- For the recent several years submicron aerosol size distributions are measured in and around the Korean Peninsula, which include continuous measurements in the highly populated city of Seoul, several short term intensive measurements at the coastal sites in Anmyeon and Gosan, Jeju Island, ship measurements over the Yellow Sea, South Sea of Korea, and East China Sea. Submicron aerosol concentrations in Seoul were high as expected, averaging about 20000 cm^-3. Even at coastal sites, however, the concentrations easily exceeded 5000 cm^-3. Ship measurements also showed similar values but the minimum value reached down to 1000 cm^-3 at the remotest location from the land masses. These values are in contrast to ~300 cm^-3 measured in clean maritime environment in other places and are indicative of the ubiquitous presence of submicron aerosols in the northeast Asia. CCN concentrations were lower but still more than an order of magnitude higher than those in clean maritime air masses. To see the effects of very high CCN concentrations on cloud and precipitation development, two types of cloud models were used: a convective cloud model and an LES model. When the given thermodynamic condition was representative of weak convection, cloud and precipitation development was distinctively weaker in continental clouds than in maritime clouds, especially when the maritime clouds became a cold cloud as the cloud top reached over the freezing level but the continental clouds did not. However, strong convective clouds were not affected by the given CCN concentrations. LES model runs also showed differences in stratus cloud development due to CCN conditions. More detailed discussion will be made at the presentation.



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- Atmospheric aerosols indirectly impact climate by altering cloud development, lifetime, precipitation, and albedo. Current understanding of the aerosol indirect effect remains highly uncertain, constituting the greatest uncertainty in climate prediction. Anthropogenic aerosols may influence the cloud processes and precipitation by serving as cloud condensation nuclei (CCN), potentially forming smaller cloud droplets and higher concentrations. In this presentation, I will discuss the application of a two-moment bulk microphysical scheme incorporated into the Cloud-Resolving Weather Research and Forecast (CR-WRF) Model to consider the effects of aerosols on clouds and precipitation. Three case studies on the effects of aerosols on clouds will be presented, including an isolated cumulus cloud, a mesoscale squall line, and a large-scale cyclone over the Pacific Ocean. The effects of aerosols on the cumulus cloud event will be discussed to demonstrate a non-monotonic response of precipitation to the increase of aerosol concentrations. In the simulations of the squall line, the performance of CR-WRF model will be demonstrated to replicate the development and intensity of the mesoscale system, showing that aerosols significantly impact the distribution and amount of precipitation. I will also show a trend of increasing deep convective clouds over the Pacific in winter from long-term satellite cloud measurements (1984-2005). Simulations using the WRF model reveal that the enhanced deep convective clouds are reproduced when accounting for the aerosol effect from the Asian pollution outflow, which leads to intensified storms. The wintertime Pacific is highly vulnerable to the aerosol-cloud interaction because of favorable cloud dynamical and microphysical conditions from the coupling between the Pacific storm track and Asian pollution outflow. The intensified Pacific storm track is climatically significant and represents possibly the first detected climate signal of the aerosol-cloud interaction associated with anthropogenic pollution.



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- The Earth's polar regions are showing the first dramatic and unmistakable signatures of anthropogenic climate warming. Historically, the polar regions have shown some of the greatest sensitivity to atmospheric chemical perturbation from industrial activity. Because of their extreme remoteness and harsh environment, remote sensing - both satellite and ground based - has added importance for advancing our understanding of the physical mechanisms and their ecological effects. After a brief review of some major satellite roles in polar science, this talk will focus on three studies in detail: (1) use of DOE ARM data to ascertain the direct and indirect effects of anthropogenic Arctic haze on the climate system at high Northern latitudes, (2) use of satellite microwave, multispectral imager, and ocean color data to assess the potential ecological impact of the springtime Antarctic ozone decrease, and (3) use of satellite meteorological data to assess the dynamical "indirect effect" contributing to Antarctic Peninsula warming that is related to human atmospheric perturbation and its interaction with the Southern Annular Mode.



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- The Atmospheric Radiation Measurement (ARM) Program has continuously operated vertically pointing millimeter cloud radars at a number of global sites for over 10 years. The five fixed ARM Climate Research Facility sites (Southern Great Plains and North Slope of Alaska in the U.S. and Tropical Western Pacific locations in Darwin, Manus, Papua New Guinea and Nauru Island) operate 35GHz (8.6 mm) radars; the Southern Great Plains site and the ARM Mobile Facility (AMF) have been operating 95 GHz (3.2 mm) radars since early 2006. The radar-equipped AMF has been deployed in Niamey, Niger (2006) and Black Forest, Germany (2007) to date.

A review of basic radar meteorology is presented as relates to the ARM cloud radars. Topics include the basics of radar operation, fundamental radar parameters, sensing tradeoffs and Doppler spectra. An overview of the characteristics and capabilities of ARM's cloud radars is presented along with a description of available data products as well as those "in the works."



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- Clouds play an import role at all scales related to climate, from local to regional to global scale through vertical exchange of mass, momentum, and heat and through altering the radiation balance. The regional and general circulation models use a variety of cumulus convection schemes with somewhat limited success in predicting the occurrence of the clouds. One of the processes the models have difficulty in predicting is the growth of the clouds due to cloud-radiation interaction processes. Prediction of night time convection enhancement particularly has been a challenge. Convective cloud formation is tightly coupled to at least two interaction processes, surface and cloud, and cloud and radiation.

Initiation of clouds by various land surface processes in tropics and mid latitude locations will be presented. Challenges in modeling the cloud initiation and sustenance will be presented. Observations from Sand hills region of the Carolinas and the ARM SGP site were used to study diurnal variation of convection and the role of surface forcing on convection. Results from this study will be presented.


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- We present a new concept to study air pollution effects on weather and climate, which is based on thermodynamic principles that explain hydration and osmosis - including the required transformation of laboratory based concepts to atmospheric conditions. Under ambient conditions the equilibrium relative humidity (ERH) determines the saturation molality, solute and solvent activities (and activity coefficients), and the aerosol associated water mass, since the water content is fixed by ERH for a given aerosol concentration and type. As a consequence, aerosol water drives the gas/liquid/solid aerosol partitioning, ambient aerosol size-distributions and directly links aerosol hygroscopic growth into fog, haze and clouds.

Various modeling results indicate that a) our new concept is not limited to dilute binary solutions, b) sensitive aerosol properties such as the pH of binary and mixed inorganic/organic salt solutions up to saturation can be computed accurately, and c) that anthropogenic emissions can be directly linked to visibility reduction, cloud formation and climate forcing, if we explicitly account for the aerosol water mass.

Our new concept is more explicit than the traditional CCN concept as it abandons the use of ambiguous terms such as “marine” and “continental” aerosols, and refines lumped categories such as mineral dust, biomass burning, sea salt, organic or sulfate aerosols currently used in atmospheric modeling. Despite, our concept is computationally very efficient as it allows solving the whole gas/liquid/solid aerosol partitioning analytically without numerical iterations. It is therefore especially suited for regional high resolution, or global climate applications

Metzger, S. and J. Lelieveld, Reformulating atmospheric aerosol thermodynamics and hygroscopic growth into fog, haze and clouds, Atmos. Chem. Phys. 7, 3163-3193 (2007).

Full Article in PDF (8472 KB)
http://www.atmos-chem-phys.net/7/3163/2007/acp-7-3163-2007.html

Supplement in PDF (4673 KB)
http://www.atmos-chem-phys.net/7/3163/2007/acp-7-3163-2007-supplement.zip




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- Chemical and physical processes occurring at environmental interfaces can have a profound impact on the chemical balance of the atmosphere. I will discuss two examples from my research:

(1) Heterogeneous ice chemistry relevant to polar stratospheric ozone depletion: We have shown that trace amounts of HCl induce formation of a disordered region, or quasi-liquid layer at the ice surface at stratospheric temperatures. We also showed that surface disordering enhances the chlorine activation reaction of HCl with chlorine nitrate (ClONO₂), and also enhances acetic acid (CH₃COOH) adsorption. These results impact our understanding of the chemistry and physics of ice particles in the atmosphere, explaining the catalytic role that ice particles play in chlorine activation.

(2) Surface active organic films on aqueous aerosols: We have shown that submonolayer films of expanded-state surfactants can significantly suppress the reactive uptake of N₂O₅ by submicron aqueous aerosols. We used aerosol flow tube reactors with chemical ionization mass spectrometry detection of the gas and particle phases in order to assess the lifetimes of such films when subject to oxidation in the atmosphere. We conclude that for the aerosol compositions studied, oxidation occurs near the gas-aerosol interface and that the 1 e-fold lifetime of unsaturated organics at the aerosol surface is ~10 minutes due to O₃ oxidation under atmospheric conditions. Results will also be shown for the OH oxidation of pure and mixed organic-inorganic aerosols containing palmitic acid.

1. McNeill,V. F., Loerting, T., Geiger, F. M., Trout, B. L., and Molina, M. J. Hydrogen chloride-induced surface disordering on ice. Proc. Natl. Acad. Sci. USA 103, 9422-9427 (2006).
2. McNeill,V. F., Patterson, J., Wolfe, G. M., and Thornton, J. A. The effect of varying levels of surfactant on the reactive uptake of N₂O₅ to aqueous aerosol. Atmos. Chem. Phys. 6, 1635-1644 (2006).
3. McNeill, V. F., Wolfe, G. M., and Thornton, J. A. The Oxidation of Oleate in Submicron Aqueous Salt Particles: Evidence of a Surface Process. J. Phys. Chem. A. 111, 1073-1083 (2007).
4. McNeill, V. F., Geiger, F. M., Loerting,T., Trout, B. L., Molina, L. T., and Molina, M. J. Interaction of Hydrogen Chloride with Ice Surfaces: The Effects of Grain Size, Surface Roughness, and Surface Disorder. J. Phys. Chem. A. 111, 6274-6284 (2007).



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- ARM has from its beginning placed extraordinary emphasis on radiative flux measurements, which are the quantities that enter the energy balance equation in climate models. However, in order to provide input to radiative transfer models that predict fluxes, ARM has also invested heavily in remote sensing instruments like radars and lidars that look only at a narrow vertical field of view, not at the full hemisphere. This causes a fundamental disconnect: radiative fluxes are essentially polling the whole sky, while the remote sensors are polling only the sky directly overhead (in so-called "soda-straw mode") and thus tell us nothing about the rest of the sky hemisphere. In order to more directly connect radiation and soda-straw radar-lidar-microwave remote sensing, ARM has belatedly fielded a new class of radiation instruments that measure zenith radiance in narrow spectral channels. These instruments also measure at a rate fast enough (1 Hz) to resolve cloud temporal evolution, unlike radiative flux measurements which are averages over 30 sec to one minute. This talk will describe some new methods for using these measurements of zenith radiance to learn more about cloud properties like optical depth that are difficult to get from the radar-lidar-microwave combination. Of particular interest will be new methods for using the passive solar background signal measured by all lidars (but in the past used only to subtract from the active signal) to retrieve cloud optical depth, making the lidar twice as useful at no increase in cost.


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- Autoconversion process is the first step of cloud droplets growing into small raindrops. Accurate representation of this process is key to improving atmospheric models of various scales ranging from large eddy simulations to cloud-resolving models to climate models. This talk will give an overview of physical understanding and existing parameterizations, discuss our theoretical development in this subject, and explore applications of our theoretical formulation of the autoconversion process to other areas such as the cloud Radar detection of drizzles and analytical formulation of the second aerosol effect.


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- A complete series of non-orthogonal Thermal Decay Modes (TDMs) of surface temperature is derived from a two dimensional (2D) linear Energy Balance Climate Model (EBCM) and their properties are investigated. These modes are proven useful in studying the global surface temperature field. The development of the TDM theory makes it possible to analyze more generally time-dependent surface-temperature problems in a framework with physical interpretation. The same EBCM is used to illustrate an objective means of deriving the Probability Density Function (PDF) of climate sensitivity to external influences, leading to a better understanding of the origins of the spread of the sensitivity. The method employs a prior distribution that constrains the PDF to favor better fits to the present climate. It is found that the uncertainty in climate sensitivity is difficult to eliminate if climate models are tuned to fit observations of surface temperature alone.

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- During the past 20 years there has been substantial progress on the development and application of millimeter-wavelength (3.2 mm and 8.6 mm, corresponding to frequencies of 94-GHz and 35-GHz) radars in atmospheric cloud research, boosted by continuous advancements in radar technology and the need to better understand clouds and their role in the Earth's climate. Applications of millimeter-wavelength radars range from detailed cloud and precipitation process studies to long-term monitoring activities that strive to improve our understanding of cloud processes over a wide range of spatial and temporal scales. These activities are the result of a long period of successful research, starting from the 1980s, in which research tools and sophisticated retrieval techniques were developed, tested and evaluated in field experiments. Here, we present a cohesive, chronological overview of millimeter-wavelength radar advancements during this period and describes the potential of new applications of millimeter-wavelength radars on sophisticated platforms and the benefits of both lower and higher frequency radars for cloud and precipitation research.


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- To aid in understanding the role that marine boundary layer (MBL) clouds play in climate and assist in improving their representations in general circulation models (GCMs), we quantify their long-term microphysical and macroscale characteristics using observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard the National Aeronautic and Space Administrations’ (NASA’s) Terra satellite. We use five years of MODIS pixel-level cloud products from oceanic study regions off the west coasts of California, Peru, Canary Islands, Angola and Australia where these cloud types are common.  We characterize their organization (macroscale structure), the associated microphysical properties, and the seasonal dependence of their variations. MBL mesoscale structure is quantified using effective cloud diameter, CD, which we introduce here as a measure of bulk cloud organization that is straightforward to compute and provides descriptive information beyond that offered by cloud fraction. The interrelationships of these characteristics are explored while considering the influences of the MBL state such as the MBL depth and the occurrence of drizzle. 

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- The trans-Atlantic Aerosol and Ocean Science Expedition experiments (AEROSE) are designed to investigate the chemical and microphysical evolution of the Saharan air layer (SAL) during its long range transport into the eastern seaboard of the United States and the Caribbean, and to quantify the effects of the SAL on the regional environment and climate. AEROSE-I was conducted in spring 2004 and AEROSE-II took place during summer 2006. Analyses of air mass history, satellite imagery, surface weather maps, and trace gas and aerosol datasets allowed the characterization of three distinct air mass transport regimes for both AEROSE-I and AEROSE-II: marine background, dust, and mixed dust and biomass burning. During the AEROSE experiments continuous in-situ measurements of ozone were collected. Along the AEROSE-I ship track, the ship encountered air masses with significant Saharan dust loading early in the cruise and mixed dust and biomass burning aerosols later along the cruise track. While traveling through the dominant dust regime, ozone concentrations were reduced by up to 70%. Photochemistry was not found to be dominant during the dust regime and biomass burning smoke was found to dominate the chemistry of the air mass during the mixed smoke and dust regimes.


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- For a better understanding and projection of future climate changes, it is important to quantify and reduce the uncertainties of aerosol indirect effects (AIE).

The first AIE (i.e., modifying the initial cloud drop size distribution) is generally supported by observations and model results. Our numerical results show that the cloud droplet number concentration increases and droplet size decreases with increasing aerosol loading.

The second AIE (i.e., modifying cloud lifetime and morphology) is not easily observed. For a spring continental stratus observed at the Southern Great Plains, our numerical results show that the cloud liquid water path (LWP) could either increase, decrease, or remain unchanged with increasing aerosol loading. For summer maritime stratocumulus observed at the sub-tropical northeast Atlantic, our numerical results show that the LWP and cloud fraction (CF) could decrease or remain nearly unchanged with increasing aerosol loading. Further investigation indicates that thermodynamic feedbacks (more vapor condensation near cloud base caused by drizzle evaporative cooling) and the large-scale meteorological conditions (large-scale subsidence) are important for the response of the LWP and CF to changes in aerosols when precipitation is so small that it is not a dominant sink of cloud water.

The cloud droplet dispersion effects on cloud properties and indirect effects will be discussed.


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- Field measurements have shown that organic material is abundant in the atmosphere, comprising 20-90% of the total fine particulate mass. Pure organic particulate matter can consist most likely of a variety of organic compounds which may form in some cases multiphase mixtures. Organic particles while in the at- mosphere can be oxidized by trace gas species such as O₃ and NO₃. This could potentially lead to the modification of the particle composition and morphology resulting in a change in hygroscopicity and possibly lead to volatilization. To bet- ter understand the oxidation of organic particles, we investigate the reaction of O₃ with lauric acid/oleic acid, myristic acid/oleic acid, and multicomponent mixtures representing closely the composition of meat cooking aerosols as a function of com- position, physical state, and microstructure. These experiments are performed using a rotating-wall flow-tube reactor coupled to a chemical ionization mass spectrometer (CIMS). To address possible volatilization of organic aerosols we study the oxidation of organic substrates by NO₃ radicals. Self assembled monolayers serve as a proxy for an organic aerosol particle. The reactive uptake coefficient is determined using a coated-wall flow tube reactor coupled to CIMS and changes in surface properties are determined using X-ray photoelectron spectroscopy. Surface-active organic molecules (organic molecules that have both a hydrophobic group and a hydrophilic group) are common constituents of tropospheric aerosol particles. Several researchers have suggested that these organic molecules form organic coatings or films on the surface of aqueous particles in the troposphere. Here, we investigate the effect of these organic coatings on the hydrolysis of N₂O₅ by aqueous H₂SO₄ surfaces. A newly developed rectangular channel flow reactor coupled to CIMS is used to study the uptake of N₂O₅ by an aqueous planar surface coated with an organic monolayer. This instrument is theoretically and experimentally validated by measuring reactive uptake coefficients of know heterogeneous reactions. The effect of the monolayer on the reactive uptake coefficient as a function of monolayer packing density and molecular chain length is investigated.


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- Aerosols (small particles suspended in air) play major roles in climate forcing and the hydrological cycle, and also on human health effects, visibility degradation, and deposition of acids, toxics, and nutrients to ecosystems. Organic compounds account for a large fraction (~40%) of ambient submicron aerosol mass, but their sources and transformation processes are poorly understood. The Aerodyne Aerosol Mass Spectrometers (AMS) have emerged as powerful tools for the characterization of organic aerosols due to their sensitivity, speed, and quantitative ability. Recent AMS developments will be summarized, including the high-resolution time-of-flight AMS (HR-ToF-AMS) and its first aircraft deployment, the thermal denuder AMS, new component analysis techniques for AMS spectra, and a detailed intercomparison with the PILS-WSOC technique. Results from several recent field campaigns will be presented, including SOAR-1 in Riverside, the MILAGRO campaigns in Mexico City, and the FLAME biomass burning campaign. Secondary organic aerosols from anthropogenic precursors are greatly underestimated by current models, and SOA likely accounts for most of the organic aerosol mass in the polluted regions of the Northern Hemisphere.


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- Understanding the microphysics and radiative effects of clouds requires detailed characterization of the aerosol particles that serve as the precursors of cloud droplets. Focusing on marine stratus clouds, we determined a number of key properties of marine aerosol particles, including chemical composition and cloud condensation nucleus (CCN) properties, on board the DOE G-1 aircraft during MASE over the coastal waters of northern California in July 2005. Aerosol components, including sea-salt (sodium, chloride, magnesium, methansulfonate) and those derived from terrestrial/pollution sources (ammonium, sulfate, nitrate, organics) were determined using the PILS-IC technique and an Aerodyne Aerosol Mass Spectrometer. Sulfate and/or organic aerosols were always present and sea-salt aerosols were observed only on half of the flights. CCN concentrations were determined as a function of supersaturation (S) using a CCN spectrometer and two CCN counters at two different S levels. Based on clear-air CCN data and aerosol size distributions, the critical dry diameter (Dpc) of CCN particles was evaluated as a function of S. The estimated maximum S experienced by the marine stratus, based on cloud droplet number concentration (CDNC) and pre-cloud CCN spectrum, was rather low, ~0.06-0.08%, in agreement with an upper limit of 0.08% judged from in-cloud interstitial CCN data. The Dpc corresponding to this S value was estimated to be ~0.15 µm using CDNC and pre-cloud aerosol size distributions, consistent with that observed in clear air and that predicted for soluble inorganic salts. A progressive retardation of clear-air CCN ability with increasing S above 0.2% was observed and is attributed to an increasing proportion of hydrophobic organics contained in smaller size aerosol particles.


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- There is an increasing need to determine the 3D distribution of the cloud liquid water content. ARM's potential move into scanning radar would be partly directed at this need. But there are also passive remote sensing options. One such option is microwave cloud tomography, originally presented by Warner et al. in 1980s. In this work, we revisit 3D cloud tomography as a potential routine means to measure cloud liquid water field at ARM sites. We find that the reconstruction of cloud liquid water field from microwave emission is highly ill-posed, and requires specific techniques to solve the ill-posed inverse problem. In this work, the method of truncated singular value decomposition is used to examine the ill-posedness of the problem, and obtain optimal solutions. Sensitivity studies show that the reconstruction quality is determined by number of radiometers, the total number of scanning angles, the noise level of the radiometers, and reconstruction resolution. With 4 microwave radiometers of typical noise level 0.3 K, the method is capable of retrieving the liquid water content to within 5% of the maximum water content in the simulated stratocumulus and broken cumulus clouds with a spatial resolution of a few hundred meters.


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- Since the second year of the Ford Administration when Junge outlined the problem, atmospheric scientists have been engaged in a mission to beat down the uncertainties in Aerosol Climate Forcing. The intervening years have seen exponential increases in the number of scientist attacking this problem, the power of their instrumental and computational weaponry, and, of course, the overall cost of the mission. Publications have also increased exponentially, and yet, five Presidents and four party switches later, any semblance of victory remains elusive. Even our weakest enemy (the "direct forcing" problem), though targeted in well-armed field campaigns, has managed to stage repeated comebacks via such unanticipated tactics as the insertion of absorbing aerosol above boundary layer clouds, where its effects may be great and yet are almost impossible to measure. Meanwhile, the hydra-headed monster known as "indirect forcing", while surrendering tiny slivers of territory, has only grown in overall strength and incomprehensibility. Our great nation stands this very day at a turning point - a moment of decision. Shall we battle on with our bottom-up techniques, as the mad-dogs of the Red Party advocate? Shall we abandon the field to top-down (or inverse) methods, wherein we merely pick the forcing value that allows a climate model to fit the temperature record, as called for by the cowards of the Blue Party? Should we listen to those queer Third Party voices, urging, for example, approaches based on monitoring the heat content of the ocean or the albedo of the entire planet? These are trying and confusing times, and yet the choice is upon us. My goal in this presentation and the discussion to follow is not to recommend any particular course of action, but to help equip us to choose wisely. Specific topics will include: What do recent, so-called "observation-based" estimates of direct forcing tell us about the state of the science? What do we know about the accuracy of AERONET retrievals of absorption optical depth and fine-mode fraction? How does the notion of an aerosol/cloud continuum affect our observational and modeling strategies? Even though they cannot vote today, non-U.S. citizens are encouraged to come and participate - we need all the help we can get!



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