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Johannes Mülmenstädt, Dan Lubin, Lynn M. Russell, and Andrew M. Vogelmann

Abstract

Long time series of Arctic atmospheric measurements are assembled into meteorological categories that can serve as test cases for climate model evaluation. The meteorological categories are established by applying an objective k-means clustering algorithm to 11 years of standard surface-meteorological observations collected from 1 January 2000 to 31 December 2010 at the North Slope of Alaska (NSA) site of the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM). Four meteorological categories emerge. These meteorological categories constitute the first classification by meteorological regime of a long time series of Arctic meteorological conditions. The synoptic-scale patterns associated with each category, which include well-known synoptic features such as the Aleutian low and Beaufort Sea high, are used to explain the conditions at the NSA site. Cloud properties, which are not used as inputs to the k-means clustering, are found to differ significantly between the regimes and are also well explained by the synoptic-scale influences in each regime. Since the data available at the ARM NSA site include a wealth of cloud observations, this classification is well suited for model–observation comparison studies. Each category comprises an ensemble of test cases covering a representative range in variables describing atmospheric structure, moisture content, and cloud properties. This classification is offered as a complement to standard case-study evaluation of climate model parameterizations, in which models are compared against limited realizations of the Earth–atmosphere system (e.g., from detailed aircraft measurements).

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Lynn M. Russell, Shou-Hua Zhang, Richard C. Flagan, John H. Seinfeld, Mark R. Stolzenburg, and Robert Caldow

Abstract

A radially classified aerosol detector (RCAD) for fast characterization of fine particle size distributions aboard aircraft has been designed and implemented. The measurement system includes a radial differential mobility analyzer and a high-flow, high-efficiency condensation nuclei counter based on modifications to a commercial model (TST, model 3010). Variations in pressure encountered during changes in altitude in flight are compensated by feedback control of volumetric flow rates with a damped proportional control algorithm. Sampling resolution is optimized with the use of an automated dual-bag sampling system. This new system has been tested aboard the University of Washington Cl31a research aircraft to demonstrate its in-flight performance capabilities. The system was used to make measurements of aerosol, providing observations of the spatial variability within the cloud-topped boundary layer off the coast of Monterey, California.

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Lynn M. Russell, Kevin J. Noone, Ronald J. Ferek, Robert A. Pockalny, Richard C. Flagan, and John H. Seinfeld

Abstract

Polycyclic aromatic hydrocarbons (PAHs) have been sampled in marine stratiform clouds to identify the contribution of anthropogenic combustion emissions in activation of aerosol to cloud droplets. The Monterey Area Ship Track experiment provided an opportunity to acquire data on the role of organic compounds in ambient clouds and in ship tracks identified in satellite images. Identification of PAHs in cloud droplet residual samples indicates that several PAHs are present in cloud condensation nuclei in anthropogenically influenced air and do result in activated droplets in cloud. These results establish the presence of combustion products, such as PAHs, in submicrometer aerosols in anthropogenically influenced marine air, with enhanced concentrations in air polluted by ship effluent. The presence of PAHs in droplet residuals in anthropogenically influenced air masses indicates that some fraction of those combustion products is present in the cloud condensation nuclei that activate in cloud. Although a sufficient mass of droplet residuals was not collected to establish a similar role for organics from measurements in satellite-identified ship tracks, the available evidence from the fraction of organics present in the interstitial aerosol is consistent with part of the organic fraction partitioning to the droplet population. In addition, the probability that a compound will be found in cloud droplets rather than in the unactivated aerosol and the compound’s water solubility are compared. The PAHs studied are only weakly soluble in water, but most of the sparse data collected support more soluble compounds having a higher probability of activation.

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Yang Yang, Lynn M. Russell, Sijia Lou, Maryam A. Lamjiri, Ying Liu, Balwinder Singh, and Steven J. Ghan

Abstract

Two 150-yr preindustrial simulations with and without interactive sea salt emissions from the Community Earth System Model (CESM) are performed to quantify the interactions between sea salt emissions and El Niño–Southern Oscillation (ENSO). Variations in sea salt emissions over the tropical Pacific Ocean are affected by changing wind speed associated with ENSO variability. ENSO-induced interannual variations in sea salt emissions result in decreasing (increasing) aerosol optical depth (AOD) by 0.03 over the equatorial central-eastern (western) Pacific Ocean during El Niño events compared to those during La Niña events. These changes in AOD further increase (decrease) radiative fluxes into the atmosphere by +0.2 (−0.4) W m−2 over the tropical eastern (western) Pacific. Thereby, sea surface temperature increases (decreases) by 0.2–0.4 K over the tropical eastern (western) Pacific Ocean during El Niño compared to La Niña events and enhances ENSO variability by 10%. The increase in ENSO amplitude is a result of systematic heating (cooling) during the warm (cold) phase of ENSO in the eastern Pacific. Interannual variations in sea salt emissions then produce the anomalous ascent (subsidence) over the equatorial eastern (western) Pacific between El Niño and La Niña events, which is a result of heating anomalies. Owing to variations in sea salt emissions, the convective precipitation is enhanced by 0.6–1.2 mm day−1 over the tropical central-eastern Pacific Ocean and weakened by 0.9–1.5 mm day−1 over the Maritime Continent during El Niño compared to La Niña events, enhancing the precipitation variability over the tropical Pacific.

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Robert Wood, Michael P. Jensen, Jian Wang, Christopher S. Bretherton, Susannah M. Burrows, Anthony D. Del Genio, Ann M. Fridlind, Steven J. Ghan, Virendra P. Ghate, Pavlos Kollias, Steven K. Krueger, Robert L. McGraw, Mark A. Miller, David Painemal, Lynn M. Russell, Sandra E. Yuter, and Paquita Zuidema
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Dan Lubin, Damao Zhang, Israel Silber, Ryan C. Scott, Petros Kalogeras, Alessandro Battaglia, David H. Bromwich, Maria Cadeddu, Edwin Eloranta, Ann Fridlind, Amanda Frossard, Keith M. Hines, Stefan Kneifel, W. Richard Leaitch, Wuyin Lin, Julien Nicolas, Heath Powers, Patricia K. Quinn, Penny Rowe, Lynn M. Russell, Sangeeta Sharma, Johannes Verlinde, and Andrew M. Vogelmann

Abstract

The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE) performed comprehensive meteorological and aerosol measurements and ground-based atmospheric remote sensing at two Antarctic stations using the most advanced instrumentation available. A suite of cloud research radars, lidars, spectral and broadband radiometers, aerosol chemical and microphysical sampling equipment, and meteorological instrumentation was deployed at McMurdo Station on Ross Island from December 2015 through December 2016. A smaller suite of radiometers and meteorological equipment, including radiosondes optimized for surface energy budget measurement, was deployed on the West Antarctic Ice Sheet between 4 December 2015 and 17 January 2016. AWARE provided Antarctic atmospheric data comparable to several well-instrumented high Arctic sites that have operated for many years and that reveal numerous contrasts with the Arctic in aerosol and cloud microphysical properties. These include persistent differences in liquid cloud occurrence, cloud height, and cloud thickness. Antarctic aerosol properties are also quite different from the Arctic in both seasonal cycle and composition, due to the continent’s isolation from lower latitudes by Southern Ocean storm tracks. Antarctic aerosol number and mass concentrations are not only non-negligible but perhaps play a more important role than previously recognized because of the higher sensitivities of clouds at the very low concentrations caused by the large-scale dynamical isolation. Antarctic aerosol chemical composition, particularly organic components, has implications for local cloud microphysics. The AWARE dataset, fully available online in the ARM Program data archive, offers numerous case studies for unique and rigorous evaluation of mixed-phase cloud parameterization in climate models.

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John H. Seinfeld, Gregory R. Carmichael, Richard Arimoto, William C. Conant, Frederick J. Brechtel, Timothy S. Bates, Thomas A. Cahill, Antony D. Clarke, Sarah J. Doherty, Piotr J. Flatau, Barry J. Huebert, Jiyoung Kim, Krzysztof M. Markowicz, Patricia K. Quinn, Lynn M. Russell, Philip B. Russell, Atsushi Shimizu, Yohei Shinozuka, Chul H. Song, Youhua Tang, Itsushi Uno, Andrew M. Vogelmann, Rodney J. Weber, Jung-Hun Woo, and Xiao Y. Zhang

Although continental-scale plumes of Asian dust and pollution reduce the amount of solar radiation reaching the earth's surface and perturb the chemistry of the atmosphere, our ability to quantify these effects has been limited by a lack of critical observations, particularly of layers above the surface. Comprehensive surface, airborne, shipboard, and satellite measurements of Asian aerosol chemical composition, size, optical properties, and radiative impacts were performed during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) study. Measurements within a massive Chinese dust storm at numerous widely spaced sampling locations revealed the highly complex structure of the atmosphere, in which layers of dust, urban pollution, and biomass- burning smoke may be transported long distances as distinct entities or mixed together. The data allow a first-time assessment of the regional climatic and atmospheric chemical effects of a continental-scale mixture of dust and pollution. Our results show that radiative flux reductions during such episodes are sufficient to cause regional climate change.

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Kevin J. Noone, Doug W. Johnson, Jonathan P. Taylor, Ronald J. Ferek, Tim Garrett, Peter V. Hobbs, Philip A. Durkee, Kurt Nielsen, Elisabeth Öström, Colin O’Dowd, Michael H. Smith, Lynn M. Russell, Richard C. Flagan, John H. Seinfeld, Lieve De Bock, René E. Van Grieken, James G. Hudson, Ian Brooks, Richard F. Gasparovic, and Robert A. Pockalny

Abstract

A case study of the effects of ship emissions on the microphysical, radiative, and chemical properties of polluted marine boundary layer clouds is presented. Two ship tracks are discussed in detail. In situ measurements of cloud drop size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside-cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to remotely sensed measurements of cloud radiative properties.

The authors examine the processes behind ship track formation in a polluted marine boundary layer as an example of the effects of anthropogenic particulate pollution on the albedo of marine stratiform clouds.

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Kevin J. Noone, Elisabeth Öström, Ronald J. Ferek, Tim Garrett, Peter V. Hobbs, Doug W. Johnson, Jonathan P. Taylor, Lynn M. Russell, Richard C. Flagan, John H. Seinfeld, Colin D. O’Dowd, Michael H. Smith, Philip A. Durkee, Kurt Nielsen, James G. Hudson, Robert A. Pockalny, Lieve De Bock, René E. Van Grieken, Richard F. Gasparovic, and Ian Brooks

Abstract

The effects of anthropogenic particulate emissions from ships on the radiative, microphysical, and chemical properties of moderately polluted marine stratiform clouds are examined. A case study of two ships in the same air mass is presented where one of the vessels caused a discernible ship track while the other did not. In situ measurements of cloud droplet size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to measurements of cloud radiative properties. The differences between the aerosol in the two ship plumes are discussed;these indicate that combustion-derived particles in the size range of about 0.03–0.3-μm radius were those that caused the microphysical changes in the clouds that were responsible for the ship track.

The authors examine the processes behind ship track formation in a moderately polluted marine boundary layer as an example of the effects that anthropogenic particulate pollution can have in the albedo of marine stratiform clouds.

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Peter V. Hobbs, Timothy J. Garrett, Ronald J. Ferek, Scott R. Strader, Dean A. Hegg, Glendon M. Frick, William A. Hoppel, Richard F. Gasparovic, Lynn M. Russell, Douglas W. Johnson, Colin O’Dowd, Philip A. Durkee, Kurt E. Nielsen, and George Innis

Abstract

Emissions of particles, gases, heat, and water vapor from ships are discussed with respect to their potential for changing the microstructure of marine stratiform clouds and producing the phenomenon known as “ship tracks.” Airborne measurements are used to derive emission factors of SO2 and NO from diesel-powered and steam turbine-powered ships, burning low-grade marine fuel oil (MFO); they were ∼15–89 and ∼2–25 g kg−1 of fuel burned, respectively. By contrast a steam turbine–powered ship burning high-grade navy distillate fuel had an SO2 emission factor of ∼6 g kg−1.

Various types of ships, burning both MFO and navy distillate fuel, emitted from ∼4 × 1015 to 2 × 1016 total particles per kilogram of fuel burned (∼4 × 1015–1.5 × 1016 particles per second). However, diesel-powered ships burning MFO emitted particles with a larger mode radius (∼0.03–0.05 μm) and larger maximum sizes than those powered by steam turbines burning navy distillate fuel (mode radius ∼0.02 μm). Consequently, if the particles have similar chemical compositions, those emitted by diesel ships burning MFO will serve as cloud condensation nuclei (CCN) at lower supersaturations (and will therefore be more likely to produce ship tracks) than the particles emitted by steam turbine ships burning distillate fuel. Since steam turbine–powered ships fueled by MFO emit particles with a mode radius similar to that of diesel-powered ships fueled by MFO, it appears that, for given ambient conditions, the type of fuel burned by a ship is more important than the type of ship engine in determining whether or not a ship will produce a ship track. However, more measurements are needed to test this hypothesis.

The particles emitted from ships appear to be primarily organics, possibly combined with sulfuric acid produced by gas-to-particle conversion of SO2. Comparison of model results with measurements in ship tracks suggests that the particles from ships contain only about 10% water-soluble materials. Measurements of the total particles entering marine stratiform clouds from diesel-powered ships fueled by MFO, and increases in droplet concentrations produced by these particles, show that only about 12% of the particles serve as CCN.

The fluxes of heat and water vapor from ships are estimated to be ∼2–22 MW and ∼0.5–1.5 kg s−1, respectively. These emissions rarely produced measurable temperature perturbations, and never produced detectable perturbations in water vapor, in the plumes from ships. Nuclear-powered ships, which emit heat but negligible particles, do not produce ship tracks. Therefore, it is concluded that heat and water vapor emissions do not play a significant role in ship track formation and that particle emissions, particularly from those burning low-grade fuel oil, are responsible for ship track formation. Subsequent papers in this special issue discuss and test these hypotheses.

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