doi:10.1007/s00376-017-7091-5

Ackerman A. S., O. B. Toon, D. E. Stevens, A. J. Heymsfield, V. V. Ramanathan, and E. J. Welton, 2000: Reduction of tropical cloudiness by soot. Science,288, 1042-1047, https://doi.org/10.1126/science.288.5468.1042.10.1126/science.288.5468.1042

6021863ab1dad74ba0db14715d4ddd03

http%3A%2F%2Fwww.jstor.org%2Fstable%2F10.2307%2F3075107%3Fsearch%3Dyes%26amp%3Bresultitemclick%3Dtrue%26amp%3Bsearchtext%3Dau%3A%26amp%3Bsearchtext%3D%22j.%2520welton%22%26amp%3Bsearchuri%3D%252faction%252fdobasicsearch%253fymod%253dyour%252binbound%252blink%252bdid%252bnot%252bhave%252ban%252bexact%252bmatch%252bin%252bour%252bdatabase.%252bbut%252bbased%252bon%252bthe%252belements%252bwe%252bcould%252bmatch%25252c%252bwe%252bhave%252breturned%252bthe%252bfollowing%252bresults.%2526amp%253bquery%253dau%253a%252522j.%252bwelton%252522%2526amp%253bsi%253d1

http://www.sciencemag.org/cgi/doi/10.1126/science.288.5468.1042

Albrecht B. A., 1989: Aerosols,cloud microphysics, and fractional cloudiness. Science ,245, 1227-1230, https://doi.org/10.1126/science.245.4923.1227.10.1126/science.245.4923.1227

17747885

c9baaf4335e0dd08fd75f5b2eceee53d

http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpubmed%2F17747885

http://www.sciencemag.org/cgi/doi/10.1126/science.245.4923.1227Abstract Increases in aerosol concentrations over the oceans may increase the amount of low-level cloudiness through a reduction in drizzle-a process that regulates the liquid-water content and the energetics of shallow marine clouds. The resulting increase in the global albedo would be in addition to the increase due to enhancement in reflectivity associated with a decrease in droplet size and would contribute to a cooling of the earth's surface.

Cheng C.-T., W.-C. Wang, and J.-P. Chen, 2007: A modelling study of aerosol impacts on cloud microphysics and radiative properties.Quart. J. Roy. Meteor. Soc.,133,283-297,https://doi.org/10.1002/qj.25.10.1002/qj.25

f7decf824d58c563a0da32d06a1a77f2

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fqj.25%2Fpdf

http://doi.wiley.com/10.1002/%28ISSN%291477-870XConsistent with other studies, simulations conducted for a warm cloud system indicate that more aerosols result in more cloud water and more, but smaller, cloud drops, yielding increases in cloud albedo and decreases in surface precipitation. For example, the cloud drop effective radius decreased from 9 m for clean continental aerosols to 5 and 2 m, respectively, for average continental and urban aerosols, resulting in an increase in the respective cloud water path by 10% and 35% and cloud albedo by 6% and 12%. On the other hand, the accumulated precipitation decreased from 2.2 mm for clean continental aerosols to 1.9 and 1.2 mm, respectively, for average continental and urban aerosols. The presence of giant nuclei increased both the cloud drop effective radius and the precipitation, while the use of volumetric cloud drop radius tended to result in larger estimated cloud solar radiative forcing than the use of effective cloud drop radius. Copyright 漏 2007 Royal Meteorological Society

Fan J. W., R. Y. Zhang, G. H. Li, and W.-K. Tao, 2007b: Effects of aerosols and relative humidity on cumulus clouds.J. Geophys. Res.,112,D14204,https://doi.org/10.1029/2006JD008136.10.1029/2006JD008136

b03f0505cb8d7b9661037fc43db257b7

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2006JD008136%2Ffull

http://doi.wiley.com/10.1029/2006JD008136[1] The influences of the aerosol type and concentration and relative humidity (RH) on cumulus clouds have been investigated using a two-dimensional spectral-bin cloud model. Three simulations are conducted to represent the polluted continental, clean continental, and marine aerosol types. Under the same initial dynamic and thermodynamic conditions, the maritime aerosol case results in more intensive radar reflectivity in both developing and mature stages than the continental aerosol cases, because of enhanced warm rain by collisions and ice processes by deposition growth due to larger droplet sizes and higher supersaturation, respectively. The considerable delay in convective development due to reduced droplet condensation is responsible for the longer cloud lifetime in the marine aerosol case. For the continental case, the most noticeable effects of increasing aerosol number concentrations (with 15 different initial values) are the increases of the cloud droplet number concentration and cloud water content but a decrease in the effective droplet radius. More latent heat release from increasing condensation results in stronger convection and more melting precipitation at the higher aerosol concentrations. Melting precipitation and secondary clouds primarily contribute to enhanced precipitation with increasing aerosols. The precipitation, however, decreases with increasing aerosol in the extremely high aerosol cases (over 5 脙聴 104 cm3) due to suppression of convection from depleted water vapor and inefficient coalescence. When the initial aerosol concentration exceeds a critical level, most of the cloud properties become less sensitive to aerosols, implying that the aerosol effect on deep convection is more pronounced in relatively clean air than in heavily polluted air. The aerosol effect on the cloud properties is strongly dependent on RH. As the surface RH increases from 40 to 70%, the cloud changes from shallow warm to deep convective types due to a significant increase of convective available potential energy (CAPE). The aerosol effects on the cloud microphysical properties and precipitation are negligible in dry air (40% surface RH), but much more significant in humid air (60-70% surface RH). The rain delay is sensitive to RH, but not to aerosols under similar initial thermodynamic conditions.

Fan J. E., R. Y. Zhang, W.-K. Tao, and K. I. Mohr, 2008: Effects of aerosol optical properties on deep convective clouds and radiative forcing.J. Geophys. Res.,113,D08209,https://doi.org/10.1029/2007JD009257.10.1029/2007JD009257

42e4927b4c50c5a7f91083f5b5cc5367

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2007JD009257%2Fcitedby

http://onlinelibrary.wiley.com/doi/10.1029/2007JD009257/citedby[1] The aerosol radiative effects (ARE) on the deep convective clouds are investigated by using a spectral-bin cloud-resolving model coupled with a radiation scheme and an explicit land surface model. The sensitivity of cloud properties and the associated radiative forcing to aerosol single-scattering albedo (SSA) are examined. The ARE on cloud properties is pronounced for mid-visible SSA of 0.85. Relative to the case without ARE, the cloud fraction and optical depth decrease by about 18% and 20%, respectively. Ice particle number concentrations, liquid water path, ice water path, and droplet size decrease by more than 15% when the ARE is introduced. The ARE causes a surface cooling of about 0.35 K and significantly high heating rates in the lower troposphere (about 0.6 K day0908081 higher at 2 km), both of which lead to a more stable atmosphere and hence weaker convection. The weaker convection explains the less cloudiness, lower cloud optical depth, less LWP and IWP, smaller droplet size, and less precipitation resulting from the ARE. The daytime-mean direct forcing induced by black carbon is about 2.2 W m0908082 at the top of atmosphere (TOA) and 09080817.4 W m0908082 at the surface for SSA of 0.85. The semi-direct forcing is positive, about 10 and 11.2 W m0908082 at the TOA and surface, respectively. Both the TOA and surface total radiative forcing values are strongly negative for the deep convective clouds, attributed mostly to aerosol indirect forcing. Aerosol direct and semi-direct effects are very sensitive to SSA when aerosol optical depth is high. Because the positive semi-direct forcing compensates the negative direct forcing at the surface, the surface temperature and heat fluxes decrease less significantly with the increase of aerosol absorption (decreasing SSA). The cloud fraction, optical depth, convective strength, and precipitation decrease with the increase of absorption, resulting from a more stable atmosphere due to enhanced surface cooling and atmospheric heating.

Fan J. W., L. R. Leung, Z. P. Li, H. Morrison, H. B. Chen, Y. Q. 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,https://doi.org/10.1029/2011JD016537.10.1029/2011JD016537

908da331884122c6ea055a96cda40546

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2011JD016537%2Fpdf

http://onlinelibrary.wiley.com/doi/10.1029/2011JD016537/pdf[1] Using the Weather Research and Forecasting model coupled with a spectral-bin microphysics (090008SBM090009) and measurements from the Atmospheric Radiation Measurement Mobile Facility field campaign in China (AMF-China), the authors examine aerosol indirect effects (AIE) in the typical cloud regimes of the warm and cold seasons in Southeast China: deep convective clouds (DCC) and stratus clouds (SC), respectively. Comparisons with a two-moment bulk microphysics (090008Bulk090009) are performed to gain insights for improving bulk schemes in estimating AIE in weather and climate simulations. For the first time, measurements of aerosol and cloud properties acquired in China are used to evaluate model simulations to better understand aerosol impact on clouds in the southeast of China. It is found that changes in cloud condensation nuclei (CCN) concentration significantly change the timing of storms, the spatial and temporal distributions of precipitation, the frequency distribution of precipitation rate, as well as cloud base and top heights for the DCC, but not for the SC. Increasing CCN increases cloud droplet number (Nc) and mass concentrations, decreases raindrop number concentration, and delays the onset of precipitation. Compared with SBM, Bulk predicts much higher Ncand the opposite CCN effects on convection and heavy rain, stemming from the fixed CCN prescribed in Bulk. CCN have a significant effect on ice microphysical properties with SBM but not Bulk and different condensation/deposition freezing parameterizations employed could be the main reason. This study provided insights to further improve the bulk scheme to better account for aerosol-cloud interactions in regional and global climate simulations, which will be the focus for a follow-on paper.

Fan J. W., R. Y. Zhang, G. H. Li, W.-K. Tao, and X. W. Li, 2007a: Simulations of cumulus clouds using a spectral microphysics cloud-resolving model.J. Geophys. Res.,112,D04201,https://doi.org/10.1029/2006JD007688.10.1029/2006JD007688

18557ed1e971033b6e749e5ae4ad862a

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2006JD007688%2Fpdf

http://onlinelibrary.wiley.com/doi/10.1029/2006JD007688/pdf[1] We have investigated the effects of aerosols on the development of cumulus clouds using a two-dimensional spectral-bin cloud-resolving model. A convective cloud event occurring on 24 August 2000 in Houston, Texas, was simulated and the model results were compared with available radar and rain gauge measurements. Simulations assuming different aerosol chemical compositions were conducted to examine the impacts on cumulus development. The cloud microphysical and macrophysical properties changed considerably with the aerosol chemical properties. With varying the aerosol composition from only (NH4)2SO4, (NH4)2SO4 with soluble organics, to (NH4)2SO4 with slightly soluble organics, the number of activated aerosols in cloud decreased accordingly, leading to a decrease in the cloud droplet number concentration and an increase in the droplet size. Increasing activated aerosols resulted in the increase of ice crystal formation by homogeneous freezing, more extensive riming, lower supersaturation (Sw and Sice), less efficient growth of graupel, and more melting precipitation. Ice microphysical processes were more sensitive to the changes of aerosol chemical properties than the warm rain processes. The changes in macrophysical properties were more evident: The increase of activated aerosols resulted in longer cell lifetime, larger cell size, stronger secondary convective cell, and more accumulated precipitation. The simulation with the aerosol composition of (NH4)2SO4 with slightly soluble organics and an activation scheme of a reformulation of the Khler theory to include the effect of slightly soluble organics and soluble HNO3 agreed well with the observations. The simulation captured the major convective cell observed from the field measurements. The predicted convective cell intensity, cell size, cell lifetime, and accumulated rain were in agreement with the observations.

Fan J. W., Y. Wang, D. Rosenfeld, and X. H. Liu, 2016: Review of aerosol-cloud interactions: Mechanisms,significance, and challenges. J. Atmos. Sci., 73(11),4221-4252, https://doi.org/ 10.1175/JAS-D-16-0037. 1.10.1175/JAS-D-16-0037.1

5914f04f895edb29cec3843d95b1737f

http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F305218594_Review_of_Aerosol-Cloud_Interactions_Mechanisms_Significance_and_Challenges

http://journals.ametsoc.org/doi/10.1175/JAS-D-16-0037.1Abstract Over the past decade, the number of studies that investigate aerosol-cloud interactions has increased considerably. Although tremendous progress has been made to improve the understanding of basic physical mechanisms of aerosol-cloud interactions and reduce their uncertainties in climate forcing, there is still poor understanding of 1) some of the mechanisms that interact with each other over multiple spatial and temporal scales, 2) the feedbacks between microphysical and dynamical processes and between local-scale processes and large-scale circulations, and 3) the significance of cloud-aerosol interactions on weather systems as well as regional and global climate. This review focuses on recent theoretical studies and important mechanisms on aerosol-cloud interactions and discusses the significances of aerosol impacts on radiative forcing and precipitation extremes associated with different cloud systems. The authors summarize the main obstacles preventing the science from making a leap-for example, the lack of concurrent profile measurements of cloud dynamics, microphysics, and aerosols over a wide region on the observation side and the large variability of cloud microphysics parameterizations resulting in a large spread of modeling results on the modeling side. Therefore, large efforts are needed to escalate understanding. Future directions should focus on obtaining concurrent measurements of aerosol properties and cloud microphysical and dynamic properties over a range of temporal and spatial scales collected over typical climate regimes and closure studies, as well as improving understanding and parameterizations of cloud microphysics such as ice nucleation, mixed-phase properties, and hydrometeor size and fall speed.

Hansen J., M. Sato, and R. Ruedy, 1997: Radiative forcing and climate response.J. Geophys. Res.,102,6831-6864,https://doi.org/10.1029/96JD03436.10.1029/96JD03436

e2b09375076378c05ce7cd0f7bb6a9f2

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F96JD03436%2Fcitedby

http://doi.wiley.com/10.1029/96JD03436We examine the sensitivity of a climate model to a wide range of radiative forcings, including changes of solar irradiance, atmospheric CO2, O3, CFCs, clouds, aerosols, surface albedo, and a 090008ghost090009 forcing introduced at arbitrary heights, latitudes, longitudes, seasons, and times of day. We show that, in general, the climate response, specifically the global mean temperature change, is sensitive to the altitude, latitude, and nature of the forcing; that is, the response to a given forcing can vary by 50% or more depending upon characteristics of the forcing other than its magnitude measured in watts per square meter. The consistency of the response among different forcings is higher, within 20% or better, for most of the globally distributed forcings suspected of influencing global mean temperature in the past century, but exceptions occur for certain changes of ozone or absorbing aerosols, for which the climate response is less well behaved. In all cases the physical basis for the variations of the response can be understood. The principal mechanisms involve alterations of lapse rate and decrease (increase) of large-scale cloud cover in layers that are preferentially heated (cooled). Although the magnitude of these effects must be model-dependent, the existence and sense of the mechanisms appear to be reasonable. Overall, we reaffirm the value of the radiative forcing concept for predicting climate response and for comparative studies of different forcings; indeed, the present results can help improve the accuracy of such analyses and define error estimates. Our results also emphasize the need for measurements having the specificity and precision needed to define poorly known forcings such as absorbing aerosols and ozone change. Available data on aerosol single scatter albedo imply that anthropogenic aerosols cause less cooling than has commonly been assumed. However, negative forcing due to the net ozone change since 1979 appears to have counterbalanced 3009000950% of the positive forcing due to the increase of well-mixed greenhouse gases in the same period. As the net ozone change includes halogen-driven ozone depletion with negative radiative forcing and a tropospheric ozone increase with positive radiative forcing, it is possible that the halogen-driven ozone depletion has counterbalanced more than half of the radiative forcing due to well-mixed greenhouse gases since 1979.

IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, S. Solomon et al., Eds., Cambridge University Press, Cambridge, United Kingdom, New York, NY, USA.

Jiang, J. H., Coauthors, 2011: Influence of convection and aerosol pollution on ice cloud particle effective radius. Atmos. Chem. Phys.11,457-463, https://doi.org/10.5194/acp-11-457-2011.10.5194/acp-11-457-2011

cad3386034dce7519fdc38cb7291538a

http%3A%2F%2Fwww.oalib.com%2Fpaper%2F1369506

http://www.oalib.com/paper/1369506Satellite observations show that ice cloud effective radius (r) increases with ice water content (IWC) but decreases with aerosol optical thickness (AOT). Using least-squares fitting to the observed data, we obtain an analytical formula to describe the variations of rwith IWC and AOT for several regions with distinct characteristics of r-IWC-AOT relationships. As IWC directly relates to convective strength and AOT represents aerosol loading, our empirical formula provides a means to quantify the relative roles of dynamics and aerosols in controlling rin different geographical regions, and to establish a framework for parameterization of aerosol effects on rin climate models.

Johnson B. T., K. P. Shine, and P. M. Forster, 2004: The semi-direct aerosol effect: Impact of absorbing aerosols on marine stratocumulus.Quart. J. Roy. Meteor. Soc.,130,1407-1422,https://doi.org/10.1256/qj.03.61.10.1256/qj.03.61

a70de7a46e42fcd94ab21f01c6567935

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1256%2Fqj.03.61%2Ffull

http://doi.wiley.com/10.1256/qj.03.61Abstract Aerosols that absorb solar radiation may lead to a decrease of low-cloud cover and liquid-water path (LWP), leading to a positive radiative forcing. A large-eddy model was used to investigate this ‘semi-direct effect’ for marine stratocumulus and examine the dependency on the vertical distribution of the aerosol. In this study, the aerosols influenced clouds by directly altering the short-wave heating rate (the semi-direct effect), but did not interact with the cloud microphysics (i.e. indirect aerosol effects are excluded). Absorbing aerosols within the boundary layer (BL) decreased LWP by 10 g m 612 , leading to a positive semi-direct forcing. Even for mildly absorbing aerosols (mid-visible single-scattering albedo of 0.96), the semi-direct forcing was three times stronger, and opposite in sign, to the aerosol direct forcing. The semi-direct forcing was found to be proportional to aerosol single-scattering co-albedo (tested to a value of 0.12). Conversely, with the absorbing aerosol layer above the cloud, the LWP increased by 5 to 10 g m 612 , leading to a negative semi-direct forcing. Absorbing aerosols located in the BL heat the cloud layer, enhancing the daytime decoupling and thinning of the stratocumulus layer. Absorbing aerosols immediately above the BL increased the contrast in potential temperature across the inversion, leading to a lower cloud-top entrainment rate. With aerosol both within and above the BL, the semidirect forcing was positive but half the magnitude of that experienced when aerosol was only in the BL. As marine stratocumulus covers about 20% of the globe, the semi-direct effect could significantly influence the radiative forcing by absorbing aerosols. Copyright 08 2004 Royal Meteorological Society

Khain A. P., 2009: Notes on state-of-the-art investigations of aerosol effects on precipitation: A critical review.Environ. Res. Lett.4,015004,https://doi.org/10.1088/1748-9326/4/1/ 015004.

10.1088/1748-9326/4/1/015004

aa909dbf7f53c3b1b5eaf17d6d844a45

http%3A%2F%2Fwww.cabdirect.org%2Fabstracts%2F20093057784.html

http://stacks.iop.org/1748-9326/4/i=1/a=015004?key=crossref.f3822b3727d7592b4fcede1d70b76ea2There is no agreement between the results of different studies as regards quantitative and even qualitative evaluation of aerosol effects on precipitation. While some observational and numerical studies report a decrease in precipitation in polluted areas, in some other observations and numerical studies aerosol-induced precipitation enhancement was reported. This study analyses possible reason...

Khalizov A.F., H. Xue, L. Wang, J. Zheng, and R. Zhang, 2009: Enhanced light absorption and scattering by carbon soot aerosol internally mixed with sulfuric acid,J.Phys. Chem. A,113(6),1066-1074,https://doi.org/10.1021/jp807531n.

10.1021/jp807531n

19146408

18a4a70c2fded30b68eb2ba369d3a2e3

http%3A%2F%2Fpubs.acs.org%2Fdoi%2Fabs%2F10.1021%2Fjp807531n

http://pubs.acs.org/doi/abs/10.1021/jp807531nLight absorption by carbon soot increases when the particles are internally mixed with nonabsorbing materials, leading to increased radiative forcing, but the magnitude of this enhancement is a subject of great uncertainty. We have performed laboratory experiments of the optical properties of fresh and internally mixed carbon soot aerosols with a known particle size, morphology, and the mixing state. Flame-generated soot aerosol is size-selected with a double-differential mobility analyzer (DMA) setup to eliminate multiply charged particle modes and then exposed to gaseous sulfuric acid (10(9)-10(10) molecule cm(-3)) and water vapor (5-80% relative humidity, RH). Light extinction and scattering by fresh and internally mixed soot aerosol are measured at 532 nm wavelength using a cavity ring-down spectrometer and an integrating nephelometer, respectively, and the absorption is derived as the difference between extinction and scattering. The optical properties of fresh soot are independent of RH, whereas soot internally mixed with sulfuric acid exhibits significant enhancement in light absorption and scattering, increasing with the mass fraction of sulfuric acid coating and relative humidity. For soot particles with an initial mobility diameter of 320 nm and a 40% H(2)SO(4) mass coating fraction, absorption and scattering are increased by 1.4- and 13-fold at 80% RH, respectively. Also, the single scattering albedo of soot aerosol increases from 0.1 to 0.5 after coating and humidification. Additional measurements with soot particles that are first coated with sulfuric acid and then heated to remove the coating show that both scattering and absorption are enhanced by irreversible restructuring of soot aggregates to more compact globules. Depending on the initial size and density of soot aggregates, restructuring acts to increase or decrease the absorption cross-section, but the combination of restructuring and encapsulation always results in an increased absorption for internally mixed soot. Mass absorption cross-sections (MAC) for fresh soot aggregates are size dependent, increasing from 6.7 +/- 0.7 m(2) g(-1) for 155 nm particles to 8.7 +/- 0.1 m(2) g(-1) for 320 nm particles. After exposure of soot to sulfuric acid, MAC is as high as 12.6 m(2) g(-1) for 320 nm particles at 80% RH. Our results imply that optical properties of soot are significantly altered within its atmospheric lifetime, leading to greater impact on visibility, local air quality, and radiative climate forcing.

Koren I., G. Feingold, and L. A. Remer, 2010: The invigoration of deep convective clouds over the Atlantic: Aerosol effect,meteorology or retrieval artifact? Atmos. Chem. Phys., 10, 8855-8872, https://doi.org/10.5194/acp-10-8855-2010.10.5194/acp-10-8855-2010

0f8b47c92e180f099ac222d7b789b937

http%3A%2F%2Fwww.oalib.com%2Fpaper%2F1369377

http://www.atmos-chem-phys.net/10/8855/2010/The effects of the aerosol on convective clouds in the tropical Atlantic Ocean are explored using satellite remote sensing, a chemical transport model, and a reanalysis of meteorological fields. Two of the most challenging problems are addressed: the potential for elements of the cloud field to be erroneously ascribed to aerosol optical depth; and the potential for correlations between aerosol and cloud parameters to be erroneously considered to be causal. Results show that there is a robust positive correlation between cloud fraction or cloud top height and the aerosol optical depth, regardless of whether a stringent filtering of aerosol measurements in the vicinity of clouds is applied, or not. These same positive correlations emerge when replacing the observed aerosol field with that derived from a chemical transport model. A correlation exercise between the full suite of meteorological fields derived from model reanalysis and satellite-derived cloud fields shows that observed cloud top height and cloud fraction correlate best with pressure updraft velocity and relative humidity. Observed aerosol optical depth does correlate with meteorological parameters but usually different parameters from those that correlate with observed cloud fields. The result is a near-orthogonal influence of aerosol and meteorological fields on cloud top height and cloud fraction. The results strengthen the case that the aerosol does play a role in invigorating convective clouds.

Koren I., O. Altaratz, L. A. Remer, G. Feingold, J. V. Martins, and R. H. Heiblum, 2012: Aerosol-induced intensification of rain from the tropics to the mid-latitudes.Nat. Geosci.,5(2),118-122,https://doi.org/10.1038/ngeo1364.10.1038/ngeo1364

98774e42c097e7349304140296993511

http%3A%2F%2Fwww.nature.com%2Fngeo%2Fjournal%2Fv5%2Fn2%2Fabs%2Fngeo1364.html

http://www.nature.com/doifinder/10.1038/ngeo1364Atmospheric aerosols affect cloud properties, and thereby the radiation balance of the planet and the water cycle. However, the influence of aerosols on clouds, and in particular on precipitation, is far from understood, and seems to depend on factors such as location, season and the spatiotemporal scale of the analysis. Here, we examine the relationship between aerosol abundance and rain rate--a key factor in climate and hydrological processes--using rain data from a satellite-based instrument sensitive to stronger rain rates (Tropical Rainfall Measuring Mission, TRMM), aerosol and cloud property data from the Moderate Resolution Imaging Spectroradiometer onboard the Aqua satellite and meteorological information from the Global Data Assimilation System. We show that for a range of conditions, increases in aerosol abundance are associated with the local intensification of rain rates detected by the TRMM. The relationship is apparent over both the ocean and land, and in the tropics, subtropics and mid-latitudes. Further work is needed to determine how aerosols influence weaker rain rates, not picked up in the analysis. We also find that increases in aerosol levels are associated with a rise in cloud-top height. We suggest that the invigoration of clouds and the intensification of rain rates is a preferred response to an increase in aerosol concentration.

Lee J., P. Yang, A. E. Dessler, B.-C. Gao, and S. Platnick, 2009: Distribution and radiative forcing of tropical thin cirrus clouds.J. Atmos. Sci.,66,3721-3731,https://doi.org/10.1175/2009JAS3183.1.10.1175/2009JAS3183.1

06e341c226347bc93a77a34b92dafbd2

http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2009JAtS...66.3721L

http://journals.ametsoc.org/doi/abs/10.1175/2009JAS3183.1To understand the radiative impact of tropical thin cirrus clouds, the frequency of occurrence and optical depths of these clouds have been derived. "Thin" cirrus clouds are defined here as being those that are not detected by the operational Moderate Resolution Imaging Spectroradiometer (MODIS) cloud mask, corresponding to an optical depth value of approximately 0.3 or smaller, but that are detectable in terms of the cirrus reflectance product based on the MODIS 1.375-micron channel. With such a definition, thin cirrus clouds were present in more than 40% of the pixels flagged as "clear sky" by the operational MODIS cloud mask algorithm. It is shown that these thin cirrus clouds are frequently observed in deep convective regions in the western Pacific. Thin cirrus optical depths were derived from the cirrus reflectance product. Regions of significant cloud fraction and large optical depths were observed in the Northern Hemisphere during the boreal spring and summer and moved southward during the boreal autumn and winter. The radiative effects of tropical thin cirrus clouds were studied on the basis of the retrieved cirrus optical depths, the atmospheric profiles derived from the Atmospheric Infrared Sounder (AIRS) observations, and a radiative transfer model in conjunction with a parameterization of ice cloud spectral optical properties. To understand how these clouds regulate the radiation field in the atmosphere, the instantaneous net fluxes at the top of the atmosphere (TOA) and at the surface were calculated. The present study shows positive and negative net forcings at the TOA and at the surface, respectively. The positive (negative) net forcing at the TOA (surface) is due to the dominance of longwave (shortwave) forcing. Both the TOA and surface forcings are in a range of 0-20 W/sq m, depending on the optical depths of thin cirrus clouds.

Lee S. S., L. J. Donner, V. T. J. Phillips, and Y. Ming, 2008: The dependence of aerosol effects on clouds and precipitation on cloud-system organization,shear and stability.J. Geophys. Res.,113,D16202,https://doi.org/10.1029/2007JD009224.

10.1029/2007JD009224

b86815b70fadf4a52b98ca910db32324

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2007JD009224%2Ffull

http://doi.wiley.com/10.1029/2007JD009224[1] Precipitation suppression due to an increase of aerosol number concentration in stratiform cloud is well-known. It is not certain whether the suppression applies for deep convection. Recent studies have suggested increasing precipitation from deep convection with increasing aerosols under some, but not all, conditions. Increasing precipitation with increasing aerosols can result from strong interactions in deep convection between dynamics and microphysics. High cloud liquid, due to delayed autoconversion, provides more evaporation, leading to more active downdrafts, convergence fields, condensation, collection of cloud liquid by precipitable hydrometeors, and precipitation. Evaporation of cloud liquid is a primary determinant of the intensity of the interactions. It is partly controlled by wind shear modulating the entrainment of dry air into clouds and transport of cloud liquid into unsaturated areas. Downdraft-induced convergence, crucial to the interaction, is weak for shallow clouds, generally associated with low convective available potential energy (CAPE). Aerosol effects on cloud and precipitation can vary with CAPE and wind shear. Pairs of idealized numerical experiments for high and low aerosol cases were run for five different environmental conditions to investigate the dependence of aerosol effect on stability and wind shear. In the environment of high CAPE and strong wind shear, cumulonimbus- and cumulus-type clouds were dominant. Transport of cloud liquid to unsaturated areas was larger at high aerosol, leading to stronger downdrafts. Because of the large vertical extent of those clouds, strong downdrafts and convergence developed for strong interactions between dynamics and microphysics. These led to larger precipitation at high aerosol. Detrainment of cloud liquid and associated evaporation were less with lower CAPE and wind shear, where dynamically weaker clouds dominated. Transport of cloud liquid to unsaturated areas was not as active as in the environment of high CAPE and strong shear. Also, evaporatively driven differences in downdrafts at their level of initial descent were not magnified in clouds with shallow depth as much as in deep convective clouds as they accelerated to the surface over shorter distances. Hence the interaction between dynamics and microphysics was reduced, leading to precipitation suppression at high aerosol. These results demonstrate that increasing aerosol can either decrease or increase precipitation for an imposed large-scale environment supporting cloud development. The implications for larger-scale aspects of the hydrological cycle will require further study with larger-domain models and cumulus parameterizations with advanced microphysics.

Levy, M. E., Coauthors, 2013: Measurements of submicron aerosols in Houston,Texas during the 2009 SHARP field campaign.J. Geophys. Res.,118,10 518-10 534,https://doi.org/10.1002/jgrd.50785.10.1002/jgrd.50785

1d0a38c634cdc4f7fa50ad54fce6750e

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fjgrd.50785%2Fabstract

http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50785/abstractthe field campaign of the Study of Houston Atmospheric Radical Precursors/Surface-Induced Oxidation of Organics in the Troposphere (SHARP/SOOT) in Houston, Texas, a suite of aerosol instruments was deployed to directly measure a comprehensive set of aerosol properties, including the particle size distribution, effective density, hygroscopicity, and light extinction and scattering coefficients. Those aerosol properties are employed to quantify the mixing state and composition of ambient particles and to gain a better understanding of the formation and transformation of fine particulate matter in this region. During the measurement period, aerosols are often internally mixed, with one peak in the effective density distribution at 1.55 0.07 g cm, consistent with a population composed largely of sulfates and organics. Episodically, a second mode below 1.0 g cmis identified in the effective density distributions, reflecting the presence of freshly emitted black carbon (BC) particles. The measured effective density demonstrates a clear diurnal cycle associated with primary emissions from transportation and photochemical aging, with a minimum during the morning rush hour, increasing from 1.4 to 1.5 g cmon average over 5 h, and remaining nearly constant throughout the afternoon. The average BC concentration derived from light-absorption measurements is 0.31 0.22 g m, and the average measured particle single scattering albedo is 0.94 0.04. When elevated BC concentrations are observed, typically during the morning rush hours, single scattering albedo decreases, with a smallest measured value of about 0.7. Aerosol hygroscopicity measurements indicate that larger particles (e.g., 400 nm) are more hygroscopic than smaller particles (e.g., 100 nm). The measurements also reveal discernable meteorological impacts on the aerosol properties. After a frontal passage, the average particle effective density decreases, the average BC concentration increases, and the aerosol size distribution is dominated by new particle formation.

Li G. H., Y. Wang, and R. Y. Zhang, 2008: Implementation of a two-moment bulk microphysics scheme to the WRF model to investigate aerosol-cloud interaction.J. Geophys. Res.,113,D15211,https://doi.org/10.1029/2007JD009361.10.1029/2007JD009361

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http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2007JD009361%2Fcitedby

http://doi.wiley.com/10.1029/2007JD009361[1] A two-moment bulk microphysical scheme has been implemented into the Weather Research and Forecasting (WRF) model to investigate the aerosol-cloud interaction. The microphysical scheme calculates the mass mixing ratios and number concentrations of aerosols and five types of hydrometeors and accounts for various cloud processes including warm and mixed phase microphysics. The representation of the aerosol size distribution is evaluated, showing that the three-moment modal method produces results better in agreement with the sectional approach than the two-moment modal method for variable supersaturation conditions in clouds. The effects of aerosols on cloud processes are investigated using the two-moment bulk microphysical scheme in a convective cumulus cloud event occurring on 24 August 2000 in Houston, Texas. The modeled evolution of the distribution of radar reflectivity in the y-z section, the cell lifetime, and averaged accumulated precipitation with the aerosol concentration under the polluted urban condition are qualitatively consistent with the measurements. Sensitivity simulations are initialized using a set of aerosol profiles with the number concentrations ranging from 200 to 50,000 cm0908083 and mass ranging from 1 to 10 0204g m0908083 at the surface level. The response of precipitation to the increase of aerosol concentrations is nonmonotonic, because of the complicated interaction between cloud microphysics and dynamics. The precipitation increases with aerosol concentrations from clean maritime to continental background conditions, but is considerably reduced and completely suppressed under highly polluted conditions, indicating that the aerosol concentration exhibits distinct effects on the precipitation efficiency under different aerosol conditions. The maximal cloud cover, core updraft, and maximal vertical velocity exhibit similar responses as precipitation. Comparison is made to evaluate the effects of different autoconversion parameterizations and bulk microphysical schemes on cloud properties. Because of its broad application in numerical weather prediction, implementation of the two-moment microphysical scheme to the WRF model will greatly facilitate assessment of aerosol-cloud interaction from individual cumulus to mesoscale convective systems.

Li G. H., Y. Wang, K.-H. Lee, Y. W. Diao, and R. Y. Zhang, 2009: Impacts of aerosols on the development and precipitation of a mesoscale squall line.J. Geophys. Res.,114,D17205,https://doi.org/10.1029/2008JD011581.10.1029/2008JD011581

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http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2008JD011581%2Fcitedby

http://doi.wiley.com/10.1029/2008JD011581[1] The effects of aerosols on the development and precipitation for a mesoscale squall line occurring in the south plains of the United States have been investigated using a cloud-resolving Weather Research and Forecasting (CR-WRF) model with a two-moment bulk microphysical scheme. Different aerosol scenarios are considered in the CR-WRF model experiments, including polluted continental aerosols with a mean concentration of 2000 cm3. The simulated temporal evolution of composite radar reflectivity and the 24-h accumulated precipitation in the polluted aerosol experiment are in agreement with the measurements. The influence of aerosol concentrations is insignificant on the rainfall distribution but is remarkable on the precipitation intensity. The CR-WRF experiment with the polluted aerosol case predicts about 13% more precipitation and more locally intensive rainfall than do those with the clean aerosol case. Both the convection zone and the storm convective strength are increased in the polluted aerosol experiment in response to the increase in aerosol concentrations. The two-moment microphysical scheme is compared with three single-moment bulk schemes in the WRF model, including the Lin, WRF single-moment six-class, and Thompson schemes. Only the Thompson schemes reproduce the observed precipitation and radar reflectivity pattern, in agreement with the two-moment scheme with a leading convective line and a trailing stratiform precipitation regime. All of the single-moment schemes significantly overestimate the precipitation, especially with the Lin scheme, while the two-moment scheme yields the precipitation simulation comparable with the measurement.

Li Z. Q., F. Niu, J. W. Fan, Y. G. Liu, D. Rosenfeld, and Y. N. Ding, 2011: Long-term impacts of aerosols on the vertical development of clouds and precipitation.Nature Geosci.,4,888-894,https://doi.org/10.1038/ngeo1313.10.1038/ngeo1313

0cb62c142b25d233b197d374beb75bd6

http%3A%2F%2Fwww.nature.com%2Fabstractpagefinder%2F10.1038%2Fngeo1313

http://www.nature.com/articles/ngeo1313Aerosols alter cloud density and the radiative balance of the atmosphere. This leads to changes in cloud microphysics and atmospheric stability, which can either suppress or foster the development of clouds and precipitation. The net effect is largely unknown, but depends on meteorological conditions and aerosol properties. Here, we examine the long-term impact of aerosols on the vertical development of clouds and rainfall frequencies, using a 10-year dataset of aerosol, cloud and meteorological variables collected in the Southern Great Plains in the United States. We show that cloud-top height and thickness increase with aerosol concentration measured near the ground in mixed-phase clouds攚hich contain both liquid water and icehat have a warm, low base. We attribute the effect, which is most significant in summer, to an aerosol-induced invigoration of upward winds. In contrast, we find no change in cloud-top height and precipitation with aerosol concentration in clouds with no ice or cool bases. We further show that precipitation frequency and rain rate are altered by aerosols. Rain increases with aerosol concentration in deep clouds that have a high liquid-water content, but declines in clouds that have a low liquid-water content. Simulations using a cloud-resolving model confirm these observations. Our findings provide unprecedented insights of the long-term net impacts of aerosols on clouds and precipitation.

Lin Y., Y. Wang, B. W. Pan, J. X. Hu, Y. G. Liu, and R. Y. Zhang, 2016: Distinct impacts of aerosols on an evolving continental cloud complex during the RACORO field campaign.J. Atmos. Sci.,73(9),3681-3700,https://doi.org/10.1175/jas-d-15-0361.1.10.1175/JAS-D-15-0361.1

18d4f6a588f736e8c0a158779a835039

http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F304187244_Distinct_impacts_of_aerosols_on_an_evolving_continental_cloud_complex_during_the_RACORO_field_campaign

http://journals.ametsoc.org/doi/10.1175/JAS-D-15-0361.1Abstract A continental cloud complex, consisting of shallow cumuli, a deep convective cloud (DCC), and stratus, is simulated by a cloud-resolving Weather Research and Forecasting Model to investigate the aerosol microphysical effect (AME) and aerosol radiative effect (ARE) on the various cloud regimes and their transitions during the Department of Energy Routine Atmospheric Radiation Measurement Aerial Facility Clouds with Low Optical Water Depths Optical Radiative Observations (RACORO) campaign. Under an elevated aerosol loading with AME only, a reduced cloudiness for the shallow cumuli and stratus resulted from more droplet evaporation competing with suppressed precipitation, but an enhanced cloudiness for the DCC is attributed to more condensation. With the inclusion of ARE, the shallow cumuli are suppressed owing to the thermodynamic effects of light-absorbing aerosols. The responses of DCC and stratus to aerosols are monotonic with AME only but nonmonotonic with both AME and ARE. The DCC is invigorated because of favorable convection and moisture conditions at night induced by daytime ARE, via the so-called aerosol-enhanced conditional instability mechanism. The results reveal that the overall aerosol effects on the cloud complex are distinct from the individual cloud types, highlighting that the aerosol-cloud interactions for diverse cloud regimes and their transitions need to be evaluated to assess the regional and global climatic impacts.

Liu Y. G., P. H. Daum, 2004: Parameterization of the autoconversion process. Part I: Analytical formulation of the Kessler-type parameterizations. J. Atmos. Sci., 61( 13), 1539- 1548.10.1175/1520-0469(2004)0612.0.CO;2

63329be392ddc5cfd8d1d64ffdaba559

http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2005JAtS...62.3003W

http://journals.ametsoc.org/doi/abs/10.1175/1520-0469%282004%29061%3C1539%3APOTAPI%3E2.0.CO%3B2ABSTRACT Various commonly used Kessler-type parameterizations of the autoconversion of cloud droplets to embryonic raindrops are theoretically derived from the same formalism by applying the generalized mean value theorem for integrals to the general collection equation. The new formalism clearly reveals the approximations and assumptions that are implicitly embedded in these different parameterizations. A new Kessler-type parameterization is further derived by eliminating the incorrect and/or unnecessary assumptions inherent in the existing Kessler-type parameterizations. The new parameterization exhibits a different dependence on liquid water content and droplet concentration, and provides theoretical explanations for the multitude of values assigned to the tunable coefficients associated with the commonly used parameterizations. Relative dispersion of the cloud droplet size distribution (defined as the ratio of the standard deviation to the mean radius of the cloud droplet size distribution) is explicitly included in the new parameterization, allowing for investigation of the influences of the relative dispersion on the autoconversion rate and, hence, on the second indirect aerosol effect. The new analytical parameterization compares favorably with those parameterizations empirically obtained by curve-fitting results from simulations of detailed microphysical models.

Mitchell D. L., R. Zhang, and R. L. Pitter, 1990: The mass-dimensional relations for ice crystals and the influence of riming on the snowfall rate. J. Appl. Meteor., 29, 153-163,https://doi.org/10.1175/1520-0450(1990)029<0153:MDRFIP>2.0.CO;2.

Nesbitt S. W., R. Y. Zhang, and R. E. Orville, 2000: Seasonal and global NO_x production by lightning estimated from the optical transient detector (OTD).Tellus B52,1206-1215,https://doi.org/10.1034/j.1600-0889.2000.01121.x.

10.1034/j.1600-0889.2000.01121.x

93c6b710031738bccc95126311cbeb34

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1034%2Fj.1600-0889.2000.01121.x%2Fabstract

https://www.tandfonline.com/doi/full/10.3402/tellusb.v52i5.17098The Optical Transient Detector (OTD) lightning data for the 12090006month period of 1996 are used to estimate the seasonal and global distributions of lightning090006produced NO x . The relatively small viewing footprint and the low detection efficiency of the OTD sensor and other difficulties require extrapolations of the OTD data to the actual global flash distributions. Furthermore, available measurements for the ratios of intracloud (IC) to cloud090006to090006ground (CG) flashes have been used to partition lightning counts for IC versus CG flashes from the OTD observations. The resulting lightning distributions are then used to calculate the global and seasonal production of NO x , assuming a NO production rate of 6.2010310 25 molecules for each CG flash and 8.7010310 24 molecules for each IC flash. Consequently, we find that CG flashes produce more NO x than IC flashes despite fewer CG flashes by a factor of 3 or more. NO x production by lightning varies seasonally in accordance with the global lightning distribution, with the maximum production occurring in the Northern Hemisphere in the local summer. The latitudinal distribution of NO x production exhibits a strong seasonal variation outside the tropics with the production occurring mainly in the summer hemisphere, whereas in the tropics the production is high throughout the year. The annual contribution to NO x production by lightning is higher in the Northern Hemisphere than that in the Southern Hemisphere.

Orville, R. E., Coauthors, 2001: Enhancement of cloud-to-ground lightning over Houston,Texas.Geophys. Res. Lett.,28,2597-2600,https://doi.org/10.1029/2001GL012990.

10.1029/2001GL012990

8168d01ac7b0dc0eef2ccaab9d880889

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2001GL012990%2Ffull

http://doi.wiley.com/10.1029/2001GL012990Cloud-to-ground lightning flash data have been analyzed for the twelve-year period 1989-2000, for a geographical area centered on Houston, Texas. Of the 1.6 million cloud-to-ground flashes in this area of study, approximately 752,000 flashes occurred in the summer months of June, July, and August, and 119,000 flashes in the months of December, January, and February. The highest flash densities, greater than 4 flashes kmin the summer and 0.7 flashes/kmin the winter, are near the urban areas of Houston. We suggest that the elevated flash densities could result from several factors, including, 1) the convergence due to the urban heat island effect, and 2) the increasing levels of air pollution from anthropogenic sources producing numerous small droplets and thereby suppressing mean droplet size. The latter effect would enable more cloud water to reach the mixed phase region where it is involved in the formation of precipitation and the separation of electric charge, leading to an enhancement of lightning.

Peng, J. F., Coauthors, 2016: Markedly enhanced absorption and direct radiative forcing of black carbon under polluted urban environments.Proc. Natl. Acad. Sci. USA113,4266-4271,https://doi.org/10.1073/pnas.1602310113.10.1073/pnas.1602310113

27035993

7d91162909d84f12b31e1c1928e6f003

http%3A%2F%2Feuropepmc.org%2Fabstract%2FMED%2F27035993

http://www.pnas.org/lookup/doi/10.1073/pnas.1602310113Abstract Black carbon (BC) exerts profound impacts on air quality and climate because of its high absorption cross-section over a broad range of electromagnetic spectra, but the current results on absorption enhancement of BC particles during atmospheric aging remain conflicting. Here, we quantified the aging and variation in the optical properties of BC particles under ambient conditions in Beijing, China, and Houston, United States, using a novel environmental chamber approach. BC aging exhibits two distinct stages, i.e., initial transformation from a fractal to spherical morphology with little absorption variation and subsequent growth of fully compact particles with a large absorption enhancement. The timescales to achieve complete morphology modification and an absorption amplification factor of 2.4 for BC particles are estimated to be 2.3 h and 4.6 h, respectively, in Beijing, compared with 9 h and 18 h, respectively, in Houston. Our findings indicate that BC under polluted urban environments could play an essential role in pollution development and contribute importantly to large positive radiative forcing. The variation in direct radiative forcing is dependent on the rate and timescale of BC aging, with a clear distinction between urban cities in developed and developing countries, i.e., a higher climatic impact in more polluted environments. We suggest that mediation in BC emissions achieves a cobenefit in simultaneously controlling air pollution and protecting climate, especially for developing countries.

Pincus R., M. B. Baker, 1994: Effect of precipitation on the albedo susceptibility of clouds in the marine boundary layer.Nature372,250-252,https://doi.org/10.1038/372250a0.

10.1038/372250a0

a4e5e90d071d6c497e795db24d4cae5d

http%3A%2F%2Fwww.nature.com%2Fdoifinder%2F10.1038%2F372250a0

http://www.nature.com/doifinder/10.1038/372250a0TROPOSPHERIC aerosols are thought to have three important effects on the Earth's radiation budget: the direct radiative effect 1 (pertur-bation of clear-sky reflectivity), the indirect radiative effect 2 (modi-fication of cloud albedo) and the effect on the hydrological cycle 3 (modification of the vertical thickness and horizontal extent of clouds). The first two effects have been understood in principle for nearly 20 years and quantitative estimates of their magnitudes have been provided by models and observations 4 . The third phe-nomenon and its relation to the other two, has received far less attention. Previous work 3 has shown, however, that increases in aerosol concentration may act to increase cloud albedo by increas-ing horizontal cloud fraction as well as cloud reflectivity. Here we use a simple model of the marine cloud-topped boundary layer to investigate the changes in cloud thickness and albedo that result from changes in precipitation as particle concentrations vary. We find that the sensitivity of layer cloud albedo to droplet number concentration (the albedo susceptibility) is increased by 50200% when the dependence of cloud thickness on particle number is included. The results suggest that the response of cloud thickness to changes in aerosol particle concentration must be taken into account for accurate prediction of global albedo by climate models.

Rogers R. R., M. K. Yau, 1989: A Short Course in Cloud Physics. 3rd ed., Pergamon Press.

10.1007/BF00876948

7e67e143d229771562ac4f85af66812c

http%3A%2F%2Fci.nii.ac.jp%2Fncid%2FBA29653451

http://ci.nii.ac.jp/ncid/BA29653451Covers essential parts of cloud and precipitation physics and has been extensively rewritten with over 60 new illustrations and many new and up to date references. Many current topics are covered such as mesoscale meteorology, radar cloud studies and numerical cloud modelling, and topics from the second edition, such as severe storms, precipitation processes and large scale aspects of cloud physics, have been revised. Problems are included as examples and to supplement the text.

Rosenfeld D., 1999: TRMM observed first direct evidence of smoke from forest fires inhibiting rainfall.Geophys. Res. Lett.,26,3105-3108,https://doi.org/10.1029/1999GL006066.10.1029/1999GL006066

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http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F1999GL006066%2Ffull

http://doi.wiley.com/10.1029/1999GL006066Although it has been known that smoke from biomass burning suppresses warm rain processes, it was not known to what extent this occurs. The satellite observations of the Tropical-Rainfall-Measuring-Mission (TRMM), presented here, show that warm rain processes in convective tropical clouds infected by heavy smoke from forest fires are practically shut off. The tops of the smoke-infected clouds must exceed the freezing level, i.e., grow to altitudes colder than about -10℃C, for the clouds to start precipitating. In contrast, adjacent tropical clouds in the cleaner air precipitate most of their water before ever freezing. There are indications that rain suppression due to air pollution prevails also in the extra-tropics.

Rosenfeld D., andCoauthors., 2014: Global observations of aerosol-cloud-precipitation-climate interactions. Rev. Geophys.,52(4),750-808,https://doi.org/10.1002/2013rg000441.

10.1002/2013RG000441

c7db803ae0484b534befbe923b7153a4

http%3A%2F%2Fwww.ingentaconnect.com%2Fcontent%2Fbpl%2Frog%2F2014%2F00000052%2F00000004%2Fart00006

http://www.ingentaconnect.com/content/bpl/rog/2014/00000052/00000004/art00006Abstract Cloud drop condensation nuclei (CCN) and ice nuclei (IN) particles determine to a large extent cloud microstructure and, consequently, cloud albedo and the dynamic response of clouds to aerosol-induced changes to precipitation. This can modify the reflected solar radiation and the thermal radiation emitted to space. Measurements of tropospheric CCN and IN over large areas have not been possible and can be only roughly approximated from satellite-sensor-based estimates of optical properties of aerosols. Our lack of ability to measure both CCN and cloud updrafts precludes disentangling the effects of meteorology from those of aerosols and represents the largest component in our uncertainty in anthropogenic climate forcing. Ways to improve the retrieval accuracy include multiangle and multipolarimetric passive measurements of the optical signal and multispectral lidar polarimetric measurements. Indirect methods include proxies of trace gases, as retrieved by hyperspectral sensors. Perhaps the most promising emerging direction is retrieving the CCN properties by simultaneously retrieving convective cloud drop number concentrations and updraft speeds, which amounts to using clouds as natural CCN chambers. These satellite observations have to be constrained by in situ observations of aerosol-cloud-precipitation-climate (ACPC) interactions, which in turn constrain a hierarchy of model simulations of ACPC. Since the essence of a general circulation model is an accurate quantification of the energy and mass fluxes in all forms between the surface, atmosphere and outer space, a route to progress is proposed here in the form of a series of box flux closure experiments in the various climate regimes. A roadmap is provided for quantifying the ACPC interactions and thereby reducing the uncertainty in anthropogenic climate forcing.

Rosenfeld D., U. Lohmann, G. B. Raga, C. D. O'Dowd, M. Kulmala, S. Fuzzi, A. Reissell, and M. O. Andreae, 2008: Flood or drought: How do aerosols affect precipitation? Science,321, 1309-1313, https://doi.org/10.1126/science.1160606.10.1126/science.1160606

18772428

2e53b2c54e98295c28176b844e81c9ef

http%3A%2F%2Feuropepmc.org%2Fabstract%2Fmed%2F18772428

http://www.sciencemag.org/cgi/doi/10.1126/science.1160606Aerosols serve as cloud condensation nuclei (CCN) and thus have a substantial effect on cloud properties and the initiation of precipitation. Large concentrations of human-made aerosols have been reported to both decrease and increase rainfall as a result of their radiative and CCN activities. At one extreme, pristine tropical clouds with low CCN concentrations rain out too quickly to mature into long-lived clouds. On the other hand, heavily polluted clouds evaporate much of their water before precipitation can occur, if they can form at all given the reduced surface heating resulting from the aerosol haze layer. We propose a conceptual model that explains this apparent dichotomy.

Sassen, K., Coauthors, 1995: The 5-6 December 1991 FIRE IFO II jet stream cirrus case study: Possible influences of volcanic aerosols. J. Atmos. Sci., 52, 97-123, https://doi.org/10.1175/1520-0469(1995)052<0097:TDFIIJ>2.0.CO; 2.

10.1175/1520-0469(1995)0522.0.CO;2

a3f26a690fbe71acee638f95a03be29d

http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F1995JAtS...52...97S

http://journals.ametsoc.org/doi/abs/10.1175/1520-0469%281995%29052%3C0097%3ATDFIIJ%3E2.0.CO%3B2In presenting an overview of the cirrus clouds comprehensively studied by ground-based and airborne sensors from Coffeyville, Kansas, during the 5-6 December 1992 Project FIRE IFO II case study period, evidence is provided that volcanic aerosols from the June 1991 Pinatubo eruptions may have significantly influenced the formation and maintenance of the cirrus. Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streaks subsequently conditioned the troposphere through tropopause foldings with sulfur-based particles that became effective cloud-forming nuclei in cirrus clouds. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded within the upper-level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol-enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations include abnormally high ice crystal concentrations (up to {approximately}600 L{sup {minus}1}), complex radial ice crystal types, and relatively large haze particles in cirrus uncinus cell heads at temperatures between {minus}40{degrees} and {minus}50{degrees}C. Implications for volcanic-cirrus cloud climate effects and usual (nonvolcanic aerosol) jet stream cirrus cloud formation are discussed. 42 refs., 25 figs., 3 tabs.

Seifert A., T. Heus, R. Pincus, and B. Stevens, 2015: Large-eddy simulation of the transient and near-equilibrium behavior of precipitating shallow convection.Journal of Advances in Modeling Earth Systems7,1918-1937,https://doi.org/10.1002/2015MS000489.

10.1002/2015MS000489

e2576bfba571341cbf4a4a72fe7d5113

http%3A%2F%2Fmeetings.aps.org%2Flink%2FBAPS.2016.MAR.H51.8

http://doi.wiley.com/10.1002/jame.v7.4Large-eddy simulation is used to study the sensitivity of trade wind cumulus clouds to perturbations in cloud droplet number concentrations. We find that the trade wind cumulus system approaches a radiative-convective equilibrium state, modified by net warming and drying from imposed large-scale advective forcing. The system requires several days to reach equilibrium when cooling rates are specified but much less time, and with less sensitivity to cloud droplet number density, when radiation depends realistically on the vertical distribution of water vapor. The transient behavior and the properties of the near-equilibrium cloud field depend on the microphysical state and therefore on the cloud droplet number density, here taken as a proxy for the ambient aerosol. The primary response of the cloud field to changes in the cloud droplet number density is deepening of the cloud layer. This deepening leads to a decrease in relative humidity and a faster evaporation of small clouds and cloud remnants constituting a negative lifetime effect. In the near-equilibrium regime, the decrease in cloud cover compensates much of the Twomey effect, i.e., the brightening of the clouds, and the overall aerosol effect on the albedo of the organized precipitating cumulus cloud field is small.

Stevens B., G. Feingold, 2009: Untangling aerosol effects on clouds and precipitation in a buffered system.Nature461,607-613,https://doi.org/10.1038/nature08281.

10.1038/nature08281

19794487

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http%3A%2F%2Fwww.nature.com%2Fnature%2Fjournal%2Fv461%2Fn7264%2Fabs%2Fnature08281.html

http://www.nature.com/articles/nature08281Abstract It is thought that changes in the concentration of cloud-active aerosol can alter the precipitation efficiency of clouds, thereby changing cloud amount and, hence, the radiative forcing of the climate system. Despite decades of research, it has proved frustratingly difficult to establish climatically meaningful relationships among the aerosol, clouds and precipitation. As a result, the climatic effect of the aerosol remains controversial. We propose that the difficulty in untangling relationships among the aerosol, clouds and precipitation reflects the inadequacy of existing tools and methodologies and a failure to account for processes that buffer cloud and precipitation responses to aerosol perturbations.

Ström, J., S. Ohlsson, 1998: In situ measurements of enhanced crystal number densities in cirrus clouds caused by aircraft exhaust.J. Geophys. Res.,103,11 355-11 361,https://doi.org/10.1029/98JD00807.10.1029/98JD00807

a917c4a8d6bb96c0ea68b3f9b830bf21

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F98JD00807%2Fpdf

http://doi.wiley.com/10.1029/98JD00807Concurrent measurements of crystal number densities and concentrations of absorbing material contained in cirrus crystals reveal statistically higher crystal number densities in areas of the cloud where absorbing material exceeds 0.01 0204g m0908083. This enhancement in crystal number density ranged between a factor 1.6 and 2.8 depending on the aerosol number density. The absorption signature appeared as banded structures 2 to 8 km wide, which suggests aged aircraft plumes as the source of absorbing material. In the altitudes of the most frequently used flight levels, the concentration of absorbing material in crystals exceeded 0.01 0204g m0908083 during more than 40% of the time in cirrus clouds.

Tao W.-K., X. W. Li, A. Khain, T. Matsui, S. Lang, and J. Simpson, 2007: Role of atmospheric aerosol concentration on deep convective precipitation: Cloud-resolving model simulations.J. Geophys. Res.,112,D24S18,https://doi.org/10.1029/2007JD008728.10.1029/2007JD008728

5b6cc405732d031bc3486e638202e4f3

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2007JD008728%2Ffull

http://onlinelibrary.wiley.com/doi/10.1029/2007JD008728/full[1] A two-dimensional cloud-resolving model with detailed spectral bin microphysics is used to examine the effect of aerosols on three different deep convective cloud systems that developed in different geographic locations: south Florida, Oklahoma, and the central Pacific. A pair of model simulations, one with an idealized low cloud condensation nuclei (CCN) (clean) and one with an idealized high CCN (dirty environment), is conducted for each case. In all three cases, rain reaches the ground earlier for the low-CCN case. Rain suppression is also evident in all three cases with high CCN. However, this suppression only occurs during the early stages of the simulations. During the mature stages of the simulations the effects of increasing aerosol concentration range from rain suppression in the Oklahoma case to almost no effect in the Florida case to rain enhancement in the Pacific case. The model results suggest that evaporative cooling in the lower troposphere is a key process in determining whether high CCN reduces or enhances precipitation. Stronger evaporative cooling can produce a stronger cold pool and thus stronger low-level convergence through interactions with the low-level wind shear. Consequently, precipitation processes can be more vigorous. For example, the evaporative cooling is more than two times stronger in the lower troposphere with high CCN for the Pacific case. Sensitivity tests also suggest that ice processes are crucial for suppressing precipitation in the Oklahoma case with high CCN. A comparison and review of other modeling studies are also presented.

Tao W.-K., J.-P. Chen, Z. Q. Li, C. E. Wang, and C. D. Zhang, 2012: Impact of aerosols on convective clouds and precipitation.Rev. Geophys.,50,RG2001,https://doi.org/10.1029/2011RG000369.10.1029/2011RG000369

48840b499ce94efa20ebd04bb41be328

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2011RG000369%2Fpdf

http://onlinelibrary.wiley.com/doi/10.1029/2011RG000369/pdf[1] Aerosols are a critical factor in the atmospheric hydrological cycle and radiation budget. As a major agent for clouds to form and a significant attenuator of solar radiation, aerosols affect climate in several ways. Current research suggests that aerosol effects on clouds could further extend to precipitation, both through the formation of cloud particles and by exerting persistent radiative forcing on the climate system that disturbs dynamics. However, the various mechanisms behind these effects, in particular, the ones connected to precipitation, are not yet well understood. The atmospheric and climate communities have long been working to gain a better grasp of these critical effects and hence to reduce the significant uncertainties in climate prediction resulting from such a lack of adequate knowledge. Here we review past efforts and summarize our current understanding of the effect of aerosols on convective precipitation processes from theoretical analysis of microphysics, observational evidence, and a range of numerical model simulations. In addition, the discrepancies between results simulated by models, as well as those between simulations and observations, are presented. Specifically, this paper addresses the following topics: (1) fundamental theories of aerosol effects on microphysics and precipitation processes, (2) observational evidence of the effect of aerosols on precipitation processes, (3) signatures of the aerosol impact on precipitation from large-scale analyses, (4) results from cloud-resolving model simulations, and (5) results from large-scale numerical model simulations. Finally, several future research directions for gaining a better understanding of aerosol-cloud-precipitation interactions are suggested.

Twomey S., 1977: The influence of pollution on the shortwave albedo of clouds. J. Atmos. Sci., 34, 1149-1152, https:// doi.org/10.1175/1520-0469(1977)034<1149:TIOPOT>2.0.CO;2.

10.1175/1520-0469(1977)0342.0.CO;2

87d30a8ee5cb88296547d53b6f7b6dba

http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F1977JAtS...34.1149T

http://adsabs.harvard.edu/abs/1977JAtS...34.1149TBy increasing droplet concentration and thereby the optical thickness of a cloud, pollution acts to increase the reflectance (albedo) of clouds; by increasing the absorption coefficient it acts to decrease the reflectance. Calculations suggest that the former effect (brightening of the clouds in reflection, hence climatically a cooling effect) dominates for thin to moderately thick clouds, whereas for sufficiently thick clouds the latter effect (climatically a warming effect) can become dominant.

Wang Y., A. Khalizov, M. Levy, and R. Y. Zhang, 2013a: New directions: Light absorbing aerosols and their atmospheric impacts.Atmos. Environ.,81,713-715,https://doi.org/10.1016/j.atmosenv.2013.09.034.10.1016/j.atmosenv.2013.09.034

a18cf03ff06ec4c2de4d1384bf6a8349

http%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS135223101300722X

http://linkinghub.elsevier.com/retrieve/pii/S135223101300722XNot Available Not Available

Wang Y., J. W. Fan, R. Y. Zhang, L. R. Leung, and C. Franklin, 2013b: Improving bulk microphysics parameterizations in simulations of aerosol indirect effects.J. Geophys. Res.,118,5361-5379,https://doi.org/10.1002/jgrd.50432.10.1002/jgrd.50421

ec22fa12f7f6c1baacc3d1566f344c77

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fjgrd.50432%2Fabstract

http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50432/abstract[1] To improve the microphysical parameterizations for simulations of the aerosol effects in regional and global climate models, the Morrison double-moment bulk microphysical scheme presently implemented in the Weather Research and Forecasting model is modified by replacing the prescribed aerosols in the original bulk scheme (Bulk-OR) with a prognostic double-moment aerosol representation to predict both aerosol number concentration and mass mixing ratio (Bulk-2M). Sensitivity modeling experiments are performed for two distinct cloud regimes: maritime warm stratocumulus clouds (Sc) over southeast Pacific Ocean from the VOCALS project and continental deep convective clouds in the southeast of China. The results from Bulk-OR and Bulk-2M are compared against atmospheric observations and simulations produced by a spectral bin microphysical scheme (SBM). The prescribed aerosol approach (Bulk-OR) produces unreliable aerosol and cloud properties throughout the simulation period, when compared to the results from those using Bulk-2M and SBM, although all of the model simulations are initiated by the same initial aerosol concentration on the basis of the field observations. The impacts of the parameterizations of diffusional growth and autoconversion of cloud droplets and the selection of the embryonic raindrop radius on the performance of the bulk microphysical scheme are also evaluated by comparing the results from the modified Bulk-2M with those from SBM simulations. Sensitivity experiments using four different types of autoconversion schemes reveal that the autoconversion parameterization is crucial in determining the raindrop number, mass concentration, and drizzle formation for warm stratocumulus clouds. An embryonic raindrop size of 40m is determined as a more realistic setting in the autoconversion parameterization. The saturation adjustment employed in calculating condensation/evaporation in the bulk scheme is identified as the main factor responsible for the large discrepancies in predicting cloud water in the Sc case, suggesting that an explicit calculation of diffusion growth with predicted supersaturation is necessary to improve the bulk microphysics scheme. Lastly, a larger rain evaporation rate below clouds is found in the bulk scheme in comparison to the SBM simulation, which may contribute to a lower surface precipitation in the bulk scheme.

Wang Y., J. Jiang, H. Su, 2015: Atmospheric Responses to the Redistribution of Anthropogenic Aerosols,J.Geophys. Res.,120(18),9625-9641,https://doi.org/10.1002/2015JD023665.

10.1002/2015JD023665

18c530d9e551a6c3604b38e4f6b9dba0

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2F2015JD023665%2Fpdf

http://onlinelibrary.wiley.com/doi/10.1002/2015JD023665/pdfAbstract The geographical shift of global anthropogenic aerosols from the developed countries to the Asian continent since the 1980s could potentially perturb the regional and global climate due to aerosol-cloud-radiation interactions. We use an atmospheric general circulation model with different aerosol scenarios to investigate the radiative and microphysical effects of anthropogenic aerosols from different regions on the radiation budget, precipitation, and large-scale circulations. An experiment contrasting anthropogenic aerosol scenarios in 1970 and 2010 shows that the altered cloud reflectivity and solar extinction by aerosols results in regional surface temperature cooling in East and South Asia, and warming in the US and Europe, respectively. These aerosol-induced temperature changes are consistent with the relative temperature trends from 1980 to 2010 over different regions in the reanalysis data. A reduced meridional streamfunction and zonal winds over the 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 assessments of the aerosol effects over the different regions suggest that the increasing Asian pollution accounts for the weakening of the tropics circulation, while the decreasing pollution in Europe and US tends to shift the circulation systems southward. Moreover, the aerosol indirect forcing is predominant over the total aerosol forcing in magnitude, while aerosol radiative and microphysical effects jointly shape the meridional energy distributions and modulate the circulation systems.

Wang Y., K.-H. Lee, Y. Lin, M. Levy, R. Y. Zhang, 2014b: Distinct effects of anthropogenic aerosols on tropical cyclones.Nat. Clim. Change4,368-373,https://doi.org/10.1038/nclimate2144.

10.1038/nclimate2144

ce5cbd4222b986caae04fb6b3a1fe710

http%3A%2F%2Fwww.nature.com%2Fnclimate%2Fjournal%2Fv4%2Fn5%2Fnclimate2144%2Fmetrics%2Fnews

http://www.nature.com/articles/nclimate2144Long-term observations have revealed large amplitude fluctuations in the frequency and intensity of tropical cyclones (TCs; refs , , , ), but the anthropogenic impacts, including greenhouse gases and particulate matter pollution, remain to be elucidated. Here, we show distinct aerosol effects on the development of TCs: the coupled microphysical and radiative effects of anthropogenic aerosols result in delayed development, weakened intensity and early dissipation, but an enlarged rainband and increased precipitation under polluted conditions. Our results imply that anthropogenic aerosols probably exhibit an opposite effect to that of greenhouse gases, highlighting the necessity of incorporating a realistic microphysical-radiative interaction of aerosols for accurate forecasting and climatic prediction of TCs in atmospheric models.

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.Atmospheric Chemistry and Physics11,12 421-12 436,https://doi.org/10.5194/acp-11-12421-2011.10.5194/acp-11-12421-2011

fb8eec45c806e86a00f33e0325b21452

http%3A%2F%2Fwww.oalib.com%2Fpaper%2F2698174

http://www.atmos-chem-phys.net/11/12421/2011/Seven-year measurements of precipitation, lightning flashes, and visibility from 2000 to 2006 have been analyzed in the Pearl River Delta (PRD) region, China, with a focus on the Guangzhou megacity area. Statistical analysis shows that the occurrence of heavy rainfall (>25 mm per day) and frequency of lightning strikes are reversely correlated to visibility during this period. To elucidate the effects of aerosols on cloud processes, precipitation, and lightning activity, a cloud resolving Weather Research and Forecasting (CR-WRF) model with a two-moment bulk microphysical scheme is employed to simulate a mesoscale convective system occurring on 28 Match 2009 in the Guangzhou megacity area. The model predicted evolutions of composite radar reflectivity and accumulated precipitation are in agreement with measurements from S-band weather radars and automatic gauge stations. The calculated lightning potential index (LPI) exhibits temporal and spatial consistence with lightning flashes recorded by a local lightning detection network. Sensitivity experiments have been performed to reflect aerosol conditions representative of polluted and clean cases. The simulations suggest that precipitation and LPI are enhanced by about 16% and 50%, respectively, under the polluted aerosol condition. Our results suggest that elevated aerosol loading suppresses light and moderate precipitation (less than 25 mm per day), but enhances heavy precipitation. The responses of hydrometeors and latent heat release to different aerosol loadings reveal the physical mechanism for the precipitation and lightning enhancement in the Guangzhou megacity area, showing more efficient mixed phase processes and intensified convection under the polluted aerosol condition.

Wang Y., R. Y. Zhang, and R. Saravanan, 2014a: Asian pollution climatically modulates mid-latitude cyclones following hierarchical modelling and observational analysis.Nat. Commun.,5,3098,https://doi.org/10.1038/ncomms4098.10.1038/ncomms4098

24448316

ca255990c57637719c1929b71cedbd4b

http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpubmed%2F24448316

http://www.ncbi.nlm.nih.gov/pubmed/24448316Abstract Increasing levels of anthropogenic aerosols in Asia have raised considerable concern regarding its potential impact on the global atmosphere, but the magnitude of the associated climate forcing remains to be quantified. Here, using a novel hierarchical modelling approach and observational analysis, we demonstrate modulated mid-latitude cyclones by Asian pollution over the past three decades. Regional and seasonal simulations using a cloud-resolving model show that Asian pollution invigorates winter cyclones over the northwest Pacific, increasing precipitation by 7% and net cloud radiative forcing by 1.0 W m(-2) at the top of the atmosphere and by 1.7 W m(-2) at the Earth's surface. A global climate model incorporating the diabatic heating anomalies from Asian pollution produces a 9% enhanced transient eddy meridional heat flux and reconciles a decadal variation of mid-latitude cyclones derived from the Reanalysis data. Our results unambiguously reveal a large impact of the Asian pollutant outflows on the global general circulation and climate.

Williams E. R., R. Zhang, and J. Rydock, 1991: Mixed-phase microphysics and cloud electrification. J. Atmos. Sci., 48, 2195-2203, https://doi.org/10.1175/1520-0469(1991)048 <2195:MPMACE>2.0.CO; 2.

10.1175/1520-0469(1991)0482.0.CO;2

46c4652582acbbce37f69e6cf66896eb

http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F1991JAtS...48.2195W

http://adsabs.harvard.edu/abs/1991JAtS...48.2195WA number of experimental studies have shown that sublimating ice acquires negative charge and ice undergoing vapor deposition acquires positive charge. Microphysical calculations are performed to determine the diffusional state (i.e., sublimation versus deposition) of riming graupel particles. Comparisons with earlier laboratory measurements of charge transfer to a rotating rimer in a cloud of supercooled water droplets and ice crystals again suggest that sublimating graupel particles charge negatively and graupel undergoing deposition charge positively. Implications for charge separation in thunderstorms are discussed.

Yuan T. L., Z. Q. Li, R. Y. Zhang, and J. W. Fan, 2008: Increase of cloud droplet size with aerosol optical depth: An observation and modeling study.J. Geophys. Res.,113,D04201,https://doi.org/10.1029/2007JD008632.10.1029/2007JD008632

88998c52fb5097b29de42ed4e421b637

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2007JD008632%2Fpdf

http://onlinelibrary.wiley.com/doi/10.1029/2007JD008632/pdf[1] Cloud droplet effective radius (DER) is generally negatively correlated with aerosol optical depth (AOD) as a proxy of cloud condensation nuclei. In this study, cases of positive correlation were found over certain portions of the world by analyzing the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite products, together with a general finding that DER may increase or decrease with aerosol loading depending on environmental conditions. The slope of the correlation between DER and AOD is driven primarily by water vapor amount, which explains 70% of the variance in our study. Various potential artifacts that may cause the positive relation are investigated including the effects of aerosol swelling, partially cloudy, atmospheric dynamics, cloud three-dimensional (3-D) and surface influence effects. None seems to be the primary cause for the observed phenomenon, although a certain degree of influence exists for some of the factors. Analyses are conducted over seven regions around the world representing different types of aerosols and clouds. Only two regions show positive dependence of DER on AOD, near coasts of the Gulf of Mexico and South China Sea, which implies physical processes may at work. Using a 2-D Goddard Cumulus Ensemble model (GCE) with spectral-bin microphysics which incorporated a reformulation of the Khler theory, two possible physical mechanisms are hypothesized. They are related to the effects of slightly soluble organics (SSO) particles and giant cloud condensation nuclei (CCN). Model simulations show a positive correlation between DER and AOD, due to a decrease in activated aerosols with an increasing SSO content. Addition of a few giant CCNs also increases the DER. Further investigations are needed to fully understand and clarify the observed phenomenon.

Zhang M. H., S. Klein, D. Rand all, R. Cederwall, and A. Del Genio, 2005: Introduction to special section on toward reducing cloud-climate feedback uncertainties in atmospheric general circulation models.J. Geophys. Res.,110,D15S01,https://doi.org/10.1029/2005JD005923.10.1029/2005JD005923

a2888ba9119f84dbdd9be278f72212bb

http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2005JD005923%2Ffull

http://onlinelibrary.wiley.com/doi/10.1029/2005JD005923/fullNo abstract is available for this article.

Zhang R. Y., I. Suh, J. Zhao, D. Zhang, E. C. Fortner, X. X. Tie, L. T. Molina, and M. J. Molina, 2004: Atmospheric new particle formation enhanced by organic acids.Science304,1487-1490,https://doi.org/10.1126/science.1095139.10.1126/science.1095139

cd9caed39125fa65989c85828884c8c6

http%3A%2F%2Fscitation.aip.org%2Fgetabs%2Fservlet%2FGetabsServlet%3Fprog%3Dnormal%26amp%3Bid%3DVIRT01000009000023000052000001%26amp%3Bidtype%3Dcvips%26amp%3Bgifs%3DYes

http://www.sciencemag.org/cgi/doi/10.1126/science.1095139

Zhang R. Y., G. H. Li, J. W. Fan, D. L. Wu, and M. J. Molina, 2007: Intensification of pacific storm track linked to Asian pollution.Proc. Nat. Acad. Sci.,104,5295-5299,https://doi.org/10.1073/pnas.0700618104.10.1073/pnas.0700618104

17374719

759d53e76e9f7ab249fe6f2e73927485

http%3A%2F%2Flabs.europepmc.org%2Fabstract%2FPMC%2FPMC1828943

http://www.pnas.org/cgi/doi/10.1073/pnas.0700618104Abstract Indirect radiative forcing of atmospheric aerosols by modification of cloud processes poses the largest uncertainty in climate prediction. We show here a trend of increasing deep convective clouds over the Pacific Ocean in winter from long-term satellite cloud measurements (1984-2005). Simulations with a cloud-resolving weather research and forecast model reveal that the increased deep convective clouds are reproduced when accounting for the aerosol effect from the Asian pollution outflow, which leads to large-scale enhanced convection and precipitation and hence an intensified storm track over the Pacific. We suggest that the wintertime Pacific is highly vulnerable to the aerosol-cloud interaction because of favorable cloud dynamical and microphysical conditions from the coupling between the Pacific storm track and Asian pollution outflow. The intensified Pacific storm track is climatically significant and represents possibly the first detected climate signal of the aerosol-cloud interaction associated with anthropogenic pollution. In addition to radiative forcing on climate, intensification of the Pacific storm track likely impacts the global general circulation due to its fundamental role in meridional heat transport and forcing of stationary waves.

Zhang, R. Y., Coauthors, 2015: Formation of urban fine particulate matter.Chem. Rev.,115(10),3803-3855,https://doi.org/10.1021/acs.chemrev.5b00067.10.1021/acs.chemrev.5b00067

25942499

1e43dabd94bfa3a28211792b051d0d6b

http%3A%2F%2Fpubs.acs.org%2Fdoi%2Fabs%2F10.1021%2Facs.chemrev.5b00067

http://pubs.acs.org/doi/10.1021/acs.chemrev.5b00067Urban air pollution represents one of the greatest environmental challenges facing mankind in the 21st century. Noticeably, many developing countries, such as China and India, have experienced severe air pollution because of their fast-developing economy and urbanization. Globally, the urbanization trend is projected to continue: 70% of the world population will reside in urban centers by 2050, and there will exist 41 megacities (with more than 10 million inhabitants) by 2030. Air pollutants consist of a complex combination of gases and particulate matter (PM). In particular, fine PM (particles with the aerodynamic diameter smaller than 2.5 m or PM_(2.5)) profoundly impacts human health, visibility, the ecosystem, the weather, and the climate, and these PM effects are largely dependent on the aerosol properties, including the number concentration, size, and chemical composition. PM is emitted directly into the atmosphere (primary) or formed in the atmosphere through gas-to-particle conversion (secondary) (Figure 1). Also, primary and secondary PM undergoes chemical and physical transformations and is subjected to transport, cloud processing, and removal from the atmosphere.