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Sample records for aerosol indirect effect

  1. Model Intercomparison of Indirect Aerosol Effects

    NASA Technical Reports Server (NTRS)

    Penner, J. E.; Quaas, J.; Storelvmo, T.; Takemura, T.; Boucher, O.; Guo, H.; Kirkevag, A.; Kristjansson, J. E.; Seland, O.

    2006-01-01

    Modeled differences in predicted effects are increasingly used to help quantify the uncertainty of these effects. Here, we examine modeled differences in the aerosol indirect effect in a series of experiments that help to quantify how and why model-predicted aerosol indirect forcing varies between models. The experiments start with an experiment in which aerosol concentrations, the parameterization of droplet concentrations and the autoconversion scheme are all specified and end with an experiment that examines the predicted aerosol indirect forcing when only aerosol sources are specified. Although there are large differences in the predicted liquid water path among the models, the predicted aerosol first indirect effect for the first experiment is rather similar, about -0.6 W/sq m to -0.7 W/sq m. Changes to the autoconversion scheme can lead to large changes in the liquid water path of the models and to the response of the liquid water path to changes in aerosols. Adding an autoconversion scheme that depends on the droplet concentration caused a larger (negative) change in net outgoing shortwave radiation compared to the 1st indirect effect, and the increase varied from only 22% to more than a factor of three. The change in net shortwave forcing in the models due to varying the autoconversion scheme depends on the liquid water content of the clouds as well as their predicted droplet concentrations, and both increases and decreases in the net shortwave forcing can occur when autoconversion schemes are changed. The parameterization of cloud fraction within models is not sensitive to the aerosol concentration, and, therefore, the response of the modeled cloud fraction within the present models appears to be smaller than that which would be associated with model "noise". The prediction of aerosol concentrations, given a fixed set of sources, leads to some of the largest differences in the predicted aerosol indirect radiative forcing among the models, with values of

  2. A Simple Model of Global Aerosol Indirect Effects

    SciTech Connect

    Ghan, Steven J.; Smith, Steven J.; Wang, Minghuai; Zhang, Kai; Pringle, K. J.; Carslaw, K. S.; Pierce, Jeffrey; Bauer, Susanne E.; Adams, P. J.

    2013-06-28

    Most estimates of the global mean indirect effect of anthropogenic aerosol on the Earth’s energy balance are from simulations by global models of the aerosol lifecycle coupled with global models of clouds and the hydrologic cycle. Extremely simple models have been developed for integrated assessment models, but lack the flexibility to distinguish between primary and secondary sources of aerosol. Here a simple but more physically-based model expresses the aerosol indirect effect using analytic representations of droplet nucleation, cloud and aerosol vertical structure, and horizontal variability in cloud water and aerosol concentration. Although the simple model is able to produce estimates of aerosol indirect effects that are comparable to those from some global aerosol models using the same global mean aerosol properties, the estimates are found to be sensitive to several uncertain parameters, including the preindustrial cloud condensation nuclei concentration, primary and secondary anthropogenic emissions, the size of the primary particles, the fraction of the secondary anthropogenic emissions that accumulates on the coarse mode, the fraction of the secondary mass that forms new particles, and the sensitivity of liquid water path to droplet number concentration. Aerosol indirect effects are surprisingly linear in emissions. This simple model provides a much stronger physical basis for representing aerosol indirect effects than previous representations in integrated assessment models designed to quickly explore the parameter space of emissions-climate interactions. The model also produces estimates that depend on parameter values in ways that are consistent with results from detailed global aerosol-climate simulation models.

  3. Evaluating aerosol indirect effect through marine stratocumulus clouds

    SciTech Connect

    Kogan, Z.N.; Kogan, Y.L.; Lilly, D.K.

    1996-04-01

    During the last decade much attention has been focused on anthropogenic aerosols and their radiative influence on the global climate. Charlson et al. and Penner et al. have demonstrated that tropospheric aerosols and particularly anthropogenic sulfate aerosols may significantly contribute to the radiative forcing exerting a cooling influence on climate (-1 to -2 W/m{sup 2}) which is comparable in magnitude to greenhouse forcing, but opposite in sign. Aerosol particles affect the earth`s radiative budget either directly by scattering and absorption of solar radiation by themselves or indirectly by altering the cloud radiative properties through changes in cloud microstructure. Marine stratocumulus cloud layers and their possible cooling influence on the atmosphere as a result of pollution are of special interest because of their high reflectivity, durability, and large global cover. We present an estimate of thet aerosol indirect effect, or, forcing due to anthropogenic sulfate aerosols.

  4. Indirect aerosol effect increases CMIP5 models projected Arctic warming

    DOE PAGESBeta

    Chylek, Petr; Vogelsang, Timothy J.; Klett, James D.; Hengartner, Nicholas; Higdon, Dave; Lesins, Glen; Dubey, Manvendra K.

    2016-02-20

    Phase 5 of the Coupled Model Intercomparison Project (CMIP5) climate models’ projections of the 2014–2100 Arctic warming under radiative forcing from representative concentration pathway 4.5 (RCP4.5) vary from 0.9° to 6.7°C. Climate models with or without a full indirect aerosol effect are both equally successful in reproducing the observed (1900–2014) Arctic warming and its trends. However, the 2014–2100 Arctic warming and the warming trends projected by models that include a full indirect aerosol effect (denoted here as AA models) are significantly higher (mean projected Arctic warming is about 1.5°C higher) than those projected by models without a full indirect aerosolmore » effect (denoted here as NAA models). The suggestion is that, within models including full indirect aerosol effects, those projecting stronger future changes are not necessarily distinguishable historically because any stronger past warming may have been partially offset by stronger historical aerosol cooling. In conclusion, the CMIP5 models that include a full indirect aerosol effect follow an inverse radiative forcing to equilibrium climate sensitivity relationship, while models without it do not.« less

  5. A Simple Model of Global Aerosol Indirect Effects

    NASA Technical Reports Server (NTRS)

    Ghan, Steven J.; Smith, Steven J.; Wang, Minghuai; Zhang, Kai; Pringle, Kirsty; Carslaw, Kenneth; Pierce, Jeffrey; Bauer, Susanne; Adams, Peter

    2013-01-01

    Most estimates of the global mean indirect effect of anthropogenic aerosol on the Earth's energy balance are from simulations by global models of the aerosol lifecycle coupled with global models of clouds and the hydrologic cycle. Extremely simple models have been developed for integrated assessment models, but lack the flexibility to distinguish between primary and secondary sources of aerosol. Here a simple but more physically based model expresses the aerosol indirect effect (AIE) using analytic representations of cloud and aerosol distributions and processes. Although the simple model is able to produce estimates of AIEs that are comparable to those from some global aerosol models using the same global mean aerosol properties, the estimates by the simple model are sensitive to preindustrial cloud condensation nuclei concentration, preindustrial accumulation mode radius, width of the accumulation mode, size of primary particles, cloud thickness, primary and secondary anthropogenic emissions, the fraction of the secondary anthropogenic emissions that accumulates on the coarse mode, the fraction of the secondary mass that forms new particles, and the sensitivity of liquid water path to droplet number concentration. Estimates of present-day AIEs as low as 5 W/sq m and as high as 0.3 W/sq m are obtained for plausible sets of parameter values. Estimates are surprisingly linear in emissions. The estimates depend on parameter values in ways that are consistent with results from detailed global aerosol-climate simulation models, which adds to understanding of the dependence on AIE uncertainty on uncertainty in parameter values.

  6. GCM Simulations of the Aerosol Indirect Effect: Sensitivity to Cloud Parameterization and Aerosol Burden

    NASA Technical Reports Server (NTRS)

    Menon, Surabi; DelGenio, Anthony D.; Koch, Dorothy; Tselioudis, George; Hansen, James E. (Technical Monitor)

    2001-01-01

    We describe the coupling of the Goddard Institute for Space Studies (GISS) general circulation model (GCM) to an online sulfur chemistry model and source models for organic matter and sea-salt that is used to estimate the aerosol indirect effect. The cloud droplet number concentration is diagnosed empirically from field experiment datasets over land and ocean that observe droplet number and all three aerosol types simultaneously; corrections are made for implied variations in cloud turbulence levels. The resulting cloud droplet number is used to calculate variations in droplet effective radius, which in turn allows us to predict aerosol effects on cloud optical thickness and microphysical process rates. We calculate the aerosol indirect effect by differencing the top-of-the-atmosphere net cloud radiative forcing for simulations with present-day vs. pre-industrial emissions. Both the first (radiative) and second (microphysical) indirect effects are explored. We test the sensitivity of our results to cloud parameterization assumptions that control the vertical distribution of cloud occurrence, the autoconversion rate, and the aerosol scavenging rate, each of which feeds back significantly on the model aerosol burden. The global mean aerosol indirect effect for all three aerosol types ranges from -1.55 to -4.36 W m(exp -2) in our simulations. The results are quite sensitive to the pre-industrial background aerosol burden, with low pre-industrial burdens giving strong indirect effects, and to a lesser extent to the anthropogenic aerosol burden, with large burdens giving somewhat larger indirect effects. Because of this dependence on the background aerosol, model diagnostics such as albedo-particle size correlations and column cloud susceptibility, for which satellite validation products are available, are not good predictors of the resulting indirect effect.

  7. GCM Simulations of the Aerosol Indirect Effect: Sensitivity to Cloud Parameterization and Aerosol Burden

    NASA Technical Reports Server (NTRS)

    Menon, Surabi; DelGenio, Anthony D.; Koch, Dorothy; Tselioudis, George; Hansen, James E. (Technical Monitor)

    2001-01-01

    We describe the coupling of the Goddard Institute for Space Studies (GISS) general circulation model (GCM) to an online sulfur chemistry model and source models for organic matter and sea-salt that is used to estimate the aerosol indirect effect. The cloud droplet number concentration is diagnosed empirically from field experiment datasets over land and ocean that observe droplet number and all three aerosol types simultaneously; corrections are made for implied variations in cloud turbulence levels. The resulting cloud droplet number is used to calculate variations in droplet effective radius, which in turn allows us to predict aerosol effects on cloud optical thickness and microphysical process rates. We calculate the aerosol indirect effect by differencing the top-of-the-atmosphere net cloud radiative forcing for simulations with present-day vs. pre-industrial emissions. Both the first (radiative) and second (microphysical) indirect effects are explored. We test the sensitivity of our results to cloud parameterization assumptions that control the vertical distribution of cloud occurrence, the autoconversion rate, and the aerosol scavenging rate, each of which feeds back significantly on the model aerosol burden. The global mean aerosol indirect effect for all three aerosol types ranges from -1.55 to -4.36 W/sq m in our simulations. The results are quite sensitive to the pre-industrial background aerosol burden, with low pre-industrial burdens giving strong indirect effects, and to a lesser extent to the anthropogenic aerosol burden, with large burdens giving somewhat larger indirect effects. Because of this dependence on the background aerosol, model diagnostics such as albedo-particle size correlations and column cloud susceptibility, for which satellite validation products are available, are not good predictors of the resulting indirect effect.

  8. Evidence for a Glaciation Aerosol Indirect Effect from Ship Tracks

    NASA Astrophysics Data System (ADS)

    Christensen, M.; Suzuki, K.; Stephens, G. L.

    2013-12-01

    Ship tracks are a prominent manifestation of the aerosol indirect effect that provides a unique opportunity to study aerosol interactions in both warm and mixed-phase clouds. While ample evidence supports that an increase in aerosol concentration generally suppresses warm phase precipitation leading to longer cloud lifetime and more reflected sunlight (Albrecht, 1989) there is less understood about these effects in mixed-phase clouds. Lohmann, (2002) propose that an increase in IN (Ice Nuclei) may cause a glaciation indirect effect which results in more frequent glaciation of super-cooled droplets via the Bergeron process thereby increasing the amount of precipitation, which could decrease cloud cover, cloud longevity, and reflected sunlight. In this study, over 200 ship tracks are identified in mixed phase clouds using MODIS (MODerate resolution Imaging Spectroradiometer) imagery. Retrievals of the ice phase are obtained using CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations). These measurements provide evidence that glaciation is more frequent in polluted clouds compared to the unpolluted clouds that lie adjacent to ship tracks. Larger ice fractions may result from the increased IN emitted from the ship or by other processes (e.g., immersion/contact freezing) that lead to faster ice multiplication in polluted clouds with smaller and more numerous supercooled droplets. Observations from the profiling radar on CloudSat show that aerosol suppresses warm phase precipitation but enhances the cold phase precipitation. For mixed-phase clouds, these differences roughly cancel resulting in small changes in precipitation between polluted and unpolluted clouds. When cloud tops are warm, aerosol decreases precipitation rates and cloud water paths due to the entrainment effect but the differences in cloud water amount are considerably smaller than those found in cold phase clouds. These results provide the first glance of ship tracks in mixed

  9. Aerosol Indirect effect on Stratocumulus Organization

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Heus, T.; Kollias, P.

    2015-12-01

    Large-eddy simulations are used to investigate the role of aerosol loading on organized Stratocumulus. We prescribed the cloud droplet number concentration (Nc) and considered it as the proxy for different aerosol loading. While the presence of drizzle amplifies the mesoscale variability as is in Savic-Jovcic and Stevens (JAS, 2008), two noticeable findings are discussed here: First, the scale of marine boundary layer circulation appears to be independent of aerosol loading, suggesting a major role of the turbulence. The precise role of the turbulence in stratocumulus organization is studied by modifying the large scale fluctuations from the LES domain. Second, while it is commonly thought that the whole circulation needs to be represented for robust cloud development, we find that stratocumulus dynamics, including variables like w'w' and w'w'w', are remarkably robust even if large scales are ignored by simply reducing the domain sizes. The only variable that is sensitive to the change of the scale is the amount of cloudiness. Despite their smaller cloud thickness and inhomogeneous macroscopic structure for low Nc, individual drizzling clouds have sizes that are commensurate with circulation scale. We observe an Nc threshold below which stratocumulus is thin enough so that a little decrease of Nc would lead to great change of cloud fraction. The simulated cloud albedo is more sensitive to in-cloud liquid water content than to the amount of cloudiness since the former decreases at least three times faster than the latter due to drizzle. The main impact of drizzle evaporation is observed to keep the sub-cloud layer moist and as a result to extend the lifetime of stratocumulus by a couple of hours.

  10. Parameterizations of Cloud Microphysics and Indirect Aerosol Effects

    SciTech Connect

    Tao, Wei-Kuo

    2014-05-19

    1. OVERVIEW Aerosols and especially their effect on clouds are one of the key components of the climate system and the hydrological cycle [Ramanathan et al., 2001]. Yet, the aerosol effect on clouds remains largely unknown and the processes involved not well understood. A recent report published by the National Academy of Science states "The greatest uncertainty about the aerosol climate forcing - indeed, the largest of all the uncertainties about global climate forcing - is probably the indirect effect of aerosols on clouds [NRC, 2001]." The aerosol effect on clouds is often categorized into the traditional "first indirect (i.e., Twomey)" effect on the cloud droplet sizes for a constant liquid water path [Twomey, 1977] and the "semi-direct" effect on cloud coverage [e.g., Ackerman et al., 2000]. Enhanced aerosol concentrations can also suppress warm rain processes by producing a narrow droplet spectrum that inhibits collision and coalescence processes [e.g., Squires and Twomey, 1961; Warner and Twomey, 1967; Warner, 1968; Rosenfeld, 1999]. The aerosol effect on precipitation processes, also known as the second type of aerosol indirect effect [Albrecht, 1989], is even more complex, especially for mixed-phase convective clouds. Table 1 summarizes the key observational studies identifying the microphysical properties, cloud characteristics, thermodynamics and dynamics associated with cloud systems from high-aerosol continental environments. For example, atmospheric aerosol concentrations can influence cloud droplet size distributions, warm-rain process, cold-rain process, cloud-top height, the depth of the mixed phase region, and occurrence of lightning. In addition, high aerosol concentrations in urban environments could affect precipitation variability by providing an enhanced source of cloud condensation nuclei (CCN). Hypotheses have been developed to explain the effect of urban regions on convection and precipitation [van den Heever and Cotton, 2007 and Shepherd

  11. Emulation of Cloud-Aerosol Indirect Radiative Effects (ECLAIRE)

    NASA Astrophysics Data System (ADS)

    Dunne, E. M.; Korhonen, H.; Kokkola, H.; Lee, L.; Romakkaniemi, S.

    2014-12-01

    Resolving sub-grid-scale interactions between clouds and aerosols is one of the biggest challenges facing climate models in the 21st century. By carefully selecting boundary conditions to represent grid boxes in larger-scale models, an emulator of a cloud-resolving model can be created and implemented in a regional or global model. Emulators can estimate the output of a model, based on a statistical analysis of outputs from simulations with known inputs. This method may reduce uncertainties in a range of cloud-scale processes, including calculations of aerosol indirect radiative effects, precipitation rates, and wet removal rates of aerosol. The Finnish Academy has recently funded the Emulation of Cloud-Aerosol Indirect Radiative Effects (ECLAIRE) project, whose aim is to construct emulators of cloud-scale processes from the WRF-Chem model and implement them into the ECHAM climate model. This poster will describe the goals and proposed methods of the project, together with any initial results.

  12. Assessing aerosol indirect effect through ice clouds in CAM5

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Liu, Xiaohong; Yoon, Jin-Ho; Wang, Minghuai; Comstock, Jennifer M.; Barahona, Donifan; Kooperman, Gabriel

    2013-05-01

    Ice clouds play an important role in regulating the Earth's radiative budget and influencing the hydrological cycle. Aerosols can act as solution droplets or ice nuclei for ice crystal formation, thus affecting the physical properties of ice clouds. Because the related dynamical and microphysical processes happen at very small spatial and temporal scales, it is a great challenge to accurately represent them in global climate models. Consequently, the aerosol indirect effect through ice clouds (ice AIE) estimated by global climate models is associated with large uncertainties. In order to better understand these processes and improve ice cloud parameterization in the Community Atmospheric Model, version 5 (CAM5), we analyze in-situ measurements from various research campaigns, and use the derived statistical information to evaluate and constrain the model [1]. We also make use of new model capabilities (prescribed aerosols and nudging) to estimate the aerosol indirect effect through ice clouds, and quantify the uncertainties associated with ice nucleation processes. In this study, a new approach is applied to separate the impact of aerosols on warm and cold clouds by using the prescribed-aerosol capability in CAM5 [2]. This capability allows a single simulation to simultaneously include up to three aerosol fields: online calculated, as well as prescribed pre-industrial (PI) and present-day conditions (PD). In a set of sensitivity simulations, we use the same aerosol fields to drive droplet activation in warm clouds, and different (PD and PI) conditions for different components of the ice nucleation parameterization in pure ice clouds, so as to investigate various ice nucleation mechanisms in an isolated manner. We also applied nudging in our simulations, which helps to increase the signal-to-noise ratio in much shorter simulation period [3] and isolate the impact of aerosols on ice clouds from other factors, such as temperature and relative humidity change. The

  13. Aerosol Indirect Effects on Cirrus Clouds in Global Aerosol-Climate Models

    NASA Astrophysics Data System (ADS)

    Liu, X.; Zhang, K.; Wang, Y.; Neubauer, D.; Lohmann, U.; Ferrachat, S.; Zhou, C.; Penner, J.; Barahona, D.; Shi, X.

    2015-12-01

    Cirrus clouds play an important role in regulating the Earth's radiative budget and water vapor distribution in the upper troposphere. Aerosols can act as solution droplets or ice nuclei that promote ice nucleation in cirrus clouds. Anthropogenic emissions from fossil fuel and biomass burning activities have substantially perturbed and enhanced concentrations of aerosol particles in the atmosphere. Global aerosol-climate models (GCMs) have now been used to quantify the radiative forcing and effects of aerosols on cirrus clouds (IPCC AR5). However, the estimate uncertainty is very large due to the different representation of ice cloud formation and evolution processes in GCMs. In addition, large discrepancies have been found between model simulations in terms of the spatial distribution of ice-nucleating aerosols, relative humidity, and temperature fluctuations, which contribute to different estimates of the aerosol indirect effect through cirrus clouds. In this presentation, four GCMs with the start-of-the art representations of cloud microphysics and aerosol-cloud interactions are used to estimate the aerosol indirect effects on cirrus clouds and to identify the causes of the discrepancies. The estimated global and annual mean anthropogenic aerosol indirect effect through cirrus clouds ranges from 0.1 W m-2 to 0.3 W m-2 in terms of the top-of-the-atmosphere (TOA) net radiation flux, and 0.5-0.6 W m-2 for the TOA longwave flux. Despite the good agreement on global mean, large discrepancies are found at the regional scale. The physics behind the aerosol indirect effect is dramatically different. Our analysis suggests that burden of ice-nucleating aerosols in the upper troposphere, ice nucleation frequency, and relative role of ice formation processes (i.e., homogeneous versus heterogeneous nucleation) play key roles in determining the characteristics of the simulated aerosol indirect effects. In addition to the indirect effect estimate, we also use field campaign

  14. Observations of the first aerosol indirect effect in shallow cumuli

    SciTech Connect

    Berg, Larry K.; Berkowitz, Carl M.; Barnard, James C.; Senum, Gunar; Springston, Stephen R.

    2011-02-08

    Data from the Cumulus Humilis Aerosol Processing Study (CHAPS) are used to estimate the impact of both aerosol indirect effects and cloud dynamics on the microphysical and optical properties of shallow cumuli observed in the vicinity of Oklahoma City, Oklahoma. Not surprisingly, we find that the amount of light scattered by the clouds is dominated by their liquid water content (LWC), which in turn is driven by cloud dynamics. However, removing the effect of cloud dynamics by examining the scattering normalized by LWC shows a strong sensitivity of scattering to pollutant loading. These results suggest that even moderately sized cities, like Oklahoma City, can have a measureable impact on the optical properties of shallow cumuli.

  15. Impact of Cloud-Borne Aerosol Representation on Aerosol Direct and Indirect Effects

    SciTech Connect

    Ghan, Steven J.; Easter, Richard C.

    2006-09-21

    Aerosol particles attached to cloud droplets are much more likely to be removed from the atmosphere and are much less efficient at scattering sunlight than if unattached. Models used to estimate direct and indirect effects of aerosols employ a variety of representations of such cloud-borne particles. Here we use a global aerosol model with a relatively complete treatment of cloud-borne particles to estimate the sensitivity of simulated aerosol, cloud and radiation fields to various approximations to the representation of cloud-borne particles. We find that neglecting transport of cloud-borne particles introduces little error, but that diagnosing cloud-borne particles produces global mean biases of 20% and local errors of up to 40% for many variables of interest. A treatment that predicts the total mass concentration of cloud-borne particles for each mode yields smaller errors and runs 20% faster than the complete treatment.

  16. Modeling the Relationships Between Aerosol Properties and the Direct and Indirect Effects of Aerosols on Climate

    NASA Technical Reports Server (NTRS)

    Toon, Owen B.

    1994-01-01

    Aerosols may affect climate directly by scattering and absorbing visible and infrared energy, They may also affect climate indirectly by modifying the properties of clouds through microphysical processes, and by altering abundances of radiatively important gases through heterogeneous chemistry. Researchers understand which aerosol properties control the direct effect of aerosols on the radiation budget. Unfortunately, despite an abundance of data on certain types of aerosols, much work remains to be done to determine the values of these properties. For instance we have little idea about the global distribution, seasonal variation, or interannual variability of the aerosol optical depth. Also we do not know the visible light absorption properties of tropical aerosols which may contain much debris from slash and burn agriculture. A positive correlation between aerosol concentrations and albedos of marine stratus clouds is observed, and the causative microphysics is understood. However, models suggest that it is difficult to produce new particles in the marine boundary layer. Some modelers have suggested that the particles in the marine boundary layer may originate in the free troposphere and be transported into the boundary layer. Others argue that the aerosols are created in the marine boundary layer. There are no data linking aerosol concentration and cirrus cloud albedo, and models suggest cirrus properties may not be very sensitive to aerosol abundance. There is clear evidence of a radiatively significant change in the global lower stratospheric ozone abundance during the past few decades. These changes are caused by heterogeneous chemical reactions occurring on the surfaces of particles. The rates of these reactions depend upon the chemical composition of the particles. Although rapid advances in understanding heterogeneous chemistry have been made, much remains to be done.

  17. An investigation of Raman lidar aerosol measurements and their application to the study of the aerosol indirect effect

    NASA Astrophysics Data System (ADS)

    Russo, Felicita

    The problem of the increasing global atmospheric temperature has motivated a large interest in studying the mechanisms that can influence the radiative balance of the planet. Aerosols are responsible for several radiative effects in the atmosphere: an increase of aerosol loading in the atmosphere increases the reflectivity of the atmosphere and has an estimated cooling effect and is called the aerosol direct effect. Another process involving aerosols is the effect that an increase in their concentration in the atmosphere has on the formation of clouds and is called the aerosol indirect effect. In the latest IPCC report, the aerosol indirect effect was estimated to be responsible for a radiative forcing ranging between -0.3 W/m2 to -1.8 W/m2, which can be as large as, but opposite in sign to, the radiative forcing due to greenhouse gases. The main goal of this dissertation is to study the Raman lidar measurements of quantities relevant for the investigation of the aerosol indirect effect and ultimately to apply these measurements to a quantification of the aerosol indirect effect. In particular we explore measurements of the aerosol extinction from both the NASA Goddard Space Flight Center Scanning Raman Lidar (SRL) and the US Department of Energy (DOE) ARM Climate Research Facility Raman Lidar (CARL). An algorithm based on the chi-squared technique to calculate the aerosol extinction, which was introduced first by Whiteman (1999), is here validated using both simulated and experimental data. It has been found as part of this validation that the aerosol extinction uncertainty retrieved with this technique is on average smaller that the uncertainty calculated with the technique traditionally used. This algorithm was then used to assess the performance of the CARL aerosol extinction retrieval for low altitudes. Additionally, since CARL has been upgraded with a channel for measuring Raman liquid water scattering, measurements of cloud liquid water content, droplet

  18. Effects of aerosol organics on cloud condensation nucleus (CCN) concentration and first indirect aerosol effect

    SciTech Connect

    Wang, J. X.; Lee, Y.- N.; Daum, Peter H.; Jayne, John T.; Alexander, M. L.

    2008-11-03

    Abstract. Aerosol microphysics, chemical composition, and CCN properties were measured on the Department of Energy Gulfstream-1 aircraft during the Marine Stratus/ Stratocumulus Experiment (MASE) conducted over the coastal waters between Point Reyes National Seashore and Monterey Bay, California, in July 2005. Aerosols measured during MASE included free tropospheric aerosols, marine boundary layer aerosols, and aerosols with high organic concentration within a thin layer above the cloud. Closure analysis was carried out for all three types of aerosols by comparing the measured CCN concentrations at 0.2% supersaturation to those predicted based on size distribution and chemical composition using K¨ohler theory. The effect of aerosol organic species on predicted CCN concentration was examined using a single hygroscopicity parameterization.

  19. On the characteristics of aerosol indirect effect based on dynamic regimes in global climate models

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Wang, M.; Ghan, S. J.; Ding, A.; Wang, H.; Zhang, K.; Neubauer, D.; Lohmann, U.; Ferrachat, S.; Takeamura, T.; Gettelman, A.; Morrison, H.; Lee, Y. H.; Shindell, D. T.; Partridge, D. G.; Stier, P.; Kipling, Z.; Fu, C.

    2015-09-01

    Aerosol-cloud interactions continue to constitute a major source of uncertainty for the estimate of climate radiative forcing. The variation of aerosol indirect effects (AIE) in climate models is investigated across different dynamical regimes, determined by monthly mean 500 hPa vertical pressure velocity (ω500), lower-tropospheric stability (LTS) and large-scale surface precipitation rate derived from several global climate models (GCMs), with a focus on liquid water path (LWP) response to cloud condensation nuclei (CCN) concentrations. The LWP sensitivity to aerosol perturbation within dynamic regimes is found to exhibit a large spread among these GCMs. It is in regimes of strong large-scale ascend (ω500 < -25 hPa d-1) and low clouds (stratocumulus and trade wind cumulus) where the models differ most. Shortwave aerosol indirect forcing is also found to differ significantly among different regimes. Shortwave aerosol indirect forcing in ascending regimes is as large as that in stratocumulus regimes, which indicates that regimes with strong large-scale ascend are as important as stratocumulus regimes in studying AIE. It is further shown that shortwave aerosol indirect forcing over regions with high monthly large-scale surface precipitation rate (> 0.1 mm d-1) contributes the most to the total aerosol indirect forcing (from 64 to nearly 100 %). Results show that the uncertainty in AIE is even larger within specific dynamical regimes than that globally, pointing to the need to reduce the uncertainty in AIE in different dynamical regimes.

  20. On the characteristics of aerosol indirect effect based on dynamic regimes in global climate models

    NASA Astrophysics Data System (ADS)

    Zhang, Shipeng; Wang, Minghuai; Ghan, Steven J.; Ding, Aijun; Wang, Hailong; Zhang, Kai; Neubauer, David; Lohmann, Ulrike; Ferrachat, Sylvaine; Takeamura, Toshihiko; Gettelman, Andrew; Morrison, Hugh; Lee, Yunha; Shindell, Drew T.; Partridge, Daniel G.; Stier, Philip; Kipling, Zak; Fu, Congbin

    2016-03-01

    Aerosol-cloud interactions continue to constitute a major source of uncertainty for the estimate of climate radiative forcing. The variation of aerosol indirect effects (AIE) in climate models is investigated across different dynamical regimes, determined by monthly mean 500 hPa vertical pressure velocity (ω500), lower-tropospheric stability (LTS) and large-scale surface precipitation rate derived from several global climate models (GCMs), with a focus on liquid water path (LWP) response to cloud condensation nuclei (CCN) concentrations. The LWP sensitivity to aerosol perturbation within dynamic regimes is found to exhibit a large spread among these GCMs. It is in regimes of strong large-scale ascent (ω500 < -25 hPa day-1) and low clouds (stratocumulus and trade wind cumulus) where the models differ most. Shortwave aerosol indirect forcing is also found to differ significantly among different regimes. Shortwave aerosol indirect forcing in ascending regimes is close to that in subsidence regimes, which indicates that regimes with strong large-scale ascent are as important as stratocumulus regimes in studying AIE. It is further shown that shortwave aerosol indirect forcing over regions with high monthly large-scale surface precipitation rate (> 0.1 mm day-1) contributes the most to the total aerosol indirect forcing (from 64 to nearly 100 %). Results show that the uncertainty in AIE is even larger within specific dynamical regimes compared to the uncertainty in its global mean values, pointing to the need to reduce the uncertainty in AIE in different dynamical regimes.

  1. Aerosol Indirect Effects on Stratocumulus Clouds in the Southeast Pacific

    NASA Astrophysics Data System (ADS)

    Twohy, C. H.; Adams, A.; Toohey, D. W.; Anderson, J.; Shank, L.; Howell, S.; Clarke, A. D.; Wood, R.

    2009-12-01

    The southeast Pacific Ocean is covered by the world’s largest stratocumulus cloud layer, which has a strong impact on ocean temperatures and climate in the region. Anthropogenic sources of aerosol particles such as smelters, power plants and urban pollution are expected to impact properties of the eastern portion of the stratocumulus deck. During the VOCALS (VAMOS Ocean-Cloud-Atmosphere-Land Study) field experiment, aerosol measurements below and above cloud were made with a ultra-high sensitivity aerosol spectrometer, an aerosol mass spectrometer, and analytical electron microscopy. In addition to more standard in-cloud measurements, droplets were collected and evaporated using a counterflow virtual impactor (CVI), and the non-volatile residual particles were analyzed. Many flights focused on the gradient in cloud properties along an E-W track from near the Chilean coast to remote areas offshore. Mean statistics from seven flights and about forty individual legs were compiled. Consistent with a continental source of cloud condensation nuclei, below-cloud aerosol and droplet number concentration generally decreased from near shore to offshore. This applied for particles larger than 0.05 and 0.1 µm in diameter, but not for total particles larger than 0.01 µm diameter. This suggests pollution contributed aged accumulation-mode aerosols to the stratocumulus layer, but fresher nuclei-mode particles were generated from other sources as well. Liquid water content and drizzle concentration tended to increase with distance from shore, but exhibited much greater variability. Aerosol number concentration in the >0.05 and >0.1 µm size range was correlated with droplet number concentration, and anti-correlated with droplet effective radius. These variables were especially well correlated on individual flights with near constant liquid water content (LWC), but were also statistically significant for the data set as a whole. When data were stratified into different LWC

  2. Potential Aerosol Indirect Effects on Atmospheric Circulation and Radiative Forcing through Deep Convection

    SciTech Connect

    Fan, Jiwen; Rosenfeld, Daniel; Ding, Yanni; Leung, Lai-Yung R.; Li, Zhanqing

    2012-05-10

    Aerosol indirect effects, i.e., the interactions of aerosols with clouds by serving as cloud condensation nuclei (CCN) or ice nuclei (IN), constitute the largest uncertainty in climate forcing and projection. Previous IPCC reported aerosol indirect forcing is negative, which does not account for aerosol-convective cloud interactions because the complex processes involved are poorly understood and represented in climate models. Here we report that aerosol indirect effect on deep convective cloud systems can lead to enhanced regional convergence and a strong top-of atmosphere (TOA) warming. Aerosol invigoration effect on convection can result in a strong radiative warming in the atmosphere (+5.6 W m-2) due to strong night-time warming, a lofted latent heating, and a reduced diurnal temperature difference, all of which could remarkably impact regional circulation and modify weather systems. We further elucidated how aerosols change convective intensity, diabatic heating, and regional circulation under different environmental conditions and concluded that wind shear and cloud base temperature play key roles in determining the significance of aerosol invigoration effect for convective systems.

  3. New understanding and quantification of the regime dependence of aerosol-cloud interaction for studying aerosol indirect effects

    NASA Astrophysics Data System (ADS)

    Chen, Jingyi; Liu, Yangang; Zhang, Minghua; Peng, Yiran

    2016-02-01

    Aerosol indirect effects suffer from large uncertainty in climate models and among observations. This study focuses on two plausible factors: regime dependence of aerosol-cloud interactions and the effect of cloud droplet spectral shape. We show, using a new parcel model, that combined consideration of droplet number concentration (Nc) and relative dispersion (ɛ, ratio of standard deviation to mean radius of the cloud droplet size distribution) better characterizes the regime dependence of aerosol-cloud interactions than considering Nc alone. Given updraft velocity (w), ɛ increases with increasing aerosol number concentration (Na) in the aerosol-limited regime, peaks in the transitional regime, and decreases with further increasing Na in the updraft-limited regime. This new finding further reconciles contrasting observations in literature and reinforces the compensating role of dispersion effect. The nonmonotonic behavior of ɛ further quantifies the relationship between the transitional Na and w that separates the aerosol- and updraft-limited regimes.

  4. Estimating the direct and indirect effects of secondary organic aerosols using ECHAM5-HAM

    NASA Astrophysics Data System (ADS)

    O'Donnell, D.; Tsigaridis, K.; Feichter, J.

    2011-08-01

    Secondary organic aerosol (SOA) has been introduced into the global climate-aerosol model ECHAM5/HAM. The SOA module handles aerosols originating from both biogenic and anthropogenic sources. The model simulates the emission of precursor gases, their chemical conversion into condensable gases, the partitioning of semi-volatile condenable species into the gas and aerosol phases. As ECHAM5/HAM is a size-resolved model, a new method that permits the calculation of partitioning of semi-volatile species between different size classes is introduced. We compare results of modelled organic aerosol concentrations against measurements from extensive measurement networks in Europe and the United States, running the model with and without SOA. We also compare modelled aerosol optical depth against measurements from the AERONET network of grond stations. We find that SOA improves agreement between model and measurements in both organic aerosol mass and aerosol optical depth, but does not fully correct the low bias that is present in the model for both of these quantities. Although many models now include SOA, any overall estimate of the direct and indirect effects of these aerosols is still lacking. This paper makes a first step in that direction. The model is applied to estimate the direct and indirect effects of SOA under simulated year 2000 conditions. The modelled SOA spatial distribution indicates that SOA is likely to be an important source of free and upper tropospheric aerosol. We find a negative shortwave (SW) forcing from the direct effect, amounting to -0.31 Wm-2 on the global annual mean. In contrast, the model indicates a positive indirect effect of SOA of +0.23 Wm-2, arising from the enlargement of particles due to condensation of SOA, together with an enhanced coagulation sink of small particles. In the longwave, model results are a direct effect of +0.02 Wm-2 and an indirect effect of -0.03 Wm-2.

  5. Ground Based Remote Sensing of the First Aerosol Indirect Effect: An Update

    NASA Astrophysics Data System (ADS)

    Previdi, M.; Feingold, G.; Veron, D. E.; Eberhard, W. L.

    2003-12-01

    The first aerosol indirect effect can be defined as an increase in the shortwave albedo of clouds due to higher concentrations of atmospheric aerosol, whereby the aerosol acts as cloud condensation nuclei to produce increased cloud droplet concentrations and smaller, more reflective droplets. The current work is one step toward achieving a more complete understanding of the indirect effect, which will consequently allow for a better determination of how changes in cloud induced by aerosol may affect the radiation budget and thus the climate. We utilize a series of continuous ground-based measurements from the Southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) program to investigate the indirect effect. Days that exhibit ice-free, single layered, nonprecipitating clouds are analyzed, with the indirect effect quantified as the relative change in cloud droplet effective radius for a relative change in aerosol extinction (under conditions of equivalent cloud liquid water path). Several cases from the first six years of our analysis (1998-2003) are described here, and probable reasons for the differences in the cloud response to aerosol among the cases are discussed.

  6. Cloud Condensation Nuclei Prediction Error from Application of Kohler Theory: Importance for the Aerosol Indirect Effect

    NASA Technical Reports Server (NTRS)

    Sotiropoulou, Rafaella-Eleni P.; Nenes, Athanasios; Adams, Peter J.; Seinfeld, John H.

    2007-01-01

    In situ observations of aerosol and cloud condensation nuclei (CCN) and the GISS GCM Model II' with an online aerosol simulation and explicit aerosol-cloud interactions are used to quantify the uncertainty in radiative forcing and autoconversion rate from application of Kohler theory. Simulations suggest that application of Koehler theory introduces a 10-20% uncertainty in global average indirect forcing and 2-11% uncertainty in autoconversion. Regionally, the uncertainty in indirect forcing ranges between 10-20%, and 5-50% for autoconversion. These results are insensitive to the range of updraft velocity and water vapor uptake coefficient considered. This study suggests that Koehler theory (as implemented in climate models) is not a significant source of uncertainty for aerosol indirect forcing but can be substantial for assessments of aerosol effects on the hydrological cycle in climatically sensitive regions of the globe. This implies that improvements in the representation of GCM subgrid processes and aerosol size distribution will mostly benefit indirect forcing assessments. Predictions of autoconversion, by nature, will be subject to considerable uncertainty; its reduction may require explicit representation of size-resolved aerosol composition and mixing state.

  7. Aerosol Indirect Effect on Warm Clouds over Eastern China Using Combined CALIOP and MODIS Observations

    NASA Astrophysics Data System (ADS)

    Guo, Jianping; Wang, Fu; Huang, Jingfeng; Li, Xiaowen

    2015-04-01

    Aerosol, one of key components of the climate system, is highly variable, both temporally and spatially. It often exerts great influences on the cloud-precipitation chain processes by serving as CCN/IN, altering cloud microphysics and its life cycle. Yet, the aerosol indirect effect on clouds remains largely unknown, because the initial changes in clouds due to aerosols may be enhanced or dampened by such feedback processes as modified cloud dynamics, or evaporation of the smaller droplets due to the competition for water vapor. In this study, we attempted to quantify the aerosol effects on warm cloud over eastern China, based on near-simultaneous retrievals from MODIS/AQUA, CALIOP/CALIPSO and CPR/CLOUDSAT during the period 2006 to 2010. The seasonality of aerosol from ground-based PM10 is quite different from that estimated from MODIS AOD. This result is corroborated by lower level profile of aerosol occurrence frequency from CALIOP, indicating the significant role CALIOP could play in aerosol-cloud interaction. The combined use of CALIOP and CPR facilitate the process to exactly determine the (vertical) position of warm cloud relative to aerosol, out of six scenarios in terms of aerosol-cloud mixing status in terms of aerosol-cloud mixing status, which shows as follows: AO (Aerosol only), CO (Cloud only), SASC (Single aerosol-single cloud), SADC (single aerosol-double cloud), DASC (double aerosol-single cloud), and others. Results shows that about 54% of all the cases belong to mixed status, among all the collocated aerosol-cloud cases. Under mixed condition, a boomerang shape is observed, i.e., reduced cloud droplet radius (CDR) is associated with increasing aerosol at moderate aerosol pollution (AOD<0.4), becoming saturated at AOD of 0.5, followed by an increase in CDR with aerosol. In contrast, there is no such boomerang shape found for (aerosol-cloud) separated cases. We categorize dataset into warm-season and cold-season subsets to figure out how the

  8. Evaluation of Global Anthropogenic Aerosol Indirect Effects in the GISS Model III

    NASA Astrophysics Data System (ADS)

    Chen, W.; Nenes, A.; Liao, H.; Adams, P. J.; Seinfeld, J. H.

    2008-12-01

    In this study the implementation of the aerosol indirect effect in the 23-layer Goddard Institute for Space Studies (GISS) Global Climate Middle Atmosphere Model III is described. Explicit dependence on cloud droplet number concentrations (Nc) is introduced in the calculations of cloud optical depths and autoconversion rates in liquid-phase stratiform clouds to account for both first and second indirect effects. To diagnose Nc, correlation with concentrations of aerosol soluble ions is developed separately for each model grid and in each month, to reflect seasonal and spatial variations in aerosol-cloud interactions. Based on estimates of pre-industrial, present-day (year 2000), and future (year 2100) concentrations of sulfate, nitrate, ammonium, sea salt, and organic aerosols from the fully coupled Caltech unified model, corresponding offline, monthly averaged Nc were derived and applied to equilibrium climate simulations. Modeled present-day global distributions of Nc, droplet size, cloud cover, and radiative balance are in good agreement with satellite-retrieved climatology. A global anthropogenic indirect forcing of -1.7 W m-2, with a decrease in mean droplet radius of 0.8 μm, and an increase in total liquid water path of 0.2 g cm-2, from pre-industrial to year 2000 is estimated. Future climate responses to aerosol direct and indirect effects are also analyzed and compared to previous studies that consider chemistry- aerosol-climate coupling, revealing the influences of this coupling on climate predictions.

  9. FY 2011 4th Quarter Metric: Estimate of Future Aerosol Direct and Indirect Effects

    SciTech Connect

    Koch, D

    2011-09-21

    The global and annual mean aerosol direct and indirect effects, relative to 1850 conditions, estimated from CESM simulations are 0.02 W m-2 and -0.39 W m-2, respectively, for emissions in year 2100 under the IPCC RCP8.5 scenario. The indirect effect is much smaller than that for 2000 emissions because of much smaller SO2 emissions in 2100; the direct effects are small due to compensation between warming by black carbon and cooling by sulfate.

  10. Model simulations of the first aerosol indirect effect and comparison of cloud susceptibility fo satellite measurements

    SciTech Connect

    Chuang, C; Penner, J E; Kawamoto, K

    2002-03-08

    Present-day global anthropogenic emissions contribute more than half of the mass in submicron particles primarily due to sulfate and carbonaceous aerosol components derived from fossil fuel combustion and biomass burning. These anthropogenic aerosols modify the microphysics of clouds by serving as cloud condensation nuclei (CCN) and enhance the reflectivity of low-level water clouds, leading to a cooling effect on climate (the Twomey effect or first indirect effect). The magnitude of the first aerosol indirect effect is associated with cloud frequency as well as a quantity representing the sensitivity of cloud albedo to changes in cloud drop number concentration. This quantity is referred to as cloud susceptibility [Twomey, 1991]. Analysis of satellite measurements demonstrates that marine stratus clouds are likely to be of higher susceptibility than continental clouds because of their lower number concentrations of cloud drops [Platnick and Twomey, 1994]. Here, we use an improved version of the fully coupled climate/chemistry model [Chuang et al., 1997] to calculate the global concentrations Of sulfate, dust, sea salt, and carbonaceous aerosols (biomass smoke and fossil fuel organic matter and black carbon). We investigated the impact of anthropogenic aerosols on cloud susceptibility and calculated the associated changes of shortwave radiative fluxes at the top of the atmosphere. We also examined the correspondence between the model simulation of cloud susceptibility and that inferred from satellite measurements to test whether our simulated aerosol concentrations and aerosol/cloud interactions give a faithful representation of these features.

  11. Direct and indirect methods for correcting the aerosol effect on remote sensing

    NASA Technical Reports Server (NTRS)

    Kaufman, Yoram J.; Tanre, Didier

    1994-01-01

    Aspects of aerosol studies and remote sensing are reviewed. Aerosol scatters solar radiation before it reaches the surface and scatters and absorbs it again after it is reflected from the surface and before it reaches the satellite sensor. The effect is spectrally and spatially dependent. Therefore atmospheric aerosol (dust, smoke and air pollution particles) has a significant effect on remote sensing. Correction for the aerosol effect was never achieved on an operational basis though several case studies were demonstrated. Correction can be done in a direct way by deriving the aerosol loading from the image itself and correcting for it using the appropriate radiative transfer model or by an indirect way, by defining remote sensing functions that are less dependent on the aerosol loading. To some degree this was already achieved in global remote sensing of vegetation where a composite of several days of NDVI (Normalized Difference Vegetation Index) measurements, choosing the maximal value, was used instead of a single cloud screened value. The Atmospheric Resistant Vegetation Index (ARVI) introduced recently for the NASA Earth Observing System EOS-MODIS is the most appropriate example of indirect correction, where the index is defined in such a way that the atmospheric effect in the blue spectral channel cancels to a large degree the atmospheric in the red channel in computations of a vegetation index. Atmospheric corrections can also use aerosol climatology and ground based instrumentation.

  12. Evaluation of aerosol indirect radiative effects on climate in the EMAC model

    NASA Astrophysics Data System (ADS)

    Chang, Dong Yeong; Tost, Holger; Steil, Benedikt; Lelieveld, Jos

    2013-04-01

    Anthropogenic aerosol particles directly and indirectly influence cloud properties and the Earth's radiative energy budget. Several studies have estimated the effects on climate using global circulation models (GCMs), indicating large differences between different models and large uncertainty ranges. These are mostly attributed to different cloud microphysical process parameterizations and uncertainties in the representation of aerosols. Without detailed cloud microphysical processes, using empirical relations between aerosol number or mass and cloud droplet number potentially even large discrepancies may arise. In the present study, a mechanistic aerosol activation scheme, based on double moment cloud microphysics, is used to compute aerosol indirect radiative and cloud effects in the EMAC model. Aerosol activation is linked to the cloud droplet nucleation processes in warm clouds, accounting for the number, size, and chemical composition of particles under ambient meteorological conditions. This approach uses a combination of empirical and semi-empirical parameters to represent aerosol water uptake and hygroscopic growth into cloud droplets. To evaluate the performance of our approach satellite datasets are used; for example, total cloud fraction from MODIS data and cloud radiative forcing at the top of atmosphere from CERES EBAF data.

  13. On the characteristics of aerosol indirect effect based on dynamic regimes in global climate models

    DOE PAGESBeta

    Zhang, Shipeng; Wang, Minghuai; Ghan, Steven J.; Ding, Aijun; Wang, Hailong; Zhang, Kai; Neubauer, David; Lohmann, Ulrike; Ferrachat, Sylvaine; Takeamura, Toshihiko; et al

    2016-03-04

    Aerosol–cloud interactions continue to constitute a major source of uncertainty for the estimate of climate radiative forcing. The variation of aerosol indirect effects (AIE) in climate models is investigated across different dynamical regimes, determined by monthly mean 500 hPa vertical pressure velocity (ω500), lower-tropospheric stability (LTS) and large-scale surface precipitation rate derived from several global climate models (GCMs), with a focus on liquid water path (LWP) response to cloud condensation nuclei (CCN) concentrations. The LWP sensitivity to aerosol perturbation within dynamic regimes is found to exhibit a large spread among these GCMs. It is in regimes of strong large-scale ascentmore » (ω500  <  −25 hPa day−1) and low clouds (stratocumulus and trade wind cumulus) where the models differ most. Shortwave aerosol indirect forcing is also found to differ significantly among different regimes. Shortwave aerosol indirect forcing in ascending regimes is close to that in subsidence regimes, which indicates that regimes with strong large-scale ascent are as important as stratocumulus regimes in studying AIE. It is further shown that shortwave aerosol indirect forcing over regions with high monthly large-scale surface precipitation rate (> 0.1 mm day−1) contributes the most to the total aerosol indirect forcing (from 64 to nearly 100 %). Results show that the uncertainty in AIE is even larger within specific dynamical regimes compared to the uncertainty in its global mean values, pointing to the need to reduce the uncertainty in AIE in different dynamical regimes.« less

  14. Aerosol indirect effects -- general circulation model intercomparison and evaluation with satellite data

    SciTech Connect

    Quaas, Johannes; Ming, Yi; Menon, Surabi; Takemura, Toshihiko; Wang, Minghuai; Penner, Joyce E.; Gettelman, Andrew; Lohmann, Ulrike; Bellouin, Nicolas; Boucher, Olivier; Sayer, Andrew M.; Thomas, Gareth E.; McComiskey, Allison; Feingold, Graham; Hoose, Corinna; Kristjansson, Jon Egill; Liu, Xiaohong; Balkanski, Yves; Donner, Leo J.; Ginoux, Paul A.; Stier, Philip; Feichter, Johann; Sednev, Igor; Bauer, Susanne E.; Koch, Dorothy; Grainger, Roy G.; Kirkevag, Alf; Iversen, Trond; Seland, Oyvind; Easter, Richard; Ghan, Steven J.; Rasch, Philip J.; Morrison, Hugh; Lamarque, Jean-Francois; Iacono, Michael J.; Kinne, Stefan; Schulz, Michael

    2009-04-10

    Aerosol indirect effects continue to constitute one of the most important uncertainties for anthropogenic climate perturbations. Within the international AEROCOM initiative, the representation of aerosol-cloud-radiation interactions in ten different general circulation models (GCMs) is evaluated using three satellite datasets. The focus is on stratiform liquid water clouds since most GCMs do not include ice nucleation effects, and none of the model explicitly parameterizes aerosol effects on convective clouds. We compute statistical relationships between aerosol optical depth (Ta) and various cloud and radiation quantities in a manner that is consistent between the models and the satellite data. It is found that the model-simulated influence of aerosols on cloud droplet number concentration (Nd) compares relatively well to the satellite data at least over the ocean. The relationship between Ta and liquid water path is simulated much too strongly by the models. It is shown that this is partly related to the representation of the second aerosol indirect effect in terms of autoconversion. A positive relationship between total cloud fraction (fcld) and Ta as found in the satellite data is simulated by the majority of the models, albeit less strongly than that in the satellite data in most of them. In a discussion of the hypotheses proposed in the literature to explain the satellite-derived strong fcld - Ta relationship, our results indicate that none can be identified as unique explanation. Relationships similar to the ones found in satellite data between Ta and cloud top temperature or outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR - Ta relationship show a strong positive correlation between Ta and fcld The short-wave total aerosol radiative forcing as simulated by the GCMs is strongly influenced by the simulated anthropogenic fraction of Ta, and parameterisation assumptions such as a lower bound on Nd

  15. Cloud microphysics and aerosol indirect effects in the global climate model ECHAM5-HAM

    NASA Astrophysics Data System (ADS)

    Lohmann, U.; Stier, P.; Hoose, C.; Ferrachat, S.; Kloster, S.; Roeckner, E.; Zhang, J.

    2007-07-01

    The double-moment cloud microphysics scheme from ECHAM4 that predicts both the mass mixing ratios and number concentrations of cloud droplets and ice crystals has been coupled to the size-resolved aerosol scheme ECHAM5-HAM. ECHAM5-HAM predicts the aerosol mass, number concentrations and mixing state. The simulated liquid, ice and total water content and the cloud droplet and ice crystal number concentrations as a function of temperature in stratiform mixed-phase clouds between 0 and -35° C agree much better with aircraft observations in the ECHAM5 simulations. ECHAM5 performs better because more realistic aerosol concentrations are available for cloud droplet nucleation and because the Bergeron-Findeisen process is parameterized as being more efficient. The total anthropogenic aerosol effect includes the direct, semi-direct and indirect effects and is defined as the difference in the top-of-the-atmosphere net radiation between present-day and pre-industrial times. It amounts to -1.9 W m-2 in ECHAM5, when a relative humidity dependent cloud cover scheme and aerosol emissions representative for the years 1750 and 2000 from the AeroCom emission inventory are used. The contribution of the cloud albedo effect amounts to -0.7 W m-2. The total anthropogenic aerosol effect is larger when either a statistical cloud cover scheme or a different aerosol emission inventory are employed because the cloud lifetime effect increases.

  16. Surface-based observation of aerosol indirect effect in the Mid-Atlantic region

    NASA Astrophysics Data System (ADS)

    Nzeffe, Fonya; Joseph, Everette; Min, Qilong

    2008-11-01

    A method for assessing the aerosol indirect effect based on back trajectory analysis and cloud and aerosol properties derived from a combination of observations from the Multifilter Rotating Shadow Band Radiometer and microwave radiometer at a newly established atmospheric measurement field station in the Baltimore-Washington corridor is reported in this article. Six months of aerosol and cloud optical depth data are segregated according to air mass history based on back trajectory analysis. Under stagnant and polluted conditions where air flow across the region is predominantly from west-southwest, aerosol optical depth is on average three to four times greater than in air masses that advect rapidly from north and east. When sorted by mean cloud liquid water path, cloud-droplet effective radius in polluted air masses is on average 0.9 μm smaller than that observed under more pristine conditions. Analysis is presented to confirm the statistical significance of this result.

  17. New understanding and quantification of the regime dependence of aerosol-cloud interaction for studying aerosol indirect effects

    DOE PAGESBeta

    Chen, Jingyi; Liu, Yangang; Zhang, Minghua; Peng, Yiran

    2016-02-28

    In this study, aerosol indirect effects suffer from large uncertainty in climate models and among observations. This study focuses on two plausible factors: regime dependence of aerosol-cloud interactions and the effect of cloud droplet spectral shape. We show, using a new parcel model, that combined consideration of droplet number concentration (Nc) and relative dispersion (ε, ratio of standard deviation to mean radius of the cloud droplet size distribution) better characterizes the regime dependence of aerosol-cloud interactions than considering Nc alone. Given updraft velocity (w), ε increases with increasing aerosol number concentration (Na) in the aerosol-limited regime, peaks in the transitionalmore » regime, and decreases with further increasing Na in the updraft-limited regime. This new finding further reconciles contrasting observations in literature and reinforces the compensating role of dispersion effect. The nonmonotonic behavior of ε further quantifies the relationship between the transitional Na and w that separates the aerosol- and updraft-limited regimes.« less

  18. Indirect Radiative Warming Effect in the Winter and Spring Arctic Associated with Aerosol Pollution from Mid-latitude Regions

    NASA Astrophysics Data System (ADS)

    Zhao, Chuanfeng; Garrett, Timothy

    2016-04-01

    Different from global cooling effects of aerosols and aerosol-cloud interactions, anthropogenic aerosols from mid-latitude are found to play an increased warming effect in the Arctic in later winter and early spring. Using four-year (2000-2003) observation of aerosol, cloud and radiation at North Slope of Alaska, it is found that the aerosols can increase cloud droplet effective radius 3 um for fixed liquid water path, and increase cloud thermal emissivity about 0.05-0.08. In other words, aerosols are associated with a warming of 1-1.6 degrees (3-5 W/m2) in the Arctic during late winter and early spring solely due to their first indirect effect. Further analysis indicates that total aerosol climate effects are even more significant (8-10 W/m2), with about 50% contribution from aerosol first indirect effect and another 50% contribution from complicated feedbacks. It also shows strong seasonal distribution of the aerosol indirect radiative effects, with warming effects in seasons other than in summer. However, only the significant warming effect in winter and spring passes through the significance test. The strong warming effect due to aerosol indirect effect could be further strengthened through following feedbacks involving the surface albedo (early ice melting).

  19. Aerosol indirect effects ? general circulation model intercomparison and evaluation with satellite data

    SciTech Connect

    Quaas, Johannes; Ming, Yi; Menon, Surabi; Takemura, Toshihiko; Wang, Minghuai; Penner, Joyce E.; Gettelman, Andrew; Lohmann, Ulrike; Bellouin, Nicolas; Boucher, Olivier; Sayer, Andrew M.; Thomas, Gareth E.; McComiskey, Allison; Feingold, Graham; Hoose, Corinna; Kristansson, Jon Egill; Liu, Xiaohong; Balkanski, Yves; Donner, Leo J.; Ginoux, Paul A.; Stier, Philip; Grandey, Benjamin; Feichter, Johann; Sednev, Igor; Bauer, Susanne E.; Koch, Dorothy; Grainger, Roy G.; Kirkevag, Alf; Iversen, Trond; Seland, Oyvind; Easter, Richard; Ghan, Steven J.; Rasch, Philip J.; Morrison, Hugh; Lamarque, Jean-Francois; Iacono, Michael J.; Kinne, Stefan; Schulz, Michael

    2010-03-12

    Aerosol indirect effects continue to constitute one of the most important uncertainties for anthropogenic climate perturbations. Within the international AEROCOM initiative, the representation of aerosol-cloud-radiation interactions in ten different general circulation models (GCMs) is evaluated using three satellite datasets. The focus is on stratiform liquid water clouds since most GCMs do not include ice nucleation effects, and none of the model explicitly parameterises aerosol effects on convective clouds. We compute statistical relationships between aerosol optical depth ({tau}{sub a}) and various cloud and radiation quantities in a manner that is consistent between the models and the satellite data. It is found that the model-simulated influence of aerosols on cloud droplet number concentration (N{sub d}) compares relatively well to the satellite data at least over the ocean. The relationship between {tau}{sub a} and liquid water path is simulated much too strongly by the models. This suggests that the implementation of the second aerosol indirect effect mainly in terms of an autoconversion parameterisation has to be revisited in the GCMs. A positive relationship between total cloud fraction (f{sub cld}) and {tau}{sub a} as found in the satellite data is simulated by the majority of the models, albeit less strongly than that in the satellite data in most of them. In a discussion of the hypotheses proposed in the literature to explain the satellite-derived strong f{sub cld} - {tau}{sub a} relationship, our results indicate that none can be identified as a unique explanation. Relationships similar to the ones found in satellite data between {tau}{sub a} and cloud top temperature or outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR - {tau}{sub a} relationship show a strong positive correlation between {tau}{sub a} and f{sub cld} The short-wave total aerosol radiative forcing as simulated by the GCMs is

  20. Attribution of the United States “warming hole”: Aerosol indirect effect and precipitable water vapor

    PubMed Central

    Yu, Shaocai; Alapaty, Kiran; Mathur, Rohit; Pleim, Jonathan; Zhang, Yuanhang; Nolte, Chris; Eder, Brian; Foley, Kristen; Nagashima, Tatsuya

    2014-01-01

    Aerosols can influence the climate indirectly by acting as cloud condensation nuclei and/or ice nuclei, thereby modifying cloud optical properties. In contrast to the widespread global warming, the central and south central United States display a noteworthy overall cooling trend during the 20th century, with an especially striking cooling trend in summertime daily maximum temperature (Tmax) (termed the U.S. “warming hole”). Here we used observations of temperature, shortwave cloud forcing (SWCF), longwave cloud forcing (LWCF), aerosol optical depth and precipitable water vapor as well as global coupled climate models to explore the attribution of the “warming hole”. We find that the observed cooling trend in summer Tmax can be attributed mainly to SWCF due to aerosols with offset from the greenhouse effect of precipitable water vapor. A global coupled climate model reveals that the observed “warming hole” can be produced only when the aerosol fields are simulated with a reasonable degree of accuracy as this is necessary for accurate simulation of SWCF over the region. These results provide compelling evidence of the role of the aerosol indirect effect in cooling regional climate on the Earth. Our results reaffirm that LWCF can warm both winter Tmax and Tmin. PMID:25373416

  1. Attribution of the United States “warming hole”: Aerosol indirect effect and precipitable water vapor

    NASA Astrophysics Data System (ADS)

    Yu, Shaocai; Alapaty, Kiran; Mathur, Rohit; Pleim, Jonathan; Zhang, Yuanhang; Nolte, Chris; Eder, Brian; Foley, Kristen; Nagashima, Tatsuya

    2014-11-01

    Aerosols can influence the climate indirectly by acting as cloud condensation nuclei and/or ice nuclei, thereby modifying cloud optical properties. In contrast to the widespread global warming, the central and south central United States display a noteworthy overall cooling trend during the 20th century, with an especially striking cooling trend in summertime daily maximum temperature (Tmax) (termed the U.S. ``warming hole''). Here we used observations of temperature, shortwave cloud forcing (SWCF), longwave cloud forcing (LWCF), aerosol optical depth and precipitable water vapor as well as global coupled climate models to explore the attribution of the ``warming hole''. We find that the observed cooling trend in summer Tmax can be attributed mainly to SWCF due to aerosols with offset from the greenhouse effect of precipitable water vapor. A global coupled climate model reveals that the observed ``warming hole'' can be produced only when the aerosol fields are simulated with a reasonable degree of accuracy as this is necessary for accurate simulation of SWCF over the region. These results provide compelling evidence of the role of the aerosol indirect effect in cooling regional climate on the Earth. Our results reaffirm that LWCF can warm both winter Tmax and Tmin.

  2. Attribution of the United States "warming hole": aerosol indirect effect and precipitable water vapor.

    PubMed

    Yu, Shaocai; Alapaty, Kiran; Mathur, Rohit; Pleim, Jonathan; Zhang, Yuanhang; Nolte, Chris; Eder, Brian; Foley, Kristen; Nagashima, Tatsuya

    2014-01-01

    Aerosols can influence the climate indirectly by acting as cloud condensation nuclei and/or ice nuclei, thereby modifying cloud optical properties. In contrast to the widespread global warming, the central and south central United States display a noteworthy overall cooling trend during the 20(th) century, with an especially striking cooling trend in summertime daily maximum temperature (Tmax) (termed the U.S. "warming hole"). Here we used observations of temperature, shortwave cloud forcing (SWCF), longwave cloud forcing (LWCF), aerosol optical depth and precipitable water vapor as well as global coupled climate models to explore the attribution of the "warming hole". We find that the observed cooling trend in summer Tmax can be attributed mainly to SWCF due to aerosols with offset from the greenhouse effect of precipitable water vapor. A global coupled climate model reveals that the observed "warming hole" can be produced only when the aerosol fields are simulated with a reasonable degree of accuracy as this is necessary for accurate simulation of SWCF over the region. These results provide compelling evidence of the role of the aerosol indirect effect in cooling regional climate on the Earth. Our results reaffirm that LWCF can warm both winter Tmax and Tmin. PMID:25373416

  3. On the reliability of geostationary satellite observations for diagnosing indirect aerosol effects

    NASA Astrophysics Data System (ADS)

    Merk, Daniel; Deneke, Hartwig; Pospichal, Bernhard; Seifert, Patric

    2015-10-01

    Aerosol indirect effects are poorly understand and constitute a highly uncertain anthropogenic forcing of climate change. The interaction of aerosols with clouds together with entrainment and turbulent mixing processes modulate cloud microphysics and radiative effects. In the current study we present preliminary results to diagnose indirect aerosol effects from the synergy of geostationary satellite observations, surface observations and MACC aerosol analysis. We examine if the sub-adiabatic factor - representative for entrainment - can be obtained from the combination of passive-satellite observations with ground-based cloud base height from a ceilometer network. Therefore the uncertainty of the sub-adiabatic factor due to its required input parameters, the cloud geometrical thickness and liquid water path, is explored. We use a two year dataset from SEVIRI and compare it to the LACROS supersite at Leipzig, Germany. We find that the comparison of satellite-retrieved cloud top heights shows a RMSD of 1100 m and the liquid water path of 75 gm-2, which are too large to provide a meaningful estimate of the instantaneous sub-adiabtic factor. Linking the cloud microphysical properties from passive satellites with aerosol properties obtained from MACC, we investigate the Twomey hypothesis, namely that smaller droplets and a higher cloud droplet number concentration result from higher aerosol load for a given liquid water path (positive change). A positive relative change is obtained for aerosol optical depth and the sulphate mass integrated from the surface to the cloud top. In contrast, a negative relative change is however found for sea salt.

  4. Regional Biases in Droplet Activation Parameterizations: Strong Influence on Aerosol Second Indirect Effect in the Community Atmosphere Model v5.

    NASA Astrophysics Data System (ADS)

    Morales, R.; Nenes, A.

    2014-12-01

    Aerosol-cloud interactions constitute one of the most uncertain aspects of anthropogenic climate change estimates. The magnitude of these interactions as represented in climate models strongly depends on the process of aerosol activation. This process is the most direct physical link between aerosols and cloud microphysical properties. Calculation of droplet number in GCMs requires the computation of new droplet formation (i.e., droplet activation), through physically based activation parameterizations. Considerable effort has been placed in ensuring that droplet activation parameterizations have a physically consistent response to changes in aerosol number concentration. However, recent analyses using an adjoint sensitivity approach showed that parameterizations can exhibit considerable biases in their response to other aerosol properties, such as aerosol modal diameter or to the aerosol chemical composition. This is a potentially important factor in estimating aerosol indirect effects since changes in aerosol properties from pre-industrial times to present day exhibit a very strong regional signature. In this work we use the Community Atmosphere Model (CAM5) to show that the regional imprint of the changes in aerosol properties during the last century interacts with the droplet activation parameterization in a way that these biases are amplified over climatically relevant regions. Two commonly used activation routines, the CAM5 default, Abdul-Razzak and Ghan parameterization, as well as the Fountoukis and Nenes parameterization are used in this study. We further explored the impacts of Nd parameterization biases in the first and second aerosol indirect effects separately, by performing simulations were droplet number was not allowed to intervene in the precipitation initiation process. The simulations performed show that an unphysical response to changes in the diameter of accumulation mode aerosol translates into extremely high Nd concentrations over South

  5. Use of ARM Mobile Facility (AMF) Data to Study Aerosol Indirect Effects in China

    SciTech Connect

    Li, Zhanqing

    2012-12-19

    General goals: 1) Facilitating the deployment of the ARM Mobile Facility (AMF) and Ancillary Facility (AAF) in China in 2008, 2) Processing, retrieving, improving and analyzing observation data from ground-based, air-borne and space-borne instruments; 3) Conducting a series of studies to gain insights into the direct and indirect effects of these aerosols on radiation, clouds, and precipitation using both

  6. Climate impact of biofuels in shipping: global model studies of the aerosol indirect effect.

    PubMed

    Righi, Mattia; Klinger, Carolin; Eyring, Veronika; Hendricks, Johannes; Lauer, Axel; Petzold, Andreas

    2011-04-15

    Aerosol emissions from international shipping are recognized to have a large impact on the Earth's radiation budget, directly by scattering and absorbing solar radiation and indirectly by altering cloud properties. New regulations have recently been approved by the International Maritime Organization (IMO) aiming at progressive reductions of the maximum sulfur content allowed in marine fuels from current 4.5% by mass down to 0.5% in 2020, with more restrictive limits already applied in some coastal regions. In this context, we use a global bottom-up algorithm to calculate geographically resolved emission inventories of gaseous (NO(x), CO, SO(2)) and aerosol (black carbon, organic matter, sulfate) species for different kinds of low-sulfur fuels in shipping. We apply these inventories to study the resulting changes in radiative forcing, attributed to particles from shipping, with the global aerosol-climate model EMAC-MADE. The emission factors for the different fuels are based on measurements at a test bed of a large diesel engine. We consider both fossil fuel (marine gas oil) and biofuels (palm and soy bean oil) as a substitute for heavy fuel oil in the current (2006) fleet and compare their climate impact to that resulting from heavy fuel oil use. Our simulations suggest that ship-induced surface level concentrations of sulfate aerosol are strongly reduced, up to about 40-60% in the high-traffic regions. This clearly has positive consequences for pollution reduction in the vicinity of major harbors. Additionally, such reductions in the aerosol loading lead to a decrease of a factor of 3-4 in the indirect global aerosol effect induced by emissions from international shipping. PMID:21428387

  7. Aerosol indirect effects – general circulation model intercomparison and evaluation with satellite data

    SciTech Connect

    Quaas, Johannes; Ming, Yi; Menon, Surabi; Takemura, T.; Wang, Minghuai; Penner, Joyce E.; Gettelman, A.; Lohmann, U.; Bellouin, N.; Boucher, Olivier; Sayer, Andrew M.; Thomas, Gareth E.; McComiskey, A.; Feingold, G.; Hoose, Corinna; Kristjansson, J. E.; Liu, Xiaohong; Balkanski, Y.; Donner, Leo J.; Ginoux, P.; Stier, P.; Grandey, B.; Feichter, J.; Sednev, Igor; Bauer, Susanne E.; Koch, D.; Grainger, Roy G.; Kirkevag, A.; Iversen, T.; Seland, O.; Easter, Richard C.; Ghan, Steven J.; Rasch, Philip J.; Morrison, H.; Lamarque, J. F.; Iacono, Michael J.; Kinne, Stefan; Schulz, M.

    2009-11-16

    Aerosol indirect effects continue to constitute one of the most important uncertainties for anthropogenic climate perturbations. Within the international AEROCOM initiative, the representation of aerosol-cloud-radiation interactions in ten different general circulation models (GCMs) is evaluated in the present study using three satellite datasets. The satellite datasets are taken as reference bearing in mind that cloud and aerosol retrievals include uncertainties. We compute statistical relationships between aerosol optical depth (τa) and various cloud and radiation quantities consistently in models and satellite data. It is found that the model-simulated influence of aerosols on cloud droplet number concentration (Nd) compares relatively well to the satellite data at least over oceans. The relationship between τa and liquid water path is simulated much too strongly by the models. It is shown that this is partly related to rep¬resentation of the second aerosol indirect effect in terms of autoconversion. A positive re¬lationship between total cloud fraction (fcld) and τa as found in the satellite data is simulated by the majority of the models, albeit less strongly in most of them. In a discussion of the hypo¬theses proposed in the literature to explain the satellite-derived strong fcld – τa relation¬ship, we find that none is unequivocally confirmed by our results. Relationships similar to the ones found in satellite data between τa and cloud top tem¬perature and outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR - τa relationship show a strong positive cor¬relation between τa and cloud fraction. The short-wave total aerosol radiative forcing as simulated by the GCMs is strongly influenced by the simulated anthropogenic fraction of τa, and parameterisation assumptions such as a lower bound on Nd. Nevertheless, the strengths of the statistical relationships are good predictors for the short

  8. Evaluating WRF-Chem aerosol indirect effects in Southeast Pacific marine stratocumulus during VOCALS-REx

    SciTech Connect

    Saide, Pablo; Spak, S. N.; Carmichael, Gregory; Mena-Carrasco, M. A.; Yang, Qing; Howell, S. G.; Leon, Dolislager; Snider, Jefferson R.; Bandy, Alan R.; Collett, Jeffrey L.; Benedict, K. B.; de Szoeke, S.; Hawkins, Lisa; Allen, Grant; Crawford, I.; Crosier, J.; Springston, S. R.

    2012-03-30

    We evaluate a regional-scale simulation with the WRF-Chem model for the VAMOS (Variability of the American Monsoon Systems) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx), which sampled the Southeast Pacific's persistent stratocumulus deck. Evaluation of VOCALS-REx ship-based and aircraft observations focuses on analyzing how aerosol loading affects marine boundary layer (MBL) dynamics and cloud microphysics. We compare local time series and campaign averaged longitudinal gradients, and highlight differences in model simulations with (W) and without wet (NW) deposition processes. The higher aerosol loadings in the NW case produce considerable changes in MBL dynamics and cloud microphysics, in accordance with the established conceptual model of aerosol indirect effects. These include increase in cloud albedo, increase in MBL and cloud heights, drizzle suppression, increase in liquid water content, and increase in cloud lifetime. Moreover, better statistical representation of aerosol mass and number concentration improves model fidelity in reproducing observed spatial and temporal variability in cloud properties, including top and base height, droplet concentration, water content, rain rate, optical depth (COD) and liquid water path (LWP). Together, these help to quantify confidence in WRF-Chem's modeled aerosol-cloud interactions, while identifying structural and parametric uncertainties including: irreversibility in rain wet removal; overestimation of marine DMS and sea salt emissions and accelerated aqueous sulfate conversion. Our findings suggest that WRF-Chem simulates marine cloud-aerosol interactions at a level sufficient for applications in forecasting weather and air quality and studying aerosol climate forcing, including the reliability required for policy analysis and geo-engineering applications.

  9. Evaluating WRF-Chem aerosol indirect effects in Southeast Pacific marine stratocumulus during VOCALS-REx

    SciTech Connect

    Saide P. E.; Springston S.; Spak, S. N.; Carmichael, G. R.; Mena-Carrasco, M. A.; Yang, Q.; Howell, S.; Leon, D. C.; Snider, J. R.; Bandy, A. R.; Collett, J. L.; Benedict, K. B.; de Szoeke, S. P.; Hawkins, L. N.; Allen, G.; Crawford, I.; Crosier, J.

    2012-03-29

    We evaluate a regional-scale simulation with the WRF-Chem model for the VAMOS (Variability of the American Monsoon Systems) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx), which sampled the Southeast Pacific's persistent stratocumulus deck. Evaluation of VOCALS-REx ship-based and three aircraft observations focuses on analyzing how aerosol loading affects marine boundary layer (MBL) dynamics and cloud microphysics. We compare local time series and campaign-averaged longitudinal gradients, and highlight differences in model simulations with (W) and without (NW) wet deposition processes. The higher aerosol loadings in the NW case produce considerable changes in MBL dynamics and cloud microphysics, in accordance with the established conceptual model of aerosol indirect effects. These include increase in cloud albedo, increase in MBL and cloud heights, drizzle suppression, increase in liquid water content, and increase in cloud lifetime. Moreover, better statistical representation of aerosol mass and number concentration improves model fidelity in reproducing observed spatial and temporal variability in cloud properties, including top and base height, droplet concentration, water content, rain rate, optical depth (COD) and liquid water path (LWP). Together, these help to quantify confidence in WRF-Chem's modeled aerosol-cloud interactions, especially in the activation parameterization, while identifying structural and parametric uncertainties including: irreversibility in rain wet removal; overestimation of marine DMS and sea salt emissions, and accelerated aqueous sulfate conversion. Our findings suggest that WRF-Chem simulates marine cloud-aerosol interactions at a level sufficient for applications in forecasting weather and air quality and studying aerosol climate forcing, and may do so with the reliability required for policy analysis.

  10. Evaluating WRF-Chem aerosol indirect effects in Southeast Pacific marine stratocumulus during VOCALS-REx

    NASA Astrophysics Data System (ADS)

    Saide, P. E.; Spak, S. N.; Carmichael, G. R.; Mena-Carrasco, M. A.; Howell, S.; Leon, D. C.; Snider, J. R.; Bandy, A. R.; Collett, J. L.; Benedict, K. B.; de Szoeke, S. P.; Hawkins, L. N.; Allen, G.; Crawford, I.; Crosier, J.; Springston, S. R.

    2011-11-01

    We evaluate a regional-scale simulation with the WRF-Chem model for the VAMOS (Variability of the American Monsoon Systems) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx), which sampled the Southeast Pacific's persistent stratocumulus deck. Evaluation of VOCALS-REx ship-based and aircraft observations focuses on analyzing how aerosol loading affects marine boundary layer (MBL) dynamics and cloud microphysics. We compare local time series and campaign-averaged longitudinal gradients, and highlight differences in model simulations with (W) and without wet (NW) deposition processes. The higher aerosol loadings in the NW case produce considerable changes in MBL dynamics and cloud microphysics, in accordance with the established conceptual model of aerosol indirect effects. These include increase in cloud albedo, increase in MBL and cloud heights, drizzle suppression, increase in liquid water content, and increase in cloud lifetime. Moreover, better statistical representation of aerosol mass and number concentration improves model fidelity in reproducing observed spatial and temporal variability in cloud properties, including top and base height, droplet concentration, water content, rain rate, optical depth (COD) and liquid water path (LWP). Together, these help to quantify confidence in WRF-Chem's modeled aerosol-cloud interactions, while identifying structural and parametric uncertainties including: irreversibility in rain wet removal; overestimation of marine DMS and sea salt emissions and accelerated aqueous sulfate conversion. Our findings suggest that WRF-Chem simulates marine cloud-aerosol interactions at a level sufficient for applications in forecasting weather and air quality and studying aerosol climate forcing, including the reliability required for policy analysis and geo-engineering applications.

  11. Aerosol indirect effects from shipping emissions: sensitivity studies with the global aerosol-climate model ECHAM-HAM

    NASA Astrophysics Data System (ADS)

    Peters, K.; Stier, P.; Quaas, J.; Graßl, H.

    2012-07-01

    In this study, we employ the global aerosol-climate model ECHAM-HAM to globally assess aerosol indirect effects (AIEs) resulting from shipping emissions of aerosols and aerosol precursor gases. We implement shipping emissions of sulphur dioxide (SO2), black carbon (BC) and particulate organic matter (POM) for the year 2000 into the model and quantify the model's sensitivity towards uncertainties associated with the emission parameterisation as well as with the shipping emissions themselves. Sensitivity experiments are designed to investigate (i) the uncertainty in the size distribution of emitted particles, (ii) the uncertainty associated with the total amount of emissions, and (iii) the impact of reducing carbonaceous emissions from ships. We use the results from one sensitivity experiment for a detailed discussion of shipping-induced changes in the global aerosol system as well as the resulting impact on cloud properties. From all sensitivity experiments, we find AIEs from shipping emissions to range from -0.32 ± 0.01 W m-2 to -0.07 ± 0.01 W m-2 (global mean value and inter-annual variability as a standard deviation). The magnitude of the AIEs depends much more on the assumed emission size distribution and subsequent aerosol microphysical interactions than on the magnitude of the emissions themselves. It is important to note that although the strongest estimate of AIEs from shipping emissions in this study is relatively large, still much larger estimates have been reported in the literature before on the basis of modelling studies. We find that omitting just carbonaceous particle emissions from ships favours new particle formation in the boundary layer. These newly formed particles contribute just about as much to the CCN budget as the carbonaceous particles would, leaving the globally averaged AIEs nearly unaltered compared to a simulation including carbonaceous particle emissions from ships.

  12. Aerosol indirect effects from shipping emissions: sensitivity studies with the global aerosol-climate model ECHAM-HAM

    NASA Astrophysics Data System (ADS)

    Peters, K.; Stier, P.; Quaas, J.; Graßl, H.

    2012-03-01

    In this study, we employ the global aerosol-climate model ECHAM-HAM to globally assess aerosol indirect effects (AIEs) resulting from shipping emissions of aerosols and aerosol precursor gases. We implement shipping emissions of sulphur dioxide (SO2), black carbon (BC) and particulate organic matter (POM) for the year 2000 into the model and quantify the model's sensitivity towards uncertainties associated with the emission parameterisation as well as with the shipping emissions themselves. Sensitivity experiments are designed to investigate (i) the uncertainty in the size distribution of emitted particles, (ii) the uncertainty associated with the total amount of emissions, and (iii) the impact of reducing carbonaceous emissions from ships. We use the results from one sensitivity experiment for a detailed discussion of shipping-induced changes in the global aerosol system as well as the resulting impact on cloud properties. From all sensitivity experiments, we find AIEs from shipping emissions to range from -0.07 ± 0.01 W m-2 to -0.32 ± 0.01 W m-2 (global mean value and inter-annual variability as a standard deviation). The magnitude of the AIEs depends much more on the assumed emission size distribution and subsequent aerosol microphysical interactions than on the magnitude of the emissions themselves. It is important to note that although the strongest estimate of AIEs from shipping emissions in this study is relatively large, still much larger estimates have been reported in the literature before on the basis of modelling studies. We find that omitting just carbonaceous particle emissions from ships favours new particle formation in the boundary layer. These newly formed particles contribute just about as much to the CCN budget as the carbonaceous particles would, leaving the globally averaged AIEs nearly unaltered compared to a simulation including carbonaceous particle emissions from ships.

  13. Aerosol indirect effects from ground-based retrievals over the rain shadow region in Indian subcontinent

    NASA Astrophysics Data System (ADS)

    Harikishan, G.; Padmakumari, B.; Maheskumar, R. S.; Pandithurai, G.; Min, Q. L.

    2016-03-01

    Aerosol-induced changes in cloud microphysical and radiative properties have been studied for the first time using ground-based and airborne observations over a semiarid rain shadow region. The study was conducted for nonprecipitating, ice-free clouds during monsoon (July to September) and postmonsoon (October) months, when cloud condensation nuclei (CCN) concentrations over the region of interest increased monotonically and exhibited characteristics of continental origin. A multifilter rotating shadowband radiometer and microwave radiometric profiler were used to retrieve the cloud optical depth and liquid water path (LWP), respectively, from which cloud effective radius (CER) was obtained. CER showed wide variability from 10-18 µm and a decreasing trend toward the postmonsoon period. During monsoon, the estimated first aerosol indirect effect (AIE) increased from 0.01 to 0.23 with increase in LWP. AIE at different super saturations (SS) showed maximum value (significant at 95%) at 0.4% SS and higher LWP bin (250-300 g/m2). Also, statistically significant AIE values were found at 0.6% and 0.8% SSs but at lower LWP bin (200-250 g/m2). The relationship between CCN and CER showed high correlation at 0.4% SS at higher LWP bin, while at higher SSs good correlations were observed at lower LWPs. Data combined from ground-based and aircraft observations showed dominance of microphysical effect at aerosol concentrations up to 1500 cm-3 and radiative effect at higher concentrations. This combined cloud microphysical and aerosol radiative effect is more prominent during postmonsoon period due to an increase in aerosol concentration.

  14. Evaluation of cloud microphysical schemes on aerosol indirect effects from different scale models

    NASA Astrophysics Data System (ADS)

    Shiu, C. J.; Chen, Y. H.; Hashino, T.; Tsai, I. C.; Chen, W. T.; Chen, J. P.; Hsu, H. H.

    2014-12-01

    Quantification of aerosol indirect effects in climate modeling remain unresolved and of large uncertainties. The complicated aerosol-cloud-precipitation interactions in climate model are suggested to be quite sensitive to some tunable microphysical parameters such as the threshold radius associated with autoconversion of cloud droplets to rain droplets. More fundamental studies regarding to different microphysical processes used in various cloud microphysical schemes should be devoted, evaluated and investigated. In this study, we apply a synergy of different scale models with the same cloud and aerosol microphysical schemes (Chen and Liu, 2004; Cheng et al., 2007; and Chen et al., 2013) to understand and evaluate how cloud microphysical processes can be influenced by different microphysical schemes and their interaction with aerosols and radiation. These models include Kinematic Driver (KiD), Single Column Model of Community Atmosphere Model (SCAM), Large Eddy Simulation (LES), and NCAR CESM model. Simulation results from these models will be further validated and compared to either field campaign or satellite observations depending on the scale of the models. Off-line satellite simulator approach (i.e. Joint-Simulator) will also be applied for evaluating cloud microphysics against CloudSat and CALIPSO. Such type of synergy of models can be very useful for improvement, development and evaluation of physical parameterizations for global climate prediction and weather forecast in the near future especially for processes related to cloud macrophysics and microphysics.

  15. Corrigendum to "Impact of cloud-borne aerosol representation on aerosol direct and indirect effects" published in Atmos. Chem. Phys., 6, 4163-4174, 2006

    SciTech Connect

    Ghan, Steven J; Easter, Richard C

    2007-01-19

    Ghan and Easter (2006) (hereafter referred to as GE2006) used a global aerosol model to estimate the sensitivity of aerosol direct and indirect effects to a variety of simplified treatments of the cloud-borne aerosol. They found that neglecting transport of cloud-borne particles introduces little error, but that diagnosing cloud-borne particles produces global mean biases of 20% and local errors of up to 40% for aerosol, droplet number, and direct and indirect radiative forcing However, we have recently found that in those experiments we had inadvertently turned off the first aerosol indirect effect. In the radiation module, the droplet effective radius was prescribed at 10 microns rather than related to the droplet number concentration. The second indirect effect, in which droplet number influences droplet collision and coalescence, was treated, so that the simulations produced an aerosol indirect effect, albeit one that is much smaller (about -0.2Wm-2 for anthropogenic sulfate) than other previous estimates.

  16. Aerosol indirect effect during the aberrant Indian Summer Monsoon breaks of 2009

    NASA Astrophysics Data System (ADS)

    Manoj, M. G.; Devara, P. C. S.; Joseph, Susmitha; Sahai, A. K.

    2012-12-01

    The significant role of aerosol-cloud interaction during the large-scale drought producing breaks of 2009 Indian Summer Monsoon is investigated in the present paper. This mega drought had already been attributed to two long breaks, one in June and the other in July-August. While Central India (CI) and northern parts of the country experienced deficient rainfall, the rainfall over the southern Peninsular India (PI) remained close to normal. During the first break in June, which was associated with mid-latitude intrusion of dry air, the Twomey effect (positive aerosol indirect effect - AIE) was a dominant factor inhibiting efficient precipitation over CI region, as compared to that over PI. Moreover, the number of days that experienced significant (at 5% level of significance) positive AIE during the first break was more over CI compared to the same during the second break. The AIE on ice clouds was not as significant as that of the low-clouds. The resulting cloud properties during both break and active phases over CI differ significantly from that over PI for the corresponding periods. The positive AIE mentioned here is attributed to the large-scale deficit of moisture supply to the CI region due to dynamical reasons. However, it is shown that under ample availability of moisture, more aerosols could invigorate deep clouds over specific regions even during the break spells.

  17. GCM estimate of the indirect aerosol forcing using satellite-retrieved cloud droplet effective radii

    SciTech Connect

    Boucher, O.

    1995-05-01

    In a recent paper, satellite data radiances were analyzed to retrieve cloud droplet effective radii and significant interhemispheric differences for both maritime and continental clouds were reported. The mean cloud droplet radius in the Northern Hemisphere is smaller than in the Southern Hemisphere by about 0.7 {mu}m. This hemispheric contrast suggests the presence of an aerosol effect on cloud droplet size and is consistent with higher cloud condensation nuclei number concentration in the Northern Hemisphere due to anthropogenic production of aerosol precursors. In the present study, we constrain a climate model with the satellite retrievals and discuss the climate forcing that can be inferred from the observed distribution of cloud droplet radius. Based on two sets of experiments, this sensitivity study suggests that the indirect radiative forcing by anthropogenic aerosols could be about -0.6 or -1 W m{sup -2} averaged in the 0{degrees}-50{degrees}N latitude band. The uncertainty of these estimates is difficult to assess but is at least 50%. 30 refs., 3 figs., 1 tab.

  18. Study of Mechanisms of Aerosol Indirect Effects on Glaciated Clouds: Progress during the Project Final Technical Report

    SciTech Connect

    Phillips, Vaughan T. J.

    2013-10-18

    This 3-year project has studied how aerosol pollution influences glaciated clouds. The tool applied has been an 'aerosol-cloud model'. It is a type of Cloud-System Resolving Model (CSRM) modified to include 2-moment bulk microphysics and 7 aerosol species, as described by Phillips et al. (2009, 2013). The study has been done by, first, improving the model and then performing sensitivity studies with validated simulations of a couple of observed cases from ARM. These are namely the Tropical Warm Pool International Cloud Experiment (TWP-ICE) over the tropical west Pacific and the Cloud and Land Surface Interaction Campaign (CLASIC) over Oklahoma. During the project, sensitivity tests with the model showed that in continental clouds, extra liquid aerosols (soluble aerosol material) from pollution inhibited warm rain processes for precipitation production. This promoted homogeneous freezing of cloud droplets and aerosols. Mass and number concentrations of cloud-ice particles were boosted. The mean sizes of cloud-ice particles were reduced by the pollution. Hence, the lifetime of glaciated clouds, especially ice-only clouds, was augmented due to inhibition of sedimentation and ice-ice aggregation. Latent heat released from extra homogeneous freezing invigorated convective updrafts, and raised their maximum cloud-tops, when aerosol pollution was included. In the particular cases simulated in the project, the aerosol indirect effect of glaciated clouds was twice than of (warm) water clouds. This was because glaciated clouds are higher in the troposphere than water clouds and have the first interaction with incoming solar radiation. Ice-only clouds caused solar cooling by becoming more extensive as a result of aerosol pollution. This 'lifetime indirect effect' of ice-only clouds was due to higher numbers of homogeneously nucleated ice crystals causing a reduction in their mean size, slowing the ice-crystal process of snow production and slowing sedimentation. In addition

  19. Investigation of Aerosol Indirect Effects on Simulated Flash-flood Heavy Rainfall over Korea

    SciTech Connect

    Lim, Kyo-Sun; Hong, Songyou

    2012-11-01

    This study investigates aerosol indirect effects on the development of heavy rainfall near Seoul, South Korea, on 12 July 2006, focusing on precipitation amount. The impact of the aerosol concentration on simulated precipitation is evaluated by varying the initial cloud condensation nuclei (CCN) number concentration in the Weather Research and Forecasting (WRF) Double-Moment 6-class (WDM6) microphysics scheme. The simulations are performed under clean, semi-polluted, and polluted conditions. Detailed analysis of the physical processes that are responsible for surface precipitation, including moisture and cloud microphysical budgets shows enhanced ice-phase processes to be the primary driver of increased surface precipitation under the semi-polluted condition. Under the polluted condition, suppressed autoconversion and the enhanced evaporation of rain cause surface precipitation to decrease. To investigate the role of environmental conditions on precipitation response under different aerosol number concentrations, a set of sensitivity experiments are conducted with a 5 % decrease in relative humidity at the initial time, relative to the base simulations. Results show ice-phase processes having small sensitivity to CCN number concentration, compared with the base simulations. Surface precipitation responds differently to CCN number concentration under the lower humidity initial condition, being greatest under the clean condition, followed by the semi-polluted and polluted conditions.

  20. Common summertime total cloud cover and aerosol optical depth weekly variabilities over Europe: Sign of the aerosol indirect effects?

    NASA Astrophysics Data System (ADS)

    Georgoulias, A. K.; Kourtidis, K. A.; Alexandri, G.; Rapsomanikis, S.; Sanchez-Lorenzo, A.

    2015-02-01

    In this study, the summer total cloud cover (TCC) weekly cycle over Europe is investigated using MODIS and ISCCP satellite data in conjunction with aerosol optical depth (AOD) MODIS data. Spatial weekly patterns are examined at a 1° × 1° (MODIS) and 250 × 250 km2 (ISCCP) resolution. Despite the noise in the TCC weekly cycle patterns, their large-scale features show similarities with the AOD550 patterns. Regions with a positive (higher values during midweek) weekly cycle appear over Central Europe, while a strong negative (higher values during weekend) weekly plume appears over the Iberian Peninsula and the North-Eastern Europe. The TCC weekly variability exhibits a very good agreement with the AOD550 weekly variability over Central, South-Western Europe and North-Eastern Europe and a moderate agreement for Central Mediterranean. The MODIS derived TCC weekly variability shows reasonable agreement with the independent ISCCP observations, thus supporting the credibility of the results. TCC and AOD550 correlations exhibit a strong slope for the total of the 6 regions investigated in this work with the slopes being higher for regions with common TCC-AOD550 weekly variabilities. The slope is much stronger for AOD550 values less than 0.2 for Central and South-Western Europe, in line with previous studies around the world. Possible scenarios that could explain the common weekly variability of aerosols and cloud cover through the aerosol indirect effects are discussed here also taking into account the weekly variability appearing in ECA&D E-OBS rainfall data.

  1. Evidence for a Third aerosol Indirect Effect from Ship Tracks Observed by Calipso

    NASA Astrophysics Data System (ADS)

    Christensen, M.; Stephens, G. L.

    2009-12-01

    Ship tracks are a phenomenon that provide a unique way of studying aerosol effects on clouds because the regions of clouds that are heavily contaminated by pollution can be separated from adjacent regions of clean clouds formed in a marine boundary layer. Ship tracks have been used to study the 1st indirect radiative effect (Twomey, 1974) and also the 2nd indirect effect (Albrecht, 1989) because they often persist while the surrounding unpolluted clouds dissipate. A 3rd indirect effect is the change to cloud geometrical depth associated with the reduced precipitation in polluted clouds (Pincus and Baker, 1995). Presented for the first time, the vertical structure of ship tracks are used to confirm the presence of this 3rd indirect effect. Using the Lidar from Calipso, high vertical resolution data of cloud top height along ship track cross sections were used to calculate differences in height between ship tracks and the clean clouds adjacent to them. Using MODIS imagery to locate ship tracks collocated to the Calipso orbital track, over 100 ship track vertical profiles were used in the analysis. In addition, atmospheric stability was assessed for each ship track using temperature and moisture data from the ECMWF-AUX product collocated to the Calipso orbit. Height differences between ship tracks and unpolluted clouds were found to be strongly correlated with cloud cover fraction, dew point depression above cloud top, and lower tropospheric static stability. Ship tracks were most often observed to be elevated above the surrounding clouds by approximately 100 - 200 meters when the cloud cover fraction was below 90% and capped by a weak temperature inversion. Ship tracks were not elevated above the surrounding clouds when either cloud cover fraction was high, the stability was high, or the air above the clouds was dry. Since mean cloud top heights were about 650 m, ship tracks in partly cloudy regions were often elevated above the surrounding clouds by ~15-30%. The

  2. Attribution of the United States “warming hole”: Aerosol indirect effect andprecipitable water vapor

    EPA Science Inventory

    Aerosols can influence the climate indirectly by acting as cloud condensation nuclei and /or ice nuclei, thereby modifying cloud optical properties. Observations show a striking cooling trend in summertime daily maximum temperature (Tmax) in the central and...

  3. QUantifying the Aerosol Direct and Indirect Effect over Eastern Mediterranean from Satellites (QUADIEEMS): Overview and preliminary results

    NASA Astrophysics Data System (ADS)

    Georgoulias, Aristeidis K.; Zanis, Prodromos; Pöschl, Ulrich; Kourtidis, Konstantinos A.; Alexandri, Georgia; Ntogras, Christos; Marinou, Eleni; Amiridis, Vassilis

    2013-04-01

    An overview and preliminary results from the research implemented within the framework of QUADIEEMS project are presented. For the scopes of the project, satellite data from five sensors (MODIS aboard EOS TERRA, MODIS aboard EOS AQUA, TOMS aboard Earth Probe, OMI aboard EOS AURA and CALIOP aboard CALIPSO) are used in conjunction with meteorological data from ECMWF ERA-interim reanalysis and data from a global chemical-aerosol-transport model as well as simulation results from a regional climate model (RegCM4) coupled with a simplified aerosol scheme. QUADIEEMS focuses on Eastern Mediterranean [30oN-45No, 17.5oE-37.5oE], a region situated at the crossroad of different aerosol types and thus ideal for the investigation of the direct and indirect effects of various aerosol types at a high spatial resolution. The project consists of five components. First, raw data from various databases are acquired, analyzed and spatially homogenized with the outcome being a high resolution (0.1x0.1 degree) and a moderate resolution (1.0x1.0 degree) gridded dataset of aerosol and cloud optical properties. The marine, dust and anthropogenic fraction of aerosols over the region is quantified making use of the homogenized dataset. Regional climate model simulations with REGCM4/aerosol are also implemented for the greater European region for the period 2000-2010 at a resolution of 50 km. REGCM4's ability to simulate AOD550 over Europe is evaluated. The aerosol-cloud relationships, for sub-regions of Eastern Mediterranean characterized by the presence of predominant aerosol types, are examined. The aerosol-cloud relationships are also examined taking into account the relative position of aerosol and cloud layers as defined by CALIPSO observations. Within the final component of the project, results and data that emerged from all the previous components are used in satellite-based parameterizations in order to quantify the direct and indirect (first) radiative effect of the different

  4. Aerosol indirect effect on warm clouds over South-East Atlantic, from co-located MODIS and CALIPSO observations

    NASA Astrophysics Data System (ADS)

    Costantino, L.; Bréon, F.-M.

    2013-01-01

    In this study, we provide a comprehensive analysis of aerosol interaction with warm boundary layer clouds over the South-East Atlantic. We use aerosol and cloud parameters derived from MODIS observations, together with co-located CALIPSO estimates of the layer altitudes, to derive statistical relationships between aerosol concentration and cloud properties. The CALIPSO products are used to differentiate between cases of mixed cloud-aerosol layers from cases where the aerosol is located well-above the cloud top. This technique allows us to obtain more reliable estimates of the aerosol indirect effect than from simple relationships based on vertically integrated measurements of aerosol and cloud properties. Indeed, it permits us to somewhat distinguish the effects of aerosol and meteorology on the clouds, although it is not possible to fully ascertain the relative contribution of each on the derived statistics. Consistently with the results from previous studies, our statistics clearly show that aerosol affects cloud microphysics, decreasing the Cloud Droplet Radius (CDR). The same data indicate a concomitant strong decrease in cloud Liquid Water Path (LWP), which is inconsistent with the hypothesis of aerosol inhibition of precipitation (Albrecht, 1989). We hypothesise that the observed reduction in LWP is the consequence of dry air entrainment at cloud top. The combined effect of CDR decrease and LWP decrease leads to rather small sensitivity of the Cloud Optical Thickness (COT) to an increase in aerosol concentration. The analysis of MODIS-CALIPSO coincidences also evidences an aerosol enhancement of low cloud cover. Surprisingly, the Cloud Fraction (CLF) response to aerosol invigoration is much stronger when (absorbing) particles are located above cloud top than in cases of physical interaction. This result suggests a relevant aerosol radiative effect on low cloud occurrence: absorbing particles above the cloud top may heat the corresponding atmosphere layer

  5. Aerosol indirect effect on warm clouds over South-East Atlantic, from co-located MODIS and CALIPSO observations

    NASA Astrophysics Data System (ADS)

    Costantino, Lorenzo; Bréon, François-Marie

    2013-04-01

    In this study, we provide a comprehensive analysis of aerosol interaction with warm boundary layer clouds over the South-East Atlantic. We use aerosol and cloud parameters derived from MODIS observations, together with co-located CALIPSO estimates of the layer altitudes, to derive statistical relationships between aerosol concentration and cloud properties. The CALIPSO products are used to differentiate between cases of mixed cloud-aerosol layers from cases where the aerosol is located well-above the cloud top. This technique allows us to obtain more reliable estimates of the aerosol indirect effect than from simple relationships based on vertically integrated measurements of aerosol and cloud properties. Indeed, it permits us to somewhat distinguish the effects of aerosol and meteorology on the clouds, although it is not possible to fully ascertain the relative contribution of each on the derived statistics. Consistently with the results from previous studies, our statistics clearly show that aerosol affects cloud microphysics, decreasing the Cloud Droplet Radius (CDR). The same data indicate a concomitant strong decrease in cloud Liquid Water Path (LWP), which is inconsistent with the hypothesis of aerosol inhibition of precipitation (Albrecht, 1989). We hypothesise that the observed reduction in LWP is the consequence of dry air entrainment at cloud top. The combined effect of CDR decrease and LWP decrease leads to rather small sensitivity of the Cloud Optical Thickness (COT) to an increase in aerosol concentration. The analysis of MODIS-CALIPSO coincidences also evidences an aerosol enhancement of low cloud cover. Surprisingly, the Cloud Fraction (CLF) response to aerosol invigoration is much stronger when (absorbing) particles are located above cloud top than in cases of physical interaction. This result suggests a relevant aerosol radiative effect on low cloud occurrence: absorbing particles above the cloud top may heat the corresponding atmosphere layer

  6. Anthropogenic contribution to cloud condensation nuclei and the first aerosol indirect climate effect modelled by GEOS-Chem/APM

    NASA Astrophysics Data System (ADS)

    Yu, F.

    2013-05-01

    Atmospheric particles influence climate indirectly by acting as cloud condensation nuclei (CCN) that affect cloud properties (albedo, lifetime, etc.) and precipitation. The first aerosol indirect radiative forcing (FAIRF) (i.e., cloud albedo effect) constitutes the largest uncertainty among the various radiative forcings quantified by the latest IPCC assessment report (IPCC2007). In order to confidently interpret climate change over the past century and project future change, it is essential to reduce the FAIRF uncertainty. One of the large sources of the uncertainty is the poor knowledge of the number concentrations and spatial distributions of pre-industrial and present-day aerosols. All previous and recent FAIRF studies are based on global models with simplified chemistry and aerosol microphysics, which may lead to large uncertainties in predicted aerosol properties and FAIRF values. Here, we investigate the anthropogenic contribution to CCN and associated FAIRF using a state-of-the-art global chemical transport and aerosol model (GEOS-Chem/APM) that contains a number of advanced features (including size-resolved sectional particle microphysics, online comprehensive SOx-NOx-Ox-VOCs chemistry, consideration of nitrate and secondary organic aerosols, online aerosol-cloud-radiation calculation, usage of more accurate assimilated meteorology, etc.). As far as we know, this is the first time that a global model with full chemistry and size-resolved (sectional) particle microphysics is employed to study FAIRF. Key aerosol properties predicted by GEOS-Chem/APM for the present-day case have been evaluated against a large set of land-, ship-, aircraft-, and satellite- based aerosol measurements including total particle number concentrations, CCN concentrations, AODs, and vertical profiles of extinction coefficients. The GEOS-Chem/APM model, with its advanced features and ability to reproduce observed aerosol properties (including CCN) around the globe, is expected to

  7. QUantifying the Aerosol Direct and Indirect Effect over Eastern Mediterranean from Satellites (QUADIEEMS): Satellite, model and reanalysis data synergy

    NASA Astrophysics Data System (ADS)

    Georgoulias, A.; Zanis, P.; Poeschl, U.; Kourtidis, K.; Alexandri, G.; Dogras, C.; Marinou, E.; Amiridis, V.

    2013-12-01

    The research implemented within the QUADIEEMS project is presented here. Satellite data from five sensors (MODIS aboard EOS TERRA, MODIS aboard EOS AQUA, TOMS aboard Earth Probe, OMI aboard EOS AURA and CALIOP aboard CALIPSO) are combined with meteorological data from ECMWF ERA-interim reanalysis, aerosol data from a global chemical-aerosol-transport model (GOCART) and MACC reanalysis as well as simulation results from a regional climate model (RegCM4) coupled with a simplified aerosol scheme. QUADIEEMS focuses on Eastern Mediterranean [30N-45N, 17.5E-37.5E]. Various sources, like industry and transport, occasional Saharan dust intrusions, sea spray and agricultural fires in Southeastern and Eastern Europe as well as occasional fire events in the region, create an ideal environment for the investigation of the direct and indirect effects of various aerosol types. The acquired data were spatially homogenized resulting in a novel satellite-model-reanalysis high resolution (0.1x0.1 degree) dataset of aerosol and cloud optical properties. The relative contribution of marine, dust and anthropogenic aerosols to the total aerosol optical depth (AOD550) is quantified combining different parameters from our high resolution dataset. The same procedure is repeated at a moderate resolution (1.0x1.0 degree). Within QUADIEEMS, decadal REGCM4/aerosol regional climate model simulations are implemented for the greater European region at a resolution of 50 km. We evaluate the ability of REGCM4 to simulate AOD550 patterns. For different sub-regions of Eastern Mediterranean, the aerosol-cloud relationships are examined. The same procedure is repeated also taking into account the relative position of aerosol and cloud layers as defined by CALIPSO observations. Results and data from the first four components of the project are used in satellite-based parameterizations to quantify the direct and indirect (first) radiative effect of the different aerosol types at a resolution of 0.1x0

  8. Direct and indirect radiative effects of aerosols using the coupled system of aerosol HAM module and the Weather Research and Forecasting (WRF) model

    NASA Astrophysics Data System (ADS)

    Mashayekhi, Rabab; Irannejad, Parviz; Feichter, Johann; Akbari Bidokhti, Abbas Ali Ali

    2010-05-01

    The fully coupled aerosol-cloud and radiation WRF-HAM modeling system is presented. The aerosol HAM model is implemented within the chemistry version of WRF modeling system. HAM is based on a "pseudo-modal" approach for representation of the particle size distribution. Aerosols are grouped into four geometrical size classes and two types of mixed and insoluble particles. The aerosol components considered are sulfate, black carbon, particulate organic matter, sea salt and mineral dust. Microphysical processes including nucleation, condensation and coagulation of aerosol particles are considered using the microphysics M7 scheme. Horizontal transport of the aerosol particles is simulated using the advection scheme in WRF. Convective transport and vertical mixing of aerosol particles are also considered in the coupled system. A flux-resistance method is used for dry deposition of aerosol particles. Aerosol sizes and chemical compositions are used to determine the aerosol optical properties. Direct effects of aerosols on incoming shortwave radiation flux are simulated by transferring the aerosol optical parameters to the Goddard shortwave radiation scheme. Indirect effects of aerosols are simulated by using a prognostic treatment of cloud droplet number and adding modules that activate aerosol particles to form cloud droplets. The first and second indirect effects, i.e. the interactions of clouds and incoming solar radiation are implemented in WRF-Chem by linking the simulated cloud droplet number with the Goddard shortwave radiation scheme and the Lin et al. microphysics scheme. The simulations are carried out for a 6-day period from 22 to 28 February 2006 in a domain with 30-km grid spacing, encompassing the south-western Asia, North Africa and some parts of Europe. The results show a negative radiative forcing over most parts of the domain, mainly due to the presence of mineral dust aerosols. The simulations are evaluated using the measured downward radiation in

  9. Mechanisms for indirect effects from aerosol pollution on mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Phillips, Vaughan

    2015-04-01

    Aerosol pollution can have various effects on mixed-phase clouds. They can alter coalescence and raindrop-freezing for droplet activation by CCN aerosols. They can alter aggregation of ice crystals and snow formation. This can alter the lifetime of mixed-phase clouds, as well as the reflectivity for solar radiation. Simulations of observed cases of mixed-phase clouds have been performed to examine the mechanisms for effects from aerosol pollution on them. Such mechanisms are discussed in the presentation.

  10. Impact of aerosol indirect effect on surface temperature over East Asia

    PubMed Central

    Huang, Yan; Dickinson, Robert E.; Chameides, William L.

    2006-01-01

    A regional coupled climate–chemistry–aerosol model is developed to examine the impacts of anthropogenic aerosols on surface temperature and precipitation over East Asia. Besides their direct and indirect reduction of short-wave solar radiation, the increased cloudiness and cloud liquid water generate a substantial downward positive long-wave surface forcing; consequently, nighttime temperature in winter increases by +0.7°C, and the diurnal temperature range decreases by −0.7°C averaged over the industrialized parts of China. Confidence in the simulated results is limited by uncertainties in model cloud physics. However, they are broadly consistent with the observed diurnal temperature range decrease as reported in China, suggesting that changes in downward long-wave radiation at the surface are important in understanding temperature changes from aerosols. PMID:16537432

  11. Investigation on semi-direct and indirect climate effects of fossil fuel black carbon aerosol over China

    NASA Astrophysics Data System (ADS)

    Zhuang, Bingliang; Liu, Qian; Wang, Tijian; Yin, Changqin; Li, Shu; Xie, Min; Jiang, Fei; Mao, Huiting

    2013-11-01

    A Regional Climate Chemistry Modeling System that employed empirical parameterizations of aerosol-cloud microphysics was applied to investigate the spatial distribution, radiative forcing (RF), and climate effects of black carbon (BC) over China. Results showed high levels of BC in Southwest, Central, and East China, with maximum surface concentrations, column burden, and optical depth (AOD) up to 14 μg m-3, 8 mg m-2, and 0.11, respectively. Black carbon was found to result in a positive RF at the top of the atmosphere (TOA) due to its direct effect while a negative RF due to its indirect effect. The regional-averaged direct and indirect RF of BC in China was about +0.81 and -0.95 W m-2, respectively, leading to a net RF of -0.15 W m-2 at the TOA. The BC indirect RF was larger than its direct RF in South China. Due to BC absorption of solar radiation, cloudiness was decreased by 1.33 %, further resulting in an increase of solar radiation and subsequently a surface warming over most parts of China, which was opposite to BC's indirect effect. Further, the net effect of BC might cause a decrease of precipitation of -7.39 % over China. Investigations also suggested large uncertainties and non-linearity in BC's indirect effect on regional climate. Results suggested that: (a) changes in cloud cover might be more affected by BC's direct effect, while changes in surface air temperature and precipitation might be influenced by BC's indirect effect; and (b) BC second indirect effect might have more influence on cloud cover and water content compared to first indirect effect. This study highlighted a substantial role of BC on regional climate changes.

  12. Global modelling of direct and indirect effects of sea spray aerosol using a source function encapsulating wave state

    NASA Astrophysics Data System (ADS)

    Partanen, A.-I.; Dunne, E. M.; Bergman, T.; Laakso, A.; Kokkola, H.; Ovadnevaite, J.; Sogacheva, L.; Baisnée, D.; Sciare, J.; Manders, A.; O'Dowd, C.; de Leeuw, G.; Korhonen, H.

    2014-11-01

    Recently developed parameterizations for the sea spray aerosol source flux, encapsulating wave state, and its organic fraction were incorporated into the aerosol-climate model ECHAM-HAMMOZ to investigate the direct and indirect radiative effects of sea spray aerosol particles. Our simulated global sea salt emission of 805 Tg yr-1 (uncertainty range 378-1233 Tg yr-1) was much lower than typically found in previous studies. Modelled sea salt and sodium ion concentrations agreed relatively well with measurements in the smaller size ranges at Mace Head (annual normalized mean model bias -13% for particles with vacuum aerodynamic diameter Dva < 1 μm), Point Reyes (-29% for particles with aerodynamic diameter Da < 2.5 μm) and Amsterdam Island (-52% for particles with Da < 1 μm) but the larger sizes were overestimated (899% for particles with 2.5 μm < Da < 10 μm) at Amsterdam Island. This suggests that at least the high end of the previous estimates of sea spray mass emissions is unrealistic. On the other hand, the model clearly underestimated the observed concentrations of organic or total carbonaceous aerosol at Mace Head (-82%) and Amsterdam Island (-68%). The large overestimation (212%) of organic matter at Point Reyes was due to the contribution of continental sources. At the remote Amsterdam Island site, the organic concentration was underestimated especially in the biologically active months, suggesting a need to improve the parameterization of the organic sea spray fraction. Globally, the satellite-retrieved AOD over the oceans, using PARASOL data, was underestimated by the model (means over ocean 0.16 and 0.10, respectively); however, in the pristine region around Amsterdam Island the measured AOD fell well within the simulated uncertainty range. The simulated sea spray aerosol contribution to the indirect radiative effect was positive (0.3 W m-2), in contrast to previous studies. This positive effect was ascribed to the tendency of sea salt aerosol to

  13. Global modelling of direct and indirect effects of sea spray aerosol using a source function encapsulating wave state

    NASA Astrophysics Data System (ADS)

    Partanen, A.-I.; Dunne, E. M.; Bergman, T.; Laakso, A.; Kokkola, H.; Ovadnevaite, J.; Sogacheva, L.; Baisnée, D.; Sciare, J.; Manders, A.; O'Dowd, C.; de Leeuw, G.; Korhonen, H.

    2014-02-01

    Recently developed parameterizations for the sea spray aerosol source flux, encapsulating wave state, and its organic fraction were incorporated into the aerosol-climate model ECHAM-HAMMOZ to investigate the direct and indirect radiative effects of sea spray aerosol particles. Our simulated global sea salt emission of 805 Tg yr-1 (uncertainty range 378-1233 Tg yr-1) was much lower than typically found in previous studies. Modelled sea salt and sodium ion concentrations agreed relatively well with measurements in the smaller size ranges at Mace Head (annual normalized mean model bias -13% for particles with vacuum aerodynamic diameter Dva < 1 μm), Point Reyes (-29% for particles with aerodynamic diameter Da < 2.5 μm) and Amsterdam Island (-52% for particles with Da < 1 μm) but the larger sizes were overestimated (899% for particles with 2.5 μm aerosol at Mace Head (-82%) and Amsterdam Island (-68%). The large overestimation (212%) of organic matter at Point Reyes was due to the contribution of continental sources. At the remote Amsterdam Island site, the organic concentration was underestimated especially in the biologically active months, suggesting a need to improve the parameterization of the organic sea spray fraction. Globally, the satellite-retrieved AOD over the oceans, using PARASOL data, was underestimated by the model (means over ocean 0.16 and 0.10, respectively); however, in the pristine region around Amsterdam Island the measured AOD fell well within the simulated uncertainty range. The simulated sea spray aerosol contribution to the indirect radiative effect was positive (0.3 W m-2), in contrast to previous studies. This positive effect was ascribed to the tendency of sea salt aerosol to

  14. Investigation of Aerosol Indirect Effects using a Cumulus Microphysics Parameterization in a Regional Climate Model

    SciTech Connect

    Lim, Kyo-Sun; Fan, Jiwen; Leung, Lai-Yung R.; Ma, Po-Lun; Singh, Balwinder; Zhao, Chun; Zhang, Yang; Zhang, Guang; Song, Xiaoliang

    2014-01-29

    A new Zhang and McFarlane (ZM) cumulus scheme includes a two-moment cloud microphysics parameterization for convective clouds. This allows aerosol effects to be investigated more comprehensively by linking aerosols with microphysical processes in both stratiform clouds that are explicitly resolved and convective clouds that are parameterized in climate models. This new scheme is implemented in the Weather Research and Forecasting (WRF) model, which is coupled with the physics and aerosol packages from the Community Atmospheric Model version 5 (CAM5). A test case of July 2008 during the East Asian summer monsoon is selected to evaluate the performance of the new ZM scheme and to investigate aerosol effects on monsoon precipitation. The precipitation and radiative fluxes simulated by the new ZM scheme show a better agreement with observations compared to simulations with the original ZM scheme that does not include convective cloud microphysics and aerosol convective cloud interactions. Detailed analysis suggests that an increase in detrained cloud water and ice mass by the new ZM scheme is responsible for this improvement. To investigate precipitation response to increased anthropogenic aerosols, a sensitivity experiment is performed that mimics a clean environment by reducing the primary aerosols and anthropogenic emissions to 30% of that used in the control simulation of a polluted environment. The simulated surface precipitation is reduced by 9.8% from clean to polluted environment and the reduction is less significant when microphysics processes are excluded from the cumulus clouds. Ensemble experiments with ten members under each condition (i.e., clean and polluted) indicate similar response of the monsoon precipitation to increasing aerosols.

  15. Atmospheric Radiation Measurement (ARM) Data from Shouxian, China for the Study of Aerosol Indirect Effects in China

    DOE Data Explorer

    In a complex ARM Mobile Facility (AMF) deployment, monitoring data was collected at four locations in China during 2008. The various sites are located in regions with different climate regimes and with high aerosol loadings of different optical, physical, and chemical properties. Measurements obtained at all the AMF sites during the 8-month deployment in China will help scientists to validate satellite-based findings, understand the mechanisms of the aerosol indirect effects in the region, and examine the roles of aerosols in affecting regional climate and atmospheric circulation, with a special focus on the impact of the East Asian monsoon system. As with other collections from the ARM Mobile Facility, the datasets are available from the ARM Archive. The ARM Archive physically resides at the Oak Ridge National Laboratory.

  16. Potential indirect effects of aerosol on tropical cyclone intensity: convective fluxes and cold-pool activity

    NASA Astrophysics Data System (ADS)

    Krall, G. M.; Cottom, W. R.

    2012-01-01

    aerosols resulted in large amounts of condensate being thrust into the storm anvil which weakened convective downdrafts and cold-pools, yet the system did show reductions in windspeed (although weaker) compared with the clean control run. This study suggests that ingestion of elevated amounts of CCN into a tropical cyclone (TC) can appreciably alter the intensity of the storm. This implies that intensity prediction of TCs would be improved by including indirect aerosol affects. However, the pollution aerosols have very little impact on the storm track.

  17. Aerosol Indirect Effect Studies at Southern Great Plains During the May 2003 Intensive Operations Period

    NASA Technical Reports Server (NTRS)

    Feingold, Graham; Furrer, Reinhard; Pilewskie, Peter; Remer, Lorraine A.; Min, Qilong; Jonsson, Haflidi

    2006-01-01

    During May 2003 the Department of Energy's Atmospheric Radiation Measurement Program conducted an Intensive Operations Period (IOP) to measure the radiative effects of aerosol and clouds. A suite of both in situ and remote sensing measurements were available to measure aerosol and cloud parameters. This paper has three main goals: First, it focuses on comparison between in situ retrievals of the radiatively important drop effective radius r(sub e) and various satellite, airborne, and surface remote sensing retrievals of the same parameter. On 17 May 2003, there was a fortuitous, near-simultaneous sampling of a stratus cloud by five different methods. The retrievals of r(sub e) agree with one another to within approx.20%, which is approximately the error estimate for most methods. Second, a methodology for deriving a best estimate of r(sub e) from these different instruments, with their different physical properties and sampling volumes, is proposed and applied to the 17 May event. Third, the paper examines the response of r(sub e) to changes in aerosol on 3 days during the experiment and examines the consistency of remote sensing and in situ measurements of the effect of aerosol on r(sub e). It is shown that in spite of the generally good agreement in derived r(sub e), the magnitude of the response of r(sub e), to changes in aerosol is quite sensitive to the method of retrieving r(sub e) and to the aerosol proxy for cloud condensation nuclei. Nonphysical responses are sometimes noted, and it is suggested that further work needs to be done to refine these techniques.

  18. Aerosol indirect effect on the grid-scale clouds in the two-way coupled WRF-CMAQ: model description, development, evaluation and regional analysis

    EPA Science Inventory

    This study implemented first, second and glaciations aerosol indirect effects (AIE) on resolved clouds in the two-way coupled WRF-CMAQ modeling system by including parameterizations for both cloud drop and ice number concentrations on the basis of CMAQ predicted aerosol distribu...

  19. Aerosol indirect effects in the ECHAM5-HAM2 climate model with subgrid cloud microphysics in a stochastic framework

    NASA Astrophysics Data System (ADS)

    Tonttila, Juha; Räisänen, Petri; Järvinen, Heikki

    2015-04-01

    Representing cloud properties in global climate models remains a challenging topic, which to a large extent is due to cloud processes acting on spatial scales much smaller than the typical model grid resolution. Several attempts have been made to alleviate this problem. One such method was introduced in the ECHAM5-HAM2 climate model by Tonttila et al. (2013), where cloud microphysical properties, along with the processes of cloud droplet activation and autoconversion, were computed using an ensemble of stochastic subcolumns within the climate model grid columns. Moreover, the subcolumns were sampled for radiative transfer using the Monte Carlo Independent Column Approximation approach. The same model version is used in this work (Tonttila et al. 2014), where 5-year nudged integrations are performed with a series of different model configurations. Each run is performed twice, once with pre-industrial (PI, year 1750) aerosol emission conditions and once with present-day (PD, year 2000) conditions, based on the AEROCOM emission inventories. The differences between PI and PD simulations are used to estimate the impact of anthropogenic aerosols on clouds and the aerosol indirect effect (AIE). One of the key results is that when both cloud activation and autoconversion are computed in the subcolumn space, the aerosol-induced PI-to-PD change in the global-mean liquid water path is up to 19 % smaller than in the reference with grid-scale computations. Together with similar changes in the cloud droplet number concentration, this influences the cloud radiative effects and thus the AIE, which is estimated as the difference in the net cloud radiative effect between PI and PD conditions. Accordingly, the AIE is reduced by 14 %, from 1.59 W m-2 in the reference model version to 1.37 W m-2 in the experimental model configuration. The results of this work explicitly show that careful consideration of the subgrid variability in cloud microphysical properties and consistent

  20. Global Distribution of Cloud Droplet Number Concentration, Autoconversion Rate, and Aerosol Indirect Effect Under Diabatic Droplet Activation

    NASA Technical Reports Server (NTRS)

    Barahona, Donifan; Sotiropoulou, Rafaella; Nenes, Athanasios

    2011-01-01

    This study presents a global assessment of the sensitivity of droplet number to diabatic activation (i.e., including effects from entrainment of dry air) and its first-order tendency on indirect forcing and autoconversion. Simulations were carried out with the NASA Global Modeling Initiative (GMI) atmospheric and transport model using climatological metereorological fields derived from the former NASA Data Assimilation Office (DAO), the NASA Finite volume GCM (FVGCM) and the Goddard Institute for Space Studies version II (GISS) GCM. Cloud droplet number concentration (CDNC) is calculated using a physically based prognostic parameterization that explicitly includes entrainment effects on droplet formation. Diabatic activation results in lower CDNC, compared to adiabatic treatment of the process. The largest decrease in CDNC (by up to 75 percent) was found in the tropics and in zones of moderate CCN concentration. This leads to a global mean effective radius increase between 0.2-0.5 micrometers (up to 3.5 micrometers over the tropics), a global mean autoconversion rate increase by a factor of 1.1 to 1.7 (up to a factor of 4 in the tropics), and a 0.2-0.4 W m(exp -2) decrease in indirect forcing. The spatial patterns of entrainment effects on droplet activation tend to reduce biases in effective radius (particularly in the tropics) when compared to satellite retrievals. Considering the diabatic nature of ambient clouds, entrainment effects on CDNC need to be considered in GCM studies of the aerosol indirect effect.

  1. Evaluating the aerosol indirect effect in WRF-Chem simulations of the January 2013 Beijing air pollution event.

    NASA Astrophysics Data System (ADS)

    Peckham, Steven; Grell, Georg; Xie, Ying; Wu, Jian-Bin

    2015-04-01

    In January 2013, an unusual weather pattern over Northern China produced unusually cool, moist conditions for the region. Recent peer-reviewed scientific manuscripts report that during this time period, Beijing experienced a historically severe haze and smog event with observed monthly average fine particulate matter (PM2.5) concentrations exceeding 225 micrograms per cubic meter. MODIS satellite observations produced AOD values of approximately 1.5 to 2 for the same time. In addition, over eastern and northern China record-breaking hourly average PM2.5 concentrations of more than 700 μg m-3 were observed. Clearly, the severity and persistence of this air pollution episode has raised the interest of the scientific community as well as widespread public attention. Despite the significance of this and similar air pollution events, several questions regarding the ability of numerical weather prediction models to forecast such events remain. Some of these questions are: • What is the importance of including aerosols in the weather prediction models? • What is the current capability of weather prediction models to simulate aerosol impacts upon the weather? • How important is it to include the aerosol feedbacks (direct and indirect effect) in the numerical model forecasts? In an attempt to address these and other questions, a Joint Working Group of the Commission for Atmospheric Sciences and the World Climate Research Programme has been convened. This Working Group on Numerical Experimentation (WGNE), has set aside several events of interest and has asked its members to generate numerical simulations of the events and examine the results. As part of this project, weather and pollution simulations were produced at the NOAA Earth System Research Laboratory using the Weather Research and Forecasting (WRF) chemistry model. These particular simulations include the aerosol indirect effect and are being done in collaboration with a group in China that will produce

  2. Corrigendum to "Aerosol indirect effects from shipping emissions: sensitivity studies with the global aerosol-climate model ECHAM-HAM" published in Atmos. Chem. Phys., 12, 5985-6007, 2012

    NASA Astrophysics Data System (ADS)

    Peters, K.; Stier, P.; Quaas, J.; Graßl, H.

    2013-07-01

    An error in the calculation of the emitted number of primary sulfate particles for a given mass of emitted elementary sulfur has recently been identified in HAM, i.e. the aerosol module utilised in the ECHAM-HAM aerosol climate model. Correcting for this error substantially alters the estimates of top-of-atmosphere radiative forcing due to aerosol indirect effects from global shipping emissions (year 2000) as presented in Peters et al. (2012). Here, we shortly present these new results.

  3. Weak global sensitivity of cloud condensation nuclei and the aerosol indirect effect to Criegee + SO2 chemistry

    NASA Astrophysics Data System (ADS)

    Pierce, J. R.; Evans, M. J.; Scott, C. E.; D'Andrea, S. D.; Farmer, D. K.; Swietlicki, E.; Spracklen, D. V.

    2013-03-01

    H2SO4 vapor is important for the nucleation of atmospheric aerosols and the growth of ultrafine particles to cloud condensation nuclei (CCN) sizes with important roles in the global aerosol budget and hence planetary radiative forcing. Recent studies have found that reactions of stabilized Criegee intermediates (CIs, formed from the ozonolysis of alkenes) with SO2 may be an important source of H2SO4 that has been missing from atmospheric aerosol models. For the first time in a global model, we investigate the impact of this new source of H2SO4 in the atmosphere. We use the chemical transport model, GEOS-Chem, with the online aerosol microphysics module, TOMAS, to estimate the possible impact of CIs on present-day H2SO4, CCN, and the cloud-albedo aerosol indirect effect (AIE). We extend the standard GEOS-Chem chemistry with CI-forming reactions (ozonolysis of isoprene, methyl vinyl ketone, methacrolein, propene, and monoterpenes) from the Master Chemical Mechanism. Using a fast rate constant for CI+SO2, we find that the addition of this chemistry increases the global production of H2SO4 by 4%. H2SO4 concentrations increase by over 100% in forested tropical boundary layers and by over 10-25% in forested NH boundary layers (up to 100% in July) due to CI+SO2 chemistry, but the change is generally negligible elsewhere. The predicted changes in CCN were strongly dampened to the CI+SO2 changes in H2SO4 in some regions: less than 15% in tropical forests and less than 2% in most mid-latitude locations. The global-mean CCN change was less than 1% both in the boundary layer and the free troposphere. The associated cloud-albedo AIE change was less than 0.03 W m-2. The model global sensitivity of CCN and the AIE to CI+SO2 chemistry is significantly (approximately one order-of-magnitude) smaller than the sensitivity of CCN and AIE to other uncertain model inputs, such as nucleation mechanisms, primary emissions, SOA (secondary organic aerosol) and deposition. Similarly

  4. Investigation of key quantities for the first indirect aerosol effect contrasting MSG SEVIRI and ground site measurements

    NASA Astrophysics Data System (ADS)

    Merk, Daniel; Deneke, Hartwig; Pospichal, Bernhard; Seifert, Patric; Ansmann, Albert

    2014-05-01

    The first indirect aerosol effect remains one of the main uncertainties in projections of anthropogenic climate change. Satellites provide a unique possibility to globally quantify the importance of the first indirect aerosol effect. Given a constant liquid water content within the cloud, a higher cloud droplet number concentration results in higher cloud albedo. But the cloud albedo is also altered by the geometrical cloud extent. Therefore the two key quantities for this investigation are the CDNC and the geometrical cloud extent. Both quantities can not be obtained directly from current geostationary satellites. Due to necessary assumptions and missing information about the vertical cloud structure, the retrieval of both quantities remains a great challenge. Our aim is to investigate the accuracy of current satellite retrievals by contrasting the key quantities with those obtained from ground-site. The satellite retrieval is based on the method described by Nakajima and King to derive the optical cloud depth and the effective radius. In a second step, the CDNC and cloud extent is determined, assuming an adiabatically increasing liquid water content above cloud base. Single-layer liquid water clouds are simultaneously observed with ground-based remote sensing instruments at different locations in Germany (Leipzig, Juelich, Melpitz). We use a ceilometer to detect the cloud base height, a 35 GHz cloud radar to detect the cloud top height and the reflectivity profile, and a microwave radiometer to obtain the liquid water path. We developed an Optimal Estimation approach to retrieve the CDNC as well as the liquid water content profile. Our observation vector consists of the radar reflectivity profile and the liquid water path. We compare the retrieved quantities from ground with the satellite perspective to closer investigate the assumption of adiabatic cloud profiles.

  5. Toward a minimal representation of aerosol direct and indirect effects: model description and evaluation

    NASA Astrophysics Data System (ADS)

    Liu, X.; Easter, R. C.; Ghan, S. J.; Zaveri, R.; Rasch, P.; Shi, X.; Lamarque, J.-F.; Gettelman, A.; Morrison, H.; Vitt, F.; Conley, A.; Park, S.; Neale, R.; Hannay, C.; Ekman, A. M. L.; Hess, P.; Mahowald, N.; Collins, W.; Iacono, M. J.; Bretherton, C. S.; Flanner, M. G.; Mitchell, D.

    2011-12-01

    A modal aerosol module (MAM) has been developed for the Community Atmosphere Model version 5 (CAM5), the atmospheric component of the Community Earth System Model version 1 (CESM1). MAM is capable of simulating the aerosol size distribution and both internal and external mixing between aerosol components, treating numerous complicated aerosol processes and aerosol physical, chemical and optical properties in a physically based manner. Two MAM versions were developed: a more complete version with seven lognormal modes (MAM7), and a version with three lognormal modes (MAM3) for the purpose of long-term (decades to centuries) simulations. Major approximations in MAM3 include assuming immediate mixing of primary organic matter (POM) and black carbon (BC) with other aerosol components, merging of the MAM7 fine dust and fine sea salt modes into the accumulation mode, merging of the MAM7 coarse dust and coarse sea salt modes into the single coarse mode, and neglecting the explicit treatment of ammonia and ammonium cycles. Simulated sulfate and secondary organic aerosol (SOA) mass concentrations are remarkably similar between MAM3 and MAM7 as most (~90%) of these aerosol species are in the accumulation mode. Differences of POM and BC concentrations between MAM3 and MAM7 are also small (mostly within 10%) because of the assumed hygroscopic nature of POM, so that much of the freshly emitted POM and BC is wet-removed before mixing internally with soluble aerosol species. Sensitivity tests with the POM assumed to be hydrophobic and with slower aging increase the POM and BC concentrations, especially at high latitudes (by several times). The mineral dust global burden differs by 10% and sea salt burden by 30-40% between MAM3 and MAM7 mainly due to the different size ranges for dust and sea salt modes and different standard deviations of the log-normal size distribution for sea salt modes between MAM3 and MAM7. The model is able to qualitatively capture the observed geographical

  6. Aerosol First Indirect Effects on Non-Precipitating Low-Level Liquid Cloud Properties as Simulated by CAM5 at ARM Sites

    SciTech Connect

    Zhao, Chuanfeng; Klein, Stephen A.; Xie, Shaocheng; Liu, Xiaohong; Boyle, James; Zhang, Yuying

    2012-04-28

    We quantitatively examine the aerosol first indirect effects (FIE) for non-precipitating low-level single-layer liquid phase clouds simulated by the Community Atmospheric Model version 5 (CAM5) running in the weather forecast mode at three DOE Atmospheric Radiation Measurement (ARM) sites. The FIE is quantified in terms of a relative change in cloud droplet effective radius for a relative change in aerosol accumulation mode number concentration under conditions of fixed liquid water content (LWC). CAM5 simulates aerosol-cloud interactions reasonably well for this specific cloud type, and the simulated FIE is consistent with the long-term observations at the examined locations. The FIE in CAM5 generally decreases with LWC at coastal ARM sites, and is larger by using cloud condensation nuclei rather than aerosol accumulation mode number concentration as the choice of aerosol amount. However, it has no significant variations with location and has no systematic strong seasonal variations at examined ARM sites.

  7. Understanding the direct and indirect effects of Biomass Burning Aerosols over Southeast-East Asia by employing McRAS-AC in the GEOS-5 AGCM

    NASA Astrophysics Data System (ADS)

    Lee, D.; Oreopoulos, L.; Sud, Y. C.; Kim, K.; Lau, W. K.; Kang, I.

    2013-12-01

    Biomass burning (BB) aerosols can potentially be important players in the monsoon system since they may either slow down the hydrological cycle via surface dimming (Ramanathan et al., 2005), or strengthen it via atmospheric heating (the ';Elevated Heat Pump' hypothesis, Lau et al. 2006). Moreover previous studies have reported the possibility that aerosol interaction with cloud microphysics (indirect effect) may be operating in conjunction with the direct effect to bring about significant perturbations during the pre-monsoon season. In this study we focus on the massive BB aerosol production over Southeast Asia during this part of the year spring, which can be transported to southern China, and affect regional precipitation by direct/indirect effects on the early phase of the monsoon, as suggested by observations. For the investigation of combined aerosol effects, GCM experiments are designed using the GEOS-5 AGCM equipped with McRAS-AC double moment cloud microphysics, interactive GOCART aerosols model, advanced RRTMG radiative transfer package RRTMG with Monte Carlo Independent Column Approximation modes, and CFMIP Observation Simulator Package (COSP). Analysis of GEOS-5 integrations with and without biomass burning emission allows us to identify the responses of clouds and precipitation to aerosol rather than dynamics, and meteorological field. Furthermore, valuable addition would be the separation of the relative importance of direct versus indirect effects is examined in experiments where the by turning off aerosol direct effect is turned off. Ramanathan et al. 2005, Atmospheric brown clouds: Impacts on South Asian climate and hydrological cycle, PNAS Lau et al. 2006, Asian summer monsoon anomalies induced by aerosol direct forcing: the role of the Tibetan Plateau, Clim. Dyn.

  8. Observations of a substantial cloud-aerosol indirect effect during the 2014-2015 Bárðarbunga-Veiðivötn fissure eruption in Iceland

    NASA Astrophysics Data System (ADS)

    McCoy, Daniel T.; Hartmann, Dennis L.

    2015-12-01

    The Bárðarbunga-Veiðivötn fissure eruption lasted from 31 August 2014 to 28 February 2015, during which its sulfur emissions dwarfed anthropogenic emissions from Europe. This natural experiment offers an excellent opportunity to investigate the aerosol indirect effect and the effect of effusive volcanic eruptions on climate. During the eruption cloud droplet effective radius (re) over the region surrounding Iceland was at the lowest value in the 14 year Moderate Imaging Spectroradiometer data record during September and October 2014. The change in reflected solar radiation due to increased cloud reflectivity during September and October is estimated to exceed 2 W m-2 over the region surrounding Iceland, with increases of 1 W m-2 extending as far south as the Açores. The strength of the aerosol indirect effect diagnosed here reaffirms the ability of volcanic aerosols to affect cloud properties and ultimately the planetary albedo.

  9. Aerosol Indirect Forcing Dictated by Warm Low-Cloud

    NASA Astrophysics Data System (ADS)

    Christensen, M.; Chen, Y. C.; Stephens, G. L.

    2014-12-01

    Aerosol indirect forcing is one of the largest sources of uncertainty in estimating the extent of global warming. Increased aerosol levels can enhance the solar reflection from warm liquid clouds countering greenhouse gas warming. However, very little is actually known about the strength of the indirect effects for mixed-phase stratiform clouds as well as other cloud types such as cumulus, altocumulus, nimbostratus, deep convection, and cirrus. These mixed-phase cloud types are ubiquitous and typically overlooked in satellite estimates of the indirect forcing. In this study we assess the responses of each major cloud type to changes in aerosol loading and provide an estimate of their contribution to the global mean indirect forcing. Satellite data is collected from several co-located sensors in the A-train for the period starting in January of 2007 - 2010. Cloud layers are classified according to the 2B-CLDCLASS-LIDAR CloudSat product. Radiative fluxes are obtained from CERES (Clouds and the Earth's Radiant Energy System) and examined as a function of the aerosol loading obtained from MODIS (MODerate resolution Imaging Spectroradiometer) data. For low-level cloud regimes (e.g., stratus, stratocumulus, cumulus) we show that the longwave contribution to the net indirect effect is insignificant and dominated by changes in reflected shortwave radiation which also becomes insignificant as cloud top temperature decreases below 0°C. An increase in the aerosol loading in mixed-phase stratocumulus leads to more ice and precipitation that depletes cloud water and limits cloud brightening. For the more convective type clouds (e.g., altocumulus, nimbostratus, deep convection), increased aerosol loading can invigorate deep convection and promote deeper clouds with higher cloud albedo (cooling effect) and cloud tops that emit less longwave radiation to space (warming effect). As a consequence, the shortwave and longwave indirect radiative effects tend to cancel for the

  10. Constraining the Influence of Natural Variability to Improve Estimates of Global Aerosol Indirect Effects in a Nudged Version of the Community Atmosphere Model 5

    SciTech Connect

    Kooperman, G. J.; Pritchard, M. S.; Ghan, Steven J.; Wang, Minghuai; Somerville, Richard C.; Russell, Lynn

    2012-12-11

    Natural modes of variability on many timescales influence aerosol particle distributions and cloud properties such that isolating statistically significant differences in cloud radiative forcing due to anthropogenic aerosol perturbations (indirect effects) typically requires integrating over long simulations. For state-of-the-art global climate models (GCM), especially those in which embedded cloud-resolving models replace conventional statistical parameterizations (i.e. multi-scale modeling framework, MMF), the required long integrations can be prohibitively expensive. Here an alternative approach is explored, which implements Newtonian relaxation (nudging) to constrain simulations with both pre-industrial and present-day aerosol emissions toward identical meteorological conditions, thus reducing differences in natural variability and dampening feedback responses in order to isolate radiative forcing. Ten-year GCM simulations with nudging provide a more stable estimate of the global-annual mean aerosol indirect radiative forcing than do conventional free-running simulations. The estimates have mean values and 95% confidence intervals of -1.54 ± 0.02 W/m2 and -1.63 ± 0.17 W/m2 for nudged and free-running simulations, respectively. Nudging also substantially increases the fraction of the world’s area in which a statistically significant aerosol indirect effect can be detected (68% and 25% of the Earth's surface for nudged and free-running simulations, respectively). One-year MMF simulations with and without nudging provide global-annual mean aerosol indirect radiative forcing estimates of -0.80 W/m2 and -0.56 W/m2, respectively. The one-year nudged results compare well with previous estimates from three-year free-running simulations (-0.77 W/m2), which showed the aerosol-cloud relationship to be in better agreement with observations and high-resolution models than in the results obtained with conventional parameterizations.

  11. Aerosol indirect effect on warm clouds over South-East Atlantic, from co-located MODIS and CALIPSO observations

    NASA Astrophysics Data System (ADS)

    Costantino, L.; Bréon, F.-M.

    2012-06-01

    In this study, we provide a comprehensive analysis of aerosol interaction with warm boundary layer clouds, over South-East Atlantic. We use MODIS retrievals to derive statistical relationships between aerosol concentration and cloud properties, together with co-located CALIPSO estimates of cloud and aerosol layer altitudes. The latter are used to differentiate between cases of mixed and interacting cloud-aerosol layers from cases where the aerosol is located well-above the cloud top. This strategy allows, to a certain extent, to isolate real aerosol-induced effect from meteorology. Similar to previous studies, statistics clearly show that aerosol affects cloud microphysics, decreasing the Cloud Droplet Radius (CDR). The same data indicate a concomitant strong decrease in cloud Liquid Water Path (LWP), in evident contrast with the hypothesis of aerosol inhibition of precipitation (Albrecht, 1989). Because of this water loss, probably due to the entrainment of dry air at cloud top, Cloud Optical Thickness (COT) is found to be almost insensitive to changes in aerosol concentration. The analysis of MODIS-CALIPSO coincidences also evidenced an aerosol enhancement of low cloud cover. Surprising, the Cloud Fraction (CLF) response to aerosol invigoration is much stronger when (absorbing) particles are located above cloud top, than in cases of physical interaction, This result suggests a relevant aerosol radiative effect on low cloud occurrence. Heating the atmosphere above the inversion, absorbing particles above cloud top may decrease the vertical temperature gradient, increase the low tropospheric stability and provide favorable conditions for low cloud formation. We also focus on the impact of anthropogenic aerosols on precipitation, through the statistical analysis of CDR-COT co-variations. A COT value of 10 is found to be the threshold beyond which precipitation mostly forms, in both clean and polluted environments. For larger COT, polluted clouds showed evidence of

  12. Evaluation of Aerosol Indirect Radiative Forcing in MIRAGE

    SciTech Connect

    Ghan, Steven J.; Easter, Richard C.; Hudson, J D.; Breon, Francois

    2001-04-01

    We evaluate aerosol indirect radiative forcing simulated by the Model for Integrated Research on Atmospheric Global Exchanges (MIRAGE). Although explicit measurements of aerosol indirect radiative forcing do not exist, measurements of many of the links between aerosols and indirect radiative forcing are available and can be used for evaluation. These links include the cloud condensation nuclei concentration, the ratio of droplet number to aerosol number, the droplet number concentration, the column droplet number, the column cloud water, the droplet effective radius, the cloud optical depth, the correlation between cloud albedo and droplet effective radius, and the cloud radiative forcing. The CCN concentration simulated by MIRAGE agrees with measurements for supersaturations larger than 0.1%, but not for smaller supersaturations. Simulated droplet number concentrations are too low in most, but not all, locations with available measurements, even when normalized by aerosol number. MIRA GE correctly simulates the higher droplet numbers and smaller droplet sizes over continents and in the Northern Hemisphere. Biases in column cloud water, cloud optical depth, and shortwave cloud radiative forcing are evident in the Intertropical Convergence Zone and in the subtropical oceans. MIRAGE correctly simulates a negative correlation between cloud albedo and droplet size over remote oceans for cloud optical depths greater than 15 and a positive correlation for cloud optical depths less than 15, but fails to simulate a negative correlation over land.

  13. Evaluation of aerosol indirect radiative forcing in MIRAGE

    NASA Astrophysics Data System (ADS)

    Ghan, Steven; Easter, Richard; Hudson, James; BréOn, Francois-Marie

    2001-03-01

    We evaluate aerosol indirect radiative forcing simulated by the Model for Integrated Research on Atmospheric Global Exchange (MIRAGE). Although explicit measurements of aerosol indirect radiative forcing do not exist, measurements of many of the links between aerosols and indirect radiative forcing are available and can be used for evaluation. These links include the cloud condensation nuclei concentration, the ratio of droplet number to aerosol number, the droplet number concentration, the column droplet number, the column cloud water, the droplet effective radius, the cloud optical depth, the correlation between cloud albedo and droplet effective radius, and the cloud radiative forcing. The CCN concentration simulated by MIRAGE agrees with measurements for supersaturations larger than 0.1% but not for smaller supersaturations. Simulated droplet number concentrations are too low in most but not all locations with available measurements, even when normalized by aerosol number. MIRAGE correctly simulates the higher droplet numbers and smaller droplet sizes over continents and in the Northern Hemisphere. Biases in column cloud water, cloud optical depth, and shortwave cloud radiative forcing are evident in the Intertropical Convergence Zone and in the subtropical oceans. MIRAGE correctly simulates a negative correlation between cloud albedo and droplet size over remote oceans for cloud optical depths greater than 15 and a positive correlation for cloud optical depths less than 15 but fails to simulate a negative correlation over land.

  14. Describing the direct and indirect radiative effects of atmospheric aerosols over Europe by using coupled meteorology-chemistry simulations: a contribution from the AQMEII-Phase II exercise

    NASA Astrophysics Data System (ADS)

    Jimenez-Guerrero, Pedro; Balzarini, Alessandra; Baró, Rocío; Curci, Gabriele; Forkel, Renate; Hirtl, Marcus; Honzak, Luka; Langer, Matthias; Pérez, Juan L.; Pirovano, Guido; San José, Roberto; Tuccella, Paolo; Werhahn, Johannes; Zabkar, Rahela

    2014-05-01

    The study of the response of the aerosol levels in the atmosphere to a changing climate and how this affects the radiative budget of the Earth (direct, semi-direct and indirect effects) is an essential topic to build confidence on climate science, since these feedbacks involve the largest uncertainties nowadays. Air quality-climate interactions (AQCI) are, therefore, a key, but uncertain contributor to the anthropogenic forcing that remains poorly understood. To build confidence in the AQCI studies, regional-scale integrated meteorology-atmospheric chemistry models (i.e., models with on-line chemistry) that include detailed treatment of aerosol life cycle and aerosol impacts on radiation (direct effects) and clouds (indirect effects) are in demand. In this context, the main objective of this contribution is the study and definition of the uncertainties in the climate-chemistry-aerosol-cloud-radiation system associated to the direct radiative forcing and the indirect effect caused by aerosols over Europe, using an ensemble of fully-coupled meteorology-chemistry model simulations with the WRF-Chem model run under the umbrella of AQMEII-Phase 2 international initiative. Simulations were performed for Europe for the entire year 2010. According to the common simulation strategy, the year was simulated as a sequence of 2-day time slices. For better comparability, the seven groups applied the same grid spacing of 23 km and shared common processing of initial and boundary conditions as well as anthropogenic and fire emissions. With exception of a simulation with different cloud microphysics, identical physics options were chosen while the chemistry options were varied. Two model set-ups will be considered here: one sub-ensemble of simulations not taking into account any aerosol feedbacks (the baseline case) and another sub-ensemble of simulations which differs from the former by the inclusion of aerosol-radiation feedback. The existing differences for meteorological

  15. Aerosols-cloud-climate -interactions in the Norwegian Earth System Model (NorESM). Importance of biogenic particles for cloud properties and anthropogenic indirect effect.

    NASA Astrophysics Data System (ADS)

    Seland, Ø.; Iversen, T.; Kirkevâg, A.

    2012-04-01

    According to the 4th assessment report of IPCC, major sources of uncertainty in anthropogenic climate change projections are inaccurate model description and weak knowledge of aerosols and their interactions with radiation and clouds, as well as the cloud feedback to radiative forcing. One important aspect of the associated uncertainty is the natural atmosphere. Anthropogenic climate change is an increment caused by anthropogenic emissions relative to the properties of the climate system untouched by man. This is crucial for the direct and indirect effects of aerosols, since the amount, size and physical properties of natural background particles strongly influence the same properties of the anthropogenic aerosol components. In many climate models where CDNC is calculated explicitly, CDNC is constrained by prescribing a lower bound below which calculated values are not allowed. This is done in order to keep the aerosol in-direct effect within estimated values. The rationale for using such a lower bound is to keep the aerosol radiative forcing constrained by the forcing of green-house gases and 20th century climate.We hypothesize this lower bound can be removed or made less strict by including aerosols of biogenic origin. We will present results and sensitivity studies from simulations with the NorESM where we have added contributions from organic carbon of natural origin both from vegetation and oceanic sources. By including aerosols of biogenic origin we obtain close to the median indirect radiative forcing reported by IPCC AR4, as well as reproducing the temperature increase in the 20th century. NorESM is based on the Earth system model CCSM4.0 from NCAR, but is using CAM4-Oslo instead of CAM4 as atmosphere model and an updated version of MICOM from the Bergen Climate Model (BCM) instead of the ocean model POP2. The aerosol module includes sea-salt, dust, sulphate, black carbon (BC) and particulate organic matter (OM). Primary aerosol size-distributions are

  16. Cloud-resolving modelling of aerosol indirect effects in idealised radiative-convective equilibrium with interactive and fixed sea surface temperature

    NASA Astrophysics Data System (ADS)

    Khairoutdinov, M. F.; Yang, C.-E.

    2013-04-01

    The study attempts to evaluate the aerosol indirect effects over tropical oceans in regions of deep convection applying a three-dimensional cloud-resolving model run over a doubly-periodic domain. The Tropics are modelled using a radiative-convective equilibrium idealisation when the radiation, turbulence, cloud microphysics and surface fluxes are explicitly represented while the effects of large-scale circulation are ignored. The aerosol effects are modelled by varying the number concentration of cloud condensation nuclei (CCN) at 1% supersaturation, which serves as a proxy for the aerosol amount in the environment, over a wide range, from pristine maritime (50 cm-3) to polluted (1000 cm-3) conditions. No direct effects of aerosol on radiation are included. Two sets of simulations have been run: fixed (non-interactive) sea surface temperature (SST) and interactive SST as predicted by a simple slab-ocean model responding to the surface radiative fluxes and surface enthalpy flux. Both sets of experiments agree on the tendency of increased aerosol concentrations to make the shortwave cloud forcing more negative and reduce the longwave cloud forcing in response to increasing CCN concentration. These, in turn, tend to cool the SST in interactive-SST case. It is interesting that the absolute change of the SST and most other bulk quantities depends only on relative change of CCN concentration; that is, same SST change can be the result of doubling CCN concentration regardless of clean or polluted conditions. It is found that the 10-fold increase of CCN concentration can cool the SST by as much as 1.5 K. This is quite comparable to 2.1-2.3 K SST warming obtained in a simulation for clean maritime conditions, but doubled CO2 concentration. Assuming the aerosol concentration has increased from preindustrial time by 30%, the radiative forcing due to indirect aerosol effects is estimated to be -0.3 W m-2. It is found that the indirect aerosol effect is dominated by the first

  17. Satellite methods underestimate indirect climate forcing by aerosols

    PubMed Central

    Penner, Joyce E.; Xu, Li; Wang, Minghuai

    2011-01-01

    Satellite-based estimates of the aerosol indirect effect (AIE) are consistently smaller than the estimates from global aerosol models, and, partly as a result of these differences, the assessment of this climate forcing includes large uncertainties. Satellite estimates typically use the present-day (PD) relationship between observed cloud drop number concentrations (Nc) and aerosol optical depths (AODs) to determine the preindustrial (PI) values of Nc. These values are then used to determine the PD and PI cloud albedos and, thus, the effect of anthropogenic aerosols on top of the atmosphere radiative fluxes. Here, we use a model with realistic aerosol and cloud processes to show that empirical relationships for ln(Nc) versus ln(AOD) derived from PD results do not represent the atmospheric perturbation caused by the addition of anthropogenic aerosols to the preindustrial atmosphere. As a result, the model estimates based on satellite methods of the AIE are between a factor of 3 to more than a factor of 6 smaller than model estimates based on actual PD and PI values for Nc. Using ln(Nc) versus ln(AI) (Aerosol Index, or the optical depth times angstrom exponent) to estimate preindustrial values for Nc provides estimates for Nc and forcing that are closer to the values predicted by the model. Nevertheless, the AIE using ln(Nc) versus ln(AI) may be substantially incorrect on a regional basis and may underestimate or overestimate the global average forcing by 25 to 35%. PMID:21808047

  18. Aerosol Direct, Indirect, Semidirect, and Surface Albedo Effects from Sector Contributions Based on the IPCC AR5 Emissions for Preindustrial and Present-day Conditions

    NASA Technical Reports Server (NTRS)

    Bauer, Susanne E.; Menon, Surabi

    2012-01-01

    The anthropogenic increase in aerosol concentrations since preindustrial times and its net cooling effect on the atmosphere is thought to mask some of the greenhouse gas-induced warming. Although the overall effect of aerosols on solar radiation and clouds is most certainly negative, some individual forcing agents and feedbacks have positive forcing effects. Recent studies have tried to identify some of those positive forcing agents and their individual emission sectors, with the hope that mitigation policies could be developed to target those emitters. Understanding the net effect of multisource emitting sectors and the involved cloud feedbacks is very challenging, and this paper will clarify forcing and feedback effects by separating direct, indirect, semidirect and surface albedo effects due to aerosols. To this end, we apply the Goddard Institute for Space Studies climate model including detailed aerosol microphysics to examine aerosol impacts on climate by isolating single emission sector contributions as given by the Coupled Model Intercomparison Project Phase 5 (CMIP5) emission data sets developed for Intergovernmental Panel on Climate Change (IPCC) AR5. For the modeled past 150 years, using the climate model and emissions from preindustrial times to present-day, the total global annual mean aerosol radiative forcing is -0.6 W/m(exp 2), with the largest contribution from the direct effect (-0.5 W/m(exp 2)). Aerosol-induced changes on cloud cover often depends on cloud type and geographical region. The indirect (includes only the cloud albedo effect with -0.17 W/m(exp 2)) and semidirect effects (-0.10 W/m(exp 2)) can be isolated on a regional scale, and they often have opposing forcing effects, leading to overall small forcing effects on a global scale. Although the surface albedo effects from aerosols are small (0.016 W/m(exp 2)), triggered feedbacks on top of the atmosphere (TOA) radiative forcing can be 10 times larger. Our results point out that each

  19. Aerosol direct, indirect, semidirect, and surface albedo effects from sector contributions based on the IPCC AR5 emissions for preindustrial and present-day conditions

    NASA Astrophysics Data System (ADS)

    Bauer, Susanne E.; Menon, Surabi

    2012-01-01

    The anthropogenic increase in aerosol concentrations since preindustrial times and its net cooling effect on the atmosphere is thought to mask some of the greenhouse gas-induced warming. Although the overall effect of aerosols on solar radiation and clouds is most certainly negative, some individual forcing agents and feedbacks have positive forcing effects. Recent studies have tried to identify some of those positive forcing agents and their individual emission sectors, with the hope that mitigation policies could be developed to target those emitters. Understanding the net effect of multisource emitting sectors and the involved cloud feedbacks is very challenging, and this paper will clarify forcing and feedback effects by separating direct, indirect, semidirect and surface albedo effects due to aerosols. To this end, we apply the Goddard Institute for Space Studies climate model including detailed aerosol microphysics to examine aerosol impacts on climate by isolating single emission sector contributions as given by the Coupled Model Intercomparison Project Phase 5 (CMIP5) emission data sets developed for Intergovernmental Panel on Climate Change (IPCC) AR5. For the modeled past 150 years, using the climate model and emissions from preindustrial times to present-day, the total global annual mean aerosol radiative forcing is -0.6 W/m2, with the largest contribution from the direct effect (-0.5 W/m2). Aerosol-induced changes on cloud cover often depends on cloud type and geographical region. The indirect (includes only the cloud albedo effect with -0.17 W/m2) and semidirect effects (-0.10 W/m2) can be isolated on a regional scale, and they often have opposing forcing effects, leading to overall small forcing effects on a global scale. Although the surface albedo effects from aerosols are small (0.016 W/m2), triggered feedbacks on top of the atmosphere (TOA) radiative forcing can be 10 times larger. Our results point out that each emission sector has varying

  20. Quantifying the Uncertainties of Aerosol Indirect Effects and Impacts on Decadal-Scale Climate Variability in NCAR CAM5 and CESM1

    SciTech Connect

    Park, Sungsu

    2014-12-12

    The main goal of this project is to systematically quantify the major uncertainties of aerosol indirect effects due to the treatment of moist turbulent processes that drive aerosol activation, cloud macrophysics and microphysics in response to anthropogenic aerosol perturbations using the CAM5/CESM1. To achieve this goal, the P.I. hired a postdoctoral research scientist (Dr. Anna Fitch) who started her work from the Nov.1st.2012. In order to achieve the project goal, the first task that the Postdoc. and the P.I. did was to quantify the role of subgrid vertical velocity variance on the activation and nucleation of cloud liquid droplets and ice crystals and its impact on the aerosol indirect effect in CAM5. First, we analyzed various LES cases (from dry stable to cloud-topped PBL) to check whether this isotropic turbulence assumption used in CAM5 is really valid. It turned out that this isotropic turbulence assumption is not universally valid. Consequently, from the analysis of LES, we derived an empirical formulation relaxing the isotropic turbulence assumption used for the CAM5 aerosol activation and ice nucleation, and implemented the empirical formulation into CAM5/CESM1, and tested in the single-column and global simulation modes, and examined how it changed aerosol indirect effects in the CAM5/CESM1. These results were reported in the poster section in the 18th Annual CESM workshop held in Breckenridge, CO during Jun.17-20.2013. While we derived an empirical formulation from the analysis of couple of LES from the first task, the general applicability of that empirical formulation was questionable, because it was obtained from the limited number of LES simulations. The second task we did was to derive a more fundamental analytical formulation relating vertical velocity variance to TKE using other information starting from basic physical principles. This was a somewhat challenging subject, but if this could be done in a successful way, it could be directly

  1. Indirect and Semi-Direct Aerosol Campaign: The Impact of Arctic Aerosols on Clouds

    SciTech Connect

    McFarquhar, Greg; Ghan, Steven J.; Verlinde, J.; Korolev, Alexei; Strapp, J. Walter; Schmid, Beat; Tomlinson, Jason M.; Wolde, Mengistu; Brooks, Sarah D.; Cziczo, Daniel J.; Dubey, Manvendra K.; Fan, Jiwen; Flynn, Connor J.; Gultepe, Ismail; Hubbe, John M.; Gilles, Mary K.; Laskin, Alexander; Lawson, Paul; Leaitch, W. R.; Liu, Peter S.; Liu, Xiaohong; Lubin, Dan; Mazzoleni, Claudio; Macdonald, A. M.; Moffet, Ryan C.; Morrison, H.; Ovchinnikov, Mikhail; Shupe, Matthew D.; Turner, David D.; Xie, Shaocheng; Zelenyuk, Alla; Bae, Kenny; Freer, Matthew; Glen, Andrew

    2011-02-01

    A comprehensive dataset of microphysical and radiative properties of aerosols and clouds in the arctic boundary layer in the vicinity of Barrow, Alaska was collected in April 2008 during the Indirect and Semi-Direct Aerosol Campaign (ISDAC) sponsored by the Department of Energy Atmospheric Radiation Measurement (ARM) and Atmospheric Science Programs. The primary aim of ISDAC was to examine indirect effects of aerosols on clouds that contain both liquid and ice water. The experiment utilized the ARM permanent observational facilities at the North Slope of Alaska (NSA) in Barrow. These include a cloud radar, a polarized micropulse lidar, and an atmospheric emitted radiance interferometer as well as instruments specially deployed for ISDAC measuring aerosol, ice fog, precipitation and spectral shortwave radiation. The National Research Council of Canada Convair-580 flew 27 sorties during ISDAC, collecting data using an unprecedented 42 cloud and aerosol instruments for more than 100 hours on 12 different days. Data were obtained above, below and within single-layer stratus on 8 April and 26 April 2008. These data enable a process-oriented understanding of how aerosols affect the microphysical and radiative properties of arctic clouds influenced by different surface conditions. Observations acquired on a heavily polluted day, 19 April 2008, are enhancing this understanding. Data acquired in cirrus on transit flights between Fairbanks and Barrow are improving our understanding of the performance of cloud probes in ice. Ultimately the ISDAC data will be used to improve the representation of cloud and aerosol processes in models covering a variety of spatial and temporal scales, and to determine the extent to which long-term surface-based measurements can provide retrievals of aerosols, clouds, precipitation and radiative heating in the Arctic.

  2. Indirect and semi-direct aerosol campaign: The impact of Arctic aerosols on clouds

    DOE PAGESBeta

    McFarquhar, Greg M.; Ghan, Steven; Verlinde, Johannes; Korolev, Alexei; Strapp, J. Walter; Schmid, Beat; Tomlinson, Jason M.; Wolde, Menqistu; Brooks, Sarah D.; Cziczo, Dan; et al

    2011-02-01

    A comprehensive dataset of microphysical and radiative properties of aerosols and clouds in the boundary layer in the vicinity of Barrow, Alaska, was collected in April 2008 during the Indirect and Semi-Direct Aerosol Campaign (ISDAC). ISDAC's primary aim was to examine the effects of aerosols, including those generated by Asian wildfires, on clouds that contain both liquid and ice. ISDAC utilized the Atmospheric Radiation Measurement Pro- gram's permanent observational facilities at Barrow and specially deployed instruments measuring aerosol, ice fog, precipitation, and radiation. The National Research Council of Canada Convair-580 flew 27 sorties and collected data using an unprecedented 41more » stateof- the-art cloud and aerosol instruments for more than 100 h on 12 different days. Aerosol compositions, including fresh and processed sea salt, biomassburning particles, organics, and sulfates mixed with organics, varied between flights. Observations in a dense arctic haze on 19 April and above, within, and below the single-layer stratocumulus on 8 and 26 April are enabling a process-oriented understanding of how aerosols affect arctic clouds. Inhomogeneities in reflectivity, a close coupling of upward and downward Doppler motion, and a nearly constant ice profile in the single-layer stratocumulus suggests that vertical mixing is responsible for its longevity observed during ISDAC. Data acquired in cirrus on flights between Barrow and Fairbanks, Alaska, are improving the understanding of the performance of cloud probes in ice. Furthermore, ISDAC data will improve the representation of cloud and aerosol processes in models covering a variety of spatial and temporal scales, and determine the extent to which surface measurements can provide retrievals of aerosols, clouds, precipitation, and radiative heating.« less

  3. Indirect and semi-direct aerosol campaign: The impact of Arctic aerosols on clouds

    SciTech Connect

    McFarquhar, Greg M.; Ghan, Steven; Verlinde, Johannes; Korolev, Alexei; Strapp, J. Walter; Schmid, Beat; Tomlinson, Jason M.; Wolde, Menqistu; Brooks, Sarah D.; Cziczo, Dan; Dubey, Manvendra K.; Fan, Jiwen; Flynn, Connor; Gultepe, Ismail; Hubbe, John; Gilles, Mary K.; Laskin, Alexander; Lawson, Paul; Leaitch, W. Richard; Liu, Peter; Liu, Xiaohong; Lubin, Dan; Mazzoleni, Claudio; Macdonald, Ann -Marie; Moffet, Ryan C.; Morrison, Hugh; Ovchinnikov, Mikhail; Ronfeld, Debbie; Shupe, Matthew D.; Xie, Shaocheng; Zelenyuk, Alla; Bae, Kenny; Freer, Matt; Glen, Andrew

    2011-02-01

    A comprehensive dataset of microphysical and radiative properties of aerosols and clouds in the boundary layer in the vicinity of Barrow, Alaska, was collected in April 2008 during the Indirect and Semi-Direct Aerosol Campaign (ISDAC). ISDAC's primary aim was to examine the effects of aerosols, including those generated by Asian wildfires, on clouds that contain both liquid and ice. ISDAC utilized the Atmospheric Radiation Measurement Pro- gram's permanent observational facilities at Barrow and specially deployed instruments measuring aerosol, ice fog, precipitation, and radiation. The National Research Council of Canada Convair-580 flew 27 sorties and collected data using an unprecedented 41 stateof- the-art cloud and aerosol instruments for more than 100 h on 12 different days. Aerosol compositions, including fresh and processed sea salt, biomassburning particles, organics, and sulfates mixed with organics, varied between flights. Observations in a dense arctic haze on 19 April and above, within, and below the single-layer stratocumulus on 8 and 26 April are enabling a process-oriented understanding of how aerosols affect arctic clouds. Inhomogeneities in reflectivity, a close coupling of upward and downward Doppler motion, and a nearly constant ice profile in the single-layer stratocumulus suggests that vertical mixing is responsible for its longevity observed during ISDAC. Data acquired in cirrus on flights between Barrow and Fairbanks, Alaska, are improving the understanding of the performance of cloud probes in ice. Furthermore, ISDAC data will improve the representation of cloud and aerosol processes in models covering a variety of spatial and temporal scales, and determine the extent to which surface measurements can provide retrievals of aerosols, clouds, precipitation, and radiative heating.

  4. Limits to the Indirect Aerosol Forcing in Stratocumulus

    NASA Technical Reports Server (NTRS)

    Ackerman, Andrew; Toon, O.; Stevens, D.; Coakley, J., Jr.

    2003-01-01

    The indirect radiative forcing of aerosols is poorly constrained by the observational data underlying the simple cloud parameterizations in GCMs. signal of cloud response to increased aerosol concentrations from meteorological noise. Recent satellite observations indicate a significant decrease of cloud water in ship tracks, in contrast to an ensemble of in situ measurements showing no average change in cloud water relative to the surrounding clouds. Both results contradict the expectation of cloud water increasing in polluted clouds. We find through large-eddy simulations of stratocumulus that the trend in the satellite data is likely an artifact of sampling only overcast clouds. The simulations instead show cloud cover increasing with droplet concentrations. The simulations also show that increases in cloud water from suppressing drizzle by increased droplet concentrations are favored at night or at extremely low droplet concentrations. At typical droplet concentrations we find that the Twomey effect on cloud albedo is amplified very little by the secondary indirect effect of drizzle suppression, largely because the absorption of solar radiation by cloud water reduces boundary-layer mixing in the daytime and thereby restricts any possible increase in cloud water from drizzle suppression. The cloud and boundary layer respond to radiative heating variations on a time scale of hours, and on longer time scales respond to imbalances between large-scale horizontal advection and the entrainment of inversion air. We analyze the co-varying response of cloud water, cloud thickness, width of droplet size distributions, and dispersion of the optical depth, as well as the overall response of cloud albedo, to changes in droplet concentrations. We also dissect the underlying physical mechanisms through sensitivity studies. Ship tracks represent an ideal natural laboratory to extricate the

  5. Final Report for “Simulating the Arctic Winter Longwave Indirect Effects. A New Parameterization for Frost Flower Aerosol Salt Emissions” (DESC0006679) for 9/15/2011 through 9/14/2015

    SciTech Connect

    Russell, Lynn M.; Somerville, Richard C.J.; Burrows, Susannah; Rasch, Phil

    2015-12-12

    Description of the Project: This project has improved the aerosol formulation in a global climate model by using innovative new field and laboratory observations to develop and implement a novel wind-driven sea ice aerosol flux parameterization. This work fills a critical gap in the understanding of clouds, aerosol, and radiation in polar regions by addressing one of the largest missing particle sources in aerosol-climate modeling. Recent measurements of Arctic organic and inorganic aerosol indicate that the largest source of natural aerosol during the Arctic winter is emitted from crystal structures, known as frost flowers, formed on a newly frozen sea ice surface [Shaw et al., 2010]. We have implemented the new parameterization in an updated climate model making it the first capable of investigating how polar natural aerosol-cloud indirect effects relate to this important and previously unrecognized sea ice source. The parameterization is constrained by Arctic ARM in situ cloud and radiation data. The modified climate model has been used to quantify the potential pan-Arctic radiative forcing and aerosol indirect effects due to this missing source. This research supported the work of one postdoc (Li Xu) for two years and contributed to the training and research of an undergraduate student. This research allowed us to establish a collaboration between SIO and PNNL in order to contribute the frost flower parameterization to the new ACME model. One peer-reviewed publications has already resulted from this work, and a manuscript for a second publication has been completed. Additional publications from the PNNL collaboration are expected to follow.

  6. Aerosol indirect effect on the grid-scale clouds in the two-way coupled WRF–CMAQ: model description, development, evaluation and regional analysis

    SciTech Connect

    Yu, S.; Mathur, R.; Pleim, J.; Wong, D.; Gilliam, R.; Alapaty, K.; Zhao, C.; Liu, X.

    2014-01-01

    This study implemented first, second and glaciation aerosol indirect effects (AIE) on resolved clouds in the two-way coupled Weather Research and Forecasting Community Multiscale Air Quality (WRF–CMAQ) modeling system by including parameterizations for both cloud drop and ice number concentrations on the basis of CMAQ-predicted aerosol distributions and WRF meteorological conditions. The performance of the newly developed WRF–CMAQ model, with alternate Community Atmospheric Model (CAM) and Rapid Radiative Transfer Model for GCMs (RRTMG) radiation schemes, was evaluated with observations from the Clouds and the See http://ceres.larc.nasa.gov/. Earth's Radiant Energy System (CERES) satellite and surface monitoring networks (AQS, IMPROVE, CASTNET, STN, and PRISM) over the continental US (CONUS) (12 km resolution) and eastern Texas (4 km resolution) during August and September of 2006. The results at the Air Quality System (AQS) surface sites show that in August, the normalized mean bias (NMB) values for PM2.5 over the eastern US (EUS) and the western US (WUS) are 5.3% (-0.1%) and 0.4% (-5.2%) for WRF–CMAQ/CAM (WRF–CMAQ/RRTMG), respectively. The evaluation of PM2.5 chemical composition reveals that in August, WRF–CMAQ/CAM (WRF–CMAQ/RRTMG) consistently underestimated the observed SO42- by -23.0% (-27.7%), -12.5% (-18.9%) and -7.9% (-14.8%) over the EUS at the Clean Air Status Trends Network (CASTNET), Interagency Monitoring of Protected Visual Environments (IMPROVE) and Speciated Trends Network (STN) sites, respectively. Both configurations (WRF–CMAQ/CAM, WRF–CMAQ/RRTMG) overestimated the observed mean organic carbon (OC), elemental carbon (EC) and and total carbon (TC) concentrations over the EUS in August at the IMPROVE sites. Both configurations generally underestimated the cloud field (shortwave cloud forcing, SWCF) over the CONUS in August due to the

  7. Aerosol indirect effect on the grid-scale clouds in the two-way coupled WRF-CMAQ: model description, development, evaluation and regional analysis

    NASA Astrophysics Data System (ADS)

    Yu, S.; Mathur, R.; Pleim, J.; Wong, D.; Gilliam, R.; Alapaty, K.; Zhao, C.; Liu, X.

    2014-10-01

    This study implemented first, second and glaciation aerosol indirect effects (AIE) on resolved clouds in the two-way coupled Weather Research and Forecasting Community Multiscale Air Quality (WRF-CMAQ) modeling system by including parameterizations for both cloud drop and ice number concentrations on the basis of CMAQ-predicted aerosol distributions and WRF meteorological conditions. The performance of the newly developed WRF-CMAQ model, with alternate Community Atmospheric Model (CAM) and Rapid Radiative Transfer Model for GCMs (RRTMG) radiation schemes, was evaluated with observations from the Clouds and the See http://ceres.larc.nasa.gov/. Earth's Radiant Energy System (CERES) satellite and surface monitoring networks (AQS, IMPROVE, CASTNET, STN, and PRISM) over the continental US (CONUS) (12 km resolution) and eastern Texas (4 km resolution) during August and September of 2006. The results at the Air Quality System (AQS) surface sites show that in August, the normalized mean bias (NMB) values for PM2.5 over the eastern US (EUS) and the western US (WUS) are 5.3% (-0.1%) and 0.4% (-5.2%) for WRF-CMAQ/CAM (WRF-CMAQ/RRTMG), respectively. The evaluation of PM2.5 chemical composition reveals that in August, WRF-CMAQ/CAM (WRF-CMAQ/RRTMG) consistently underestimated the observed SO42- by -23.0% (-27.7%), -12.5% (-18.9%) and -7.9% (-14.8%) over the EUS at the Clean Air Status Trends Network (CASTNET), Interagency Monitoring of Protected Visual Environments (IMPROVE) and Speciated Trends Network (STN) sites, respectively. Both configurations (WRF-CMAQ/CAM, WRF-CMAQ/RRTMG) overestimated the observed mean organic carbon (OC), elemental carbon (EC) and and total carbon (TC) concentrations over the EUS in August at the IMPROVE sites. Both configurations generally underestimated the cloud field (shortwave cloud forcing, SWCF) over the CONUS in August due to the fact that the AIE on the subgrid convective clouds was not

  8. Evaluating The Indirect Effect of Cirrus Clouds

    NASA Astrophysics Data System (ADS)

    Dobbie, S.; Jonas, P. R.

    What effect would an increase in nucleating aerosols have on the radiative and cloud properties? What error would be incurred by evaluating the indirect effect by taking an evolved cloud and fixing the integrated water content and vary the number of ice crystals? These questions will be addressed in this work. We will use the UK LES cloud resolving model to perform a sensitivity study for cirrus clouds to the indirect effect, and will evaluate approximate methods in the process. In this work, we will initialize the base (no increase of aerosol) cirrus clouds so that the double moment scheme is constrained to agree with observations through the ef- fective radius. Effective radius is calculated using the local concentration and the ice water content. We then perform a sensitivity experiment to investigate the dependence of the average IWC, effective size, and radiative properties (including heating rates) to variations in the nucleation rate. Conclusions will be draw as to the possible ef- fect of changes in aerosol amounts on cirrus. We will determine how sensitive the cloud and radiative properties are to various aerosol increases. We will also discuss the applicability of the Meyer et al. (1992) nucleation formulae for our simulations. It is important to stress that in this work we only change the nucleation rate for the newly forming cloud. By doing this, we are not fixing the total water content and redistributing the water amongst increased ice crystals. We increase the number of aerosols available to be nucleated and allow the model to evolve the size distributions. In this way, there is competition for the water vapour, the ice particles are evolved dynamically with different fall speeds, the conversion rates to other hydrometers (such as aggregates) are affected, and the heating rates are different due to the different size distributions that evolve. We will look at how the water content, the distribution of water, and the radiative properties are affected

  9. Toward a Minimal Representation of Aerosols in Climate Models: Comparative Decomposition of Aerosol Direct, Semidirect, and Indirect Radiative Forcing

    SciTech Connect

    Ghan, Steven J.; Liu, Xiaohong; Easter, Richard C.; Zaveri, Rahul A.; Rasch, Philip J.; Yoon, Jin-Ho; Eaton, Brian

    2012-10-01

    The authors have decomposed the anthropogenic aerosol radiative forcing into direct contributions from each aerosol species to the planetary energy balance through absorption and scattering of solar radiation, indirect effects of anthropogenic aerosol on solar and infrared radiation through droplet and crystal nucleation on aerosol, and semidirect effects through the influence of solar absorption on the distribution of clouds. A three-mode representation of the aerosol in version 5.1 of the Community Atmosphere Model (CAM5.1) yields global annual mean radiative forcing estimates for each of these forcing mechanisms that are within 0.1 W m–2 of estimates using a more complex seven-mode representation that distinguishes between fresh and aged black carbon and primary organic matter. Simulating fresh black carbon particles separately from internally mixed accumulation mode particles is found to be important only near fossil fuel sources. In addition to the usual large indirect effect on solar radiation, this study finds an unexpectedly large positive longwave indirect effect (because of enhanced cirrus produced by homogenous nucleation of ice crystals on anthropogenic sulfate), small shortwave and longwave semidirect effects, and a small direct effect (because of cancelation and interactions of direct effects of black carbon and sulfate). Differences between the threemode and seven-mode versions are significantly larger (up to 0.2 W m–2) when the hygroscopicity of primary organic matter is decreased from 0.1 to 0 and transfer of the primary carbonaceous aerosol to the accumulation mode in the seven-mode version requires more hygroscopic material coating the primary particles. Radiative forcing by cloudborne anthropogenic black carbon is only 20.07 W m–2.

  10. Science Overview Document Indirect and Semi-Direct Aerosol Campaign (ISDAC) April 2008

    SciTech Connect

    SJ Ghan; B Schmid; JM Hubbe; CJ Flynn; A Laskin; AA Zelenyuk; DJ Czizco; CN Long; G McFarquhar; J Verlinde; J Harrington; JW Strapp; P Liu; A Korolev; A McDonald; M Wolde; A Fridlind; T Garrett; G Mace; G Kok; S Brooks; D Collins; D Lubin; P Lawson; M Dubey; C Mazzoleni; M Shupe; S Xie; DD Turner; Q Min; EJ Mlawer; D Mitchell

    2007-11-01

    The ARM Climate Research Facility’s (ACRF) Aerial Vehicle Program (AVP) will deploy an intensive cloud and aerosol observing system to the ARM North Slope of Alaska (NSA) locale for a five week Indirect and Semi-Direct Aerosol Campaign (ISDAC) during period 29 March through 30 April 2008. The deployment period is within the International Polar Year, thus contributing to and benefiting from the many ancillary observing systems collecting data synergistically. We will deploy the Canadian National Research Council Convair 580 aircraft to measure temperature, humidity, total particle number, aerosol size distribution, single particle composition, concentrations of cloud condensation nuclei and ice nuclei, optical scattering and absorption, updraft velocity, cloud liquid water and ice contents, cloud droplet and crystal size distributions, cloud particle shape, and cloud extinction. In addition to these aircraft measurements, ISDAC will deploy two instruments at the ARM site in Barrow: a spectroradiometer to retrieve cloud optical depth and effective radius, and a tandem differential mobility analyzer to measure the aerosol size distribution and hygroscopicity. By using many of the same instruments used during Mixed-Phase Arctic Cloud Experiment (M-PACE), conducted in October 2004, we will be able to contrast the arctic aerosol and cloud properties during the fall and spring transitions. The aerosol measurements can be used in cloud models driven by objectively analyzed boundary conditions to test whether the cloud models can simulate the aerosol influence on the clouds. The influence of aerosol and boundary conditions on the simulated clouds can be separated by running the cloud models with all four combinations of M-PACE and ISDAC aerosol and boundary conditions: M-PACE aerosol and boundary conditions, M-PACE aerosol and ISDAC boundary conditions, ISDAC aerosol and M-PACE boundary conditions, and ISDAC aerosol and boundary conditions. ISDAC and M-PACE boundary

  11. Sensitivity of Homogeneous Freezing to Aerosol Perturbation and Implication for Aerosol Indirect Forcing through Cirrus Clouds

    NASA Astrophysics Data System (ADS)

    Liu, X.; Shi, X.; Zhang, K.

    2014-12-01

    The susceptibility of cloud properties to aerosol perturbation is critical for the aerosol-cloud-climate interactions. Burdens of aerosols such as sulfate have substantially increased from preindustrial time to present-day. However, it is still not clear whether the number of ice crystals (Ni) resulting from homogeneous freezing of sulfate solution droplets is sensitive to the change in sulfate number concentration (Na) in the upper troposphere. Some cloud parcel modeling studies show that Ni is insensitive to Na (Kärcher and Lohmann, 2002; Kay and Wood, 2008), while others show moderate sensitivity of Ni to Na (Liu and Penner, 2005; Barahona and Nenes, 2008). The poorly understood cirrus cloud processes lead to large uncertainties in ice nucleation parameterizations in global climate models, with implications for climate change studies. In this study, we examine the sensitivity of Ni from homogeneous freezing to Na with a cloud parcel model running at different input aerosol and cloud conditions and under different model assumptions. By these sensitivity tests, we are able to reconcile the contrasting results from previous studies on the sensitivity of Ni to Na. Furthermore, the implications of these results on aerosol indirect forcing through ice clouds are quantified by comparing three ice nucleation parameterizations (Liu and Penner, 2005; Barahona and Nenes, 2008; Kärcher and Lohmann, 2002) implemented in the Community Atmospheric Model version 5 (CAM5). The global and annual mean longwave aerosol indirect forcing through cirrus clouds ranges from -0.03 (Kärcher and Lohmann, 2002) to ~0.3 W m-2 (Liu and Penner, 2005; Barahona and Nenes, 2008). Future studies should quantify the occurrence frequency of homogeneous nucleation in the upper troposphere and the relative contribution between homogeneous versus heterogeneous freezing to Ni in cirrus clouds to further narrow down the aerosol indirect forcing through cirrus clouds.

  12. The Impact of humidity above stratiform clouds on indirect aerosol climate forcing

    SciTech Connect

    Ackerman, A S; Kirkpatrick, M P; Stevens, D E; Toon, O B

    2004-12-20

    Some of the global warming effect of anthropogenic greenhouse gases is offset by increased solar reflection from clouds with smaller droplets that form on increased numbers of cloud condensation nuclei in polluted air. The global magnitude of the resulting indirect aerosol climate forcing is estimated to be comparable (and opposed) to the anthropogenic carbon dioxide forcing, but estimates are highly uncertain because of complexities in characterizing the physical process that determine global aerosol and cloud populations and their interactions. Beyond reflecting sunlight more effectively, smaller droplets are less efficient at producing precipitation, and decreased precipitation is expected to result in increased cloud water and cloud cover, further increasing the indirect forcing. Yet polluted marine boundary-layer clouds are not generally observed to hold more water. Here we use model simulations of stratocumulus clouds to show that suppression of precipitation from increased droplet concentrations leads to increased cloud water only when sufficient precipitation reaches the surface, a condition favored when the overlying air is moist. Otherwise, aerosol induced suppression of precipitation enhances entrainment of overlying dry air, thereby reducing cloud water and diminishing the indirect climate forcing.

  13. Indirect Climatic Effects of Major Volcanic Eruptions

    NASA Astrophysics Data System (ADS)

    Hofmann, D. J.

    2007-05-01

    The direct effects on climate, related to atmospheric emissions to the atmosphere following major volcanic eruptions, are well-known although the sparseness of such eruptions make detailed study on the range of such variations difficult. In general terms, infrared absorption by volcanic emissions to the stratosphere result in local heating early in the event when gaseous sulfur compounds exist. This early period is followed by gas to particle conversion, on a time scale of 1-2 months, promoting the formation of sulfuric acid-water droplets. Coagulation and droplet growth result in the "volcanic stratospheric aerosol layer" which is related to the predominant direct climatic effect of large eruptions, the cooling of the troposphere by backscattering of solar visible radiation to space with a recovery time scale of 1-2 years. In this paper we will discuss some of the less-known "indirect" effects of the volcanic stratospheric aerosol on climate. We label them indirect as they act on climate through intermediary atmospheric constituents. The intermediaries in the volcanic indirect climatic effect are generally atmospheric greenhouse gases or other atmospheric gases and conditions which affect greenhouse gases. For example, cooling of the troposphere following major eruptions reduces the growth rate of atmospheric carbon dioxide related to respiration by the terrestrial biosphere. In addition, redirection of part of the direct solar beam into diffuse radiation by the volcanic stratospheric aerosol stimulates plant photosynthesis, further reducing the carbon dioxide growth rate. The growth rate of the second-most important atmospheric greenhouse gas, methane, is also affected by volcanic emissions. Volcanic stratospheric aerosol particles provide surface area which catalyzes heterogeneous chemical reactions thus stimulating removal of stratospheric ozone, also a greenhouse gas. Although major droughts usually related to ENSO events have opposite effects on carbon

  14. Indirect radiative forcing by ion-mediated nucleation of aerosol

    SciTech Connect

    Yu, Fangqun; Luo, Gan; Liu, Xiaohong; Easter, Richard C.; Ma, Xiaoyan; Ghan, Steven J.

    2012-12-03

    A clear understanding of particle formation mechanisms is critical for assessing aerosol indirect radiative forcing and associated climate feedback processes. Recent studies reveal the importance of ion-mediated nucleation (IMN) in generating new particles and cloud condensation nuclei (CCN) in the atmosphere. Here we implement for the first time a physically based treatment of IMN into the Community Atmosphere Model version 5. Our simulations show that, compared to globally averaged results based on binary homogeneous nucleation (BHN), the presence of ionization (i.e., IMN) halves H2SO4 column burden, but increases the column integrated nucleation rate by around one order of magnitude, total particle number burden by a factor of ~ 3, CCN burden by ~ 10% (at 0.2% supersaturation) to 65% (at 1.0% supersaturation), and cloud droplet number burden by ~ 18%. Compared to BHN, IMN increases cloud liquid water path by 7.5%, decreases precipitation by 1.1%, and increases total cloud cover by 1.9%. This leads to an increase of total shortwave cloud radiative forcing by 3.67 W/m2 (more negative) and longwave cloud forcing by 1.78 W/m2 (more positive), resulting in a -1.9 W/m2 net change in cloud radiative forcing associated with IMN. The significant impacts of ionization on global aerosol formation, CCN abundance, and cloud radiative forcing may provide an important physical mechanism linking the global energy balance to various processes affecting atmospheric ionization, which should be properly represented in climate models.

  15. CARES: Carbonaceous Aerosol and Radiative Effects Study Science Plan

    SciTech Connect

    Zaveri, RA; Shaw, WJ; Cziczo, DJ

    2010-05-27

    Carbonaceous aerosol components, which include black carbon (BC), urban primary organic aerosols (POA), biomass burning aerosols, and secondary organic aerosols (SOA) from both urban and biogenic precursors, have been previously shown to play a major role in the direct and indirect radiative forcing of climate. The primary objective of the CARES 2010 intensive field study is to investigate the evolution of carbonaceous aerosols of different types and their effects on optical and cloud formation properties.

  16. Radiative Effects of Aerosols

    NASA Technical Reports Server (NTRS)

    Valero, Francisco P. J.

    1997-01-01

    During the Atlantic Stratocumulus Transition Experiment (ASTEX) in June 1992, two descents in cloud-free regions allowed comparison of the change in aerosol optical depth as determined by an onboard total-direct-diffuse radiometer (TDDR) to the change calculated from measured size resolved aerosol microphysics and chemistry. Both profiles included pollution haze layer from Europe but the second also included the effect of a Saharan dust layer above the haze. The separate contributions of supermicrometer (coarse) and submicrometer (fine) aerosol were determined and thermal analysis of the pollution haze indicated that the fine aerosol was composed primarily of a sulfate/water mixture with a refractory soot-like core.

  17. Reply to Quaas et al.: Can satellites be used to estimate indirect climate forcing by aerosols?

    SciTech Connect

    Penner, J. E.; Zhou, Cheng; Xu, Li; Wang, Minghuai

    2011-11-15

    We welcome the comments by Quaas et al. (1). In our paper (2), we used a model to show that the methods used to estimate indirect aerosol forcing using satellite data, especially those based on relating the slope of present-day (PD) drop number (Nc) to aerosol optical depth (AOD), underestimate the forcing calculated when both PD and preindustrial (PI) data are available.

  18. Radiative Effects of Aerosols

    NASA Technical Reports Server (NTRS)

    Valero, Francisco P. J.

    1996-01-01

    During the Atlantic Stratocumulus Transition Experiment (ASTEX) in June 1992, two descents in cloud-free regions allowed comparison of the change in aerosol optical depth as determined by an onboard total-direct-diffuse radiometer (TDDR) to the change calculated from measured size-resolved aerosol microphysics and chemistry. Both profiles included a pollution haze from Europe but the second also included the effect of a Saharan dust layer above the haze. The separate contributions of supermicrometer (coarse) and submicrometer (fine) aerosol were determined and thermal analysis of the pollution haze indicated that the fine aerosol was composed primarily of a sulfate/water mixture with a refractory soot-like core. The soot core increased the calculated extinction by about 10% in the most polluted drier layer relative to a pure sulfate aerosol but had significantly less effect at higher humidities. A 3 km descent through a boundary layer air mass dominated by pollutant aerosol with relative humidities (RH) 10-77% yielded a close agreement between the measured and calculated aerosol optical depths (550 nm) of 0.160 (+/- 0.07) and 0. 157 (+/- 0.034) respectively. During descent the aerosol mass scattering coefficient per unit sulfate mass varied from about 5 to 16 m(exp 2)/g and primarily dependent upon ambient RH. However, the total scattering coefficient per total fine mass was far less variable at about 4+/- 0.7 m(exp 2)/g. A subsequent descent through a Saharan dust layer located above the pollution aerosol layer revealed that both layers contributed similarly to aerosol optical depth. The scattering per unit mass of the coarse aged dust was estimated at 1.1 +/- 0.2 m(exp 2)/g. The large difference (50%) in measured and calculated optical depth for the dust layer exceeded measurements.

  19. Assessing effects of esfenvalerate aerosol applications on resident populations of Tribolium castaneum (Herbst), the red flour beetle, through direct and indirect sampling

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Small-scale field sheds were infested with resident populations of the red flour beetle, Tribolium castaneum (Herbst), and either left untreated or treated every two or four weeks with an aerosol spray of esfenvalerate (Conquer ®). The sheds were infested by placing flour food patches underneath she...

  20. Entrainment, Drizzle, and the Indirect Effect in Stratiform Clouds

    NASA Technical Reports Server (NTRS)

    Ackerman, Andrew

    2005-01-01

    Activation of some fraction of increased concentrations of sub-micron soluble aerosol particles lead to enhanced cloud droplet concentrations and hence smaller droplets, increasing their total cross sectional area and thus reflecting solar radiation more efficiently (the Twomey, or first indirect, effect). However, because of competition during condensational growth, droplet distributions tend to broaden as numbers increase, reducing the sensitivity of cloud albedo to droplet concentration on the order of 10%. Also, smaller droplets less effectively produce drizzle through collisions and coalescence, and it is widely expected (and found in large-scale models) that decreased precipitation leads to clouds with more cloud water on average (the so-called cloud lifetime, or second indirect, effect). Much of the uncertainty regarding the overall indirect aerosol effect stems from inadequate understanding of such changes in cloud water. Detailed simulations based on FIRE-I, ASTEX, and DYCOMS-II conditions show that suppression of precipitation from increased droplet concentrations leads to increased cloud water only when sufficient precipitation reaches the surface, a condition favored when the overlying air is-humid or droplet concentrations are very low. Otherwise, aerosol induced suppression of precipitation enhances entrainment of overlying dry air, thereby reducing cloud water and diminishing the indirect climate forcing.

  1. Grid-scale Indirect Radiative Forcing of Climate due to aerosols over the northern hemisphere simulated by the integrated WRF-CMAQ model: Preliminary results

    EPA Science Inventory

    In this study, indirect aerosol effects on grid-scale clouds were implemented in the integrated WRF3.3-CMAQ5.0 modeling system by including parameterizations for both cloud droplet and ice number concentrations calculated from the CMAQ-predicted aerosol particles. The resulting c...

  2. Importance of tropospheric volcanic aerosol for indirect radiative forcing of climate

    NASA Astrophysics Data System (ADS)

    Schmidt, A.; Carslaw, K. S.; Mann, G. W.; Rap, A.; Pringle, K. J.; Spracklen, D. V.; Wilson, M.; Forster, P. M.

    2012-08-01

    Observations and models have shown that continuously degassing volcanoes have a potentially large effect on the natural background aerosol loading and the radiative state of the atmosphere. We use a global aerosol microphysics model to quantify the impact of these volcanic emissions on the cloud albedo radiative forcing under pre-industrial (PI) and present-day (PD) conditions. We find that volcanic degassing increases global annual mean cloud droplet number concentrations by 40% under PI conditions, but by only 10% under PD conditions. Consequently, volcanic degassing causes a global annual mean cloud albedo effect of -1.06 W m-2 in the PI era but only -0.56 W m-2 in the PD era. This non-equal effect is explained partly by the lower background aerosol concentrations in the PI era, but also because more aerosol particles are produced per unit of volcanic sulphur emission in the PI atmosphere. The higher sensitivity of the PI atmosphere to volcanic emissions has an important consequence for the anthropogenic cloud radiative forcing because the large uncertainty in volcanic emissions translates into an uncertainty in the PI baseline cloud radiative state. Assuming a -50/+100% uncertainty range in the volcanic sulphur flux, we estimate the annual mean anthropogenic cloud albedo forcing to lie between -1.16 W m-2 and -0.86 W m-2. Therefore, the volcanically induced uncertainty in the PI baseline cloud radiative state substantially adds to the already large uncertainty in the magnitude of the indirect radiative forcing of climate.

  3. Importance of tropospheric volcanic aerosol for indirect radiative forcing of climate

    NASA Astrophysics Data System (ADS)

    Schmidt, A.; Carslaw, K. S.; Mann, G. W.; Rap, A.; Pringle, K. J.; Spracklen, D. V.; Wilson, M.; Forster, P. M.

    2012-03-01

    Observations and models have shown that continuously degassing volcanoes have a potentially large effect on the natural background aerosol loading and the radiative state of the atmosphere. Here, we use a global aerosol microphysics model to quantify the impact of these volcanic emissions on the cloud albedo radiative forcing under pre-industrial (PI) and present-day (PD) conditions. We find that volcanic degassing increases global annual mean cloud droplet number concentrations by 40% under PI conditions, but by only 10% under PD conditions. Consequently, volcanic degassing causes a global annual mean cloud albedo effect of -1.06 W m-2 in the PI era but only -0.56 W m-2 in the PD era. This non-equal effect is explained partly by the lower background aerosol concentrations in the PI era, but also because more aerosol particles are produced per unit of volcanic sulphur emission in the PI atmosphere. The higher sensitivity of the PI atmosphere to volcanic emissions has an important consequence for the anthropogenic cloud radiative forcing because the large uncertainty in volcanic emissions translates into an uncertainty in the PI baseline cloud radiative state. Assuming a -50/+100% uncertainty range in the volcanic sulphur flux, we estimate the annual mean anthropogenic cloud albedo forcing to lie between -1.16 W m-2 and -0.86 W m-2. Therefore, the volcanically induced uncertainty in the PI baseline cloud radiative state substantially adds to the already large uncertainty in the magnitude of the indirect radiative forcing of climate.

  4. The Effect of Aerosol Hygroscopicity and Volatility on Aerosol Optical Properties During Southern Oxidant and Aerosol Study

    NASA Astrophysics Data System (ADS)

    Khlystov, A.; Grieshop, A. P.; Saha, P.; Subramanian, R.

    2014-12-01

    Secondary organic aerosol (SOA) from biogenic sources can influence optical properties of ambient aerosol by altering its hygroscopicity and contributing to light absorption directly via formation of brown carbon and indirectly by enhancing light absorption by black carbon ("lensing effect"). The magnitude of these effects remains highly uncertain. A set of state-of-the-art instruments was deployed at the SEARCH site near Centerville, AL during the Southern Oxidant and Aerosol Study (SOAS) campaign in summer 2013 to measure the effect of relative humidity and temperature on aerosol size distribution, composition and optical properties. Light scattering and absorption by temperature- and humidity-conditioned aerosols was measured using three photo-acoustic extinctiometers (PAX) at three wavelengths (405 nm, 532 nm, and 870 nm). The sample-conditioning system provided measurements at ambient RH, 10%RH ("dry"), 85%RH ("wet"), and 200 C ("TD"). In parallel to these measurements, a long residence time temperature-stepping thermodenuder (TD) and a variable residence time constant temperature TD in combination with three SMPS systems and an Aerosol Chemical Speciation Monitor (ACSM) were used to assess aerosol volatility and kinetics of aerosol evaporation. We will present results of the on-going analysis of the collected data set. We will show that both temperature and relative humidity have a strong effect on aerosol optical properties. SOA appears to increase aerosol light absorption by about 10%. TD measurements suggest that aerosol equilibrated fairly quickly, within 2 s. Evaporation varied substantially with ambient aerosol loading and composition and meteorology.

  5. Importance of tropospheric volcanic aerosol for indirect radiative forcing of climate

    NASA Astrophysics Data System (ADS)

    Schmidt, A.; Carslaw, K. S.; Mann, G.; Rap, A.; Pringle, K. J.; Spracklen, D. V.; Wilson, M.; Forster, P.

    2013-12-01

    Observations and models have shown that continuously degassing volcanoes have a potentially large effect on the natural background aerosol loading and the radiative state of the atmosphere. We use a global aerosol microphysics model to quantify the impact of these volcanic emissions on the cloud albedo radiative forcing under pre-industrial (PI) and present-day (PD) conditions. We find that volcanic degassing increases global annual mean cloud droplet number concentrations by 40% under PI conditions, but by only 10% under PD conditions. Consequently, volcanic degassing causes a global annual mean cloud albedo effect of -1.06 W m-2 in the PI era but only -0.56 W m-2 in the PD era. This non-equal effect is explained partly by the lower background aerosol concentrations in the PI era, but also because more aerosol particles are produced per unit of volcanic sulphur emission in the PI atmosphere. The higher sensitivity of the PI atmosphere to volcanic emissions has an important consequence for the anthropogenic cloud radiative forcing because the large uncertainty in volcanic emissions translates into an uncertainty in the PI baseline cloud radiative state. Assuming a -50/+100% uncertainty range in the volcanic sulphur flux, we estimate the annual mean anthropogenic cloud albedo forcing to lie between -1.16 W m-2 and -0.86 W m-2. Therefore, the volcanically induced uncertainty in the PI baseline cloud radiative state substantially adds to the already large uncertainty in the magnitude of the indirect radiative forcing of climate. Effect of uncertain volcanic sulphur emissions on the annual global mean cloud albedo effect and anthropogenic cloud albedo forcing. The grey and blue bars show the magnitude and the uncertainty range for the volcanic cloud albedo effect for present-day (PD) and pre-industrial (PI), respectively. In the central panel, the top red bar shows the magnitude of the anthropogenic cloud albedo forcing as estimated by IPCC based on a range of

  6. The aerosol radiative effects of uncontrolled combustion of domestic waste

    NASA Astrophysics Data System (ADS)

    Kodros, John K.; Cucinotta, Rachel; Ridley, David A.; Wiedinmyer, Christine; Pierce, Jeffrey R.

    2016-06-01

    Open, uncontrolled combustion of domestic waste is a potentially significant source of aerosol; however, this aerosol source is not generally included in many global emissions inventories. To provide a first estimate of the aerosol radiative impacts from domestic-waste combustion, we incorporate the Wiedinmyer et al. (2014) emissions inventory into GEOS-Chem-TOMAS, a global chemical-transport model with online aerosol microphysics. We find domestic-waste combustion increases global-mean black carbon and organic aerosol concentrations by 8 and 6 %, respectively, and by greater than 40 % in some regions. Due to uncertainties regarding aerosol optical properties, we estimate the globally averaged aerosol direct radiative effect to range from -5 to -20 mW m-2; however, this range increases from -40 to +4 mW m-2 when we consider uncertainties in emission mass and size distribution. In some regions with significant waste combustion, such as India and China, the aerosol direct radiative effect may exceed -0.4 W m-2. Similarly, we estimate a cloud-albedo aerosol indirect effect of -13 mW m-2, with a range of -4 to -49 mW m-2 due to emission uncertainties. In the regions with significant waste combustion, the cloud-albedo aerosol indirect effect may exceed -0.4 W m-2.

  7. First measurements of the Twomey indirect effect using ground-based remote sensors

    NASA Astrophysics Data System (ADS)

    Feingold, Graham; Eberhard, Wynn L.; Veron, Dana E.; Previdi, Michael

    2003-03-01

    We demonstrate first measurements of the aerosol indirect effect using ground-based remote sensors at a continental US site. The response of nonprecipitating, ice-free clouds to changes in aerosol loading is quantified in terms of a relative change in cloud-drop effective radius for a relative change in aerosol extinction under conditions of equivalent cloud liquid water path. This is done in a single column of air at a temporal resolution of 20 s (spatial resolution of ~100 m). Cloud-drop effective radius is derived from a cloud radar and microwave radiometer. Aerosol extinction is measured below cloud base by a Raman lidar. Results suggest that aerosols associated with maritime or northerly air trajectories tend to have a stronger effect on clouds than aerosols associated with northwesterly trajectories that also have local influence. There is good correlation (0.67) between the cloud response and a measure of cloud turbulence.

  8. New Results from Space and Field Observations on the Aerosol Direct and Indirect Radiative Forcing

    NASA Technical Reports Server (NTRS)

    Kaufman, Yoram J.; Remer, Lorraine; Tanre, Didier; Boucher, Olivier; Chin, Mian; Dubovik, Oleg; Holben, Brent

    2002-01-01

    New space observations from the MODIS instrument on board the Terra satellite and analysis of POLDER data flown on the ADEOS satellite, show in great details the spatial and seasonal variability of the global aerosol system. These spaceborne instruments distinguish fine aerosol from man-made regional pollution and biomass burning from mostly natural coarse dust and sea salt aerosol. E.g. fine regional pollution in and around the Indian sub-continent, Europe and North America; smoke from biomass burning in Southern Africa and Southern America; coarse dust from West Africa and mixed dust pollution and smoke from West and central Africa and East Asia. These regions were also studied extensively in focused field experiments and by the distributed AERONET network. The results generate the first climatologies of the aerosol system, are used to derive the aerosol radiative effects and to estimate the anthropogenic component. The measurements are also used to evaluate each other and constrain aerosol transport models.

  9. A new chemistry option in WRF-Chem v. 3.4 for the simulation of direct and indirect aerosol effects using VBS: evaluation against IMPACT-EUCAARI data

    NASA Astrophysics Data System (ADS)

    Tuccella, P.; Curci, G.; Grell, G. A.; Visconti, G.; Crumeyrolle, S.; Schwarzenboeck, A.; Mensah, A. A.

    2015-09-01

    condensation nuclei (CCN) are also overestimated, but the bias is more contained with respect to that of CN. The CCN efficiency, which is a characterization of the ability of aerosol particles to nucleate cloud droplets, is underestimated by a factor of 1.5 and 3.8 in the PBL and FT, respectively. The comparison with MODIS data shows that the model overestimates the aerosol optical thickness (AOT). The domain averages (for 1 day) are 0.38 ± 0.12 and 0.42 ± 0.10 for MODIS and WRF-Chem data, respectively. The droplet effective radius (Re) in liquid-phase clouds is underestimated by a factor of 1.5; the cloud liquid water path (LWP) is overestimated by a factor of 1.1-1.6. The consequence is the overestimation of average liquid cloud optical thickness (COT) from a few percent up to 42 %. The predicted cloud water path (CWP) in all phases displays a bias in the range +41-80 %, whereas the bias of COT is about 15 %. In sensitivity tests where we excluded SOA, the skills of the model in reproducing the observed patterns and average values of the microphysical and optical properties of liquid and all phase clouds decreases. Moreover, the run without SOA (NOSOA) shows convective clouds with an enhanced content of liquid and frozen hydrometers, and stronger updrafts and downdrafts. Considering that the previous version of WRF-Chem coupled with a modal aerosol module predicted very low SOA content (secondary organic aerosol model (SORGAM) mechanism) the new proposed option may lead to a better characterization of aerosol-cloud feedbacks.

  10. Color indirect effects on melatonin regulation

    NASA Astrophysics Data System (ADS)

    Mian, Tian; Liu, Timon C.; Li, Yan

    2002-04-01

    Color indirect effect (CIE) is referred to as the physiological and psychological effects of color resulting from color vision. In previous papers, we have studied CIE from the viewpoints of the integrated western and Chinese traditional medicine, put forward the color-autonomic- nervous-subsystem model (CAM), and provided its time-theory foundation. In this paper, we applied it to study light effects on melatonin regulation in humans, and suggested that it is CIE that mediates light effects on melatonin suppression.

  11. Total aerosol effect: forcing or radiative flux perturbation?

    SciTech Connect

    Lohmann, Ulrike; Storelvmo, Trude; Jones, Andy; Rotstayn, Leon; Menon, Surabi; Quaas, Johannes; Ekman, Annica; Koch, Dorothy; Ruedy, Reto

    2009-09-25

    Uncertainties in aerosol forcings, especially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation introduces feedbacks which can affect the rate of rain formation. Traditionally these feedbacks were not included in estimates of total aerosol forcing. Here we argue that they should be included because these feedbacks act quickly compared with the time scale of global warming. We show that for different forcing agents (aerosols and greenhouse gases) the radiative forcings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturbations (RFP), that takes these fast feedbacks and interactions into account. Thus we propose replacing the direct and indirect aerosol forcing in the IPCC forcing chart with RFP estimates. This implies that it is better to evaluate the total anthropogenic aerosol effect as a whole.

  12. Unexpected Benefits of Reducing Aerosol Cooling Effects.

    PubMed

    Xing, Jia; Wang, Jiandong; Mathur, Rohit; Pleim, Jonathan; Wang, Shuxiao; Hogrefe, Christian; Gan, Chuen-Meei; Wong, David C; Hao, Jiming

    2016-07-19

    Impacts of aerosol cooling are not limited to changes in surface temperature since modulation of atmospheric dynamics resulting from the increased stability can deteriorate local air quality and impact human health. Health impacts from two manifestations of the aerosol direct effects (ADE) are estimated in this study: (1) the effect on surface temperature and (2) the effect on air quality through atmospheric dynamics. Average mortalities arising from the enhancement of surface PM2.5 concentration due to ADE in East Asia, North America and Europe are estimated to be 3-6 times higher than reduced mortality from decreases of temperature due to ADE. Our results suggest that mitigating aerosol pollution is beneficial in decreasing the impacts of climate change arising from these two manifestations of ADE health impacts. Thus, decreasing aerosol pollution gets direct benefits on health, and indirect benefits on health through changes in local climate and not offsetting changes associated only with temperature modulations as traditionally thought. The modulation of air pollution due to ADE also translates into an additional human health dividend in regions (e.g., U.S. Europe) with air pollution control measures but a penalty for regions (e.g., Asia) witnessing rapid deterioration in air quality. PMID:27310144

  13. Anthropogenic Aerosol Effects on Sea Surface Temperatures: Mixed-Layer Ocean Experiments with Explicit Aerosol Representation

    NASA Astrophysics Data System (ADS)

    Dallafior, Tanja; Folini, Doris; Wild, Martin; Knutti, Reto

    2014-05-01

    Anthropogenic aerosols affect the Earth's radiative balance both through direct and indirect effects. These effects can lead to a reduction of the incoming solar radiation at the surface, i.e. dimming, which may lead to a change in sea surface temperatures (SST) or SST pattern. This, in turn, may affect precipitation patterns. The goal of the present work is to achieve an estimate of the equilibrium SST changes under anthropogenic aerosol forcing since industrialisation. We show preliminary results from mixed-layer ocean (MLO) experiments with explicit aerosol representation performed with ECHAM6-HAM. The (fixed) MLO heat flux into the deep ocean was derived from atmosphere only runs with fixed climatological SSTs (1961-1990 average) and present day (year 2000) aerosols and GHG burdens. Some experiments we repeated with an alternative MLO deep ocean heat flux (based on pre-industrial conditions) to test the robustness of our results with regard to this boundary condition. The maximum surface temperature responses towards anthropogenic aerosol and GHG forcing (separately and combined) were derived on a global and regional scale. The same set of experiments was performed with aerosol and GHG forcings representative of different decades over the past one and a half centuries. This allows to assess how SST patterns at equilibrium changed with changing aerosol (and GHG) forcing. Correlating SST responses with the change in downward clear-sky and all-sky shortwave radiation provides a first estimate of the response to anthropogenic aerosols. Our results show a clear contrast in hemispheric surface temperature response, as expected from the inter-hemispheric asymmetry of aerosol forcing The presented work is part of a project aiming at quantifying the effect of anthropogenic aerosol forcing on SSTs and the consequences for global precipitation patterns. Results from this study will serve as a starting point for further experiments involving a dynamic ocean model, which

  14. Sensitivity Study of The Sulfate Aerosol Indirect Radiative Forcing To The Dms Source Representation

    NASA Astrophysics Data System (ADS)

    Boucher, O.; Aumont, O.; Belviso, S.; Cosme, E.; Moulin, C.; Pham, M.

    We use a global sulfur cycle model (LMD-ZT) to study the sensitivity of the dimethyl- sulfide (DMS) atmospheric concentrations and sulfur cycle to the representation of the DMS oceanic source. We test four different distributions of the oceanic DMS concen- trations: the Kettle et al. DMS dataset, two datasets built from Seawifs measurements of the ocean color (but with different , and one distribution from a coupled oceanic bi- ological model. There is a convergence for 3 out of 4 DMS datasets to produce a global DMS flux of 18-20 TgS/yr. There are however significant disagreements on the spa- tial and seasonal distribution of the DMS flux. A comparison of the DMS atmospheric concentrations with observations will be presented. The sulfate aerosol indirect radia- tive forcing depends strongly on the concentration of pre-industrial aerosols, which itself depends on the DMS sea-air flux. The subsequent uncertainty on the aerosol in- direct radiative forcing and the implication for climate-chemistry interactions will be discussed.

  15. Revisiting Aerosol Effects in Global Climate Models Using an Aerosol Lidar Simulator

    NASA Astrophysics Data System (ADS)

    Ma, P. L.; Chepfer, H.; Winker, D. M.; Ghan, S.; Rasch, P. J.

    2015-12-01

    Aerosol effects are considered a major source of uncertainty in global climate models and the direct and indirect radiative forcings have strong model dependency. These forcings are routinely evaluated (and calibrated) against observations, among them satellite retrievals are greatly used for their near-global coverage. However, the forcings calculated from model output are not directly comparable with those computed from satellite retrievals since sampling and algorithmic differences (such as cloud screening, noise reduction, and retrieval) between models and observations are not accounted for. It is our hypothesis that the conventional model validation procedures for comparing satellite observations and model simulations can mislead model development and introduce biases. Hence, we have developed an aerosol lidar simulator for global climate models that simulates the CALIOP lidar signal at 532nm. The simulator uses the same algorithms as those used to produce the "GCM-oriented CALIPSO Aerosol Product" to (1) objectively sample lidar signal profiles; and (2) derive aerosol fields (e.g., extinction profile, aerosol type, etc) from lidar signals. This allows us to sample and derive aerosol fields in the model and real atmosphere in identical ways. Using the Department of Energy's ACME model simulations, we found that the simulator-retrieved aerosol distribution and aerosol-cloud interactions are significantly different from those computed from conventional approaches, and that the model is much closer to satellite estimates than previously believed.

  16. Influence of Aerosols on the Shortwave Cloud Radiative Forcing from North Pacific Oceanic Clouds: Results from the Cloud Indirect Forcing Experiment (CIFEX)

    NASA Technical Reports Server (NTRS)

    Wilcox, Eric M.; Roberts, Greg; Ramanathan, V.

    2007-01-01

    Aerosols over the Northeastern Pacific Ocean enhance the cloud drop number concentration and reduce the drop size for marine stratocumulus and cumulus clouds. These microphysical effects result in brighter clouds, as evidenced by a combination of aircraft and satellite observations. In-situ measurements from the Cloud Indirect Forcing Experiment (CIFEX) indicate that the mean cloud drop number concentration in low clouds over the polluted marine boundary layer is greater by 53 cm(sup -3) compared to clean clouds, and the mean cloud drop effective radius is smaller by 4 micrometers. We link these in-situ measurements of cloud modification by aerosols, for the first time, with collocated satellite broadband radiative flux observations from the Clouds and the Earth s Radiant Energy System to show that these microphysical effects of aerosols enhance the top-of-atmosphere cooling by -.9.9 plus or minus 4.3 W m(sup -2) for overcast conditions.

  17. The Influence of Aerosols on the Shortwave Cloud Radiative Forcing from North Pacific Oceanic Clouds: Results from the Cloud Indirect Forcing Experiment (CIFEX)

    NASA Technical Reports Server (NTRS)

    Wilcox, Eric M.; Roberts, Greg; Ramanathan, V.

    2006-01-01

    Aerosols over the Northeastern Pacific Ocean enhance the cloud drop number concentration and reduce the drop size for marine stratocumulus and cumulus clouds. These microphysical effects result in brighter clouds, as evidenced by a combination of aircraft and satellite observations. In-situ measurements from the Cloud Indirect Forcing Experiment (CIFEX) indicate that the mean cloud drop number concentration in low clouds over the polluted marine boundary layer is greater by 53/cu cm compared to clean clouds, and the mean cloud drop effective radius is smaller by 4 microns. We link these in-situ measurements of cloud modification by aerosols, for the first time, with collocated satellite broadband radiative flux observations from the Clouds and the Earth's Radiant Energy System (CERES) to show that these microphysical effects of aerosols enhance the top-of-atmosphere cooling by -9.9+/-4.3 W/sq m for overcast conditions.

  18. First measurements of the indirect effect using ground-based remote sensors

    NASA Astrophysics Data System (ADS)

    Feingold, G.; Eberhard, W. L.; Lane, D. E.; Previdi, M.

    2002-12-01

    We demonstrate first measurements of the aerosol indirect effect using ground-based remote sensors at a continental US site. The response of a cloud to changes in the aerosol loading is quantified in terms of a relative change in cloud drop effective radius for a relative change in aerosol extinction under conditions of equivalent cloud liquid water path. This is done in a single column of air at a temporal resolution of 20 s (spatial resolution of ~100 m). Cloud drop effective radius is derived from a cloud radar, microwave radiometer, and where applicable, a surface measurement of the accumulation mode aerosol concentration. Aerosol extinction is measured below cloud base by a Raman lidar. The method differs from satellite remote-sensing measurements of the indirect effect in that it samples at scales appropriate to cloud drop activation, i.e., the large eddy scale, and is therefore process-based, rather than statistically-based. The method is demonstrated for non-precipitating ice-free clouds at the Southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) site. Strengths and weaknesses of the approach are discussed and recommendations are made for measurement strategies that will improve our ability to quantify this important climatic effect.

  19. Theoretical research on color indirect effects

    NASA Astrophysics Data System (ADS)

    Liu, T. C.; Liao, Changjun; Liu, Songhao

    1995-05-01

    Color indirect effects (CIE) means the physiological and psychological effects of color resulting from color vision. In this paper, we study CIE from the viewpoints of the integrated western and Chinese traditional medicine and the time quantum theory established by C. Y. Liu et al., respectively, and then put forward the color-automatic-nervous-subsystem model that could color excites parasympathetic subsystem and hot color excites sympathetic subsystem. Our theory is in agreement with modern color vision theory, and moreover, it leads to the resolution of the conflict between the color code theory and the time code theory oncolor vision. For the latitude phenomena on athlete stars number and the average lifespan, we also discuss the possibility of UV vision. The applications of our theory lead to our succeeding in explaining a number of physiological and psychological effects of color, in explaining the effects of age on color vision, and in explaining the Chinese chromophototherapy. We also discuss its application to neuroimmunology. This research provides the foundation of the clinical applications of chromophototherapy.

  20. Identification of a New Dust Indirect Effect Over the Tropical North Atlantic

    NASA Astrophysics Data System (ADS)

    Doherty, O. M.; Evan, A. T.

    2013-12-01

    Over the tropical North Atlantic stratocumulus clouds are ubiquitous, and through radiative forcing have large impacts on the regional climate, both directly and through sea surface temperature (SST) induced feedbacks. Mineral aerosols, during the boreal summer season, are also commonly found over the tropical North Atlantic, and are known to alter both the vertical profile of temperatures and moisture in the atmosphere as well as SSTs. Stratocumulus clouds fraction is dependent upon vertical profiles of temperature and moisture, as well as SSTs, thus mineral aerosols could have an impact on stratocumulus cloud cover. However, no study has identified a direct relationship between dust and stratocumulus clouds. In this work we find that low clouds fraction increase in response to high mineral aerosols loadings by 3% to 5% over much of the Tropical North Atlantic, in both ISCCP and PATMOSx observations during dusty boreal summers. In idealized CAM runs low cloud fraction shows an increase of 2% to 3% by including mineral aerosols. On daily timescales we find a 10% to 20% increase in low clouds over the Tropical North Atlantic for the three days following mineral aerosol outbreaks in MODIS products. We hypothesize that cooling of SSTs and reductions in entrainment in response to high mineral aerosols load are responsible for increases in stratocumulus clouds. The single-column CESM-SCAM model is applied to test this hypothesis, using observed radiative forcing rates. This new dust indirect effect is a potential cooling mechanism for the tropical North Atlantic. As radiative forcing on the ocean surface by stratocumulus clouds is known to be -1 W/m2 per 1% increase in stratocumulus cloudcover, we estimate this indirect effect nets a cooling of -0.33 W/m2 to -2 W/m2 per unit of AOD increase in mineral aerosols.

  1. Indirect Effects of Environmental Change in Resource Competition Models.

    PubMed

    Kleinhesselink, Andrew R; Adler, Peter B

    2015-12-01

    Anthropogenic environmental change can affect species directly by altering physiological rates or indirectly by changing competitive outcomes. The unknown strength of competition-mediated indirect effects makes it difficult to predict species abundances in the face of ongoing environmental change. Theory developed with phenomenological competition models shows that indirect effects are weak when coexistence is strongly stabilized, but these models lack a mechanistic link between environmental change and species performance. To extend existing theory, we examined the relationship between coexistence and indirect effects in mechanistic resource competition models. We defined environmental change as a change in resource supply points and quantified the resulting competition-mediated indirect effects on species abundances. We found that the magnitude of indirect effects increases in proportion to niche overlap. However, indirect effects also depend on differences in how competitors respond to the change in resource supply, an insight hidden in nonmechanistic models. Our analysis demonstrates the value of using niche overlap to predict the strength of indirect effects and clarifies the types of indirect effects that global change can have on competing species. PMID:26655983

  2. Aerosol Microphysical and Macrophysical Effects on Deep Convective Clouds

    NASA Astrophysics Data System (ADS)

    Yuan, T.; Li, Z.; Wilcox, E. M.; Oreopoulos, L.; Remer, L. A.; Yu, H.; Platnick, S. E.; Posselt, D. J.; Zhang, Z.; Martins, J. V.

    2014-12-01

    We illustrate a conceptual model of hydrometeor vertical development inside a convective cloud and its utility in studying of aerosol-DCC interactions. Both case studies and ensemble means are used to investigate aerosol-DCC interactions. We identify a few scenarios where possible signal of aerosol effect on DCC may be extracted. The results show a consistent and physically sound picture of aerosols affecting DCC microphysics as well as macrophysical properties. Specifically, pollutions and smokes are shown to consistently decrease ice particle size. On the contrary, dust particles close to source regions are shown to make cloud ice particle size more maritime like. We postulate that dust may achieve this by acting as either heterogeneous ice nuclei or giant cloud condensation nuclei. This contrast between smoke or pollution and dust also exists for their effects on cloud glaciation temperature. Smoke and pollution aerosols are shown to decrease glaciation temperature while dust particles do the opposite. Possible Implications of our results for studying aerosol indirect forcing, cirrus cloud properties, troposphere-stratosphere water vapor exchange and cloud latent heating are discussed.

  3. A new chemistry option in WRF/Chem v. 3.4 for the simulation of direct and indirect aerosol effects using VBS: evaluation against IMPACT-EUCAARI data

    NASA Astrophysics Data System (ADS)

    Tuccella, P.; Curci, G.; Grell, G. A.; Visconti, G.; Crumeroylle, S.; Schwarzenboeck, A.; Mensah, A. A.

    2015-02-01

    A parameterization for secondary organic aerosol (SOA) production based on the volatility basis set (VBS) approach has been coupled with microphysics and radiative scheme in WRF/Chem model. The new chemistry option called "RACM/MADE/VBS" was evaluated on a cloud resolving scale against ground-based and aircraft measurements collected during the IMPACT-EUCAARI campaign, and complemented with satellite data from MODIS. The day-to-day variability and the diurnal cycle of ozone (O3) and nitrogen oxides (NOx) at the surface is captured by the model. Surface aerosol mass of sulphate (SO4), nitrate (NO3), ammonium (NH4), and organic matter (OM) is simulated with a correlation larger than 0.55. WRF/Chem captures the vertical profile of the aerosol mass in both the planetary boundary layer (PBL) and free troposphere (FT) as a function of the synoptic condition, but the model does not capture the full range of the measured concentrations. Predicted OM concentration is at the lower end of the observed mass. The bias may be attributable to the missing aqueous chemistry processes of organic compounds, the uncertainties in meteorological fields, the assumption on the deposition velocity of condensable organic vapours, and the uncertainties in the anthropogenic emissions of primary organic carbon. Aerosol particle number concentration (condensation nuclei, CN) is overestimated by a factor 1.4 and 1.7 within PBL and FT, respectively. Model bias is most likely attributable to the uncertainties of primary particle emissions (mostly in the PBL) and to the nucleation rate. The overestimation of simulated cloud condensation nuclei (CCN) is more contained with respect to that of CN. The CCN efficiency, which is a measure of the ability of aerosol particles to nucleate cloud droplets, is underestimated by a factor of 1.5 and 3.8 in the PBL and FT, respectively. The comparison with MODIS data shows that the model overestimates the aerosol optical thickness (AOT). The domain averages (for

  4. Assessing Mediational Models: Testing and Interval Estimation for Indirect Effects

    ERIC Educational Resources Information Center

    Biesanz, Jeremy C.; Falk, Carl F.; Savalei, Victoria

    2010-01-01

    Theoretical models specifying indirect or mediated effects are common in the social sciences. An indirect effect exists when an independent variable's influence on the dependent variable is mediated through an intervening variable. Classic approaches to assessing such mediational hypotheses (Baron & Kenny, 1986; Sobel, 1982) have in recent years…

  5. Global profiles of the direct aerosol effect using vertically resolved aerosol data

    NASA Astrophysics Data System (ADS)

    Korras Carraca, Marios Bruno; Pappas, Vasilios; Matsoukas, Christos; Hatzianastassiou, Nikolaos; Vardavas, Ilias

    2014-05-01

    Atmospheric aerosols, both natural and anthropogenic, can cause climate change through their direct, indirect, and semi-direct effects on the radiative energy budget of the Earth-atmosphere system. In general, aerosols cause cooling of the surface and the planet, while they warm the atmosphere due to scattering and absorption of incoming solar radiation. The importance of vertically resolved direct radiative effect (DRE) and heating/cooling effects of aerosols is strong, while large uncertainties still lie with their magnitudes. In order to be able to quantify them throughout the atmosphere, a detailed vertical profile of the aerosol effect is required. Such data were made available recently by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. CALIOP is the first polarization lidar to fly in space and has been acquiring unique data on aerosols and clouds since June 2006. The aim of this study is to investigate both the vertically resolved geographic and seasonal variation of the DRE due to aerosols. The vertical profile of DRE under all-sky and clear-sky conditions is computed using the deterministic spectral radiative transfer model FORTH. From the DRE, the effect on atmospheric heating/cooling rate profiles due to aerosols can also be derived. We use CALIOP Level 2-Version 3 Layer aerosol optical depth data as input to our radiation transfer model, for a period of 3 complete years (2007-2009). These data are provided on a 5 km horizontal resolution and in up to 8 vertical layers and have been regridded on our model horizontal and vertical resolutions. We use cloud data from the International Satellite Cloud Climatology Project (ISCCP), while the aerosol asymmetry factor and single scattering albedo are taken from the Global Aerosol Data Set (GADS). The model computations are performed on a monthly, 2.5°× 2.5° resolution on global scale, at 40

  6. Aerosol effects over China investigated with a high resolution convection permitting weather model

    NASA Astrophysics Data System (ADS)

    Pagh Nielsen, Kristian; Mahura, Alexander; Yang, Xiaohua

    2016-04-01

    We investigate aerosol effects in the operational high resolution (2.5 km) convection permitting non-hydrostatical weather model HARMONIE (HIRLAM-ALADIN Regional Mesoscale Operational NWP in Euromed). Aerosol input from the global C-IFS model is downscaled and used. The impact of using realistic aerosols on both the direct and the indirect aerosol effects is studied and compared with default simulations that include only the direct aerosol effect of climatological aerosols. The study is performed as a part of the MarcoPolo FP7 project for a selected region of China during the months January and July 2010, where in particular January 2010 saw several cases of high anthropogenic aerosol loads. We also investigate the impact of accounting for realistic aerosol single scattering albedos and asymmetry factors in the simulations of the direct aerosol forcing. In many studies only variations in the aerosol optical depth are accounted for. We show this to be inadequate, when the assumed aerosol types have different optical properties than the actual aerosols.

  7. Simultaneous Measurements of direct, semi-direct and indirect aerosol forcing with Stacked Autonomous UAVs: A New Observing Platform

    NASA Astrophysics Data System (ADS)

    Ramanathan, V.; Roberts, G.; Ramana, M. V.; Corrigan, C.; Nguyen, H.

    2006-12-01

    We report here first time demonstration with three autonomously flying Unmanned Aerial Vehicles (UAVs) of cloudy sky albedo, transmission atmospheric solar absorption, aerosol and cloud droplet concentrations and number densities. From these direct measurements we derive the direct, semi-direct and the first indirect aerosol forcing. The observing system consisted of 3 light weight UAVs, instrumented with miniaturized instruments (Roberts et al, 2006; Ramana et al, 2006; Corrigan et al 2006) for measuring aerosol concentrations and size distribution, cloud microphysical properties, black carbon concentration and broad band and narrow band solar fluxes. The airborne measurements were validated and augmented by the Atmospheric Brown Clouds Maldives Climate Observatory (ABC_MCO) in the island of Hanimaadhoo in the N. Indian Ocean (Corrigan et al, 2006; Ramana and Ramanathan 2006). The campaign was conducted during March and early April of 2006 when this region is subject to long range transport of pollution from S. Asia. In the stacked 3_UAV configuration, one flew in the boundary layer below clouds to characterize the aerosols feeding the clouds and the transmission of solar radiation by the absorbing aerosol layer and clouds above; the second inside the trade cumulus clouds to directly observe the fully nucleated cloud drop size and concentrations and total liquid water content; and the third above the cloud to determine the incoming solar and the reflected solar radiation. The 3-UAVs were programmed to sample the same region(or clouds) within seconds of each other, thus providing unique insights into how aerosols and boundary layer dynamics modulate the cloud microphysics and thus the albedo and solar absorption of cloudy skies in the planet. The period of observations also included a major dust-soot event which revealed a large increase in atmospheric solar absorption. We will present results on how 3- dimensional clouds with absorbing aerosols modulate

  8. Impacts of emission reductions on aerosol radiative effects

    NASA Astrophysics Data System (ADS)

    Pietikainen, J.-P.; Kupiainen, K.; Klimont, Z.; Makkonen, R.; Korhonen, H.; Karinkanta, R.; Hyvarinen, A.-P.; Karvosenoja, N.; Laaksonen, A.; Lihavainen, H.; Kerminen, V.-M.

    2015-05-01

    The global aerosol-climate model ECHAM-HAMMOZ was used to investigate changes in the aerosol burden and aerosol radiative effects in the coming decades. Four different emissions scenarios were applied for 2030 (two of them applied also for 2020) and the results were compared against the reference year 2005. Two of the scenarios are based on current legislation reductions: one shows the maximum potential of reductions that can be achieved by technical measures, and the other is targeted to short-lived climate forcers (SLCFs). We have analyzed the results in terms of global means and additionally focused on eight subregions. Based on our results, aerosol burdens show an overall decreasing trend as they basically follow the changes in primary and precursor emissions. However, in some locations, such as India, the burdens could increase significantly. The declining emissions have an impact on the clear-sky direct aerosol effect (DRE), i.e. the cooling effect. The DRE could decrease globally 0.06-0.4 W m-2 by 2030 with some regional increases, for example, over India (up to 0.84 W m-2). The global changes in the DRE depend on the scenario and are smallest in the targeted SLCF simulation. The aerosol indirect radiative effect could decline 0.25-0.82 W m-2 by 2030. This decrease takes place mostly over the oceans, whereas the DRE changes are greatest over the continents. Our results show that targeted emission reduction measures can be a much better choice for the climate than overall high reductions globally. Our simulations also suggest that more than half of the near-future forcing change is due to the radiative effects associated with aerosol-cloud interactions.

  9. A modeling study of the effects of aerosols on clouds and precipitation over East Asia

    NASA Astrophysics Data System (ADS)

    Liu, Xiaodong; Xie, Xiaoning; Yin, Zhi-Yong; Liu, Changhai; Gettelman, Andrew

    2011-12-01

    The National Center for Atmospheric Research Community Atmosphere Model (version 3.5) coupled with the Morrison-Gettelman two-moment cloud microphysics scheme is employed to simulate the aerosol effects on clouds and precipitation in two numerical experiments, one representing present-day conditions (year 2000) and the other the pre-industrial conditions (year 1750) over East Asia by considering both direct and indirect aerosol effects. To isolate the aerosol effects, we used the same set of boundary conditions and only altered the aerosol emissions in both experiments. The simulated results show that the cloud microphysical properties are markedly affected by the increase in aerosols, especially for the column cloud droplet number concentration (DNC), liquid water path (LWP), and the cloud droplet effective radius (DER). With increased aerosols, DNC and LWP have been increased by 137% and 28%, respectively, while DER is reduced by 20%. Precipitation rates in East Asia and East China are reduced by 5.8% and 13%, respectively, by both the aerosol's second indirect effect and the radiative forcing that enhanced atmospheric stability associated with the aerosol direct and first indirect effects. The significant reduction in summer precipitation in East Asia is also consistent with the weakening of the East Asian summer monsoon, resulting from the decreasing thermodynamic contrast between the Asian landmass and the surrounding oceans induced by the aerosol's radiative effects. The increase in aerosols reduces the surface net shortwave radiative flux over the East Asia landmass, which leads to the reduction of the land surface temperature. With minimal changes in the sea surface temperature, hence, the weakening of the East Asian summer monsoon further enhances the reduction of summer precipitation over East Asia.

  10. Climatic Effects of 1950-2050 Changes in US Anthropogenic Aerosols. Part 1; Aerosol Trends and Radiative Forcing

    NASA Technical Reports Server (NTRS)

    Leibensperger, E. M.; Mickley, L. J.; Jacob, D. J.; Chen, W.-T.; Seinfeld, J. H.; Nenes, A.; Adams, P. J.; Streets, D. G.; Kumar, N.; Rind, D.

    2012-01-01

    We calculate decadal aerosol direct and indirect (warm cloud) radiative forcings from US anthropogenic sources over the 1950-2050 period. Past and future aerosol distributions are constructed using GEOS-Chem and historical emission inventories and future projections from the IPCC A1B scenario. Aerosol simulations are evaluated with observed spatial distributions and 1980-2010 trends of aerosol concentrations and wet deposition in the contiguous US. Direct and indirect radiative forcing is calculated using the GISS general circulation model and monthly mean aerosol distributions from GEOS-Chem. The radiative forcing from US anthropogenic aerosols is strongly localized over the eastern US. We find that its magnitude peaked in 1970-1990, with values over the eastern US (east of 100 deg W) of -2.0Wm(exp-2 for direct forcing including contributions from sulfate (-2.0Wm-2), nitrate (-0.2Wm(exp-2), organic carbon (-0.2Wm(exp-2), and black carbon (+0.4Wm(exp-2). The uncertainties in radiative forcing due to aerosol radiative properties are estimated to be about 50 %. The aerosol indirect effect is estimated to be of comparable magnitude to the direct forcing. We find that the magnitude of the forcing declined sharply from 1990 to 2010 (by 0.8Wm(exp-2) direct and 1.0Wm(exp-2 indirect), mainly reflecting decreases in SO2 emissions, and project that it will continue declining post-2010 but at a much slower rate since US SO2 emissions have already declined by almost 60% from their peak. This suggests that much of the warming effect of reducing US anthropogenic aerosol sources has already been realized. The small positive radiative forcing from US BC emissions (+0.3Wm(exp-2 over the eastern US in 2010; 5% of the global forcing from anthropogenic BC emissions worldwide) suggests that a US emission control strategy focused on BC would have only limited climate benefit.

  11. A Global Modeling Study on Carbonaceous Aerosol Microphysical Characteristics and Radiative Effects

    NASA Technical Reports Server (NTRS)

    Bauer, S. E.; Menon, S.; Koch, D.; Bond, T. C.; Tsigaridis, K.

    2010-01-01

    Recently, attention has been drawn towards black carbon aerosols as a short-term climate warming mitigation candidate. However the global and regional impacts of the direct, indirect and semi-direct aerosol effects are highly uncertain, due to the complex nature of aerosol evolution and the way that mixed, aged aerosols interact with clouds and radiation. A detailed aerosol microphysical scheme, MATRIX, embedded within the GISS climate model is used in this study to present a quantitative assessment of the impact of microphysical processes involving black carbon, such as emission size distributions and optical properties on aerosol cloud activation and radiative effects. Our best estimate for net direct and indirect aerosol radiative flux change between 1750 and 2000 is -0.56 W/m2. However, the direct and indirect aerosol effects are quite sensitive to the black and organic carbon size distribution and consequential mixing state. The net radiative flux change can vary between -0.32 to -0.75 W/m2 depending on these carbonaceous particle properties at emission. Taking into account internally mixed black carbon particles let us simulate correct aerosol absorption. Absorption of black carbon aerosols is amplified by sulfate and nitrate coatings and, even more strongly, by organic coatings. Black carbon mitigation scenarios generally showed reduced radiative fluxeswhen sources with a large proportion of black carbon, such as diesel, are reduced; however reducing sources with a larger organic carbon component as well, such as bio-fuels, does not necessarily lead to a reduction in positive radiative flux.

  12. Global aerosol effects on convective clouds

    NASA Astrophysics Data System (ADS)

    Wagner, Till; Stier, Philip

    2013-04-01

    Atmospheric aerosols affect cloud properties, and thereby the radiation balance of the planet and the water cycle. The influence of aerosols on clouds is dominated by increase of cloud droplet and ice crystal numbers (CDNC/ICNC) due to enhanced aerosols acting as cloud condensation and ice nuclei. In deep convective clouds this increase in CDNC/ICNC is hypothesised to increase precipitation because of cloud invigoration through enhanced freezing and associated increased latent heat release caused by delayed warm rain formation. Satellite studies robustly show an increase of cloud top height (CTH) and precipitation with increasing aerosol optical depth (AOD, as proxy for aerosol amount). To represent aerosol effects and study their influence on convective clouds in the global climate aerosol model ECHAM-HAM, we substitute the standard convection parameterisation, which uses one mean convective cloud for each grid column, with the convective cloud field model (CCFM), which simulates a spectrum of convective clouds, each with distinct values of radius, mixing ratios, vertical velocity, height and en/detrainment. Aerosol activation and droplet nucleation in convective updrafts at cloud base is the primary driver for microphysical aerosol effects. To produce realistic estimates for vertical velocity at cloud base we use an entraining dry parcel sub cloud model which is triggered by perturbations of sensible and latent heat at the surface. Aerosol activation at cloud base is modelled with a mechanistic, Köhler theory based, scheme, which couples the aerosols to the convective microphysics. Comparison of relationships between CTH and AOD, and precipitation and AOD produced by this novel model and satellite based estimates show general agreement. Through model experiments and analysis of the model cloud processes we are able to investigate the main drivers for the relationship between CTH / precipitation and AOD.

  13. Uncertainties in global aerosols and climate effects due to biofuel emissions

    NASA Astrophysics Data System (ADS)

    Kodros, J. K.; Scott, C. E.; Farina, S. C.; Lee, Y. H.; L'Orange, C.; Volckens, J.; Pierce, J. R.

    2015-08-01

    Aerosol emissions from biofuel combustion impact both health and climate; however, while reducing emissions through improvements to combustion technologies will improve health, the net effect on climate is largely unconstrained. In this study, we examine sensitivities in global aerosol concentration, direct radiative climate effect, and cloud-albedo aerosol indirect climate effect to uncertainties in biofuel emission factors, optical mixing state, and model nucleation and background secondary organic aerosol (SOA). We use the Goddard Earth Observing System global chemical-transport model (GEOS-Chem) with TwO Moment Aerosol Sectional (TOMAS) microphysics. The emission factors include amount, composition, size, and hygroscopicity, as well as optical mixing-state properties. We also evaluate emissions from domestic coal use, which is not biofuel but is also frequently emitted from homes. We estimate the direct radiative effect assuming different mixing states (homogeneous, core-shell, and external) with and without absorptive organic aerosol (brown carbon). We find the global-mean direct radiative effect of biofuel emissions ranges from -0.02 to +0.06 W m-2 across all simulation/mixing-state combinations with regional effects in source regions ranging from -0.2 to +0.8 W m-2. The global-mean cloud-albedo aerosol indirect effect (AIE) ranges from +0.01 to -0.02 W m-2 with regional effects in source regions ranging from -1.0 to -0.05 W m-2. The direct radiative effect is strongly dependent on uncertainties in emissions mass, composition, emissions aerosol size distributions, and assumed optical mixing state, while the indirect effect is dependent on the emissions mass, emissions aerosol size distribution, and the choice of model nucleation and secondary organic aerosol schemes. The sign and magnitude of these effects have a strong regional dependence. We conclude that the climate effects of biofuel aerosols are largely unconstrained, and the overall sign of the aerosol

  14. Direct and indirect effects of sea spray geoengineering and the role of injected particle size

    NASA Astrophysics Data System (ADS)

    Partanen, Antti-Ilari; Kokkola, Harri; Romakkaniemi, Sami; Kerminen, Veli-Matti; Lehtinen, Kari E. J.; Bergman, Tommi; Arola, Antti; Korhonen, Hannele

    2012-01-01

    Climate-aerosol model ECHAM5.5-HAM2 was used to investigate how geoengineering with artificial sea salt emissions would affect marine clouds and the Earth's radiative balance. Prognostic cloud droplet number concentration and interaction of aerosol particles with clouds and radiation were calculated explicitly, thus making this the first time that aerosol direct effects of sea spray geoengineering are considered. When a wind speed dependent baseline geoengineering flux was applied over all oceans (total annual emissions 443.9 Tg), we predicted a radiative flux perturbation (RFP) of -5.1 W m-2, which is enough to counteract warming from doubled CO2 concentration. When the baseline flux was limited to three persistent stratocumulus regions (3.3% of Earth's surface, total annual emissions 20.6 Tg), the RFP was -0.8 Wm-2 resulting mainly from a 74-80% increase in cloud droplet number concentration and a 2.5-4.4 percentage point increase in cloud cover. Multiplying the baseline mass flux by 5 or reducing the injected particle size from 250 to 100 nm had comparable effects on the geoengineering efficiency with RFPs -2.2 and -2.1 Wm-2, respectively. Within regions characterized with persistent stratocumulus decks, practically all of the radiative effect originated from aerosol indirect effects. However, when all oceanic regions were seeded, the direct effect with the baseline flux was globally about 29% of the total radiative effect. Together with previous studies, our results indicate that there are still large uncertainties associated with the sea spray geoengineering efficiency due to variations in e.g., background aerosol concentration, updraft velocity, cloud altitude and onset of precipitation.

  15. Constraining cloud lifetime effects of aerosols using A-Train satellite observations

    SciTech Connect

    Wang, Minghuai; Ghan, Steven J.; Liu, Xiaohong; Ecuyer, Tristan L.; Zhang, Kai; Morrison, H.; Ovchinnikov, Mikhail; Easter, Richard C.; Marchand, Roger; Chand, Duli; Qian, Yun; Penner, Joyce E.

    2012-08-15

    Aerosol indirect effects have remained the largest uncertainty in estimates of the radiative forcing of past and future climate change. Observational constraints on cloud lifetime effects are particularly challenging since it is difficult to separate aerosol effects from meteorological influences. Here we use three global climate models, including a multi-scale aerosol-climate model PNNL-MMF, to show that the dependence of the probability of precipitation on aerosol loading, termed the precipitation frequency susceptibility (S{sub pop}), is a good measure of the liquid water path response to aerosol perturbation ({lambda}), as both Spop and {lambda} strongly depend on the magnitude of autoconversion, a model representation of precipitation formation via collisions among cloud droplets. This provides a method to use satellite observations to constrain cloud lifetime effects in global climate models. S{sub pop} in marine clouds estimated from CloudSat, MODIS and AMSR-E observations is substantially lower than that from global climate models and suggests a liquid water path increase of less than 5% from doubled cloud condensation nuclei concentrations. This implies a substantially smaller impact on shortwave cloud radiative forcing (SWCF) over ocean due to aerosol indirect effects than simulated by current global climate models (a reduction by one-third for one of the conventional aerosol-climate models). Further work is needed to quantify the uncertainties in satellite-derived estimates of S{sub pop} and to examine S{sub pop} in high-resolution models.

  16. Synopsis of Direct and Indirect Lightning Effects on Composite Materials

    NASA Technical Reports Server (NTRS)

    Clark, Tony

    1998-01-01

    NASA's Space Environments and Effects (SEE) Program funded a study on electromagnetic environmental effect issues of composite materials used by the aerospace industry. The results of which are published by Ross Evans, Tec-Masters Inc., in NASA-CR-4783, "Test Report - Direct and Indirect Lightning Effects on Composite Materials." Indirect effects include the electric and magnetic field shielding provided by a composite material illuminated by a near or direct lightning strike. Direct effects includes the physical damage of composites and/or assembly joint with a direct strike injection. This paper provides a synopsis of NASA-CR-4783. A short description is provided of the direct and indirect tests performed during the sturdy. General results and design guidelines are discussed.

  17. Measuring indirect effects of rotavirus vaccine in low income countries.

    PubMed

    Bennett, Aisleen; Bar-Zeev, Naor; Cunliffe, Nigel A

    2016-08-17

    Widespread introduction of rotavirus vaccines has led to major reductions in the burden of rotavirus gastroenteritis worldwide. Vaccine effectiveness is diminished, however, in low income countries, that harbour the greatest burden of rotavirus attributed morbidity and mortality. Indirect effects of rotavirus vaccine (herd immunity and herd protection) could increase population level impact and improve vaccine cost effectiveness in such settings. While rotavirus vaccine indirect effects have been demonstrated in high and middle income countries, there are very little data from low income countries where force of infection, population structures and vaccine schedules differ. Targeted efforts to evaluate indirect effects of rotavirus vaccine in low income countries are required to understand the total impact of rotavirus vaccine on the global burden of rotavirus disease. PMID:27443593

  18. Assessment of dust aerosol effect on cloud properties over Northwest China using CERES SSF data

    NASA Astrophysics Data System (ADS)

    Huang, J.; Wang, X.; Wang, T.; Su, J.; Minnis, P.; Lin, B.; Hu, Y.; Yi, Y.

    Dust aerosols not only have direct effects on the climate through reflection and absorption of the short and long wave radiation but also modify cloud properties such as the number concentration and size of cloud droplets indirect effect and contribute to diabatic heating in the atmosphere that often enhances cloud evaporation and reduces the cloud water path In this study indirect and semi-direct effects of dust aerosols are analyzed over eastern Asia using two years June 2002 to June 2004 of CERES Clouds and the Earth s Radiant Energy Budget Scanner and MODIS MODerate Resolution Imaging Spectroradiometer Aqua Edition 1B SSF Single Scanner Footprint data sets The statistical analysis shows evidence for both indirect and semi-direct effect of Asia dust aerosols The dust appears to reduce the ice cloud effective particle diameter and increase high cloud amount On average ice cloud effective particle diameters of cirrus clouds under dust polluted conditions dusty cloud are 11 smaller than those derived from ice clouds in dust-free atmospheric environments The water paths of dusty clouds are also considerably smaller than those of dust-free clouds Dust aerosols could warm clouds thereby increasing the evaporation of cloud droplets resulting in reduced cloud water path semi-direct effect The semi-direct effect may be dominated the interaction between dust aerosols and clouds over arid and semi-arid areas and partly contribute to reduced precipitation

  19. Confounding effects of indirect connections on causality estimation.

    PubMed

    Vakorin, Vasily A; Krakovska, Olga A; McIntosh, Anthony R

    2009-10-30

    Addressing the issue of effective connectivity, this study focuses on effects of indirect connections on inferring stable causal relations: partial transfer entropy. We introduce a Granger causality measure based on a multivariate version of transfer entropy. The statistic takes into account the influence of the rest of the network (environment) on observed coupling between two given nodes. This formalism allows us to quantify, for a specific pathway, the total amount of indirect coupling mediated by the environment. We show that partial transfer entropy is a more sensitive technique to identify robust causal relations than its bivariate equivalent. In addition, we demonstrate the confounding effects of the variation in indirect coupling on the detectability of robust causal links. Finally, we consider the problem of model misspecification and its effect on the robustness of the observed connectivity patterns, showing that misspecifying the model may be an issue even for model-free information-theoretic approach. PMID:19628006

  20. Uncertainties in global aerosols and climate effects due to biofuel emissions

    NASA Astrophysics Data System (ADS)

    Kodros, J. K.; Scott, C. E.; Farina, S. C.; Lee, Y. H.; L'Orange, C.; Volckens, J.; Pierce, J. R.

    2015-04-01

    Aerosol emissions from biofuel combustion impact both health and climate; however, while reducing emissions through improvements to combustion technologies will improve health, the net effect on climate is largely unconstrained. In this study, we examine sensitivities in global aerosol concentration, direct radiative climate effect, and cloud-albedo aerosol indirect climate effect to uncertainties in biofuel emission factors, optical mixing-state, and model nucleation and background SOA. We use the Goddard Earth Observing System global chemical-transport model (GEOS-Chem) with TwO Moment Aerosol Sectional (TOMAS) microphysics. The emission factors include: amount, composition, size and hygroscopicity, as well as optical mixing-state properties. We also evaluate emissions from domestic coal use, which is not biofuel but is also frequently emitted from homes. We estimate the direct radiative effect assuming different mixing states (internal, core-shell, and external) with and without absorptive organic aerosol (brown carbon). We find the global-mean direct radiative effect of biofuel emissions ranges from -0.02 to +0.06 W m-2 across all simulation/mixing state combinations with regional effects in source regions ranging from -0.2 to +1.2 W m-2. The global-mean cloud-albedo aerosol indirect effect ranges from +0.01 to -0.02 W m-2 with regional effects in source regions ranging from -1.0 to -0.05 W m-2. The direct radiative effect is strongly dependent on uncertainties in emissions mass, composition, emissions aerosol size distributions and assumed optical mixing state, while the indirect effect is dependent on the emissions mass, emissions aerosol size distribution and the choice of model nucleation and secondary organic aerosol schemes. The sign and magnitude of these effects have a strong regional dependence. We conclude that the climate effects of biofuel aerosols are largely unconstrained, and the overall sign of the aerosol effects is unclear due to uncertainties

  1. A numerical study of the effect of different aerosol types on East Asian summer clouds and precipitation

    SciTech Connect

    Jiang, Yiquan; Liu, Xiaohong; Yang, Xiuqun; Wang, Minghuai

    2013-05-01

    The impact of anthropogenic aerosol on the East Asian summer monsoon (EASM) is investigated with NCAR CAM5, a state-of-the-art climate model with aerosol’s direct and indirect effects. Results indicate that anthropogenic aerosol tends to cause a weakened EASM with a southward shift of precipitation in East Asia mostly by its radiative effect. Anthropogenic aerosol induced surface cooling stabilizes the boundary layer, suppresses the convection and latent heat release in northern China, and reduces the tropospheric temperature over land and land-sea thermal contrast, thus leading to a weakened EASM. Meanwhile, acting as cloud condensation nuclei (CCN), anthropogenic aerosol can significantly increase the cloud droplet number concentration but decrease the cloud droplet effective radius over Indochina and Indian Peninsulas as well as over southwestern and northern China, inhibiting the precipitation in these regions. Thus, anthropogenic aerosol tends to reduce Southeast and South Asian summer monsoon precipitation by its indirect effect.

  2. Some indirect effects of positive practice overcorrection.

    PubMed

    Peters, Lindsay C; Thompson, Rachel H

    2013-01-01

    We evaluated the effects of positive practice overcorrection (PP OC) on levels of motor stereotypy and appropriate engagement in the activity practiced during treatment with 3 young men with autism. We also measured preference for the practiced activities during preference probes to determine if these activities might acquire aversive properties as a result of the frequent pairing with PP OC. Treatment reduced motor stereotypy for all 3 participants, and engagement increased for 2 of the 3 participants. Relative preference for the activities was not disrupted by the implementation of PP OC, although overall contact with the activities decreased for 1 participant. Results from 1 participant suggest that PP OC may be less effective when stereotypy results in access to a more highly preferred activity. PMID:24114224

  3. Phenylketonuria: Direct and indirect effects of phenylalanine.

    PubMed

    Schlegel, Gudrun; Scholz, Ralf; Ullrich, Kurt; Santer, René; Rune, Gabriele M

    2016-07-01

    High phenylalanine concentrations in the brain due to dysfunctional phenylalanine hydroxylase (Pah) are considered to account for mental retardation in phenylketonuria (PKU). In this study, we treated hippocampal cultures with the amino acid in order to determine the role of elevated levels of phenylalanine in PKU-related mental retardation. Synapse density and dendritic length were dramatically reduced in hippocampal cultures treated with phenylalanine. Changes in cofilin expression and phosphorylation status, which were restored by NMDA, as well as reduced activation of the small GTPase Rac1, likely underlie these structural alterations. In the Pah(enu2) mouse, which carries a mutated Pah gene, we previously found higher synaptic density due to delayed synaptic pruning in response to insufficient microglia function. Microglia activity and C3 complement expression, both of which were reduced in the Pah(enu2) mouse, however, were unaffected in hippocampal cultures treated with phenylalanine. The lack of a direct effect of phenylalanine on microglia is the key to the opposite effects regarding synapse stability in vitro and in the Pah(enu2) mouse. Judging from our data, it appears that another player is required for the inactivation of microglia in the Pah(enu2) mouse, rather than high concentrations of phenylalanine alone. Altogether, the data underscore the necessity of a lifelong phenylalanine-restricted diet. PMID:27091224

  4. Can Aerosol Offset Urban Heat Island Effect?

    NASA Astrophysics Data System (ADS)

    Jin, M. S.; Shepherd, J. M.

    2009-12-01

    The Urban Heat Island effect (UHI) refers to urban skin or air temperature exceeding the temperatures in surrounding non-urban regions. In a warming climate, the UHI may intensify extreme heat waves and consequently cause significant health and energy problems. Aerosols reduce surface insolation via the direct effect, namely, scattering and absorbing sunlight in the atmosphere. Combining the National Aeronautics and Space Administration (NASA) AERONET (AErosol RObotic NETwork) observations over large cities together with Weather Research and Forecasting Model (WRF) simulations, we find that the aerosol direct reduction of surface insolation range from 40-100 Wm-2, depending on seasonality and aerosol loads. As a result, surface skin temperature can be reduced by 1-2C while 2-m surface air temperature by 0.5-1C. This study suggests that the aerosol direct effect is a competing mechanism for the urban heat island effect (UHI). More importantly, both aerosol and urban land cover effects must be adequately represented in meteorological and climate modeling systems in order to properly characterize urban surface energy budgets and UHI.

  5. Temperament, hopelessness, and attempted suicide: direct and indirect effects.

    PubMed

    Rosellini, Anthony J; Bagge, Courtney L

    2014-08-01

    This study evaluated whether hopelessness mediated the relations between temperament and recent suicide attempter status in a psychiatric sample. Negative temperament and positive temperament (particularly the positive emotionality subscale) uniquely predicted levels of hopelessness. Although these temperament constructs also demonstrated significant indirect effects on recent suicide attempter status, the effects were partially (for the broad temperament scales) or fully (for the positive emotionality subscale) mediated by the levels of hopelessness. These findings indicate that a tendency to experience excessive negative emotions as well as a paucity of positive emotions may lead individuals to experience hopelessness. Although temperament may also indirectly influence suicide attempter status, hopelessness mediates these relations. PMID:24494785

  6. Indirect Nanoplasmonic Sensing to Probe with a High Sensitivity the Interaction of Water Vapor with Soot Aerosols.

    PubMed

    Demirdjian, Benjamin; Bedu, Frederic; Ranguis, Alain; Ozerov, Igor; Karapetyan, Artak; Henry, Claude R

    2015-10-15

    We demonstrate in this work that the indirect nanoplasmonic sensing lets us follow the adsorption/desorption of water molecules on soot particles that are a major contributor of the global warming. Increasing the relative humidity of the surrounding medium we measure a shift in wavelength of the localized surface plasmon resonance response of gold nanodisks on which soot particles are deposited. We show a singular and reversible blue shift with hydrophilic aircraft soot particles interpreted from a basic model as a reversible morphological change of the soot aggregates. This new method is highly sensitive and interesting to follow the change of optical properties of aerosols during their aging in the atmosphere, where they can adsorb and react with different gas molecules. PMID:26722790

  7. An improved recommendation algorithm via weakening indirect linkage effect

    NASA Astrophysics Data System (ADS)

    Chen, Guang; Qiu, Tian; Shen, Xiao-Quan

    2015-07-01

    We propose an indirect-link-weakened mass diffusion method (IMD), by considering the indirect linkage and the source object heterogeneity effect in the mass diffusion (MD) recommendation method. Experimental results on the MovieLens, Netflix, and RYM datasets show that, the IMD method greatly improves both the recommendation accuracy and diversity, compared with a heterogeneity-weakened MD method (HMD), which only considers the source object heterogeneity. Moreover, the recommendation accuracy of the cold objects is also better elevated in the IMD than the HMD method. It suggests that eliminating the redundancy induced by the indirect linkages could have a prominent effect on the recommendation efficiency in the MD method. Project supported by the National Natural Science Foundation of China (Grant No. 11175079) and the Young Scientist Training Project of Jiangxi Province, China (Grant No. 20133BCB23017).

  8. Aerosol-cloud interactions: effect on precipitation

    NASA Astrophysics Data System (ADS)

    Takle, Jasmine; Maheskumar, R.

    2016-05-01

    Aerosols are tiny suspended particle in the atmosphere with high variability in time and space, play a major role in modulating the cloud properties and thereby precipitation. To understand the aerosol induced Invigoration effect predictors like aerosol optical depth, cloud optical depth, cloud top temperature, cloud effective radii, ice water path, retrieved from the Moderate resolution Imaging Spectroradiometer (MODIS) level-3 aqua satellite data were analysed for pre monsoon April-May and post monsoon October-November months over the Indian subcontinent 8 ° N to 33° N, 65 °E to 100 °E during the period 2003-2013. Apart from the above data, mesoscale dynamical parameters such as vertical wind shear of horizontal wind, relative humidity, were also considered to understand their role in invigoration. Case studies have been carried out for the regions having heavy rainfall events & minimal rainfall events during high Aerosol optical depths occasions respectively. Analysis revealed that the heavy rainfall which occurred in this region with higher optical depths might be due to invigoration effect of aerosols wherein the dynamical as well as thermodynamical parameters were also found favourable. Minimal rainfall events were also observed most probably due to the suppression of rain formation/delay in precipitation due to high amount of aerosol concentration in these regions. Prominent 36 such cases were studied all over India during Pre & Post monsoon months.

  9. Investigation of multiple scattering effects in aerosols

    NASA Technical Reports Server (NTRS)

    Deepak, A.

    1980-01-01

    The results are presented of investigations on the various aspects of multiple scattering effects on visible and infrared laser beams transversing dense fog oil aerosols contained in a chamber (4' x 4' x 9'). The report briefly describes: (1) the experimental details and measurements; (2) analytical representation of the aerosol size distribution data by two analytical models (the regularized power law distribution and the inverse modified gamma distribution); (3) retrieval of aerosol size distributions from multispectral optical depth measurements by two methods (the two and three parameter fast table search methods and the nonlinear least squares method); (4) modeling of the effects of aerosol microphysical (coagulation and evaporation) and dynamical processes (gravitational settling) on the temporal behavior of aerosol size distribution, and hence on the extinction of four laser beams with wavelengths 0.44, 0.6328, 1.15, and 3.39 micrometers; and (5) the exact and approximate formulations for four methods for computing the effects of multiple scattering on the transmittance of laser beams in dense aerosols, all of which are based on the solution of the radiative transfer equation under the small angle approximation.

  10. Effect of Increasing Temperature on Carbonaceous Aerosol Direct Radiative Effect over Southeastern US

    NASA Astrophysics Data System (ADS)

    Mielonen, Tero; Kokkola, Harri; Hienola, Anca; Kühn, Thomas; Merikanto, Joonas; Korhonen, Hannele; Arola, Antti; Kolmonen, Pekka; Sogacheva, Larisa; de Leeuw, Gerrit

    2016-04-01

    Aerosols are an important regulator of the Earth's climate. They scatter and absorb incoming solar radiation and thus cool the climate by reducing the amount of energy reaching the atmospheric layers and the surface below (direct effect). A certain subset of the particles can also act as initial formation sites for cloud droplets and thereby modify the microphysics, dynamics, radiative properties and lifetime of clouds (indirect effects). The magnitude of aerosol radiative effects remains the single largest uncertainty in current estimates of anthropogenic radiative forcing. One of the key quantities needed for accurate estimates of anthropogenic radiative forcing is an accurate estimate of the radiative effects from natural unperturbed aerosol. The dominant source of natural aerosols over Earth's vast forested regions are biogenic volatile organic compounds (BVOC) which, following oxidation in the atmosphere, can condense onto aerosol particles to form secondary organic aerosol (SOA) and significantly modify the particles' properties. In accordance with the expected positive temperature dependence of BVOC emissions, several previous studies have shown that some aerosol properties, such as mass concentration and ability to act as cloud condensation nuclei (CCN), also correlate positively with temperature at many forested sites. There is conflicting evidence as to whether the aerosol direct effects have a temperature dependence due to increased BVOC emissions. The main objective of this study is to investigate the causes of the observed effect of increasing temperatures on the aerosol direct radiative effect, and to provide a quantitative estimate of this effect and of the resulting negative feedback in a warming climate. More specifically, we will investigate the causes of the positive correlation between aerosol optical depth (AOD) and land surface temperature (LST) over southeastern US where biogenic emissions are a significant source of atmospheric particles. In

  11. Simulation of the Indirect Radiative Forcing of Climate Due to Aerosols by the Two-Way Coupled WRF-CMAQ over the Eastern United States

    EPA Science Inventory

    In this study, the shortwave cloud forcing (SWCF) and longwave cloud forcing (LWCF) are estimated with the newly developed two-way coupled WRF-CMAQ over the eastern United States. Preliminary indirect aerosol forcing has been successfully implemented in WRF-CMAQ. The comparisons...

  12. Measurements of Semi-volatile Aerosol and Its Effect on Aerosol Optical Properties During Southern Oxidant and Aerosol Study

    NASA Astrophysics Data System (ADS)

    Khlystov, A.; Grieshop, A. P.; Saha, P.; Subramanian, R.

    2013-12-01

    Semi-volatile compounds, including particle-bound water, comprise a large part of aerosol mass and have a significant influence on aerosol lifecycle and its optical properties. Understanding the properties of semi-volatile compounds, especially those pertaining to gas/aerosol partitioning, is of critical importance for our ability to predict concentrations and properties of ambient aerosol. A set of state-of-the-art instruments was deployed at the SEARCH site near Centerville, AL during the Southern Oxidant and Aerosol Study (SOAS) campaign in summer 2013 to measure the effect of temperature and relative humidity on aerosol size distribution, composition and optical properties. Light scattering and absorption by temperature- and humidity-conditioned aerosols was measured using three photo-acoustic extinctiometers (PAX) at three wavelengths (405 nm, 532 nm, and 870 nm). In parallel to these measurements, a long residence time temperature-stepping thermodenuder and a variable residence time constant temperature thermodenuder in combination with three SMPS systems and an Aerosol Chemical Speciation Monitor (ACSM) were used to assess aerosol volatility and kinetics of aerosol evaporation. It was found that both temperature and relative humidity have a strong effect on aerosol optical properties. The variable residence time thermodenuder data suggest that aerosol equilibrated fairly quickly, within 2 s, in contrast to other ambient observations. Preliminary analysis show that approximately 50% and 90% of total aerosol mass evaporated at temperatures of 100 C and 180C, respectively. Evaporation varied substantially with ambient aerosol loading and composition and meteorology. During course of this study, T50 (temperatures at which 50% aerosol mass evaporates) varied from 60 C to more than 120 C.

  13. Smoke and Pollution Aerosol Effect on Cloud Cover

    NASA Technical Reports Server (NTRS)

    Kaufman, Yoram J.; Koren, Ilan

    2006-01-01

    Pollution and smoke aerosols can increase or decrease the cloud cover. This duality in the effects of aerosols forms one of the largest uncertainties in climate research. Using solar measurements from Aerosol Robotic Network sites around the globe, we show an increase in cloud cover with an increase in the aerosol column concentration and an inverse dependence on the aerosol absorption of sunlight. The emerging rule appears to be independent of geographical location or aerosol type, thus increasing our confidence in the understanding of these aerosol effects on the clouds and climate. Preliminary estimates suggest an increase of 5% in cloud cover.

  14. Effective dose from direct and indirect digital panoramic units

    PubMed Central

    Lee, Gun-Sun; Kim, Jin-Soo; Seo, Yo-Seob

    2013-01-01

    Purpose This study aimed to provide comparative measurements of the effective dose from direct and indirect digital panoramic units according to phantoms and exposure parameters. Materials and Methods Dose measurements were carried out using a head phantom representing an average man (175 cm tall, 73.5 kg male) and a limbless whole body phantom representing an average woman (155 cm tall, 50 kg female). Lithium fluoride thermoluminescent dosimeter (TLD) chips were used for the dosimeter. Two direct and 2 indirect digital panoramic units were evaluated in this study. Effective doses were derived using 2007 International Commission on Radiological Protection (ICRP) recommendations. Results The effective doses of the 4 digital panoramic units ranged between 8.9 µSv and 37.8 µSv. By using the head phantom, the effective doses from the direct digital panoramic units (37.8 µSv, 27.6 µSv) were higher than those from the indirect units (8.9 µSv, 15.9 µSv). The same panoramic unit showed the difference in effective doses according to the gender of the phantom, numbers and locations of TLDs, and kVp. Conclusion To reasonably assess the radiation risk from various dental radiographic units, the effective doses should be obtained with the same numbers and locations of TLDs, and with standard hospital exposure. After that, it is necessary to survey the effective doses from various dental radiographic units according to the gender with the corresponding phantom. PMID:23807930

  15. Assessing the Potential Effect of Anthropogenic Aerosol Dimming on Sea Surface Temperatures (SSTs)

    NASA Astrophysics Data System (ADS)

    Dallafior, Tanja; Folini, Doris; Wild, Martin; Knutti, Reto

    2014-05-01

    It is beyond doubt that anthropogenic aerosols have an impact on the Earth's radiative balance and hydrological cycle through both direct and indirect effects. The focus of this presentation is the statistically robust quantification of anthropogenic aerosol dimming over oceans, using a global climate model (ECHAM5 at T42L19 resolution) combined with a detailed aerosol microphysics module (HAM, the Hamburg Aerosol Module). The long term goal is to quantify consequences of such forcing on sea surface temperatures (SSTs). We use a series of atmosphere only experiments with prescribed observed transient SSTs covering the years 1870-2000. All experimental setups are identical except for anthropogenic aerosol emissions, which are once transient (13 ensemble members) and once held constant at pre-industrial levels (9 ensemble members). On regional scales and in recent decades, anthropogenic aerosol dimming at the sea surface can reach considerable magnitudes, exceeding 20W/m2 in the model. To quantify these findings in more detail, we assume that anthropogenic aerosols spread from the continents in plumes, and introduce identification criteria for said plumes based on statistical testing of changes in aerosol optical thickness and downward short-wave radiation (clear-sky and all-sky). Using the pre-industrial experiment data to construct a reference distribution, the above three variables are tested at each grid point for each month and decade of the transient experiment against the respective reference distribution to identify significant changes in aerosol-induced surface forcing, in the form of changes in downward clearsky shortwave radiation (direct aerosol effect) or in the form or changes of downward allsky shortwave radiation (including also indirect aerosol effects). The resulting aerosol plume regions are analysed for size, intensity and associated surface dimming, persistence, seasonality, and interdecadal trends. The sensitivity of the results towards the

  16. Direct and indirect effects in a logit model

    PubMed Central

    Buis, Maarten L.

    2012-01-01

    This article discusses a method by Erikson et al. (2005) for decomposing a total effect in a logit model into direct and indirect effects. Moreover, this article extends this method in three ways. First, in the original method the variable through which the indirect effect occurs is assumed to be normally distributed. In this article the method is generalized by allowing this variable to have any distribution. Second, the original method did not provide standard errors for the estimates. In this article the bootstrap is proposed as a method of providing those. Third, I show how to include control variables in this decomposition, which was not allowed in the original method. The original method and these extensions are implemented in the ldecomp package. PMID:22468140

  17. Weighting and indirect effects identify keystone species in food webs.

    PubMed

    Zhao, Lei; Zhang, Huayong; O'Gorman, Eoin J; Tian, Wang; Ma, Athen; Moore, John C; Borrett, Stuart R; Woodward, Guy

    2016-09-01

    Species extinctions are accelerating globally, yet the mechanisms that maintain local biodiversity remain poorly understood. The extinction of species that feed on or are fed on by many others (i.e. 'hubs') has traditionally been thought to cause the greatest threat of further biodiversity loss. Very little attention has been paid to the strength of those feeding links (i.e. link weight) and the prevalence of indirect interactions. Here, we used a dynamical model based on empirical energy budget data to assess changes in ecosystem stability after simulating the loss of species according to various extinction scenarios. Link weight and/or indirect effects had stronger effects on food-web stability than the simple removal of 'hubs', demonstrating that both quantitative fluxes and species dissipating their effects across many links should be of great concern in biodiversity conservation, and the potential for 'hubs' to act as keystone species may have been exaggerated to date. PMID:27346328

  18. The indirect effects of subsidised healthcare in rural Ghana.

    PubMed

    Powell-Jackson, Timothy; Ansah, Evelyn K

    2015-11-01

    Social networks provide a channel through which health policies and programmes can affect those with close social ties to the intended beneficiaries. We provide experimental evidence on the indirect effects of heavily subsidised healthcare. By exploiting data on 2151 households from a randomised study conducted in a rural district of Ghana in 2005, we estimate the extent to which social networks, defined by religion, influence the uptake of primary care services. We find that people socially connected to households with subsidised care are less likely to use primary care services despite the fact that the direct effect of the intervention is positive. We extend the empirical analysis to consider the implications of these changes in behaviour for welfare but find no evidence of indirect effects on child health and healthcare spending. In the context of this study, the findings highlight the potential for healthcare subsidies to have unintended consequences. PMID:26409167

  19. How Do Aerosol Radiative Effects Influence Wind? a Sensitivity Study of the Aerosol Impact on the Spatially-Distributed Wind over Europe

    NASA Astrophysics Data System (ADS)

    Baro Esteban, R.; Lorente-Plazas, R.; Jerez, S.; Montavez, J. P.; Jimenez-guerrero, P.

    2014-12-01

    Atmospheric aerosols affect the Earth's climate through their radiative effects, being one of the most uncertain areas in climate modeling. Radiative effects depend mainly on the aerosol optical properties and can be divided into direct and semi-direct effect, produced by the scattering and absorption of radiation; and indirect effect, which influences the aerosols-cloud interactions. Aerosols are widely known to affect radiation, temperature, stability, clouds, and precipitation. However, scientific literature about their effects on wind is scarce. In this sense, the effects of aerosol particles on spatially-distributed winds over Europe are examined. The methodology carried out consists of two WRF-Chem simulations for Europe for the entire year 2010 differing only in the inclusion (or not) of aerosol radiative feedbacks. These simulations have been carried out under the umbrella of the second phase of the AQMEII (Air Quality Model Evaluation International Initiative, http://aqmeii.jrc.ec.europa.eu/). A Euro-CORDEX compliant domain at 0.22º and 23 km resolution has been used. The first simulation does not take into account any aerosol feedbacks (NFB) and the second simulation differs from the base case by the inclusion of direct and indirect radiative feedbacks (FB). Results show that the presence of aerosol generally reduces the wind over Europe. The absorption and scattering of solar radiation by the aerosol particles heat the air and cool the ground temperature leading to an atmospheric stability. This increases the atmospheric stability and decreases the turbulence, as consequence the vertical transfer of momentum diminishes and the surface winds are slower. In addition, the decrease of solar radiation to the ground weakens the thermal circulations, such as land-sea breezes which is more noticeable in the southern of Europe in summer. On the other hand, the indirect effect of the aerosols through their enhancement of clouds also favors a decline of winds

  20. An attempt to quantify aerosol-cloud effects in fields of precipitating trade wind cumuli

    NASA Astrophysics Data System (ADS)

    Seifert, Axel; Heus, Thijs

    2015-04-01

    Aerosol indirect effects are notoriously difficult to understand and quantify. Using large-eddy simulations (LES) we attempt to quantify the impact of aerosols on the albedo and the precipitation formation in trade wind cumulus clouds. Having performed a set of large-domain Giga-LES runs we are able to capture the mesoscale self-organization of the cloud field. Our simulations show that self-organization is intrinsically tied to precipitation formation in this cloud regime making previous studies that did not consider cloud organization questionable. We find that aerosols, here modeled just as a perturbation in cloud droplet number concentration, have a significant impact on the transient behavior, i.e., how fast rain is formed and self-organization of the cloud field takes place. Though, for longer integration times, all simulations approach the same radiative-convective equilibrium and aerosol effects become small. The sensitivity to aerosols becomes even smaller when we include explicit cloud-radiation interaction as this leads to a much faster and more vigorous response of the cloud layer. Overall we find that aerosol-cloud interactions, like cloud lifetime effects etc., are small or even negative when the cloud field is close to equilibrium. Consequently, the Twomey effect does already provide an upper bound on the albedo effects of aerosol perturbations. Our analysis also highlights that current parameterizations that predict only the grid-box mean of the cloud field and do not take into account cloud organization are not able to describe aerosol indirect effects correctly, but overestimate them due to that lack of cloud dynamical and mesoscale buffering.

  1. Indirect estimation of absorption properties for fine aerosol particles using AATSR observations: a case study of wildfires in Russia in 2010

    NASA Astrophysics Data System (ADS)

    Rodriguez, E.; Kolmonen, P.; Virtanen, T. H.; Sogacheva, L.; Sundstrom, A.-M.; de Leeuw, G.

    2015-08-01

    The Advanced Along-Track Scanning Radiometer (AATSR) on board the ENVISAT satellite is used to study aerosol properties. The retrieval of aerosol properties from satellite data is based on the optimized fit of simulated and measured reflectances at the top of the atmosphere (TOA). The simulations are made using a radiative transfer model with a variety of representative aerosol properties. The retrieval process utilizes a combination of four aerosol components, each of which is defined by their (lognormal) size distribution and a complex refractive index: a weakly and a strongly absorbing fine-mode component, coarse mode sea salt aerosol and coarse mode desert dust aerosol). These components are externally mixed to provide the aerosol model which in turn is used to calculate the aerosol optical depth (AOD). In the AATSR aerosol retrieval algorithm, the mixing of these components is decided by minimizing the error function given by the sum of the differences between measured and calculated path radiances at 3-4 wavelengths, where the path radiances are varied by varying the aerosol component mixing ratios. The continuous variation of the fine-mode components allows for the continuous variation of the fine-mode aerosol absorption. Assuming that the correct aerosol model (i.e. the correct mixing fractions of the four components) is selected during the retrieval process, also other aerosol properties could be computed such as the single scattering albedo (SSA). Implications of this assumption regarding the ratio of the weakly/strongly absorbing fine-mode fraction are investigated in this paper by evaluating the validity of the SSA thus obtained. The SSA is indirectly estimated for aerosol plumes with moderate-to-high AOD resulting from wildfires in Russia in the summer of 2010. Together with the AOD, the SSA provides the aerosol absorbing optical depth (AAOD). The results are compared with AERONET data, i.e. AOD level 2.0 and SSA and AAOD inversion products. The RMSE

  2. The indirect effects on the computation of geoid undulations

    NASA Technical Reports Server (NTRS)

    Wichiencharoen, C.

    1982-01-01

    The indirect effects on the geoid computation due to the second method of Helmert's condensation were studied. when Helmert's anomalies are used in Stokes's equation, there are three types of corrections to the free air geoid. The first correction, the indirect effect on geoid undulation due to the potential change in Helmert's reduction, had a maximum value of 0.51 meters in the test area covering the United States. The second correction, the attraction change effect on geoid undulation, had a maximum value of 9.50 meters when the 10 deg cap was used in Stokes' equation. The last correction, the secondary indirect effect on geoid undulatin, was found negligible in the test area. The corrections were applied to uncorrected free air geoid undulations at 65 Doppler stations in the test area and compared with the Doppler undulations. Based on the assumption that the Doppler coordinate system has a z shift of 4 meters with respect to the geocenter, these comparisons showed that the corrections presented in this study yielded improved values of gravimetric undulations.

  3. Effects of stratospheric sulfate aerosol geo-engineering on cirrus clouds

    NASA Astrophysics Data System (ADS)

    Kuebbeler, Miriam; Lohmann, Ulrike; Feichter, Johann

    2012-12-01

    Cooling the Earth through the injection of sulphate into the stratosphere is one of the most discussed geo-engineering (GE) schemes. Stratospheric aerosols can sediment into the troposphere, modify the aerosol composition and thus might impact cirrus clouds. We use a global climate model with a physically based parametrization for cirrus clouds in order to investigate possible microphysical and dynamical effects. We find that enhanced stratospheric aerosol loadings as proposed by several GE approaches will likely lead to a reduced ice crystal nucleation rate and thus optically thinner cirrus clouds. These optically thinner cirrus clouds exert a strong negative cloud forcing in the long-wave which contributes by 60% to the overall net GE forcing. This shows that indirect effects of stratospheric aerosols on cirrus clouds may be important and need to be considered in order to estimate the maximum cooling derived from stratospheric GE.

  4. Aerosol effects on stratocumulus water paths in a PDF-based parameterization

    NASA Astrophysics Data System (ADS)

    Guo, H.; Golaz, J.-C.; Donner, L. J.

    2011-09-01

    Successful simulation of aerosol indirect effects in climate models requires parameterizations that capture the full range of cloud-aerosol interactions, including positive and negative liquid water path (LWP) responses to increasing aerosol concentrations, as suggested by large eddy simulations (LESs). A parameterization based on multi-variate probability density functions with dynamics (MVD PDFs) has been incorporated into the single-column version of GFDL AM3, extended to treat aerosol activation, and coupled with a two-moment microphysics scheme. We use it to explore cloud-aerosol interactions. In agreement with LESs, our single-column simulations produce both positive and negative LWP responses to increasing aerosol concentrations, depending on precipitation and free atmosphere relative humidity. We have conducted sensitivity tests to vertical resolution and droplet sedimentation parameterization. The dependence of sedimentation on cloud droplet size is essential to capture the full LWP responses to aerosols. Further analyses reveal that the MVD PDFs are able to represent changes in buoyancy profiles induced by sedimentation as well as enhanced entrainment efficiency with aerosols comparable to LESs.

  5. Effect of Organic Sea Spray Aerosol on Global and Regional Cloud Condensation Nuclei Concentrations

    NASA Astrophysics Data System (ADS)

    Westervelt, D. M.; Nenes, A.; Moore, R.; Adams, P. J.

    2009-12-01

    Physical processes on the ocean surface (bubble bursting) result in formation of sea spray aerosol. It is now recognized that this aerosol source includes a significant amount of organic matter (O’Dowd et al. 2004). Higher amounts of aerosol lead to higher cloud condensation nuclei (CCN) concentrations, which perturb climate by brightening clouds in what is known as the aerosol indirect effect (Twomey 1977). This work quantifies the marine organic aerosol global emission source as well the effect of the aerosol on CCN by implementing an organic sea spray source function into a series of global aerosol simulations. The new organic sea spray source function correlates satellite retrieved chlorophyll concentrations to fraction of organic matter in sea spray aerosol (O’Dowd et al. 2008). Using this source function, a global marine organic aerosol emission rate of 17.2 Tg C yr-1 is estimated. Effect on CCN concentrations (0.2% supersaturation) is modeled using the Two-Moment Aerosol Sectional (TOMAS) microphysics algorithm coupled to a general circulation model (Adams and Seinfeld 2002). Upon including organic sea spray aerosol in global simulations, changes in CCN concentrations are induced by the changed aerosol composition as well as the ability of the organic matter to serve as surfactants. To explore surfactant effects, surface tension depression data from seawater samples taken near the Georgia coast were applied as a function of carbon concentrations (Moore et al. 2008). Preliminary findings suggest that organic sea spray aerosol exerts a localized influence on CCN(0.2%) concentrations. Surfactant effects appear to be the most important impact of marine organic aerosol on CCN(0.2%), as changes in aerosol composition alone have a weak influence, even in regions of high organic sea spray emissions. 1. O’Dowd, C.D., Facchini, M.C. et al., Nature, 431, (2004) 2. Twomey, S., J. Atmos. Sci., 34, (1977) 3. O’Dowd C.D et al. Geophys. Res. Let., 35, (2008) 4

  6. Total, Direct and Indirect Effects of Paan on Oral Cancer

    PubMed Central

    Merchant, Anwar T; Pitiphat, Waranuch

    2014-01-01

    Purpose Paan (betel leaf and betel nut quid) used with or without tobacco has been positively associated with oral cancer. Oral submucous fibrosis (OSMF), a pre-cancerous condition caused by paan, lies on the causal pathway between paan use and oral cancer. The purpose of this analysis was to estimate the effect of paan consumption on oral cancer risk when it is mediated by OSMF. Methods We used mediation methods proposed by Vanderweele, which are based on causal inference principles, to characterize the total, direct and indirect effects of paan, consumed with and without tobacco, on oral cancer mediated by OSMF. We reanalyzed case-control data collected from three hospitals in Karachi, Pakistan between July 1996 and March 1998. Results For paan without tobacco the total effect on oral cancer was OR=7.39, 95% CI, 1.01, 38.11, natural indirect effect (due to OSMF among paan users) was OR=2.48, 95% CI, 0.99, 10.44, and the natural direct effect (due to paan with OSMF absent) was OR=3.32, 95% CI, 0.68, 10.07. For paan with tobacco the total direct effect was OR=15.68, 95% CI, 3.00, 54.90, natural indirect effect was OR=2.18, 95% CI,0.82, 5.52, and the natural direct effect was OR=7.27, 95% CI,2.15, 20.43. Conclusions Paan, whether or not it contained tobacco, raised oral cancer risk irrespective of OSMF. Oral cancer risk was higher among those who used paan with tobacco. PMID:25542140

  7. Effects of Carbon Dioxide Aerosols on the Viability of Escherichia coli during Biofilm Dispersal

    PubMed Central

    Singh, Renu; Monnappa, Ajay K.; Hong, Seongkyeol; Mitchell, Robert J.; Jang, Jaesung

    2015-01-01

    A periodic jet of carbon dioxide (CO2) aerosols is a very quick and effective mechanical technique to remove biofilms from various substrate surfaces. However, the impact of the aerosols on the viability of bacteria during treatment has never been evaluated. In this study, the effects of high-speed CO2 aerosols, a mixture of solid and gaseous CO2, on bacteria viability was studied. It was found that when CO2 aerosols were used to disperse biofilms of Escherichia coli, they led to a significant loss of viability, with approximately 50% of the dispersed bacteria killed in the process. By comparison, 75.6% of the biofilm-associated bacteria were viable when gently dispersed using Proteinase K and DNase I. Indirect proof that the aerosols are damaging the bacteria was found using a recombinant E. coli expressing the cyan fluorescent protein, as nearly half of the fluorescence was found in the supernatant after CO2 aerosol treatment, while the rest was associated with the bacterial pellet. In comparison, the supernatant fluorescence was only 9% when the enzymes were used to disperse the biofilm. As such, these CO2 aerosols not only remove biofilm-associated bacteria effectively but also significantly impact their viability by disrupting membrane integrity. PMID:26345492

  8. Dependence of the effect of aerosols on cirrus clouds on background vertical velocity

    NASA Astrophysics Data System (ADS)

    Lee, Seoung Soo

    2012-07-01

    Cirrus clouds cover approximately 20-25% of the globe and thus play an important role in the Earth's radiation budget. This important role in the radiation budget played by cirrus clouds indicates that aerosol effects on cirrus clouds can have a substantial impact on the variation of global radiative forcing if the ice-water path (IWP) changes. This study examines the aerosol indirect effect (AIE) through changes in the IWP for cirrus cloud cases. This study also examines the dependence of aerosol-cloud interactions in cirrus clouds on the large-scale vertical motion. We use a cloud-system resolving model (CSRM) coupled with a double-moment representation of cloud microphysics. Intensified interactions among the cloud ice number concentration (CINC), deposition and dynamics play a critical role in the IWP increases due to aerosol increases from the preindustrial (PI) level to the present-day (PD) level with a low large-scale vertical velocity. Increased aerosols lead to an increased CINC, providing an increased surface area for water vapor deposition. The increased surface area leads to increased deposition despite decreased supersaturation with increasing aerosols. The increased deposition causes an increased depositional heating which produces stronger updrafts, and these stronger updrafts lead to the increased IWP. However, with a high large-scale vertical velocity, the effect of increased CINC on deposition was not able to offset the effect of decreasing supersaturation with increasing aerosols. The effect of decreasing supersaturation on deposition dominant over that of increasing CINC leads to smaller deposition and IWP at high aerosol with the PD aerosol than at low aerosol with the PI aerosol. The conversion of ice crystals to aggregates through autoconversion and accretion plays a negligible role in the IWP responses to aerosols, as does the sedimentation of aggregates. The sedimentation of ice crystals plays a more important role in the IWP response to

  9. Climatic effects of 1950-2050 changes in US anthropogenic aerosols - Part 2: Climate response

    NASA Astrophysics Data System (ADS)

    Leibensperger, E. M.; Mickley, L. J.; Jacob, D. J.; Chen, W.-T.; Seinfeld, J. H.; Nenes, A.; Adams, P. J.; Streets, D. G.; Kumar, N.; Rind, D.

    2012-04-01

    We investigate the climate response to changing US anthropogenic aerosol sources over the 1950-2050 period by using the NASA GISS general circulation model (GCM) and comparing to observed US temperature trends. Time-dependent aerosol distributions are generated from the GEOS-Chem chemical transport model applied to historical emission inventories and future projections. Radiative forcing from US anthropogenic aerosols peaked in 1970-1990 and has strongly declined since due to air quality regulations. We find that the regional radiative forcing from US anthropogenic aerosols elicits a strong regional climate response, cooling the central and eastern US by 0.5-1.0 °C on average during 1970-1990, with the strongest effects on maximum daytime temperatures in summer and autumn. Aerosol cooling reflects comparable contributions from direct and indirect (cloud-mediated) radiative effects. Absorbing aerosol (mainly black carbon) has negligible warming effect. Aerosol cooling reduces surface evaporation and thus decreases precipitation along the US east coast, but also increases the southerly flow of moisture from the Gulf of Mexico resulting in increased cloud cover and precipitation in the central US. Observations over the eastern US show a lack of warming in 1960-1980 followed by very rapid warming since, which we reproduce in the GCM and attribute to trends in US anthropogenic aerosol sources. Present US aerosol concentrations are sufficiently low that future air quality improvements are projected to cause little further warming in the US (0.1 °C over 2010-2050). We find that most of the warming from aerosol source controls in the US has already been realized over the 1980-2010 period.

  10. Climatic effects of 1950-2050 changes in US anthropogenic aerosols - Part 2: Climate response

    NASA Astrophysics Data System (ADS)

    Leibensperger, E. M.; Mickley, L. J.; Jacob, D. J.; Chen, W.-T.; Seinfeld, J. H.; Nenes, A.; Adams, P. J.; Streets, D. G.; Kumar, N.; Rind, D.

    2011-08-01

    We investigate the climate response to US anthropogenic aerosol sources over the 1950 to 2050 period by using the NASA GISS general circulation model (GCM) and comparing to observed US temperature trends. Time-dependent aerosol distributions are generated from the GEOS-Chem chemical transport model applied to historical emission inventories and future projections. Radiative forcing from US anthropogenic aerosols peaked in 1970-1990 and has strongly declined since due to air quality regulations. We find that the regional radiative forcing from US anthropogenic aerosols elicits a strong regional climate response, cooling the central and eastern US by 0.5-1.0 °C on average during 1970-1990, with the strongest effects on maximum daytime temperatures in summer and autumn. Aerosol cooling reflects comparable contributions from direct and indirect (cloud-mediated) radiative effects. Absorbing aerosol (mainly black carbon) has negligible warming effect. Aerosol cooling reduces surface evaporation and thus decreases precipitation along the US east coast, but also increases the southerly flow of moisture from the Gulf of Mexico resulting in increased cloud cover and precipitation in the central US. Observations over the eastern US show a lack of warming in 1960-1980 followed by very rapid warming since, which we reproduce in the GCM and attribute to trends in US anthropogenic aerosol sources. Present US aerosol concentrations are sufficiently low that future air quality improvements are projected to cause little further warming in the US (0.1 °C over 2010-2050). We find that most of the potential warming from aerosol source controls in the US has already been realized over the 1980-2010 period.

  11. Volcanic aerosols: Chemistry, evolution, and effects

    NASA Technical Reports Server (NTRS)

    Turco, Richard

    1991-01-01

    Stratospheric aerosols have been the subject of scientific speculation since the 1880s, when the powerful eruption of Krakatoa attracted worldwide attention to the upper atmosphere through spectacular optical displays. The presence of a permanent tenuous dust layer in the lower stratosphere was postulated in the 1920s following studies of the twilight glow. Junge collected the first samples of these 'dust' particles and demonstrated that they were actually composed of sulfates, most likely concentrated sulfuric acid (Junge and Manson, 1961; Junge, 1963). Subsequent research has been spurred by the realization that stratospheric particles can influence the surface climate of earth through their effects on atmospheric radiation. Such aerosols can also influence, through chemical and physical effects, the trace composition of the atmosphere, ozone concentrations, and atmospheric electrical properties. The properties of stratospheric aerosols (both the background particles and those enhanced by volcanic eruptions) were measured in situ by balloon ascents and high altitude aircraft sorties. The aerosols were also observed remotely from the ground and from satellites using both active (lidar) and passive (solar occultation) techniques (remote sensing instruments were carried on aircraft and balloon platforms as well). In connection with the experimental work, models were developed to test theories of particle formation and evolution, to guide measurement strategies, to provide a means of connecting laboratory and field data, and to apply the knowledge gained to answer practical questions about global changes in climate, depletion of the ozone layer, and related environmental problems.

  12. Modeling Aerosol Effects on Shallow Cumuli and Turbulent Activities Under Various Meteorological Conditions

    NASA Astrophysics Data System (ADS)

    Wang, H.; McFarquhar, G. M.

    2007-12-01

    To determine conditions over the Indian Ocean for which cloud fields are most susceptible to modification from aerosols and to study how turbulent activities and shallow cumuli vary for different meteorological scenarios, the National Center for Atmospheric Research Eulerian-semi-Lagrangian (EULAG) three-dimensional large-eddy simulation model was initialized using data collected during the Indian Ocean Experiment (INDOEX). Radiosonde data were used to construct 6 soundings encompassing the range of temperature and humidity observed in the trade-wind boundary layer. By then adding the characteristics (height, depth and strength) of either a typical transition layer (TL), a strong inversion layer (IL) or no stable layer a total of 18 meteorological scenarios were produced. Separate simulations were conducted using EULAG assuming pristine and polluted conditions (i.e., cloud droplet number concentrations, aerosol extinction profiles and single-scattering albedos) using INDOEX observations. For the range of meteorological conditions observed during INDOEX, sensitivity studies showed that the semi- direct effect always dominated indirect effects, producing a positive daytime mean net indirect forcing varying between 0.2 and 4.5 W m-2. The simulations showed that changes in the environmental relative humidity (RH) and the presence of the TL had critical impacts on the cloud properties, turbulence and lateral detrainment rates, and on how aerosols affect these quantities. The net indirect forcing was larger when the RH was higher and in the absence of any dry and stable layers. It was reduced to less than 1.2 W m-2 when the TL was present. The impact of the IL was dependent on convective strength which increases with increasing RH. In fact, changes in meteorological factors had larger impacts on the simulated cloud properties than did the presence of anthropogenic aerosols, indicating large uncertainties can be introduced when solely using observations of aerosols and

  13. Conceptualizing and Testing Random Indirect Effects and Moderated Mediation in Multilevel Models: New Procedures and Recommendations

    ERIC Educational Resources Information Center

    Bauer, Daniel J.; Preacher, Kristopher J.; Gil, Karen M.

    2006-01-01

    The authors propose new procedures for evaluating direct, indirect, and total effects in multilevel models when all relevant variables are measured at Level 1 and all effects are random. Formulas are provided for the mean and variance of the indirect and total effects and for the sampling variances of the average indirect and total effects.…

  14. Atmospheric aerosols: Their Optical Properties and Effects

    NASA Technical Reports Server (NTRS)

    1976-01-01

    Measured properties of atmospheric aerosol particles are presented. These include aerosol size frequency distribution and complex retractive index. The optical properties of aerosols are computed based on the presuppositions of thermodynamic equilibrium and of Mie-theory.

  15. Direct and indirect effects of fires on the carbon balance of tropical forest ecosystems (Invited)

    NASA Astrophysics Data System (ADS)

    Randerson, J. T.; Tosca, M. G.; Ward, D. S.; Kasibhatla, P. S.; Mahowald, N. M.; Hess, P. G.

    2013-12-01

    Fires influence the carbon budget of tropical forests directly because they account for a significant component of net emissions from deforestation and forest degradation. They also have indirect effects on nearby intact forests by modifying regional climate, atmospheric composition, and patterns of nutrient deposition. These latter pathways are not well understood and are often ignored in climate mitigation efforts such as the United Nations Program on Reducing Emissions from Deforestation and forest Degradation (REDD+). Here we used the Community Atmosphere Model (CAM5) and the Global Fire Emissions Database (GFED3) to quantify the impacts of fire-emitted aerosols on the productivity of tropical forests. Across the tropical forest biome, fire-emitted aerosols reduced surface temperatures and increased the diffuse solar insolation fraction. These changes in surface meteorology increased gross primary production (GPP) in the Community Land Model. However, these drivers were more than offset in many regions by reductions in soil moisture and total solar radiation. The net effect of fire aerosols caused GPP to decrease by approximately 8% in equatorial Asia and 6% in the central Africa. In the Amazon, decreases in photosynthesis in the western part of the basin were nearly balanced by increases in the south and east. Using additional CAM5 and GEOS-Chem model simulations, we estimated fire contributions to surface concentrations of ozone. Using empirical relationships between ozone exposure and GPP from field studies and models, we estimated how tropical forest GPP was further modified by fire-induced ozone. Our results suggest that efforts to reduce the fire component of tropical land use fluxes may have sustainability benefits that extend beyond the balance sheet for greenhouse gases.

  16. An increase in aerosol burden and radiative effects in a warmer world

    NASA Astrophysics Data System (ADS)

    Allen, Robert J.; Landuyt, William; Rumbold, Steven T.

    2016-03-01

    Atmospheric aerosols are of significant environmental importance, due to their effects on air quality, as well as their ability to alter the planet’s radiative balance. Recent studies characterizing the effects of climate change on air quality and the broader distribution of aerosols in the atmosphere show significant, but inconsistent results, including the sign of the effect. Using a suite of state-of-the-art climate models, we show that climate change is associated with a negative aerosol-climate feedback of -0.02 to -0.09 W m-2 K-1 for direct radiative effects, with much larger values likely for indirect radiative effects. This is related to an increase in most aerosol species, particularly over the tropics and Northern Hemisphere midlatitudes, largely due to a decrease in wet deposition associated with less large-scale precipitation over land. Although simulation of aerosol processes in global climate models possesses uncertainty, we conclude that climate change may increase aerosol burden and surface concentration, which may have implications for future air quality.

  17. Cloud Cover Increase with Increasing Aerosol Absorptivity: A Counterexample to the Conventional Semidirect Aerosol Effect

    NASA Technical Reports Server (NTRS)

    Perlwitz, Jan; Miller, Ron L.

    2010-01-01

    We reexamine the aerosol semidirect effect using a general circulation model and four cases of the single-scattering albedo of dust aerosols. Contrary to the expected decrease in low cloud cover due to heating by tropospheric aerosols, we find a significant increase with increasing absorptivity of soil dust particles in regions with high dust load, except during Northern Hemisphere winter. The strongest sensitivity of cloud cover to dust absorption is found over land during Northern Hemisphere summer. Here even medium and high cloud cover increase where the dust load is highest. The cloud cover change is directly linked to the change in relative humidity in the troposphere as a result of contrasting changes in specific humidity and temperature. More absorption by aerosols leads to larger diabatic heating and increased warming of the column, decreasing relative humidity. However, a corresponding increase in the specific humidity exceeds the temperature effect on relative humidity. The net effect is more low cloud cover with increasing aerosol absorption. The higher specific humidity where cloud cover strongly increases is attributed to an enhanced convergence of moisture driven by dust radiative heating. Although in some areas our model exhibits a reduction of low cloud cover due to aerosol heating consistent with the conventional description of the semidirect effect, we conclude that the link between aerosols and clouds is more varied, depending also on changes in the atmospheric circulation and the specific humidity induced by the aerosols. Other absorbing aerosols such as black carbon are expected to have a similar effect.

  18. Aerosol radiative effects over BIMSTEC regions

    NASA Astrophysics Data System (ADS)

    Kumar, Sumit; Kar, S. C.; Mupparthy, Raghavendra S.

    Aerosols can have variety of shapes, composition, sizes and other properties that influence their optical characteristics and thus the radiative impact. The visible impact of aerosol is the formation of haze, a layer of particles from vehicular, industrial emissions and biomass burning. The characterization of these fine particles is important for regulators and researchers because of their potential impact on human health, their ability to travel thousands of kilometers crossing international borders, and their influence on climate forcing and global warming. The Bay of Bengal Initiative for Multi-Sectoral Technical and Economic Cooperation (BIMSTEC) with Member Countries Bangladesh, Bhutan, India, Myanmar, Nepal, Sri Lanka and Thailand has emerged as an important regional group for technical and economic Cooperation. Continuing the quest for a deeper understanding of BIMSTEC countries weather and climate, in this paper we focused on aerosols and their direct radiative effects. Because of various contrasts like geophysical, agricultural practices, heterogeneous land/ocean surface, population etc these regions present an excellent natural laboratory for studying aerosol-meteorology interactions in tropical to sub-tropical environments. We exploited data available on multiple platforms (such as MISR, MODIS etc) and models (OPAC, SBDART etc) to compute the results. Ten regions were selected with different surface characteristics, also having considerable differences in the long-term trends and seasonal distribution of aerosols. In a preliminary analysis pertaining to pre-monsoon (March-April-May) of 2013, AOD _{555nm} is found to be maximum over Bangladesh (>0.52) and minimum over Bhutan (0.22), whereas other regions have intermediate values. Concurrent to these variability of AOD we found a strong reduction in incoming flux at surface of all the regions (> -25 Wm (-2) ), except Bhutan and Sri Lanka (< -18Wm (-2) ). The top of the atmosphere (TOA) forcing values are

  19. Microphysical effects determine macrophysical response for aerosol impacts on deep convective clouds.

    PubMed

    Fan, Jiwen; Leung, L Ruby; Rosenfeld, Daniel; Chen, Qian; Li, Zhanqing; Zhang, Jinqiang; Yan, Hongru

    2013-11-26

    Deep convective clouds (DCCs) play a crucial role in the general circulation, energy, and hydrological cycle of our climate system. Aerosol particles can influence DCCs by altering cloud properties, precipitation regimes, and radiation balance. Previous studies reported both invigoration and suppression of DCCs by aerosols, but few were concerned with the whole life cycle of DCC. By conducting multiple monthlong cloud-resolving simulations with spectral-bin cloud microphysics that capture the observed macrophysical and microphysical properties of summer convective clouds and precipitation in the tropics and midlatitudes, this study provides a comprehensive view of how aerosols affect cloud cover, cloud top height, and radiative forcing. We found that although the widely accepted theory of DCC invigoration due to aerosol's thermodynamic effect (additional latent heat release from freezing of greater amount of cloud water) may work during the growing stage, it is microphysical effect influenced by aerosols that drives the dramatic increase in cloud cover, cloud top height, and cloud thickness at the mature and dissipation stages by inducing larger amounts of smaller but longer-lasting ice particles in the stratiform/anvils of DCCs, even when thermodynamic invigoration of convection is absent. The thermodynamic invigoration effect contributes up to ~27% of total increase in cloud cover. The overall aerosol indirect effect is an atmospheric radiative warming (3-5 W m(-2)) and a surface cooling (-5 to -8 W m(-2)). The modeling findings are confirmed by the analyses of ample measurements made at three sites of distinctly different environments. PMID:24218569

  20. Technical Note: Estimating Aerosol Effects on Cloud Radiative Forcing

    SciTech Connect

    Ghan, Steven J.

    2013-10-09

    Estimating anthropogenic aerosol effects on the planetary energy balance through the aerosol influence on clouds using the difference in cloud radiative forcing from simulations with and without anthropogenic emissions produces estimates that are positively biased. A more representative method is suggested using the difference in cloud radiative forcing calculated with aerosol radiative effects neglected. The method also yields an aerosol radiative forcing decomposition that includes a term quantifying the impact of changes in surface albedo. The method requires only two additional diagnostic calculations: the whole-sky and clear-sky top-of-atmosphere radiative flux with aerosol radiative effects neglected.

  1. Indirect Genetic Effects and the Dynamics of Social Interactions

    PubMed Central

    Trubenová, Barbora; Novak, Sebastian; Hager, Reinmar

    2015-01-01

    Background Indirect genetic effects (IGEs) occur when genes expressed in one individual alter the expression of traits in social partners. Previous studies focused on the evolutionary consequences and evolutionary dynamics of IGEs, using equilibrium solutions to predict phenotypes in subsequent generations. However, whether or not such steady states may be reached may depend on the dynamics of interactions themselves. Results In our study, we focus on the dynamics of social interactions and indirect genetic effects and investigate how they modify phenotypes over time. Unlike previous IGE studies, we do not analyse evolutionary dynamics; rather we consider within-individual phenotypic changes, also referred to as phenotypic plasticity. We analyse iterative interactions, when individuals interact in a series of discontinuous events, and investigate the stability of steady state solutions and the dependence on model parameters, such as population size, strength, and the nature of interactions. We show that for interactions where a feedback loop occurs, the possible parameter space of interaction strength is fairly limited, affecting the evolutionary consequences of IGEs. We discuss the implications of our results for current IGE model predictions and their limitations. PMID:25993124

  2. Improving Bulk Microphysics Parameterizations in Simulations of Aerosol Effects

    SciTech Connect

    Wang, Yuan; Fan, Jiwen; Zhang, Renyi; Leung, Lai-Yung R.; Franklin, Charmaine N.

    2013-06-05

    To improve the microphysical parameterizations for simulations of the aerosol indirect effect (AIE) in regional and global climate models, a double-moment bulk microphysical scheme presently implemented in the Weather Research and Forecasting (WRF) model is modified and the results are compared against atmospheric observations and simulations produced by a spectral bin microphysical scheme (SBM). Rather than using prescribed aerosols as in the original bulk scheme (Bulk-OR), a prognostic doublemoment aerosol representation is introduced to predict both the aerosol number concentration and mass mixing ratio (Bulk-2M). The impacts of the parameterizations of diffusional growth and autoconversion and the selection of the embryonic raindrop radius on the performance of the bulk microphysical scheme are also evaluated. 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 (DCC) in the southeast of China from the Department of Energy/ARM Mobile Facility (DOE/AMF) - China field campaign. The results from Bulk-2M exhibit a much better agreement in the cloud number concentration and effective droplet radius in both the SC and DCC cases with those from SBM and field measurements than those from Bulk-OR. In the SC case particularly, Bulk-2M reproduces the observed drizzle precipitation, which is largely inhibited in Bulk-OR. Bulk-2M predicts enhanced precipitation and invigorated convection with increased aerosol loading in the DCC case, consistent with the SBM simulation, while Bulk-OR predicts the opposite behaviors. 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 2 stratocumulus clouds. An embryonic raindrop size of 40 μm is determined as a more

  3. Effect of aerosols on evapo-transpiration

    NASA Astrophysics Data System (ADS)

    Murthy, B. S.; Latha, R.; Manoj, Kumar; Mahanti, N. C.

    2014-06-01

    Aerosol direct radiative forcing (ARF) at surface is estimated from instantaneous, simultaneous observations of global radiation and aerosol optical depth (AOD) during winter, pre-monsoon and monsoon seasons over a tropical Indian station at the south-eastern end of Indo Gangetic basin. A comparison of observed and model derived ARFs is made and possible reasons for mismatch are discussed. Aerosol-induced reduction in solar visible (0.4-0.7 μm) spectrum energy (SWvis), contributing 44% to total broad band (0.3-3.0 μm) energy (SW), and its effect on surface energy fluxes are discussed in this study. Aerosols on an average reduce SWvis at surface by ˜27%. SWvis reduces by 14.5 W m-2 for a 0.1 increase in AOD when single scattering albedo (SSA) is 0.979 where as it reduces by 67.5 W m-2 when SSA is 0.867 indicating the significant effect of absorbing aerosols. Effect of ARF on net radiation, Rn, sensible heat flux, H and latent heat flux/evapo-transpiration, LE are estimated using the observed ratios of Rn/SW, H/Rn and LE/Rn, having reasonably good correlation. Observed Rn/SW varies between 0.59 and 0.75 with a correlation of 0.99 between them. LE, calculated by energy balance method, varies from 56% to 74% of Rn but with a lesser correlation, the possible reasons are discussed. For a given ARF, LE decreases by ˜14% and Rn by ˜15% with respect to observed LE and Rn respectively. The reduction in LE increases from 37% to 54% of ARF when LE increases from 220 W m-2 to 440 W m-2, suggesting that wet soil induces relatively larger reduction in evaporation. The results agree with earlier model sensitivity studies that Rn reduces more with increase in aerosol absorption which is compensated by proportionate reductions in H and LE depending on soil and atmospheric conditions.

  4. Simulations of aerosols and their effects on photolysis and ozone formation in Mexico City

    NASA Astrophysics Data System (ADS)

    Li, G.; Zavala, M.; Lei, W.; Karydis, V. A.; Tsimpidi, A. P.; Pandis, S.; Molina, L. T.

    2009-04-01

    Atmospheric aerosols, formed from natural and anthropogenic sources, are believed to be associated with adverse human effects at high levels in polluted urban areas. They also play a key role in climate through direct and indirect effects. Therefore, accurate simulations of aerosol composition and distribution in the atmospheric models are important in evaluating their impact on environment and climate. In the present study, a flexible gas phase chemical module with SAPRC mechanism and the CMAQ/models3 aerosol module developed by EPA have been implemented into the WRF-CHEM model. Additionally, to further improve the aerosol, especially the secondary organic aerosol (SOA) simulations, an advanced SOA module [Tsimpidi et al., 2009] has been incorporated into the WRF-CHEM model. The new SOA module is based on the volatility basis-set approach in which both primary and secondary organic components are assumed to be semivolatile and photochemically reactive [Lane et al., 2008]. Gas phase species and aerosol simulation results are compared with the available measurements obtained during the MILAGRO 2006 campaign. When the advanced SOA mechanism is employed, the SOA simulations are significantly improved. Furthermore, the aerosol impacts on the photochemistry in Mexico City have been evaluated using the FTUV [Tie et al., 2005]. Aerosol optical properties are calculated using the Mie theory and compared with available observations in Mexico City [Paredes-Miranda et al., 2008]. Aerosols, principally black carbon, reduce the photolysis frequencies of J[O3(1D)] and J[NO2] in the planetary boundary layer and hence decrease the ground-level ozone concentration. Our study demonstrates that the impact of aerosols on photochemistry is significant in polluted urban atmosphere. References: Lane, T. E., N. M. Donahue, and S. N. Pandis (2008), Simulating secondary organic aerosol formation using the volatility basis-set approach in a chemical transport model, PMCAMx, Atmos. Environ

  5. Effect of aerosol vertical distribution on aerosol-radiation interaction: A theoretical prospect.

    PubMed

    Mishra, Amit Kumar; Koren, Ilan; Rudich, Yinon

    2015-10-01

    This study presents a theoretical investigation of the effect of the aerosol vertical distribution on the aerosol radiative effect (ARE). Four aerosol composition models (dust, polluted dust, pollution and pure scattering aerosols) with varying aerosol vertical profiles are incorporated into a radiative transfer model. The simulations show interesting spectral dependence of the ARE on the aerosol layer height. ARE increases with the aerosol layer height in the ultraviolet (UV: 0.25-0.42 μm) and thermal-infrared (TH-IR: 4.0-20.0 μm) regions, whereas it decreases in the visible-near infrared (VIS-NIR: 0.42-4.0 μm) region. Changes in the ARE with aerosol layer height are associated with different dominant processes for each spectral region. The combination of molecular (Rayleigh) scattering and aerosol absorption is the key process in the UV region, whereas aerosol (Mie) scattering and atmospheric gaseous absorption are key players in the VIS-NIR region. The longwave emission fluxes are controlled by the environmental temperature at the aerosol layer level. ARE shows maximum sensitivity to the aerosol layer height in the TH-IR region, followed by the UV and VIS-NIR regions. These changes are significant even in relatively low aerosol loading cases (aerosol optical depth ∼0.2-0.3). Dust aerosols are the most sensitive to altitude followed by polluted dust and pollution in all three different wavelength regions. Differences in the sensitivity of the aerosol type are explained by the relative strength of their spectral absorption/scattering properties. The role of surface reflectivity on the overall altitude dependency is shown to be important in the VIS-NIR and UV regions, whereas it is insensitive in the TH-IR region. Our results indicate that the vertical distribution of water vapor with respect to the aerosol layer is an important factor in the ARE estimations. Therefore, improved estimations of the water vapor profiles are needed for the further reduction in

  6. Effects of direct and indirect bleach on dentin fracture toughness.

    PubMed

    Tam, L E; Noroozi, A

    2007-12-01

    There are concerns that tooth-whitening procedures irreversibly damage tooth structure. We investigated the hypothesis that dental bleaches significantly affect dentin structural integrity. The objective was to evaluate the effects of peroxide bleaches on dentin fracture toughness. Compact test specimens, composed of human dentin, were used (n = 10/group). Bleach (16% or 10% carbamide peroxide or 3% hydrogen peroxide) or control material, containing 0.1% sodium fluoride, was applied directly or indirectly to dentin through enamel (6 hrs/day) for 2 or 8 weeks. Fracture toughness results were analyzed by ANOVA and Fisher's LSD test (p < 0.05). There were significant decreases in mean fracture toughness after two- and eight-week direct (19-34% and 61-68%, respectively) and indirect (up to 17% and 37%, respectively) bleach application. The in vitro reduction in dentin fracture toughness caused by the application of peroxide bleaches was greater for the direct application method, longer application time, and higher bleach concentration. PMID:18037654

  7. Stratospheric aerosol properties and their effects on infrared radiation.

    NASA Technical Reports Server (NTRS)

    Remsberg, E. E.

    1973-01-01

    This paper presents a stratospheric aerosol model and infers its effects on terrestrial radiation. Composition of the aerosol is assumed to be concentrated sulfuric acid. An appropriate size distribution has been determined from available size distribution measurements of other investigators. Aerosols composed of concentrated sulfuric acid emit energy in the atmospheric window region of the infrared spectrum, 8-13 microns. Laboratory measurements of optical constant data obtained at room temperature are presented for 75 and 90% aqueous sulfuric acid. Calculations of an aerosol extinction coefficient are then performed by using the above data. Effects of changes in aerosol phase and temperature are discussed but not resolved.

  8. Potential sensitivity of photosynthesis and isoprene emission to direct radiative effects of atmospheric aerosol pollution

    NASA Astrophysics Data System (ADS)

    Strada, Susanna; Unger, Nadine

    2016-04-01

    A global Earth system model is applied to quantify the impacts of direct anthropogenic aerosol effective radiative forcing on gross primary productivity (GPP) and isoprene emission. The impacts of different pollution aerosol sources (anthropogenic, biomass burning, and non-biomass burning) are investigated by performing sensitivity experiments. The model framework includes all known light and meteorological responses of photosynthesis, but uses fixed canopy structures and phenology. On a global scale, our results show that global land carbon fluxes (GPP and isoprene emission) are not sensitive to pollution aerosols, even under a global decline in surface solar radiation (direct + diffuse) by ˜ 9 %. At a regional scale, GPP and isoprene emission show a robust but opposite sensitivity to pollution aerosols in regions where forested canopies dominate. In eastern North America and Eurasia, anthropogenic pollution aerosols (mainly from non-biomass burning sources) enhance GPP by +5-8 % on an annual average. In the northwestern Amazon Basin and central Africa, biomass burning aerosols increase GPP by +2-5 % on an annual average, with a peak in the northwestern Amazon Basin during the dry-fire season (+5-8 %). The prevailing mechanism varies across regions: light scattering dominates in eastern North America, while a reduction in direct radiation dominates in Europe and China. Aerosol-induced GPP productivity increases in the Amazon and central Africa include an additional positive feedback from reduced canopy temperatures in response to increases in canopy conductance. In Eurasia and northeastern China, anthropogenic pollution aerosols drive a decrease in isoprene emission of -2 to -12 % on an annual average. Future research needs to incorporate the indirect effects of aerosols and possible feedbacks from dynamic carbon allocation and phenology.

  9. Overview of ACE-Asia Spring 2001 Investigations on Aerosol Radiative Effects and Related Aerosol Properties

    NASA Technical Reports Server (NTRS)

    Russell, Philip B.; Valero, F. P. J.; Flatau, P. J.; Bergin, M.; Holben, B.; Nakajima, T.; Pilewskie, P.; Bergstrom, R.; Hipskind, R. Stephen (Technical Monitor)

    2001-01-01

    A primary, ACE-Asia objective was to quantify the interactions between aerosols and radiation in the Asia-Pacific region. Toward this end, radiometric and related aerosol measurements were made from ocean, land, air and space platforms. Models that predict aerosol fields guided the measurements and are helping integrate and interpret results. Companion overview's survey these measurement and modeling components. Here we illustrate how these components were combined to determine aerosol radiative. impacts and their relation to aerosol properties. Because clouds can obscure or change aerosol direct radiative effects, aircraft and ship sorties to measure these effects depended on predicting and finding cloud-free areas and times with interesting aerosols present. Pre-experiment satellite cloud climatologies, pre-flight aerosol and cloud forecasts, and in-flight guidance from satellite imagery all helped achieve this. Assessments of aerosol regional radiative impacts benefit from the spatiotemporal coverage of satellites, provided satellite-retrieved aerosol properties are accurate. Therefore, ACE-Asia included satellite retrieval tests, as part of many comparisons to judge the consistency (closure) among, diverse measurements. Early results include: (1) Solar spectrally resolved and broadband irradiances and optical depth measurements from the C-130 aircraft and at Kosan, Korea yielded aerosol radiative forcing efficiencies, permitting comparisons between efficiencies of ACE-Asia and INDOEX aerosols, and between dust and "pollution" aerosols. Detailed results will be presented in separate papers. (2) Based on measurements of wavelength dependent aerosol optical depth (AOD) and single scattering albedo the estimated 24-h a average aerosol radiative forcing efficiency at the surface for photosynthetically active radiation (400 - 700 nm) in Yulin, China is approx. 30 W sq m per AOD(500 nm). (3) The R/V Brown cruise from Honolulu to Sea of Japan sampled an aerosol optical

  10. Modeling aerosol effects on shallow cumulus convection under various meteorological conditions observed over the Indian Ocean and implications for development of mass-flux parameterizations for climate models

    NASA Astrophysics Data System (ADS)

    Wang, Hailong; McFarquhar, Greg M.

    2008-10-01

    To determine conditions over the Indian Ocean, under which cloud fields are most susceptible to modification from aerosols, and to study how turbulent activities and shallow cumuli vary for different meteorological scenarios, a three-dimensional large-eddy simulation model was initialized using data collected during the Indian Ocean Experiment (INDOEX). Radiosonde data were used to construct six soundings encompassing the range of temperature and humidity observed. A total of 18 meteorological scenarios were then obtained by adding either an average transition layer (TL), a strong inversion layer (IL), or no stable layer to each sounding. Separate simulations were conducted for each scenario assuming pristine or polluted conditions as observed during INDOEX. For aerosol profiles measured during INDOEX, aerosol semidirect effects always dominated indirect effects, with the positive daytime net indirect forcing (semidirect plus indirect forcings) varying between 0.2 and 4.5 W m-2. Anthropogenic aerosols had a larger net indirect forcing when the environmental relative humidity (RH) was higher and in the absence of the IL and TL. Changes in meteorological factors had larger impacts on the cloud properties than did anthropogenic aerosols, indicating large uncertainties can be introduced when solely using observations to quantify aerosol effects without examining their meteorological context. Because mean lateral detrainment and entrainment rates depended on RH, aerosols, and the presence of stable layers, mass-flux parameterizations in climate models should not use single values for such rates that may not represent the range of conditions observed where trade cumuli form.

  11. Direct and indirect effects of climate change on amphibian populations

    USGS Publications Warehouse

    Blaustein, Andrew R.; Walls, Susan C.; Bancroft, Betsy A.; Lawler, Joshua J.; Searle, Catherine L.; Gervasi, Stephanie S.

    2010-01-01

    As part of an overall decline in biodiversity, populations of many organisms are declining and species are being lost at unprecedented rates around the world. This includes many populations and species of amphibians. Although numerous factors are affecting amphibian populations, we show potential direct and indirect effects of climate change on amphibians at the individual, population and community level. Shifts in amphibian ranges are predicted. Changes in climate may affect survival, growth, reproduction and dispersal capabilities. Moreover, climate change can alter amphibian habitats including vegetation, soil, and hydrology. Climate change can influence food availability, predator-prey relationships and competitive interactions which can alter community structure. Climate change can also alter pathogen-host dynamics and greatly influence how diseases are manifested. Changes in climate can interact with other stressors such as UV-B radiation and contaminants. The interactions among all these factors are complex and are probably driving some amphibian population declines and extinctions.

  12. An Overview of the 2010 Carbonaceous Aerosol and Radiative Effects Study (CARES) Field Campaign

    NASA Astrophysics Data System (ADS)

    Zaveri, R. A.; Shaw, W. J.; Cziczo, D. J.

    2010-12-01

    The primary objective of the DOE Carbonaceous Aerosol and Radiative Effects Study (CARES) in June 2010 was to investigate the evolution of carbonaceous aerosols of different types and their optical and hygroscopic properties in central California, with a focus on the Sacramento urban plume. Carbonaceous aerosol components, which include black carbon (BC), urban primary organic aerosols (POA), biomass burning aerosols, and secondary organic aerosols (SOA) from both urban and biogenic precursors, have been shown to play a major role in the direct and indirect radiative forcing of climate. However, significant knowledge gaps and uncertainties still exist in the process-level understanding of: 1) SOA formation, 2) BC mixing state evolution, and 3) the optical and hygroscopic properties of fresh and aged carbonaceous aerosols. The CARES 2010 field study was designed to address several specific science questions under these three topics. During summer the Sacramento-Blodgett Forest corridor effectively serves as a mesoscale daytime flow reactor in which the urban aerosols undergo significant aging as they are transported to the northeast by upslope flow. The CARES campaign observation strategy consisted of the DOE G-1 aircraft sampling upwind, within, and outside of the evolving Sacramento urban plume in the morning and again in the afternoon. The G-1 payload consisted of a suite of instruments to measure trace gases, aerosol size distribution, composition, and optical properties. The NASA B-200 aircraft carrying a High Spectral Resolution Lidar (HSRL) and a Research Scanning Polarimeter (RSP) was also deployed to characterize the vertical and horizontal distribution of aerosols and aerosol optical properties. The aircraft measurements were complemented by heavily-instrumented ground sites within the Sacramento urban area and at a downwind site in Cool, California, to characterize the diurnal evolution of meteorological variables, trace gases, aerosol precursors, aerosol

  13. Modelled radiative effects of sea spray aerosol using a source function encapsulating wave state

    NASA Astrophysics Data System (ADS)

    Partanen, Antti-Ilari; Dunne, Eimear M.; Bergman, Tommi; Laakso, Anton; Kokkola, Harri; Ovadnevaite, Jurgita; Sogacheva, Larisa; Baisnée, Dominique; Sciare, Jean; Manders, Astrid; O'Dowd, Colin; de Leeuw, Gerrit; Korhonen, Hannele

    2014-05-01

    Sea spray aerosol particles have significant effects on global climate by scattering solar radiation (direct effect) and modifying cloud properties (indirect effect). Sea spray consists mainly of sea salt, but in biologically active regions, major fraction of sea spray may come in the form of primary marine organic matter (PMOM). Traditionally, sea spray flux has been parameterized in global models in terms of wind speed, and organic fraction of sea spray in terms of chlorophyll-a concentration. In this study, we have incorporated recently developed parameterizations for the sea spray aerosol source flux into the global aerosol-climate model ECHAM-HAMMOZ. The parameterizations encapsulate the wave state via Reynolds number, and predict the organic fraction of the sea spray aerosol source flux. The model was then used to investigate the direct and indirect effects of sea spray aerosol particles. We compared simulated sea spray concentrations with in-situ measurements from Mace Head (North Atlantic), Point Reyes (North Pacific), and Amsterdam Island (Southern Indian Ocean). Aerosol optical depth (AOD) was compared with satellite measurements from PARASOL. Modelled annual mean global emissions of sea salt and PMOM were 805 Tg yr-1 (uncertainty range of 378-1233 Tg yr-1) and 1.1 Tg yr-1 (0.5-1.8 Tg yr-1), respectively. Sea salt emissions were considerably lower than the majority of previous estimates, but PMOM was in the range of previous studies. The model captured sea salt concentrations fairly well in the smaller size ranges at Mace Head (annual normalized mean bias of -13% for particles with vacuum aerodynamic diameter Dva

  14. Quantification of regional radiative impacts and climate effects of tropical fire aerosols

    NASA Astrophysics Data System (ADS)

    Tosca, M. G.; Zender, C. S.; Randerson, J. T.

    2011-12-01

    Regionally expansive smoke clouds originating from deforestation fires in Indonesia can modify local precipitation patterns via direct aerosol scattering and absorption of solar radiation (Tosca et al., 2010). Here we quantify the regional climate impacts of fire aerosols for three tropical burning regions that together account for about 70% of global annual fire emissions. We use the Community Atmosphere Model, version 5 (CAM5) coupled to a slab ocean model (SOM) embedded within the Community Earth System Model (CESM). In addition to direct aerosol radiative effects, CAM5 also quantifies indirect, semi-direct and cloud microphysical aerosol effects. Climate impacts are determined using regionally adjusted emissions data that produce realistic aerosol optical depths in CAM5. We first analyzed a single 12-year transient simulation (1996-2007) forced with unadjusted emissions estimates from the Global Fire Emissions Database, version 3 (GFEDv3) and compared the resulting aerosol optical depths (AODs) for 4 different burning regions (equatorial Asia, southern Africa, South America and boreal North America) to observed MISR and MODIS AODs for the same period. Based on this analysis we adjusted emissions for each burning region between 150 and 300% and forced a second simulation with the regionally adjusted emissions. Improved AODs from this simulation are compared to AERONET observations available at 15 stations throughout the tropics. We present here two transient simulations--one with the adjusted fire emissions and one without fires--to quantify the cumulative fire aerosol climate impact for three major tropical burning regions (equatorial Asia, southern Africa and South America). Specifically, we quantify smoke effects on radiation, precipitation, and temperature. References Tosca, M.G., J.T. Randerson, C.S. Zender, M.G. Flanner and P.J. Rasch (2010), Do biomass burning aerosols intensify drought in equatorial Asia during El Nino?, Atmos. Chem. Phys., 10, 3515

  15. Aerosol effects on cloud cover as evidenced by ground-based and space-based observations at five rural sites in the United States

    NASA Astrophysics Data System (ADS)

    Ten Hoeve, John E.; Augustine, John A.

    2016-01-01

    Previous studies of the second aerosol indirect (lifetime) effect on cloud cover have estimated the strength of the effect without correcting for near-cloud contamination and other confounding factors. Here we combine satellite-based observations with a multiyear ground-based data set across five rural locations in the United States to more accurately constrain the second indirect aerosol effect and quantify aerosol effects on radiative forcing. Results show that near-cloud contamination accounts for approximately 40% of the satellite-derived aerosol-cloud relationship. When contamination is removed and the effect of meteorological covariation is minimized, a strong physical aerosol effect on cloud cover remains. Averaged over all stations and after correcting for contamination, the daytime solar and total (solar + IR) radiative forcing is -52 W/m2 and -19 W/m2, respectively, due to both direct and indirect aerosol effects for aerosol optical depths (τ) between 0 and 0.3. Averaged diurnally, the average total radiative forcing is +16 W/m2.

  16. Real Effect or Artifact of Cloud Cover on Aerosol Optical Thickness?

    SciTech Connect

    Jeong, M-J.; Li, Z.

    2005-03-18

    retrievals of AOT from both satellite and ground sensors; (2) separate artifact from real effect; (3) create ''clean'' aerosol products for studying their direct and indirect effect. Presented are some very preliminary findings.

  17. The Indirect Effect of UV: Some Good News for Microbes?

    NASA Technical Reports Server (NTRS)

    Rothschild, Lynn J.; Purcell, Diane; Rogoff, Dana; Wilson, Cindy; Brass, James A. (Technical Monitor)

    2002-01-01

    Ultraviolet (UV) radiation is of great concern because its biological effects are predominantly harmful. UV damage may be direct or indirect, the latter mediated through the photochemical production of reactive oxygen species such as hydrogen peroxide. We measured the effect of H2O2 on various microbes both in the lab and in nature. At our study site in Yellowstone National Park, there is a UV-induced diurnal fluctuation of H2O2 extending up to one micron. Levels of DNA synthesis resulting from exposure to H2O2 were measured in several algal mats. Within naturally-occurring concentrations of H2O2, DNA synthesis increased. Laboratory studies showed that similar concentrations of H2O2 induce mitosis. We hypothesize that the low levels of H2O2 encountered in nature are inducing mitotic division. At higher levels of H2O2 a second peak in DNA synthesis was found which we interpret to represent DNA damage repair. These experiments suggest that in nature, the low levels of H2O2 produced may have a mitogenic rather than damaging effect. Assuming early levels of UV radiation were substantially higher at the time protists evolved, differential mitogenic effects could have influenced protistan evolution. With H2O2 likely to be present on such bodies as Mars and Europa, the response of organisms will be concentration-dependent and not linear.

  18. Organic aerosol effects on fog droplet spectra

    NASA Astrophysics Data System (ADS)

    Ming, Yi; Russell, Lynn M.

    2004-05-01

    Organic aerosol alters cloud and fog properties through surface tension and solubility effects. This study characterizes the role of organic compounds in affecting fog droplet number concentration by initializing and comparing detailed particle microphysical simulations with two field campaigns in the Po Valley. The size distribution and chemical composition of aerosol were based on the measurements made in the Po Valley Fog Experiments in 1989 and 1998-1999. Two types of aerosol with different hygroscopicity were considered: the less hygroscopic particles, composed mainly of organic compounds, and the more hygroscopic particles, composed mainly of inorganic salts. The organic fraction of aerosol mass was explicitly modeled as a mixture of seven soluble compounds [, 2001] by employing a functional group-based thermodynamic model [, 2002]. Condensable gases in the vapor phase included nitric acid, sulfuric acid, and ammonia. The maximum supersaturation in the simulation is 0.030% and is comparable to the calculation by [1992] inferred from measured residual particle fractions. The minimum activation diameters of the less and more hygroscopic particles are 0.49 μm and 0.40 μm, respectively. The predicted residual particle fractions are in agreement with measurements. The organic components of aerosol account for 34% of the droplet residual particle mass and change the average droplet number concentration by -10-6%, depending on the lowering of droplet surface tension and the interactions among dissolving ions. The hygroscopic growth of particles due to the presence of water-soluble organic compounds enhances the condensation of nitric acid and ammonia due to the increased surface area, resulting in a 9% increase in the average droplet number concentration. Assuming ideal behavior of aqueous solutions of water-soluble organic compounds overestimates the hygroscopic growth of particles and increases droplet numbers by 6%. The results are sensitive to microphysical

  19. Effects of aerosol emission pathways on future warming and human health

    NASA Astrophysics Data System (ADS)

    Partanen, Antti-Ilari; Matthews, Damon

    2016-04-01

    The peak global temperature is largely determined by cumulative emissions of long-lived greenhouse gases. However, anthropogenic emissions include also so-called short-lived climate forcers (SLCFs), which include aerosol particles and methane. Previous studies with simple models indicate that the timing of SLCF emission reductions has only a small effect on the rate of global warming and even less of an effect on global peak temperatures. However, these simple model analyses do not capture the spatial dynamics of aerosol-climate interactions, nor do they consider the additional effects of aerosol emissions on human health. There is therefore merit in assessing how the timing of aerosol emission reductions affects global temperature and premature mortality caused by elevated aerosol concentrations, using more comprehensive climate models. Here, we used an aerosol-climate model ECHAM-HAMMOZ to simulate the direct and indirect radiative forcing resulting from aerosol emissions. We simulated Representative Concentration Pathway (RCP) scenarios, and we also designed idealized low and high aerosol emission pathways based on RCP4.5 scenario (LOW and HIGH, respectively). From these simulations, we calculated the Effective Radiative Forcing (ERF) from aerosol emissions between 1850 and 2100, as well as aerosol concentrations used to estimate the premature mortality caused by particulate pollution. We then use the University of Victoria Earth System Climate Model to simulate the spatial and temporal pattern of climate response to these aerosol-forcing scenarios, in combination with prescribed emissions of both short and long-lived greenhouse gases according to the RCP4.5 scenario. In the RCP scenarios, global mean ERF declined during the 21st century from ‑1.3 W m‑2 to ‑0.4 W m‑2 (RCP8.5) and ‑0.2 W m‑2 (RCP2.6). In the sensitivity scenarios, the forcing at the end of the 21st century was ‑1.6 W m‑2 (HIGH) and practically zero (LOW). The difference in global

  20. Aerosol climate effects and air quality impacts from 1980 to 2030

    SciTech Connect

    Menon, Surabi; Menon, Surabi; Unger, Nadine; Koch, Dorothy; Francis, Jennifer; Garrett, Tim; Sednev, Igor; Shindell, Drew; Streets, David

    2007-11-26

    We investigate aerosol effects on climate for 1980, 1995 (meant to reflect present-day) and 2030 using the NASA Goddard Institute for Space Studies climate model coupled to an on-line aerosol source and transport model with interactive oxidant and aerosol chemistry. Aerosols simulated include sulfates, organic matter (OM), black carbon (BC), sea-salt and dust and additionally, the amount of tropospheric ozone is calculated, allowing us to estimate both changes to air quality and climate for different time periods and emission amounts. We include both the direct aerosol effect and indirect aerosol effects for liquid-phase clouds. Future changes for the 2030 A1B scenario are examined, focusing on the Arctic and Asia, since changes are pronounced in these regions. Our results for the different time periods include both emission changes and physical climate changes. We find that the aerosol indirect effect (AIE) has a large impact on photochemical processing, decreasing ozone amount and ozone forcing, especially for the future (2030-1995). Ozone forcings increase from 0 to 0.12 Wm{sup -2} and the total aerosol forcing increases from -0.10 Wm{sup -2} to -0.94 Wm{sup -2} (AIE increases from -0.13 to -0.68 Wm{sup -2}) for 1995-1980 versus 2030-1995. Over the Arctic we find that compared to ozone and the direct aerosol effect, the AIE contributes the most to net radiative flux changes. The AIE, calculated for 1995-1980, is positive (1.0 Wm{sup -2}), but the magnitude decreases (-0.3Wm{sup -2}) considerably for the future scenario. Over Asia, we evaluate the role of biofuel and transportation-based emissions (for BC and OM) via a scenario (2030A) that includes a projected increase (factor of two) in biofuel and transport-based emissions for 2030 A1B over Asia. Projected changes from present-day due to the 2030A emissions versus 2030 A1B are a factor of 4 decrease in summertime precipitation in Asia. Our results are sensitive to emissions used. Uncertainty in present

  1. Aircraft-Measured Indirect Cloud Effects from Biomass Burning Smoke in the Arctic and Subarctic

    NASA Technical Reports Server (NTRS)

    Zamora, Lauren; Kahn, R. A.; Cubison, M. C.; Diskin, G. S.; Jimenez, J. L.; Kondo, Y.; McFarquhar, G. M.; Nenes, A.; Wisthaler, A.; Zelenyuk, A.; Ziemba, L.

    2016-01-01

    The incidence of wildfires in the Arctic and subarctic is increasing; in boreal North America, for example, the burned area is expected to increase by 200-300 over the next 50-100 years, which previous studies suggest could have a large effect on cloud microphysics, lifetime, albedo, and precipitation. However, the interactions between smoke particles and clouds remain poorly quantified due to confounding meteorological influences and remote sensing limitations. Here, we use data from several aircraft campaigns in the Arctic and subarctic to explore cloud microphysics in liquid-phase clouds influenced by biomass burning. Median cloud droplet radii in smoky clouds were 50 smaller than in background clouds. Based on the relationship between cloud droplet number (N(liq))/ and various biomass burning tracers (BBt/ across the multi-campaign dataset, we calculated the magnitude of subarctic and Arctic smoke aerosol-cloud interactions (ACI, where ACI = (1/3) x dln(N(liq))/dln(BBt)) to be 0.12 out of a maximum possible value of 0.33 that would be obtained if all aerosols were to nucleate cloud droplets. Interestingly, in a separate subarctic case study with low liquid water content (0.02 gm/ cu m) and very high aerosol concentrations (2000-3000 cu m) in the most polluted clouds, the estimated ACI value was only 0.06. In this case, competition for water vapor by the high concentration of CCN strongly limited the formation of droplets and reduced the cloud albedo effect, which highlights the importance of cloud feedbacks across scales. Using our calculated ACI values, we estimate that the smoke-driven cloud albedo effect may decrease shortwave radiative flux by 2 and 4 W/sq or more under some low and homogeneous cloud cover conditions in the subarctic, although the changes should be smaller in high surface albedo regions of the Arctic. We lastly show evidence to suggest that numerous northern latitude background Aitken particles can interact with combustion particles

  2. Aircraft-measured indirect cloud effects from biomass burning smoke in the Arctic and subarctic

    NASA Astrophysics Data System (ADS)

    Zamora, L. M.; Kahn, R. A.; Cubison, M. J.; Diskin, G. S.; Jimenez, J. L.; Kondo, Y.; McFarquhar, G. M.; Nenes, A.; Thornhill, K. L.; Wisthaler, A.; Zelenyuk, A.; Ziemba, L. D.

    2015-08-01

    The incidence of wildfires in the Arctic and subarctic is increasing; in boreal North America, for example, the burned area is expected to increase by 200-300 % over the next 50-100 years, which previous studies suggest could have a large effect on cloud microphysics, lifetime, albedo, and precipitation. However, the interactions between smoke particles and clouds remain poorly quantified due to confounding meteorological influences and remote sensing limitations. Here, we use data from several aircraft campaigns in the Arctic and subarctic to explore cloud microphysics in liquid-phase clouds influenced by biomass burning. Median cloud droplet radii in smoky clouds were ~ 50 % smaller than in background clouds. Based on the relationship between cloud droplet number (Nliq) and various biomass burning tracers (BBt) across the multi-campaign dataset, we calculated the magnitude of subarctic and Arctic smoke aerosol-cloud interactions (ACI, where ACI = (1/3) × d ln (Nliq) / d ln (BBt)) to be ~ 0.12 out of a maximum possible value of 0.33 that would be obtained if all aerosols were to nucleate cloud droplets. Interestingly, in a separate subarctic case study with low liquid water content (~ 0.02 g m-3) and very high aerosol concentrations (2000-3000 cm-3) in the most polluted clouds, the estimated ACI value was only 0.06. In this case, competition for water vapor by the high concentration of CCN strongly limited the formation of droplets and reduced the cloud albedo effect, which highlights the importance of cloud feedbacks across scales. Using our calculated ACI values, we estimate that the smoke-driven cloud albedo effect may decrease shortwave radiative flux by 2-4 W m-2 or more under some low and homogeneous cloud cover conditions in the subarctic, although the changes should be smaller in high surface albedo regions of the Arctic. We lastly show evidence to suggest that numerous northern latitude background Aitken particles can interact with combustion particles

  3. Estimation of the direct aerosol radiative effect over China based on satellite remote sensing measurements

    NASA Astrophysics Data System (ADS)

    Sundström, A.-M.; Huttunen, J.; Arola, A.; Kolmonen, P.; Sogacheva, L.; de Leeuw, G.

    2012-04-01

    Aerosols influence the radiative budget of the Earth-atmosphere system directly by scattering and absorbing solar and thermal infrared radiation, and indirectly by modifying the microphysical, and hence the radiative properties and lifetimes of clouds. However, the quantification of aerosol radiative effects is complex and large uncertainties still exist, mainly due to the high spatial and temporal variation of the aerosol concentration and mass, as well as their relatively short lifetime in the atmosphere. The clear-sky direct aerosol radiative effect at the top of the atmosphere (TOA) is defined as the difference between the net solar flux ΔFTOA (difference between downward and upward fluxes) defined with (F) and without (F0) aerosols. The negative values of ΔFTOA correspond to planetary cooling, whereas positive values correspond to increased atmospheric warming. Satellites offer an opportunity to observe the spatial distribution of aerosol properties with adequate resolution and coverage from regional to global scales. In this work multisensor satellite observations are used to estimate the direct aerosol radiative effect at the top of the atmosphere over China within the shortwave (SW, 0.3-5 microns) region. The Moderate Imaging Spectroradiometer onboard (MODIS) NASA's Terra and Aqua platforms offer global observations of aerosol and cloud optical properties nearly on a daily basis, whereas the Clouds and the Earth's Radian Energy System (CERES) instruments measure simultaneously TOA broadband fluxes e.g. in the shortwave region. Hence, the instantaneous aerosol direct radiative effect for a month at TOA can be estimated using the MODIS aerosol optical depth (AOD) and coincident broadband flux from the CERES instrument. The values for F and F0 are obtained by performing a linear regression between MODIS AOD at 0.55 microns wavelength and CERES SW flux. The instantaneous values are converted to monthly means by using a radiative transfer code. Preliminary

  4. The contribution of aerosol hygroscopic growth to the modeled aerosol radiative effect

    NASA Astrophysics Data System (ADS)

    Kokkola, Harri; Kühn, Thomas; Kirkevåg, Alf; Romakkaniemi, Sami; Arola, Antti

    2016-04-01

    The hygroscopic growth of atmospheric aerosols can have a significant effect on the direct radiative effect of atmospheric aerosol. However, there are significant uncertainties concerning how much of the radiative forcing is due to different chemical compounds, especially water. For example, modeled optical depth of water in global aerosol-climate models varies by more than a factor of two. These differences can be attributed to differences in modeled 1) hygroscopicity, 2) ambient relative humidity, and/or 3) aerosol size distribution. In this study, we investigate which of these above-mentioned factors cause the largest variability in the modeled optical depth of water. In order to do this, we have developed a tool that calculates aerosol extinction using interchangeable global 3D data of aerosol composition, relative humidity, and aerosol size distribution fields. This data is obtained from models that have taken part in the open international initiative AeroCom (Aerosol Comparisons between Observations and Models). In addition, we use global 3D data for relative humidity from the Atmospheric Infrared Sounder (AIRS) flying on board NASA's Aqua satellite and the National Centers for Environmental Prediction (NCEP) reanalysis data. These observations are used to evaluate the modeled relative humidity fields. In the first stage of the study, we made a detailed investigation using the aerosol-chemistry-climate model ECHAM-HAMMOZ in which most of the aerosol optical depth is caused by water. Our results show that the model significantly overestimates the relative humidity over the oceans while over land, the overestimation is lower or it is underestimated. Since this overestimation occurs over the oceans, the water optical depth is amplified as the hygroscopic growth is very sensitive to changes in high relative humidities. Over land, error in modeled relative humidity is unlikely to cause significant errors in water optical depth as relative humidities are generally

  5. Indirect effects of primary prey population dynamics on alternative prey.

    PubMed

    Barraquand, Frédéric; New, Leslie F; Redpath, Stephen; Matthiopoulos, Jason

    2015-08-01

    We develop a theory of generalist predation showing how alternative prey species are affected by changes in both mean abundance and variability (coefficient of variation) of their predator's primary prey. The theory is motivated by the indirect effects of cyclic rodent populations on ground-breeding birds, and developed through progressive analytic simplifications of an empirically-based model. It applies nonetheless to many other systems where primary prey have fast life-histories and can become superabundant, thus facilitating impact on alternative prey species and generating highly asymmetric interactions. Our results suggest that predator effects on alternative prey should generally decrease with mean primary prey abundance, and increase with primary prey variability (low to high CV)-unless predators have strong aggregative responses, in which case these results can be reversed. Approximations of models including predator dynamics (general numerical response with possible delays) confirm these results but further suggest that negative temporal correlation between predator and primary prey is harmful to alternative prey. Finally, we find that measurements of predator numerical responses are crucial to predict-even qualitatively-the response of ecosystems to changes in the dynamics of outbreaking prey species. PMID:25930160

  6. Aerosol Absorption Effects in the TOMS UV Algorithm

    NASA Technical Reports Server (NTRS)

    Torres, O.; Krotkov, N.; Bhartia, P. K.

    2004-01-01

    The availability of global long-term estimates of surface UV radiation is very important, not only for preventive medicine considerations, but also as an important tool to monitor the effects of the stratospheric ozone recovery expected to occur in the next few decades as a result of the decline of the stratospheric chlorine levels. In addition to the modulating effects of ozone and clouds, aerosols also affect the levels of UV-A and W-B radiation reaching the surface. Oscillations in surface W associated with the effects of aerosol absorption may be comparable in magnitude to variations associated with the stratospheric ozone recovery. Thus, the accurate calculation of surface W radiation requires that both the scattering and absorption effects of tropospheric aerosols be taken into account. Although absorption effects of dust and elevated carbonaceous aerosols are already accounted for using Aerosol Index technique, this approach does not work for urban/industrial aerosols in the planetary boundary layer. The use of the new TOMS long-term global data record on UV aerosol absorption optical depth, can improve the accuracy of TOMS spectral UV products, by properly including the spectral attenuation effects of carbonaceous, urban/industrial and mineral aerosols. The TOMS data set on aerosol properties will be discussed, and results of its use in the TOMS surface W algorithm will be presented.

  7. A review of measurement-based assessments of the aerosol direct radiative effect and forcing

    NASA Astrophysics Data System (ADS)

    Yu, H.; Kaufman, Y. J.; Chin, M.; Feingold, G.; Remer, L. A.; Anderson, T. L.; Balkanski, Y.; Bellouin, N.; Boucher, O.; Christopher, S.; Decola, P.; Kahn, R.; Koch, D.; Loeb, N.; Reddy, M. S.; Schulz, M.; Takemura, T.; Zhou, M.

    2006-02-01

    Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. However, large uncertainties exist in current estimates of aerosol forcing because of incomplete knowledge concerning the distribution and the physical and chemical properties of aerosols as well as aerosol-cloud interactions. In recent years, a great deal of effort has gone into improving measurements and datasets. It is thus feasible to shift the estimates of aerosol forcing from largely model-based to increasingly measurement-based. Our goal is to assess current observational capabilities and identify uncertainties in the aerosol direct forcing through comparisons of different methods with independent sources of uncertainties. Here we assess the aerosol optical depth (τ), direct radiative effect (DRE) by natural and anthropogenic aerosols, and direct climate forcing (DCF) by anthropogenic aerosols, focusing on satellite and ground-based measurements supplemented by global chemical transport model (CTM) simulations. The multi-spectral MODIS measures global distributions of aerosol optical depth (τ) on a daily scale, with a high accuracy of ±0.03±0.05τ over ocean. The annual average τ is about 0.14 over global ocean, of which about 21%±7% is contributed by human activities, as estimated by MODIS fine-mode fraction. The multi-angle MISR derives an annual average AOD of 0.23 over global land with an uncertainty of ~20% or ±0.05. These high-accuracy aerosol products and broadband flux measurements from CERES make it feasible to obtain observational constraints for the aerosol direct effect, especially over global the ocean. A number of measurement-based approaches estimate the clear-sky DRE (on solar radiation) at the top-of-atmosphere (TOA) to be about -5.5±0.2 Wm-2 (median ± standard error from various methods) over the global ocean. Accounting for thin cirrus contamination

  8. Aerosol transport in the coastal environment and effects on extinction

    NASA Astrophysics Data System (ADS)

    Vignati, Elizabetta; de Leeuw, Gerrit; Berkowicz, Ruwim

    1998-11-01

    The aerosol in the coastal environment consists of a complicated mixture of anthropogenic and rural aerosol generated over land, and sea spray aerosol. Also, particles are generate dover sea by physical and chemical processes and the chemical composition may change due to condensation/evaporation of gaseous materials. The actual composition is a function of air mass history and fetch. At the land-sea transition the continental sources cease to exist, and thus the concentrations of land-based particles and gases will gradually decrease. At the same time, sea spray is generated due to the interaction between wind and waves in a developing wave field. A very intense source for sea spray aerosol is the surf zone. Consequently, the aerosol transported over sea in off-shore winds will abruptly charge at the land-sea transition and then gradually loose its continental character, while also the contribution of the surf-generated aerosol will decrease. The latter will be compensated, at least in part, by the production of sea spray aerosol. A Coastal Aerosol Transport model is being developed describing the evolution of the aerosol size distribution in an air column advected from the coast line over sea in off-shore winds. Both removal and production are taken into account. The result are applied to estimate the effect of the changing size distribution on the extinction coefficients. In this contribution, preliminary results are presented from a study of the effects of the surf-generated aerosol and the surface production.

  9. Indirect health effects of relative humidity in indoor environments.

    PubMed Central

    Arundel, A V; Sterling, E M; Biggin, J H; Sterling, T D

    1986-01-01

    A review of the health effects of relative humidity in indoor environments suggests that relative humidity can affect the incidence of respiratory infections and allergies. Experimental studies on airborne-transmitted infectious bacteria and viruses have shown that the survival or infectivity of these organisms is minimized by exposure to relative humidities between 40 and 70%. Nine epidemiological studies examined the relationship between the number of respiratory infections or absenteeism and the relative humidity of the office, residence, or school. The incidence of absenteeism or respiratory infections was found to be lower among people working or living in environments with mid-range versus low or high relative humidities. The indoor size of allergenic mite and fungal populations is directly dependent upon the relative humidity. Mite populations are minimized when the relative humidity is below 50% and reach a maximum size at 80% relative humidity. Most species of fungi cannot grow unless the relative humidity exceeds 60%. Relative humidity also affects the rate of offgassing of formaldehyde from indoor building materials, the rate of formation of acids and salts from sulfur and nitrogen dioxide, and the rate of formation of ozone. The influence of relative humidity on the abundance of allergens, pathogens, and noxious chemicals suggests that indoor relative humidity levels should be considered as a factor of indoor air quality. The majority of adverse health effects caused by relative humidity would be minimized by maintaining indoor levels between 40 and 60%. This would require humidification during winter in areas with cold winter climates. Humidification should preferably use evaporative or steam humidifiers, as cool mist humidifiers can disseminate aerosols contaminated with allergens. PMID:3709462

  10. Indirect health effects of relative humidity in indoor environments

    SciTech Connect

    Arundel, A.V.; Sterling, E.M.; Biggin, J.H.; Sterling, T.D.

    1986-03-01

    A review of the health effects of relative humidity in indoor environments suggests that relative humidity can affect the incidence of respiratory infections and allergies. Experimental studies on airborne-transmitted infectious bacteria and viruses have shown that the survival or infectivity of these organisms is minimized by exposure to relative humidities between 40 and 70%. Nine epidemiological studies examined the relationship between the number of respiratory infections or absenteeism and the relative humidity of the office, residence, or school. The incidence of absenteeism or respiratory infections was found to be lower among people working or living in environments with mid-range versus low or high relative humidities. The indoor size of allergenic mite and fungal populations is directly dependent upon the relative humidity. Mite populations are minimized when the relative humidity is below 50% and reach a maximum size at 80% relative humidity. Most species of fungi cannot grow unless the relative humidity exceeds 60%. Relative humidity also affects the rate of offgassing of formaldehyde from indoor building materials, the rate of formation of acids and salts from sulfur and nitrogen dioxide, and the rate of formation of ozone. The influence of relative humidity on the abundance of allergens, pathogens, and noxious chemicals suggests that indoor relative humidity levels should be considered as a factor of indoor air quality. The majority of adverse health effects caused by relative humidity would be minimized by maintaining indoor levels between 40 and 60%. This would require humidification during winter in areas with cold winter climates. Humidification should preferably use evaporative or steam humidifiers, as cool mist humidifiers can disseminate aerosols contaminated with allergens.

  11. Radiative Effects of Aerosols Generated from Biomass Burning, Dust Storms, and Forest Fires

    NASA Technical Reports Server (NTRS)

    Christopher Sundar A.; Vulcan, Donna V.; Welch, Ronald M.

    1996-01-01

    Atmospheric aerosol particles, both natural and anthropogenic, are important to the earth's radiative balance. They scatter the incoming solar radiation and modify the shortwave reflective properties of clouds by acting as Cloud Condensation Nuclei (CCN). Although it has been recognized that aerosols exert a net cooling influence on climate (Twomey et al. 1984), this effect has received much less attention than the radiative forcings due to clouds and greenhouse gases. The radiative forcing due to aerosols is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign (Houghton et al. 1990). Atmospheric aerosol particles generated from biomass burning, dust storms and forest fires are important regional climatic variables. A recent study by Penner et al. (1992) proposed that smoke particles from biomass burning may have a significant impact on the global radiation balance. They estimate that about 114 Tg of smoke is produced per year in the tropics through biomass burning. The direct and indirect effects of smoke aerosol due to biomass burning could add up globally to a cooling effect as large as 2 W/sq m. Ackerman and Chung (1992) used model calculations and the Earth Radiation Budget Experiment (ERBE) data to show that in comparison to clear days, the heavy dust loading over the Saudi Arabian peninsula can change the Top of the Atmosphere (TOA) clear sky shortwave and longwave radiant exitance by 40-90 W/sq m and 5-20 W/sq m, respectively. Large particle concentrations produced from these types of events often are found with optical thicknesses greater than one. These aerosol particles are transported across considerable distances from the source (Fraser et al. 1984). and they could perturb the radiative balance significantly. In this study, the regional radiative effects of aerosols produced from biomass burning, dust storms and forest fires are examined using the Advanced Very High Resolution Radiometer (AVHRR) Local Area

  12. Aerosol effects and corrections in the Halogen Occultation Experiment

    NASA Technical Reports Server (NTRS)

    Hervig, Mark E.; Russell, James M., III; Gordley, Larry L.; Daniels, John; Drayson, S. Roland; Park, Jae H.

    1995-01-01

    The eruptions of Mt. Pinatubo in June 1991 increased stratospheric aerosol loading by a factor of 30, affecting chemistry, radiative transfer, and remote measurements of the stratosphere. The Halogen Occultation Experiment (HALOE) instrument on board Upper Atmosphere Research Satellite (UARS) makes measurements globally for inferring profiles of NO2, H2O, O3, HF, HCl, CH4, NO, and temperature in addition to aerosol extinction at five wavelengths. Understanding and removing the aerosol extinction is essential for obtaining accurate retrievals from the radiometer channels of NO2, H2O and O3 in the lower stratosphere since these measurements are severely affected by contaminant aerosol absorption. If ignored, aerosol absorption in the radiometer measurements is interpreted as additional absorption by the target gas, resulting in anomalously large mixing ratios. To correct the radiometer measurements for aerosol effects, a retrieved aerosol extinction profile is extrapolated to the radiometer wavelengths and then included as continuum attenuation. The sensitivity of the extrapolation to size distribution and composition is small for certain wavelength combinations, reducing the correction uncertainty. The aerosol corrections extend the usable range of profiles retrieved from the radiometer channels to the tropopause with results that agree well with correlative measurements. In situations of heavy aerosol loading, errors due to aerosol in the retrieved mixing ratios are reduced to values of about 15, 25, and 60% in H2O, O3, and NO2, respectively, levels that are much less than the correction magnitude.

  13. Aerosol speckle effects on atmospheric pulsed lidar backscattered signals

    NASA Technical Reports Server (NTRS)

    Murty, S. R.

    1989-01-01

    Lidar systems using atmospheric aerosols as targets exhibit return signal amplitude and power fluctuations which indicate speckle effects. The effects of refractive turbulence along the path on the aerosol speckle field propagation and on the decorrelation time are studied for coherent pulsed lidar systems.

  14. Separating Real and Apparent Effects of Cloud, Humidity, and Dynamics on Aerosol Optical Thickness near Cloud Edges

    NASA Technical Reports Server (NTRS)

    Jeong, Myeong-Jae; Li, Zhanqing

    2010-01-01

    Aerosol optical thickness (AOT) is one of aerosol parameters that can be measured on a routine basis with reasonable accuracy from Sun-photometric observations at the surface. However, AOT-derived near clouds is fraught with various real effects and artifacts, posing a big challenge for studying aerosol and cloud interactions. Recently, several studies have reported correlations between AOT and cloud cover, pointing to potential cloud contamination and the aerosol humidification effect; however, not many quantitative assessments have been made. In this study, various potential causes of apparent correlations are investigated in order to separate the real effects from the artifacts, using well-maintained observations from the Aerosol Robotic Network, Total Sky Imager, airborne nephelometer, etc., over the Southern Great Plains site operated by the U.S. Department of Energy's Atmospheric Radiation Measurement Program. It was found that aerosol humidification effects can explain about one fourth of the correlation between the cloud cover and AOT. New particle genesis, cloud-processed particles, atmospheric dynamics, and aerosol indirect effects are likely to be contributing to as much as the remaining three fourth of the relationship between cloud cover and AOT.

  15. A review of measurement-based assessment of aerosol direct radiative effect and forcing

    NASA Astrophysics Data System (ADS)

    Yu, H.; Kaufman, Y. J.; Chin, M.; Feingold, G.; Remer, L. A.; Anderson, T. L.; Balkanski, Y.; Bellouin, N.; Boucher, O.; Christopher, S.; Decola, P.; Kahn, R.; Koch, D.; Loeb, N.; Reddy, M. S.; Schulz, M.; Takemura, T.; Zhou, M.

    2005-08-01

    Aerosols affect the Earth's energy budget ''directly'' by scattering and absorbing radiation and ''indirectly'' by acting as cloud condensation nuclei and, thereby, affecting cloud properties. However, large uncertainties exist in current estimates of aerosol forcing because of incomplete knowledge concerning the distribution and the physical and chemical properties of aerosols as well as aerosol-cloud interactions. In recent years, a great deal of effort has gone into improving measurements and datasets. It is thus feasible to shift the estimates of aerosol forcing from largely model-based to increasingly measurement-based. Here we assess the aerosol optical depth, direct radiative effect (DRE) by natural and anthropogenic aerosols, and direct climate forcing (DCF) by anthropogenic aerosols, focusing on satellite and ground-based measurements supplemented by global chemical transport model (CTM) simulations. The multi-spectral MODIS measures global distributions of aerosol optical thickness (τ) on a daily scale, with a high accuracy of ±0.03±0.05τ over ocean. The annual average τ is about 0.14 over global ocean, of which about 21% is contributed by human activities, as determined by MODIS fine-mode fraction. The multi-angle MISR derives an annual average AOT of 0.23 over global land with an uncertainty of ~20% or ± 0.05. These high-accuracy aerosol products and broadband flux measurements from CERES make it feasible to obtain observational constraints for the aerosol direct effect, especially over global ocean. A number of measurement-based approaches estimate the clear-sky DRE (on solar radiation) at the top-of-atmosphere (TOA) to be about -5.5±0.2 Wm-2 (median ± standard error) over global ocean. Accounting for thin cirrus contamination of the satellite derived aerosol field will reduce the TOA DRE to -5.0 Wm-2. Because of a lack of measurements of aerosol absorption and difficulty in characterizing land surface reflection, estimates of DRE over land and

  16. Effects of aerosols and relative humidity on cumulus clouds

    NASA Astrophysics Data System (ADS)

    Fan, Jiwen; Zhang, Renyi; Li, Guohui; Tao, Wei-Kuo

    2007-07-01

    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 × 104 cm-3) 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

  17. Whole-atmosphere aerosol microphysics simulations of the Mt Pinatubo eruption: Part 2: Quantifying the direct and indirect (dynamical) radiative forcings

    NASA Astrophysics Data System (ADS)

    Mann, Graham; Dhomse, Sandip; Carslaw, Ken; Chipperfield, Martyn; Lee, Lindsay; Emmerson, Kathryn; Abraham, Luke; Telford, Paul; Pyle, John; Braesicke, Peter; Bellouin, Nicolas; Dalvi, Mohit; Johnson, Colin

    2016-04-01

    The Mt Pinatubo volcanic eruption in June 1991 injected between 10 and 20 Tg of sulphur dioxide into the tropical lower stratosphere. Following chemical conversion to sulphuric acid, the stratospheric aerosol layer thickened substantially causing a strong radiative, dynamical and chemical perturbation to the Earth's atmosphere with effects lasting several years. In this presentation we show results from model experiments to isolate the different ways the enhanced stratospheric aerosol from Pinatubo influenced the Earth's climate. The simulations are carried out in the UK Chemistry and Aerosol composition-climate model (UKCA) which extends the high-top (to 80km) version of the UK Met Office Unified Model (UM). The UM-UKCA model uses the GLOMAP-mode aerosol microphysics module coupled with a stratosphere-troposphere chemistry scheme including sulphur chemistry. By running no-feedback and standard integrations, we separate the main radiative forcings due to aerosol-radiation interactions (i.e. the direct forcings) from those induced by dynamical changes which alter meridional heat transport and distributions of aerosol, ozone and water vapour.

  18. Effects of biomass burning aerosols on CO2 fluxes on Amazon Region

    NASA Astrophysics Data System (ADS)

    Soares Moreira, Demerval; Freitas, Saulo; Longo, Karla; Rosario, Nilton

    2015-04-01

    During the dry season in Central Brazil and Southern Amazon, there is an usually high concentration of aerosol particles associated with intense human activities, with extensive biomass burning. It has been observed through remote sensing that the smoke clouds in these areas often cover an area of about 4 to 5 million km2. Thus, the average aerosol optical depth of these regions at 500 ηm, is usually below 0.1 during the rainy season and can exceed 0.9 in the fire season. Aerosol particles act as condensation nuclei and also increase scattering and absorption of the incident radiation. Therefore, the layer of the aerosol alters the precipitation rate; reduces the amount of solar energy that reaches the surface, producing a cooling; and causes an increase of diffuse radiation. These factors directly and indirectly affect the CO2 fluxes at the surface. In this work, the chemical-atmospheric model CCATT-BRAMS (Coupled Chemistry-Aerosol-Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System) coupled to the surface model JULES (Joint UK Land Environment Simulator) was used to simulate the effects of biomass burning aerosols in CO2 fluxes in the Amazon region. Both the total effect of the aerosols and the contribution related only to the increase of the diffuse fraction caused by the their presence were analyzed. The results show that the effect of the scattered fraction is dominant over all other effects. It was also noted that the presence of aerosols from fires can substantially change biophysiological processes of the carbon cycle. In some situations, it can lead to a sign change in the net ecosystem exchange (NEE), turning it from a source of CO2 to the atmosphere, when the aerosol is not considered in the simulations, to a sink, when it is considered. Thus, this work demonstrates the importance of considering the presence of aerosols in numerical simulations of weather and climate, since carbon dioxide is a major

  19. Analysis of Atmospheric Aerosol Data Sets and Application of Radiative Transfer Models to Compute Aerosol Effects

    NASA Technical Reports Server (NTRS)

    Schmid, Beat; Bergstrom, Robert W.; Redemann, Jens

    2002-01-01

    This report is the final report for "Analysis of Atmospheric Aerosol Data Sets and Application of Radiative Transfer Models to Compute Aerosol Effects". It is a bibliographic compilation of 29 peer-reviewed publications (published, in press or submitted) produced under this Cooperative Agreement and 30 first-authored conference presentations. The tasks outlined in the various proposals are listed below with a brief comment as to the research performed. Copies of title/abstract pages of peer-reviewed publications are attached.

  20. Aerosol effect on Umkehr ozone profiles using Stratospheric Aerosol and Gas Experiment II measurements

    NASA Technical Reports Server (NTRS)

    Newchurch, M. J.; Cunnold, D. M.

    1994-01-01

    This study examines 1211 cases of coincident ozone profiles derived from 1164 Umkehrs and 928 Stratospheric Aerosol and Gas Experiment II (SAGE II) profiles within 1000 km and 12 hours between October 1984 and April 1989 to study the stratospheric-aerosol effect on Umkehr ozone profiles. Because of the close correspondence of stratospheric aerosol optical depth at the SAGE II-measured 0.525-micrometer wavelength and the extrapolated 0.32 Umkehr wavelength determined in this study we use the 0.525-micrometer data to determine the aerosol effect on Umkehr profiles. At the 95% confidence level, we find the following errors to the Umkehr ozone amounts: in Umkehr layer 9 (-2.9 +/- 2.1), layer 8 (-2.3 +/- 1.1), layer 7 (0.1 +/- 1.1), layer 6 (2.2 +/- 1.0), layer 5 (-1.5 +/- 0.8), and layer 4 (-2.4 +/- 1.7) in percent ozone amount per 0.01 stratospheric aerosol optical depth. These results agree with previous theoretical and empirical studies within their respective error bounds in layers 9, 8, and 7. The results in layers 6, 5, and 4 differ significantly from those in previous works. Using only those eight stations with more than 47 coincidences results in mean aerosol effects that are not significantly different from the 14-station results. Because SAGE II and Umkehr produce different ozone retrievals in layer 9 and because the intralayer correlation of SAGE II ozone and aerosol in layer 9 is nonzero, one must exercise some caution in attributing the entire SAGE II-Umkehr difference in this layer to an aerosol effect.

  1. Urban aerosol effects on surface insolation and surface temperature

    NASA Astrophysics Data System (ADS)

    Jin, M.; Burian, S. J.; Remer, L. A.; Shepherd, M. J.

    2007-12-01

    Urban aerosol particulates may play a fundamental role in urban microclimates and city-generated mesoscale circulations via its effects on energy balance of the surface. Key questions that need to be addressed include: (1) How do these particles affect the amount of solar energy reaching the surface and resulting surface temperature? (2) Is the effect the same in all cities? and (3) How does it vary from city to city? Using NASA AERONET in-situ observations, a radiative transfer model, and a regional climate mode (MM5), we assess aerosol effects on surface insolation and surf ace temperature for dense urban-polluted regions. Two big cities, one in a developing country (Beijing, P.R. China) and another in developed country (New York City, USA), are selected for inter-comparison. The study reveals that aerosol effects on surface temperature depends largely on aerosols' optical and chemical properties as well as atmosphere and land surface conditions, such as humidity and land cover. Therefore, the actual magnitudes of aerosol effects differ from city to city. Aerosol measurements from AERONET show both average and extreme cases for aerosol impacts on surface insolation. In general, aerosols reduce surface insolation by 30Wm-2. Nevertheless, in extreme cases, such reduction can exceed 100 Wm-2. Consequently, this reduces surface skin temperature 2-10C in an urban environment.

  2. Direct and semidirect aerosol effects of Southern African biomass burning aerosol

    SciTech Connect

    Sakaeda, Naoko; Wood, Robert; Rasch, Philip J.

    2011-06-21

    The direct and semi-direct radiative effects of biomass burning aerosols from Southern African fires during July-October are investigated using 20 year runs of the Community Atmospheric Model (CAM) coupled to a slab ocean model. The aerosol optical depth is constrained using observations in clear skies from MODIS and for aerosol layers above clouds from CALIPSO. Over the ocean, where the absorbing biomass burning aerosol layers are primarily located above cloud, negative top of atmosphere (TOA) semi-direct radiative effects associated with increased low cloud cover dominate over a weaker positive all-sky direct radiative effect (DRE). In contrast, over the land where the aerosols are often below or within cloud layers, reductions in cloud liquid water path (LWP) lead to a positive semi-direct radiative effect that dominates over a near-zero DRE. Over the ocean, the cloud response can be understood as a response to increased lower tropospheric stability (LTS) which is caused both by aerosol absorptive warming in overlying layers and surface cooling in response to direct aerosol forcing. The ocean cloud changes are robust to changes in the cloud parameterization (removal of the hard-wired dependence of clouds on LTS), suggesting that they are physically realistic. Over land where cloud cover changes are minimal, decreased LWP is consistent with weaker convection driven by increased static stability. Over the entire region the overall TOA radiative effect from the biomass burning aerosols is almost zero due to opposing effects over the land and ocean. However, the surface forcing is strongly negative requiring a reduction in precipitation. This is primarily realized through reductions in convective precipitation on both the southern and northern flanks of the convective precipitation region spanning the equatorial rainforest and the ITCZ in the southern Sahel. The changes are consistent with the low-level aerosol forced cooling pattern. The results highlight the

  3. EFFECT OF ACIDITY ON SECONDARY ORGANIC AEROSOL FORMATION FROM ISOPRENE

    EPA Science Inventory

    The effect of particle-phase acidity on secondary organic aerosol (SOA) formation from isoprene is investigated in a laboratory chamber study, in which the acidity of the inorganic seed aerosol was controlled systematically. The observed enhancement in SOA mass concentration is c...

  4. Modeling Trends in Tropospheric Aerosol Burden & Its Radiative Effects

    EPA Science Inventory

    Large changes in emissions of aerosol precursors have occurred across the southeast U.S., North America, as well as the northern hemisphere. The spatial heterogeneity and contrasting trends in the aerosol burden is resulting in differing effects on regional radiative balance. Mul...

  5. EFFECTS OF SULFURIC ACID AEROSOLS ON VEGETATION

    EPA Science Inventory

    A continuous flow system for exposing plants to submicron aerosols of sulfuric acid has been developed and an operational model has been constructed. Exposure chambers have been designed to allow simultaneous exposures of the same plant to aerosol and control environments. All su...

  6. Unexpected Benefits of Reducing Aerosol Cooling Effects

    EPA Science Inventory

    Impacts of aerosol cooling are not limited to changes in surface temperature since modulation of atmospheric dynamics resulting from the increased stability can deteriorate local air quality and impact human health. Health impacts from two manifestations of the aerosol direct eff...

  7. Characterization of Mojave Desert aerosols: Their effect on radiometer performance

    SciTech Connect

    Mathews, L.A.; Salgado, D.P.; Walker, P.L.

    1994-12-31

    The Antelope Valley is part of the southwestern Mojave Desert lying fifty miles north of Los Angeles International Airport. The Antelope Valley is separated from the Los Angeles and San Fernando Valley air basins by the San Gabriel Mountains. The Tehachapi Mountains, to the west, separate the Antelope Valley from the San Joaquin Valley. Combustion aerosols are transported from the San Joaquin Valley through the Tehachapi Pass and through the Soledad and Cajun passes from the Los Angeles air basin. Thus the valley`s atmosphere contains a spatially and temporally complex mixture of aerosols of urban, industrial and desert origin. The Visibility Impact Summer Study held from July to September 1990 was an intense, comprehensive study intended to measure aerosol size and chemical composition and to ascertain their optical effects. Size distributions for particle diameters from 0.01 to 10 {micro} were measured at hourly intervals and particle samplers were used to obtain chemical compositions at daily intervals at Tehachapi Pass and Edwards AFB, California. The extracted aerosol characteristics are discussed and compared to the desert aerosol model in LOWTRAN and the size and estimated composition of aerosols at China Lake reported upon earlier. The authors obtain relationships between aerosol mass and wind speed, diurnal size changes, and meteorological effects. Secondarily, extinction was calculated and used with LOWTRAN and radiosonde data for examination of aerosol effects on narrow band 3--5 and 8--12 {micro} imaging radiometer performance.

  8. Quantifying and Testing Indirect Effects in Simple Mediation Models when the Constituent Paths Are Nonlinear

    ERIC Educational Resources Information Center

    Hayes, Andrew F.; Preacher, Kristopher J.

    2010-01-01

    Most treatments of indirect effects and mediation in the statistical methods literature and the corresponding methods used by behavioral scientists have assumed linear relationships between variables in the causal system. Here we describe and extend a method first introduced by Stolzenberg (1980) for estimating indirect effects in models of…

  9. Direct radiative effect by multicomponent aerosol over China

    SciTech Connect

    Huang, Xin; Song, Yu; Zhao, Chun; Cai, Xuhui; Zhang, Hongsheng; Zhu, Tong

    2015-05-01

    The direct radiative effect (DRE) of multiple aerosol species (sulfate, nitrate, ammonium, black carbon (BC), organic carbon (OC), and mineral aerosol) and their spatiotemporal variations over China were investigated using a fully coupled meteorology–chemistry model (WRF-Chem) for the entire year of 2006. We made modifications to improve model performance, including updating land surface parameters, improving the calculation of transition metal-catalyzed oxidation of SO2, and adding in heterogeneous reactions between mineral aerosol and acid gases. The modified model well reproduced the magnitude, seasonal pattern, and spatial distribution of the measured meteorological conditions, concentrations of PM10 and its components, and aerosol optical depth (AOD). A diagnostic iteration method was used to estimate the overall DRE of aerosols and contributions from different components. At the land surface, all kinds of aerosol species reduced the incident net radiation flux with a total DRE of 10.2 W m-2 over China. Aerosols significantly warm the atmosphere with the national mean DRE of +10.8 W m-2. BC was the leading radiative-heating component (+8.7 W m-2), followed by mineral aerosol (+1.1 W m-2). At the top of the atmosphere (TOA), BC introduced the largest radiative perturbation (+4.5 W m-2), followed by sulfate (-1.4 W m-2). The overall perturbation of aerosols on radiation transfer is quite small over China, demonstrating the counterbalancing effect between scattering and adsorbing aerosols. Aerosol DRE at the TOA had distinct seasonality, generally with a summer maximum and winter minimum, mainly determined by mass loadings, hygroscopic growth, and incident radiation flux.

  10. Reallocation in modal aerosol models: impacts on predicting aerosol radiative effects

    NASA Astrophysics Data System (ADS)

    Korhola, T.; Kokkola, H.; Korhonen, H.; Partanen, A.-I.; Laaksonen, A.; Lehtinen, K. E. J.; Romakkaniemi, S.

    2014-01-01

    Atmospheric models often represent the aerosol particle size distribution with a modal approach, in which particles are described with log-normal modes within predetermined size ranges. This approach reallocates particles numerically from one mode to another for example during particle growth, potentially leading to artificial changes in the aerosol size distribution. In this study we analysed how the modal reallocation affects climate-relevant variables: cloud droplet number concentration (CDNC), aerosol-cloud interaction parameter (ACI) and light extinction coefficient (qext). The ACI parameter gives the response of CDNC to a change in total aerosol number concentration. We compared these variables between a modal model (with and without reallocation routines) and a high resolution sectional model, which was considered a reference model. We analysed the relative differences in the chosen variables in four experiments designed to assess the influence of atmospheric aerosol processes. We find that limiting the allowed size ranges of the modes, and subsequent remapping of the distribution, leads almost always to an underestimation of cloud droplet number concentrations (by up to 100%) and an overestimation of light extinction (by up to 20%). On the other hand, the aerosol-cloud interaction parameter can be either over- or underestimated by the reallocating model, depending on the conditions. For example, in the case of atmospheric new particle formation events followed by rapid particle growth, the reallocation can cause on average a 10% overestimation of the ACI parameter. Thus it is shown that the reallocation affects the ability of a model to estimate aerosol climate effects accurately, and this should be taken into account when using and developing aerosol models.