast Asian countries.AOD over the downwind regions of the pollution centers like North Pacific and North Indian Ocean is alsoelevated. In the Central Europe and Northeast US, the AOD reductions vary by 20–60%. It is important to notethat because of the emission reduction in Europe, the aerosol loading over the Arctic region decreases by upto 40%. The AOD variations over North Africa and Middle East are mainly caused by the varied dust loadingunder the modulated regional meteorological conditions. The changes in the absorption AOD in Figure 3cindicated the anthropogenic sources of black carbon and light absorbing organic carbon. It is clear thatincreases in the absorbing aerosol amount mainly occur in the East and South Asia with the highest
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9628
concentration in East China. Europe experiences a slight decrease in BC, while there is no reduction in the BCover North America. From the chemical composition analysis of the fine-mode aerosols over four targetregions (Figure 4), we find out that sulfate aerosols account for the most variations of the aerosol mass fromHD to PD in all four regions among all six types of aerosols.
The net aerosol forcing at TOA caused by the shifted aerosol distribution is �0.23W/m2 in global mean,which implies that the elevated pollution in Asian countries exerts larger influence on the radiation budgetthan the aerosol reduction in Europe and US. More specifically, the global mean TOA shortwave aerosol for-cing is�0.31W/m2, and the longwave aerosol forcing is +0.08W/m2. The global map of aerosol net forcing atTOA in Figure 5a shows the positive radiation anomaly over Europe and US due to the aerosol reductions.Interestingly, the largest decrease in TOA net radiation flux does not occur over the pollution centers likeChina and India where aerosol concentrations have been increased most dramatically. Such phenomenacan be explained by the compensating effects from the increased longwave radiation forcing and the strong
Figure 2. Model evaluation using satellite measurements. Climatology of AOD from (a) CAM5 PD simulations and (b)MODIS L3 measurements; climatology of total cloud fraction from (c) CAM5 PD simulations and (d) MODIS L3 measurements;climatology of total precipitation from (e) CAM5 PD simulations and (f) TRMM measurements; climatology of outgoingshortwave radiation at TOA from (g) CAM5 PD simulations and (h) CERES measurements.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9629
radiative absorption in the atmosphereover Asia [Ghan et al., 2012]. As shownin Table 1, TOA longwave forcings are+1.47W/m2 and +2.22W/m2 for Eastand South Asia, respectively, both ofwhich partially offset the shortwave for-cings. The enhanced longwave warm-ing effects are mainly caused by theelevated ice content with high cloudsover East and South Asia (Table 1).Meanwhile, if we contrast the short-wave fluxes between the TOA andthe surface, we find that there is a pro-nounced warming in the atmosphereover the Asian countries, +3.5W/m2
for East Asia and +2.2W/m2 for SouthAsia. Such a warming effect fromabsorbing aerosols in the atmospherealso acts to offset a part of the net cool-ing at TOA.
The contributions to the aerosol forcingsfrom aerosol direct radiative effects andfrom aerosol-cloud interactions can beinferred by decomposing the aerosolforcing into clear-sky and cloudy condi-tions. It is interesting to see that the rela-tive contributions from different aerosoleffects are distinctive over the differentregions, as shown in Table 1. In compar-ison of the clear-sky shortwave aerosolforcing and aerosol-induced shortwavecloud forcing (SWCF), we find that overEast and South Asia, the aerosol-induced cloud forcings are one to twotimes larger than the aerosol forcingsat clear-sky conditions, while in Europe,the clear-sky aerosol radiative forcing(1.02W/m2) is close to the aerosol-induced cloud forcing (1.54W/m2).More comprehensive analysis and com-parison between aerosol radiative andmicrophysical effects will be conductedwith the additional experiments insection 3.4.
With the modulated radiation budgetat the different regions, the surfacetemperatures (Ts) respond accordingly.Ts increases by 0.13 and 0.11 K forEurope and US, and decreases by 0.13and 0.1 K for East Asia and South Asia,respectively. Even though the relativechanges of emission and AOD are lar-ger in East Asia than those in Europe
Figure 4. CAM5 simulated six types of aerosol compositions in the accu-mulation mode for PD and HD.
Figure 3. CAM5 simulated (a) difference and (b) fractional change of aero-sol optical depth, and (c) difference of absorbing aerosol optical depthbetween PD and HD. Black dots indicate significance larger than 90%.Black boxes indicate four target regions of our interest, including the US(60°–135°W, 25°–45°N), Europe (0°–45°E, 40°–65°N), South Asia (65°–90°E,5°–35°N), and East Asia (90°–125°E, 20°–45°N).
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9630
(Table 1), the absorbing aerosol components buffer the surface temperature changes to the aerosol pertur-bation in East Asia, resulting in a change of similar magnitude compared to Europe. Considering the observedglobal warming rate is about 0.12 K/decade caused by the greenhouse gases since the 1950s [Hartmann et al.,2013], the temperature changes induced by the redistributed aerosols are of climatic significance over thosefour regions. As a back-of-the-envelop calculation, the aerosol effects from 1970 to 2010 may cause a
Figure 5. CAM5 simulated changes in (a) TOA radiation net flux, (b) liquid water path, (c) surface temperature, and (d) low cloud fraction between PD and HD.
Table 1. Simulated Effects of Redistributed Aerosols on the Various Atmospheric Properties Over Four Targeted Regionsa
fraction; CLDMED—middle cloud fraction; CLDHGH—high cloud fraction. For those fluxes terms, S—shortwave, L—longwave, C—clear sky, and CF—cloudforcing; positive values for downward fluxes and negative values for upward fluxes.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9631
0.03 K/decade surface warming in Europe, which is about one fourth of the observed global warming rate.Such an estimation of the contribution of aerosols to the global warming in Europe is consistent with theprevious regional modeling assessment, which is about 23% as estimated by Nabat et al. [2014]. Note thatsea surface temperature is prescribed in our simulations, so these experiments still likely underestimatethe responses of the surface temperature to the aerosol perturbations.
To further corroborate the role of the aerosols in regulating the surface temperature trend, we explore thesurface temperature record from European Centre for Medium-Range Weather Forecasts (ECMWF)ERA-Interim reanalysis data. Since the global mean surface temperature trend from 1980 to 2010 is mainlymodulated by the greenhouse gas variations, we subtract out the global land-mean temperature trend overthe continental regions to highlight the regional differences in the temperature trends. The time series andthe linear trend of the surface temperature anomaly over the four target regions in Figure 6 show thatEurope experienced the largest warming trend of the surface temperature compared to the other threeregions. A warming trend is also found in the US but with a weaker magnitude. East and South Asia havedecreasing rates of the surface temperature compared to the other regions of the world (Figures 6c and 6d).Even though there are various underlying factors that can modulate the surface temperature such asgreenhouse gas forcing and surface heat capacity changes, the observed distinct and inhomogeneoustemperature trends over different regions still suggest that the variations of aerosols could effectivelyinduce local surface temperature changes and regulate the historical temperature trends. Such a findingis supported by the recent model-evaluation study [Ekman, 2014] that revealed that parameterizations ofaerosol-cloud interactions in AOGCMs are crucial in simulating the historical surface temperature trends.By grouping and comparing CMIP5 models with respect to their sophistication in the representations ofaerosols and aerosol indirect effects, Ekman [2014] found that the more accurate aerosol forcings fromthe realistic treatment of aerosol budget and the sophisticated parameterization of cloud droplet concen-tration as a function of both aerosol concentration and supersaturation help to reproduce the observedsurface temperature trends from 1965 to 2004.
As an important indicator of the aerosol indirect effect, LWP exhibits distinct changes between PD and HD.Figure 5b shows the patterns of LWP variations are well correlated with those of AOD changes with a globalcorrelation coefficient of 0.7, implying the high sensitivity of LWP to the aerosol perturbations in CAM5 [Wanget al., 2011]. Different from the characteristic responses of LWP, the signals of cloud fraction seem to be quitecomplicated and even close to the noise level (Figure 5d). Only the regions with reduced aerosol amount likeCentral Europe, Northeast US, and Arctic experience significant reduction of the low cloud fractions, while the
Figure 6. 1980–2010 surface temperature anomaly trends over (a) East Asia, (b) South Asia, (c) US, and (d) Europe from ECMWF ERA-Interim. A global land-only meanof the surface temperature has been subtracted out over each region.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9632
low cloud fractions in other parts of the world like Asia show little response to aerosol perturbations. One pos-sible explanation is that the cloud occurrences over lower latitudes in East and South Asia are mainly regu-lated by large-scale conditions other than the microphysical factors. A quantitative comparison of theresponses of cloud number concentration, LWP, and cloud fraction in Table 1 further reveals that cloudmicrophysical properties, such as droplet number concentration, size, and water content, are more sensitiveto the aerosol perturbation than cloud macrophysical properties like cloud type and fraction, in terms of thelarger fractional changes and statistical significance.
Large-scale circulations are mainly governed by the energy distribution within the climate system [Ming andRamaswamy, 2011]. The zonal mean radiation budget at TOA in Figure 7a shows that the shifted anthropo-genic emissions mainly perturb the meridional distribution of radiation in the Northern Hemisphere. Theelevated aerosol loading over Asian countries results in the energy deficit over tropics from 0°N to 30°Nand high latitudes 50°–70°N. The reductions of aerosols over the US and Europe are responsible for theenergy surplus in the extra-tropics (30°–50°N) and Arctic region. Longwave radiation anomaly acts differentlywith shortwave, but its magnitude is smaller than that of the shortwave radiation. The redistributed energy inthe atmosphere induces the variation of temperature gradient and large-scale circulation. The increase in thetemperature above 150 hPa over the tropics (Figure 7b) and the associated reduction in tropopause heightare attributed to the weakened tropical convections induced by the redistributed aerosols. The significantcooling within PBL in the lower latitudes and warming in the higher latitudes tend to relax the meridionaltemperature gradient near the surface. As shown in Figure 7c, the reduced meridional streamfunction inthe low latitudes clearly illustrates the weakening of the Hadley circulation. Comparing the south and northbranches of the Hadley cell, the weakening is more significant in the north branch. Accordingly, the mid-latitude circulation is slowed down in the Northern Hemisphere. The transient eddy kinetic energy (TEKE) cor-responds to the jet streams and baroclinic eddy activities in the upper troposphere. The changes in TEKE fromHD to PD in Figure 7d show that the jet stream in the Northern Hemisphere is shifted toward the Arctic,which supports the widening and expansion of the Hadley cell after it gets to slow down under the influence
Figure 7. (a) Zonal mean of the changes in the TOA radiation between PD and HD. Latitude-vertical curtain profiles of thePD-HD changes (color contours) and HD climatology (contour lines) in (b) air temperature, (c) meridional streamfunction,and (d) transient eddy kinetic energy.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9633
of the emission shift. The reduced TEKEand decreased zonal winds in the lowertroposphere over tropics further revealthe weakened Walker circulation alongwith the slowdown of the Hadley cell.
Changes in precipitation are closelylinked to variations of the large-scalecirculations. Since aerosol microphysicaleffects on the deep convective cloudsare still missing in the convection para-meterization of CAM5, the responsesof the convective precipitation mainlyreflect the modulated atmosphericdynamics and instability induced byaerosol radiative effects. The changes inthe global stratiform and convectiveprecipitation with the shifted emissionsources in Figure 8 show that there is sig-nificant suppression of the convectiveprecipitation along ITCZ including theCentral Pacific, West Pacific warm pool,and central Africa in PD. The precipita-tion over the East and South Asia conti-nent is also significantly reduced.Conversely, the large-scale stratiformprecipitation which is explicitly linkedwith CCN concentration exhibits rela-tively weak sensitivity to aerosolperturbations. Globally, there is no clearpattern for stratiform precipitationchanges under the influences of redis-tributed aerosols. Over the four targetregions, the change of the stratiformprecipitation is weakly anticorrelatedwith the aerosol changes, i.e., increased
stratiform precipitation over Asia and decreased stratiform precipitation over Europe and the US (Table 1).Also note that with the one-degreemodel resolution, the global amount of large-scale precipitation from strati-form clouds is much smaller than that of convective precipitation from convection parameterizations.Therefore, the total precipitation changes are dominated by the aerosol radiative effects on convective cloudsthrough aerosol-radiation-convection interactions. The latitudinal profile of the zonal mean precipitation inFigure 8c clearly shows the suppressed precipitation in the deep tropics (5°S–15°N) and the enhanced precipi-tation in the subtropics (5°–15°S, 15°–30°N). Those precipitation changes corroborate the weakening of bothascending and descending branches of the Hadley circulation, which corresponds to the “wet” and “dry”regions at the different latitudes, respectively. Such an aerosol effect may mitigate the previously reportedgreenhouse gas effect on the hydrological cycle, i.e., the “wet” gets wetter and the “dry” gets drier [Held andSoden, 2006; Chou et al., 2009; Lau and Kim, 2015]. Also note that the fixed sea surface temperature in our experi-ments may limit the variations of water vapor availability and precipitation especially over the ocean.
In South and East Asia, the precipitation is found to be significantly reduced in PD. We examine the seasonalchanges of the precipitation in South and East Asia. The 4.5% and 4.0% reductions of the convective precipi-tation Asia are found during the summer monsoon season [June–July–August (JJA)] in South and East Asia,respectively. Those reduction rates and magnitude are highest among the four seasons and explain mostof the annual precipitation reductions (�3.3% and�2.5%) over the two regions. The significant JJA precipita-tion reductions suggest the weakening of the East Asian and South Asia summer monsoons by the
Figure 8. CAM5 simulated precipitation changes from (a) convectivesources and (b) large-scale stratiform sources between PD and HD. (c)Zonal mean of the total precipitation changes (black line) in comparisonto the simulated HD climatology (blue line).
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9634
redistributed anthropogenic aerosols. The reduced surface temperature over the Asian continent and thedecrease in the land-ocean thermal contrast may explain the weakened East and South Asian summer mon-soons with elevated local pollution. Similarly, Ganguly et al. [2012b] reported a 12% reduction of precipitationwith summer monsoon in South Asia using CAM5 coupled with a slab ocean model. The larger precipitationreduction in that study may stem from the larger aerosol perturbation between PD and preindustrial condi-tions as well as the stronger feedbacks from the prognostic sea surface temperature.
3.3. Assessing the Global Impacts of Aerosols From Different Regions
To better understand the roles of the aerosols from different regions, we perform additional experiments thatonly consider the aerosol increase in Asia or aerosol decrease in Europe and US. One experiment “PD(Asia)”has the present-day aerosol emission scenario only over South and East Asia and the historical emissionscenarios for the rest of the world. The other experiment “PD(EU)” has the present-day aerosol emission sce-nario only over Europe and US and the historical emission scenarios for the rest of the world. Figures 9a and9b show the corresponding AOD changes in the two experiments. The responses of the surface temperatureare quite localized, which closely follow the pattern of the local AOD variations (Figures 9c and 9d); i.e., theAsian pollution leads to the significant cooling over Asia, and the aerosol reduction in Europe and US resultsin the warming locally. The precipitation responses to the aerosol forcing from different regions are intriguingand distinctive from the temperature responses. Even though we perturb the aerosols over the differentregions in the different magnitude, PD(Asia) and PD(EU) exhibit similar patterns of the total precipitationchanges (Figure 10). The changes in the zonal mean precipitation clearly show three common characteristicpatterns between the two experiments, including a precipitation increase in 10°S–5°N, a decrease in 5°N–20°N,and another increase in 20°N–30°N.
The variations of the TOA energy budget and the large-scale circulations from the two experiments are inves-tigated to explain the zonal mean precipitation changes. TOA radiation analyses in Figures 11a and 11b showthe distinctive radiation budgets between PD(Asia) and PD(EU). In PD(Asia), the increase of anthropogenicaerosols in Asia exerts a large cooling effect in tropics and subtropics of the Northern Hemisphere but a moreintensive cooling around 60N due to themodulated high-latitude clouds. In PD(EU), the reduction of aerosolsin Europe and US results in a strong warming effect in 30°–80°N. The aerosol perturbations in the twoexperiments both induce the significant changes in meridional circulation in the Northern Hemisphere butin different manners as indicated by the changes in the meridional streamfunction in Figures 11c and 11d.For the Asian-aerosol-only case in PD(Asia), due to the cooling in the tropics and subtropics in the
Figure 9. (a) AOD and (c) surface temperature changes in the PD(Asia) experiment which only considers the emission changes over Asia. (b) AOD and (d) surfacetemperature changes in the PD(EU) experiment which only considers the emission changes over US and Europe.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9635
Figure 10. (a) Zonal mean of total precipitation changes in the PD(Asia) experiment which only considers the emissionchanges over Asia. Same in Figure 10b but for the PD(EU) experiment which only considers the emission changes overUS and Europe. Black lines denote precipitation differences between different experiments, and blue lines denote thesimulated HD climatology.
Figure 11. (a) Zonal mean of the changes in the TOA radiation between PD(Asia) and HD. Latitude-vertical curtain profilesof the PD(Asia)-HD changes (color contours) and HD climatology (contour lines) of the (c) meridional streamfunction and(e) transient eddy kinetic energy in the PD(Asia) experiment which only considers the emission changes over Asia. Same inFigures 11b, 11d, and 11f but for the PD(EU) experiment which only considers the emission changes over US and Europe.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9636
Northern Hemisphere, the northern branch of the Hadley cell becomes weaker. The boundaries of the Hadleycell extend toward the high latitudes, as suggested by the poleward shifts of the TEKE in both hemispheres inFigure 11e. For the Europe-US-aerosol-only case, the most prominent change in the meridional streamfunc-tion is the significant north-to-south cross-equator flux, which corresponds to the southward shift of theHadley cell. As an analogue to the previous finding about the northward shift of the tropical circulation underthe significant cooling in the Northern Hemisphere from the PD versus PI aerosol conditions [Ming andRamaswamy, 2011], the southward shift of the latitudinal circulations is attributed to the energy surplus inthe Northern Hemisphere from the aerosol reductions in Europe and US. The southward shift in the latitudinalcirculations can also be identified from the shift in the locations of the midlatitude jet stream in bothhemispheres (Figure 11f). The distinctive responses of the large-scale circulations to the different aerosolforcing imposed from different regions underline the importance of accurately considering the aerosol spatialvariations in the climate assessment.
3.4. Separating the Aerosol Indirect Forcing from Direct Forcing
In CAM5 simulations, aerosol effects on radiation and cloud formation at the grid scale are explicitly repre-sented. Since the cloud adjustment to aerosol perturbations has the single largest uncertainty in the aerosolforcing assessment [Myhre et al., 2013], it is valuable to isolate the aerosol indirect effect, i.e. aerosol serving asCCN/IN to affect cloud formation, from the overall effect of aerosols and to assess its climatic influence underthe background of the globally shifted emissions. Following the aerosol forcing decomposition method byGhan et al. [2012], we turn off all the radiation calculations relevant to the aerosol properties in the modeland perform additional ensemble simulations with only aerosol indirect effect (AIE).
The global mean in the TOA radiation flux changes for AIE is �0.32W/m2, which represents an even largerradiative cooling induced by aerosols than �0.23W/m2 in aerosol-all-effect (AAE) simulations. Over the fourtarget regions, TOA aerosol forcings are close between AIE and AAE, but the forcings over surface and in theatmosphere exhibit significant differences over different regions, as shown in Table 2. AIE induces much lar-ger shortwave cloud forcings over South/East Asia and Europe than those in AAE. It implies the aerosol directand semidirect effects could exert a negative influence on the aerosol-induced cloud formation by suppres-sing (enhancing) convection and cloud development under the polluted (pristine) conditions. Particularly inEast Asia, surface temperature becomes cooler in AIE than that in AAE, indicating a more prominent “bright-ening” effect of pollution in East Asia by only considering the aerosol-cloud interactions. All other threeregions show the weaker temperature changes when the aerosol radiative effects are excluded.
Table 2. Same With Table 1 but for the Aerosol-Indirect-Effect-Only Experiments (AIE)a
aBold numbers indicate significance of t test is larger than 90%.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9637
The zonal mean TOA forcing induced by the aerosol indirect effects (Figure 12a) varies at different latitudeswitha similar pattern to that in AAE simulations in Figure 8a. In the Northern Hemisphere, the peak of zonal meanTOA shortwave radiative cooling caused by the Asian pollution in AIE is about �1.6W/m2, which is larger than�1.3W/m2 in AAE. It can be explained by the excluded aerosol absorption in AIE. Meanwhile, by only consider-ing the aerosol microphysical effects, the net TOA radiative warming at 30°–50°N becomes much weaker andless significant. With similar meridional patterns of the TOA aerosol forcing, AIE induces circulation changesin a similar manner compared to AAE but with the smaller strength. As shown in Figure 12b, the diminishedwarming effect over US and Europe in AIE results in a weaker reduction of the near surface temperature gradi-ent over subtropics (around 30°N) than that in AAE (Figure 7b). Hence, the overall weakening effect on the tro-pical circulation in AAE becomes less significant in AIE (Figure 12c). Meanwhile, there exists a large statisticallysignificant decrease in the temperatures at the upper troposphere and lower stratosphere (UTLS, 100–300hPa)over 60°N–90°N in AIE (Figure 12b) but absent in AAE (Figure 7b), which collocates closely with a strong increasein TEKE (Figure 12d). Themuch larger net TOA radiative warming over 60°N–90°N in AIE can partially explain theenhancement of the north polar circulation, the elevation of the tropopause height, and the reduction in tem-perature at UTLS over the Arctic. The changes in midlatitude circulations as indicated by the poleward expan-sion of the midlatitude jet stream also interact with the dynamics in the Arctic region. The dramatic differencesin the Arctic region between AIE and AAE indicate the profound impacts of aerosol direct effects over highlatitudes through modulating the global circulations.
4. Conclusion and Discussions
In this modeling study, we address the emerging issue on the climatic impacts of the geospatial redistribution ofanthropogenic aerosols since the 1970s. A series of sensitivity simulations using the NCAR CAM5model are con-ducted to investigate the atmospheric responses to perturbations of the aerosol amounts over different regions.The primary task of this study is to examine the changes in radiative forcing, clouds, precipitation, and large-scale
Figure 12. Same with Figure 7 but for aerosol-indirect-effect-only (AIE) experiment.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9638
circulations induced by the elevatedpollution levels in the Asian developingcountries as well as the anthropogenicemission reductions in developed coun-tries in Europe and North America. Bycontrasting the simulations with aerosolemission scenarios in the years 1970and 2010, which represent the historicalday (HD) and present-day (PD) condi-tions, respectively, we find that there isabout �0.23W/m2 cooling at TOA inthe global mean. Shortwave radiationcontributes �0.31W/m2 due to theenlarged aerosol scattering and cloudreflectivity, while the longwave radiationchange is +0.08W/m2 because of theincrease in high clouds and columnwater vapor in the troposphere.
Regionally, the elevated pollution levels in Asia give rise to �0.1 and �0.13K surface cooling in South andEast Asia, while the pollution reductions in Central Europe and US are responsible for +0.11 and +0.13 Kincreases in the surface temperature, respectively. Such changes in the surface temperature are supportedby the different temperature trends over the different regions from ECMWF ERA reanalysis data. Under thebackground of global warming since the 1950s, the reanalysis data show that the warming trends in thesurface temperature are larger in Europe and US than those in East and South Asia from 1980 to 2010.
The comparison of the fractional changes of cloud properties between PD and HD reveals that cloudmicrophy-sical properties, such as cloud droplet number, size, and water content, are more sensitive to aerosol perturba-tions than cloud macrophysical properties like cloud fraction and distribution (Table 1). The convectiveprecipitation is susceptible to the perturbation of the redistributed aerosols in CAM5, which is attributed tothe altered atmospheric dynamics and circulations following the changes in the regional radiation budget.Conversely, the stratiform precipitation predicted by the microphysical scheme at the grid scale exhibits rela-tively less sensitivity to aerosols than convective precipitation. The suppressed precipitation over ITCZ andthe enhanced precipitation over the subtropics indicate a weaker Hadley circulation under the influence ofthe shifted anthropogenic emissions. The zonal mean of the meridional streamfunction further reveals theslowdown of the latitudinal circulations in the Northern Hemisphere due to the energy deficit at lower latitudesand surplus at higher latitudes. Both the boundary of the Hadley cell and the midlatitude jet stream exhibit apoleward shift. Therefore, we conclude that the modulation of the large-scale circulations is subject to thevariation of radiation budget and the energy distribution over the globe.
By conducting the simulations considering only the East/South Asia PD emissions or only the Europe/US PDemissions, we individually assess the effects of aerosols from certain regions of the world. Similar to the resultsfrom the redistributed-aerosol case, the Asian-aerosol-only case predicts a weaker northern branch of theHadley cell and a poleward extension of the Hadley cell due to the cooling in the tropics and subtropics.Differently, the aerosol reductions in Europe and US and associated warming effect induce an inter-hemispherical shift of the latitudinal circulation in terms of the stronger/weaker motions in thesouthern/northern branches of the Hadley circulation and the cross-equator mass fluxes. The distinctiveresponses of the large-scale circulations to the different aerosol forcings imposed from different regionssuggest the potential importance of aerosol spatial variations to the climate change.
The aerosol-indirect-effect-only experiment shows that aerosol-cloud interactions account for a larger por-tion of the aerosol forcing at TOA. Particularly, the aerosol indirect effect is critical for the “dimming” effectin East and South Asia, and the surface temperature reduction becomes even larger by only consideringthe aerosol indirect effect in East Asia (Figure 13). Excluding the aerosol direct effect can also dampen thewarming effect over the US and Europe, which limits the influence of the redistribution of aerosols on theglobal circulations. Hence, aerosol direct and indirect effects work together to modulate the meridionalenergy distribution and alter the circulation systems.
Figure 13. Comparison of aerosol radiative forcings (PD-HD) betweenaerosol-indirect-effect-only (AIE) experiment and all-aerosol-effect (AAE)experiment.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9639
As a first-order assessment, the current study focuses on the fast response of the atmospheric system tocharacteristic aerosol perturbations around the globe. The sensitivity of the aerosol effects may be con-strained by the fixed conditions of ocean and sea ice, since previous modeling study suggested a strongereffect of aerosols on the large-scale circulations with the interactive SST in a slab ocean setup [Allen andSherwood, 2010]. Future studies will employ the comprehensive atmosphere-ocean fully couple general cir-culation model to systematically examine the transient and equilibrium response of the whole earth systemto the shifted anthropogenic emissions and the redistributed aerosols.
ReferencesAbdul-Razzak, H., and S. J. Ghan (2000), A parameterization of aerosol activation: 2. Multiple aerosol types, J. Geophys. Res., 105(D5),
6837–6844, doi:10.1029/1999JD901161.Allen, R. J., and S. C. Sherwood (2010), The impact of natural versus anthropogenic aerosols on atmospheric circulation in the Community
Atmosphere Model, Clim. Dyn., 36(9–10), 1959–1978.Allen, R. J., S. C. Sherwood, J. R. Norris, and C. S. Zender (2012), Recent Northern Hemisphere tropical expansion primarily driven by black
carbon and tropospheric ozone, Nature, 485(7398), 350–354.Altaratz, O., I. Koren, L. A. Remer, and E. Hirsch (2014), Review: Cloud invigoration by aerosols—Coupling between microphysics and
dynamics, Atmos. Res., 140–141, 38–60.Andreae, M. O., and D. Rosenfeld (2008), Aerosol–cloud–precipitation interactions. Part 1. The nature and sources of cloud-active aerosols,
Earth Sci. Rev., 89(1–2), 13–41.Bollasina, M. A., Y. Ming, and V. Ramaswamy (2011), Anthropogenic aerosols and the weakening of the South Asian summer monsoon,
Science, 334(6055), 502–505.Bretherton, C. S., and S. Park (2009), A newmoist turbulence parameterization in the community atmosphere model, J. Clim., 22(12), 3422–3448.Cherian, R., J. Quaas, M. Salzmann, and M. Wild (2014), Pollution trends over Europe constrain global aerosol forcing as simulated by climate
models, Geophys. Res. Lett., 41, 2176–2181, doi:10.1002/2013GL058715.Chou, C., D. Neelin, C.-A. Chen, and J.-Y. Tu (2009), Evaluating the “rich-get-richer”mechanism in tropical precipitation change under global
warming, J. Clim., 22, 1982–2005.Ekman, A. M. L. (2014), Do sophisticated parameterizations of aerosol-cloud interactions in CMIP5 models improve the representation of
recent observed temperature trends?, J. Geophys. Res. Atmos., 119, 817–832, doi:10.1002/2013JD020511.Fan, J., L. R. Leung, Z. Li, H. Morrison, H. Chen, Y. Zhou, Y. Qian, and Y. Wang (2012), Aerosol impacts on clouds and precipitation in eastern
China: Results from bin and bulk microphysics, J. Geophys. Res., 117, D00K36, doi:10.1029/2011JD016537.Ganguly, D., P. J. Rasch, H. Wang, and J.-H. Yoon (2012a), Fast and slow responses of the South Asian monsoon system to anthropogenic
aerosols, Geophys.Res. Lett., 39, L18804, doi:10.1029/2012GL053043.Ganguly, D., P. J. Rasch, H. Wang, and J.-H. Yoon (2012b), Climate response of the South Asian monsoon system to anthropogenic aerosols,
J. Geophys. Res., 117, D13209, doi:10.1029/2012JD017508.Ghan, S. J., X. Liu, R. C. Easter, R. Zaveri, P. J. Rasch, J. H. Yoon, and B. Eaton (2012), Toward a minimal representation of aerosols in climate
models: Comparative decomposition of aerosol direct, semidirect, and indirect radiative forcing, J. Clim., 25(19), 6461–6476.Hartmann, D. L., et al. (2013), Observations: Atmosphere and surface, in Climate Change 2013: The Physical Science Basis, Contrib. Work. Group I
Fifth Assess. Rep. Intergovernmental Panel Clim. Change, Cambridge Univ. Press, Cambridge, U. K., and New York.Held, I. M., and B. J. Soden (2006), Robust responses of the hydrological cycle to global warming, J. Clim., 19(21), 5686–5699.Iacono, M. J., J. S. Delamere, E. J. Mlawer, M. W. Shephard, S. A. Clough, and W. D. Collins (2008), Radiative forcing by long-lived greenhouse
gases: Calculations with the AER radiative transfer models, J. Geophys. Res., 113, D13103, doi:10.1029/2008JD009944.Jiang, J. H., et al. (2012), Evaluation of cloud and water vapor simulations in CMIP5 climate models using NASA “A-Train” satellite observa-
tions, J. Geophys. Res., 117, D14105, doi:10.1029/2011JD017237.Lamarque, J. F., et al. (2010), Historical (1850–2000) gridded anthropogenic and biomass burning emissions of reactive gases and aerosols:
Methodology and application, Atmos. Chem. Phys., 10(15), 7017–7039.Lau, W. K. M., and K. M. Kim (2015), Robust Hadley circulation changes and increasing global dryness due to CO2 warming from CMIP5 model
projections, Proc. Natl. Acad. Sci. U.S.A., 112(12), 3630–3635.Liu, X., and J. E. Penner (2005), Ice nucleation parameterization for global models, Meteorol. Z., 14(4), 499–514.Liu, X., et al. (2012), Toward a minimal representation of aerosols in climate models: Description and evaluation in the Community
Atmosphere Model CAM5, Geosci. Model Dev., 5(3), 709–739.Mårtensson, E. M. (2003), Laboratory simulations and parameterization of the primary marine aerosol production, J. Geophys. Res., 108(D9),
4297, doi:10.1029/2002JD002263.Ming, Y., and V. Ramaswamy (2011), A model investigation of aerosol-induced changes in tropical circulation, J. Clim., 24(19), 5125–5133.Ming, Y., V. Ramaswamy, and G. Chen (2011), A model investigation of aerosol-induced changes in boreal winter extratropical circulation,
J. Clim., 24(23), 6077–6091.Morrison, H., and A. Gettelman (2008), A new two-moment bulk stratiform cloudmicrophysics scheme in the community atmosphere model,
version 3 (CAM3). Part I: Description and numerical tests, J. Clim., 21(15), 3642–3659.Murphy, D. M. (2013), Little net clear-sky radiative forcing from recent regional redistribution of aerosols, Nat. Geosci., 6(4), 258–262.Myhre, G., et al. (2013), Anthropogenic and natural radiative forcing, in Climate Change 2013: The Physical Science Basis, Contrib. Work. Group I
Fifth Assess. Rep. Intergovernmental Panel Clim. Change, Cambridge Univ. Press, Cambridge, U. K., and New York.Nabat, P., S. Somot, M. Mallet, A. Sanchez-Lorenzo, and M. Wild (2014), Contribution of anthropogenic sulfate aerosols to the changing
Euro-Mediterranean climate since 1980, Geophys. Res. Lett., 41, 5605–5611, doi:10.1002/2014GL060798.Neale, R. B., J. H. Richter, and M. Jochum (2008), The impact of convection on ENSO: From a delayed oscillator to a series of events, J. Clim., 21,
5904–5924.Qian, Y., D. Gong, J. Fan, L. R. Leung, R. Bennartz, D. Chen, and W. Wang (2009), Heavy pollution suppresses light rain in China: Observations
and modeling, J. Geophys. Res., 114, D00K02, doi:10.1029/2008JD011575.Riahi, K., S. Rao, V. Krey, C. Cho, V. Chirkov, G. Fischer, G. Kindermann, N. Nakicenovic, and P. Rafaj (2011), RCP 8.5—A scenario of
comparatively high greenhouse gas emissions, Clim. Change, 109(1–2), 33–57.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9640
AcknowledgmentsWe appreciate the funding supportby the NASA ROSES14-ACMAP. Theresearch was carried out at the JetPropulsion Laboratory, CaliforniaInstitute of Technology, under a con-tract with the National Aeronautics andSpace Administration. The simulationsare performed on NASA PleiadesSupercomputer. We thank JonathanMurphy from JPL for English editing.All model results are archived at theJPL cluster and available upon request.Please contact Yuan Wang [email protected] to access themodeling data.
Rosenfeld, D., et al. (2014), Global observations of aerosol-cloud-precipitation-climate interactions, Rev. Geophys., 52, 750–808, doi:10.1002/2013RG000441.
Rotstayn, L. D., M. A. Collier, S. J. Jeffrey, J. Kidston, J. I. Syktus, and K. K. Wong (2013), Anthropogenic effects on the subtropical jet in theSouthern Hemisphere: Aerosols versus long-lived greenhouse gases, Environ. Res. Lett., 8(1), 014030.
Shindell, D. T., et al. (2013), Radiative forcing in the ACCMIP historical and future climate simulations, Atmos. Chem. Phys., 13(6), 2939–2974.Smith, S. J., J. van Aardenne, Z. Klimont, R. J. Andres, A. Volke, and S. Delgado Arias (2011), Anthropogenic sulfur dioxide emissions:
1850–2005, Atmos. Chem. Phys., 11(3), 1101–1116.Song, F., T. Zhou, and Y. Qian (2014), Responses of East Asian summer monsoon to natural and anthropogenic forcings in the 17 latest CMIP5
models, Geophys. Res. Lett., 41, 596–603, doi:10.1002/2013GL058705.Wang, Y., Q. Wan, W. Meng, F. Liao, H. Tan, and R. Zhang (2011), Long-term impacts of aerosols on precipitation and lightning over the Pearl
River Delta megacity area in China, Atmos. Chem. Phys., 11(23), 12,421–12,436.Wang, Y., A. Khalizov, M. Levy, and R. Zhang (2013), New directions: Light absorbing aerosols and their atmospheric impacts, Atmos. Environ.,
81, 713–715.Wang, Y., M. H. Wang, R. Y. Zhang, S. J. Ghan, Y. Lin, J. X. Hu, B. W. Pan, M. Levy, J. H. Jiang, and M. J. Molina (2014a), Assessing the effects of
anthropogenic aerosols on Pacific storm track using a multiscale global climate model, Proc. Natl. Acad. Sci. U.S.A., 111(19), 6894–6899.Wang, Y., R. Zhang, and R. Saravanan (2014b), Asian pollution climatically modulates mid-latitude cyclones following hierarchical modelling
and observational analysis, Nat. Commun., 5, 3098.Wu, L., H. Su, and J. H. Jiang (2013), Regional simulation of aerosol impacts on precipitation during the East Asian summer monsoon,
J. Geophys. Res. Atmos., 118, 6454–6467, doi:10.1002/jgrd.50527.Xie, S.-P., B. Lu, and B. Xiang (2013), Similar spatial patterns of climate responses to aerosol and greenhouse gas changes, Nat. Geosci., 6(10),
828–832.Yang, Q., C. M. Bitz, and S. J. Doherty (2014), Offsetting effects of aerosols on Arctic and global climate in the late 20th century, Atmos. Chem.
Phys., 14(8), 3969–3975.Yoshioka, M., N. M. Mahowald, A. J. Conley, W. D. Collins, D. W. Fillmore, C. S. Zender, and D. B. Coleman (2007), Impact of desert dust radiative
forcing on Sahel precipitation: Relative importance of dust compared to sea surface temperature variations, vegetation changes, andgreenhouse gas warming, J. Clim., 20(8), 1445–1467.
Zhang, G. J., and N. A. McFarlane (1995), Sensitivity of climate simulations to the parameterization of convection in the Canadian ClimateCentre general circulation model, Atmos. Ocean, 33, 407–446.
Zhang, R., G. Wang, S. Guo, M. Zamora, Y. Lin, W. Wang, M. Hu, and Y. Wang (2015), Formation of urban fine particulate matter, Chem. Rev.,115(10), 3803–3855.
Journal of Geophysical Research: Atmospheres 10.1002/2015JD023665
WANG ET AL. REDISTRIBUTION OF ANTHROPOGENIC AEROSOLS 9641
