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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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John H. Seinfeld, Ralph A. Kahn, Theodore L. Anderson, Robert J. Charlson, Roger Davies, David J. Diner, John A. Ogren, Stephen E. Schwartz, and Bruce A. Wielicki

Aerosols are involved in a complex set of processes that operate across many spatial and temporal scales. Understanding these processes, and ensuring their accurate representation in models of transport, radiation transfer, and climate, requires knowledge of aerosol physical, chemical, and optical properties and the distributions of these properties in space and time. To derive aerosol climate forcing, aerosol optical and microphysical properties and their spatial and temporal distributions, and aerosol interactions with clouds, need to be understood. Such data are also required in conjunction with size-resolved chemical composition in order to evaluate chemical transport models and to distinguish natural and anthropogenic forcing. Other basic parameters needed for modeling the radiative influences of aerosols are surface reflectivity and three-dimensional cloud fields. This large suite of parameters mandates an integrated observing and modeling system of commensurate scope. The Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) concept, designed to meet this requirement, is motivated by the need to understand climate system sensitivity to changes in atmospheric constituents, to reduce climate model uncertainties, and to analyze diverse collections of data pertaining to aerosols. This paper highlights several challenges resulting from the complexity of the problem. Approaches for dealing with them are offered in the set of companion papers.

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Phillip B. Chilson, Winifred F. Frick, Jeffrey F. Kelly, Kenneth W. Howard, Ronald P. Larkin, Robert H. Diehl, John K. Westbrook, T. Adam Kelly, and Thomas H. Kunz

Aeroecology is an emerging scientific discipline that integrates atmospheric science, Earth science, geography, ecology, computer science, computational biology, and engineering to further the understanding of biological patterns and processes. The unifying concept underlying this new transdisciplinary field of study is a focus on the planetary boundary layer and lower free atmosphere (i.e., the aerosphere), and the diversity of airborne organisms that inhabit and depend on the aerosphere for their existence. Here, we focus on the role of radars and radar networks in aeroecological studies. Radar systems scanning the atmosphere are primarily used to monitor weather conditions and track the location and movements of aircraft. However, radar echoes regularly contain signals from other sources, such as airborne birds, bats, and arthropods. We briefly discuss how radar observations can be and have been used to study a variety of airborne organisms and examine some of the many potential benefits likely to arise from radar aeroecology for meteorological and biological research over a wide range of spatial and temporal scales. Radar systems are becoming increasingly sophisticated with the advent of innovative signal processing and dual-polarimetric capabilities. These capabilities should be better harnessed to promote both meteorological and aeroecological research and to explore the interface between these two broad disciplines. We strongly encourage close collaboration among meteorologists, radar scientists, biologists, and others toward developing radar products that will contribute to a better understanding of airborne fauna.

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Ralph A. Kahn, John A. Ogren, Thomas P. Ackerman, Jens Bösenberg, Robert J. Charlson, David J. Diner, Brent N. Holben, Robert T. Menzies, Mark A. Miller, and John H. Seinfeld

We briefly but systematically review major sources of aerosol data, emphasizing suites of measurements that seem most likely to contribute to assessments of global aerosol climate forcing. The strengths and limitations of existing satellite, surface, and aircraft remote sensing systems are described, along with those of direct sampling networks and ship-based stations. It is evident that an enormous number of aerosol-related observations have been made, on a wide range of spatial and temporal sampling scales, and that many of the key gaps in this collection of data could be filled by technologies that either exist or are expected to be available in the near future. Emphasis must be given to combining remote sensing and in situ active and passive observations and integrating them with aerosol chemical transport models, in order to create a more complete environmental picture, having sufficient detail to address current climate forcing questions. The Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) initiative would provide an organizational framework to meet this goal.

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Soroosh Sorooshian, Amir AghaKouchak, Phillip Arkin, John Eylander, Efi Foufoula-Georgiou, Russell Harmon, Jan M. H. Hendrickx, Bisher Imam, Robert Kuligowski, Brian Skahill, and Gail Skofronick-Jackson

No abstract available.

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Burkely T. Gallo, Christina P. Kalb, John Halley Gotway, Henry H. Fisher, Brett Roberts, Israel L. Jirak, Adam J. Clark, Curtis Alexander, and Tara L. Jensen

Abstract

Evaluation of numerical weather prediction (NWP) is critical for both forecasters and researchers. Through such evaluation, forecasters can understand the strengths and weaknesses of NWP guidance, and researchers can work to improve NWP models. However, evaluating high-resolution convection-allowing models (CAMs) requires unique verification metrics tailored to high-resolution output, particularly when considering extreme events. Metrics used and fields evaluated often differ between verification studies, hindering the effort to broadly compare CAMs. The purpose of this article is to summarize the development and initial testing of a CAM-based scorecard, which is intended for broad use across research and operational communities and is similar to scorecards currently available within the enhanced Model Evaluation Tools package (METplus) for evaluating coarser models. Scorecards visualize many verification metrics and attributes simultaneously, providing a broad overview of model performance. A preliminary CAM scorecard was developed and tested during the 2018 Spring Forecasting Experiment using METplus, focused on metrics and attributes relevant to severe convective forecasting. The scorecard compared attributes specific to convection-allowing scales such as reflectivity and surrogate severe fields, using metrics like the critical success index (CSI) and fractions skill score (FSS). While this preliminary scorecard focuses on attributes relevant to severe convective storms, the scorecard framework allows for the inclusion of further metrics relevant to other applications. Development of a CAM scorecard allows for evidence-based decision-making regarding future operational CAM systems as the National Weather Service transitions to a Unified Forecast system as part of the Next-Generation Global Prediction System initiative.

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Thorwald H. M. Stein, Robin J. Hogan, Peter A. Clark, Carol E. Halliwell, Kirsty E. Hanley, Humphrey W. Lean, John C. Nicol, and Robert S. Plant

Abstract

A new frontier in weather forecasting is emerging by operational forecast models now being run at convection-permitting resolutions at many national weather services. However, this is not a panacea; significant systematic errors remain in the character of convective storms and rainfall distributions. The Dynamical and Microphysical Evolution of Convective Storms (DYMECS) project is taking a fundamentally new approach to evaluate and improve such models: rather than relying on a limited number of cases, which may not be representative, the authors have gathered a large database of 3D storm structures on 40 convective days using the Chilbolton radar in southern England. They have related these structures to storm life cycles derived by tracking features in the rainfall from the U.K. radar network and compared them statistically to storm structures in the Met Office model, which they ran at horizontal grid length between 1.5 km and 100 m, including simulations with different subgrid mixing length. The authors also evaluated the scale and intensity of convective updrafts using a new radar technique. They find that the horizontal size of simulated convective storms and the updrafts within them is much too large at 1.5-km resolution, such that the convective mass flux of individual updrafts can be too large by an order of magnitude. The scale of precipitation cores and updrafts decreases steadily with decreasing grid lengths, as does the typical storm lifetime. The 200-m grid-length simulation with standard mixing length performs best over all diagnostics, although a greater mixing length improves the representation of deep convective storms.

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Robert B. Lee III, Bruce R. Barkstrom, G. Louis Smith, John E. Cooper, Leonard P. Kopia, R. Wes Lawrence, Susan Thomas, Dhirendra K. Pandey, and Dominique A. H. Crommelynck

Abstract

The Clouds and the Earth's Radiant Energy System (CERES) spacecraft sensors are designed to measure broadband earth-reflected solar shortwave (0.3–5 µm) and earth-emitted longwave (5– > 100 µm) radiances at the top of the atmosphere as part of the Mission to Planet Earth program. The scanning thermistor bolometer sensors respond to radiances in the broadband shortwave (0.3–5 µm) and total-wave (0.3– > 100 µm) spectral regions, as well as to radiances in the narrowband water vapor window (8–12 µm) region. The sensors are designed to operate for a minimum of 5 years aboard the NASA Tropical Rainfall Measuring Mission and Earth Observing System AM-I spacecraft platforms that are scheduled for launches in 1997 and 1998, respectively. The flight sensors and the in-flight calibration systems will he calibrated in a vacuum ground facility using reference radiance sources, tied to the international temperature scale of 1990. The calibrations will be used to derive sensor gains, offsets, spectral responses, and point spread functions within and outside of the field of view. The shortwave, total-wave, and window ground calibration accuracy requirements (1 sigma) are ±0.8, ±0.6, and ±0.3 W m−2 sr−1, respectively, while the corresponding measurement precisions are ±0.5% and ±1.0% for the broadband longwave and shortwave radiances, respectively. The CERES sensors, in-flight calibration systems, and ground calibration instrumentation are described along with outlines of the preflight and in-flight calibration approaches.

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Carl E. Hane, Jill D. Watts, David L. Andra Jr., John A. Haynes, Edward Berry, Robert M. Rabin, and Frederick H. Carr

Abstract

The factors that influence the evolution of convective systems during the late morning over much of the Great Plains are not understood well. It is known that in this region the majority of such systems dissipate or decrease in intensity during this period. With this fact in mind, a summary is given of comments made during the occurrence of morning convective systems by forecasters at two National Weather Service (NWS) offices relating to factors that were most important in determining their forecasts of system evolution. In addition, results of a preliminary climatological study covering eight summer months for 181 summer precipitation systems affecting the county warning areas of the two NWS offices during late morning are presented. Revealed among the significant system characteristics is that approximately two-thirds of the included systems either decreased in intensity or dissipated during the late morning.

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