Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: David Stock x
  • Refine by Access: All Content x
Clear All Modify Search
Paul Dawson, David E. Stock, and Brian Lamb

Abstract

A three-dimensional, nonhydrostatic numerical code using the two-equation turbulence closure was developed to model the atmospheric transport and diffusion of pollutants over buildings and a three-dimensional hill. The standard engineering two-equation, first-order turbulence closure was modified to account for surface layer effects and the reduced production of dissipation in the region above the surface layer found in an atmospheric boundary layer.

The computations for the dispersion of a building rooftop release showed good agreement with wind tunnel measurements, except when very close to the ground. The transport and dispersion of a plume over a 300-m conical hill, Steptoe Butte, was also simulated. The computations are compared with near ground-level field measurements.

Full access
Alex Guenther, Brian Lamb, and David Stock

Abstract

Plume downwash at a large oil-gathering facility in the Prudhoe Bay, Alaska oil-field reservation was simulated in a series of numerical experiments. The purpose of this study was to investigate the potential of the numerical model as a means of assessing the impact of pollutants emitted from buoyant sources influenced by complex aerodynamic wakes. The model is a three-dimensional, Cartesian coordinate, finite difference code that solves the nonhydrostatic, time-averaged equations for the conservation of momentum and energy. The code uses a modified form of the standard first-order, two-equation (k–ε) engineering turbulence closure model.

Wind tunnel and field investigations of dispersion at this arctic industrial complex indicate that dispersion is significantly influenced by building-generated airflow disturbances. We have used the numerical model to simulate directly the mean features of the flow field and dispersion from a buoyant source at an industrial site. The flow features varied depending on the size, number, and orientation of the buildings. A recirculation cavity was present in all model simulations and varied from 0.8 HB to 2 HB (building height). This agrees closely with results of wind tunnel studies. The model simulates a velocity defect of 0.6, a factor of 3.4 increase (relative to the approach flow) in turbulent kinetic energy (k), a factor of 5 increase in dissipation of k(ε), and a 45% increase in turbulent viscosity at a downwind distance of 2 HB from the building. At a downwind distance of 5 HB, the plume rise of the simulated thermal plume decreased by 70% compared to the no-building case while the vertical and horizontal widths of the plume increased by 45% and 30%, respectively. These results generally reproduce the plume downwash and dispersion observed in wind tunnel and field investigations.

Full access
Holly Peterson, Brian Lamb, and David Stock

Abstract

Simultaneous instantaneous concentration and wind velocity fluctuations were measured 100 to 752 m downwind of a point source release of SF6 tracer during two field studies conducted amid rolling wheat fields and at a flat desert site in eastern Washington. Data from stable, neutron, and unstable conditions are interpreted using a meandering plume model where the meander is defined to be sinusoidal and the instantaneous plume profile is Gaussian. A sensitivity analysis of the model shows that the characteristic concentration time scale is a direct function of the meander time scale and the receptor position relative to the meander centerline. For narrow instantaneous plumes relative to the meander amplitude, the predicted mean crosswind profiles of concentration, intermittency factor, concentration fluctuation intensity, and peak-to-mean ratios exhibit bimodal distributions. Conditional (nonzero) concentration fluctuation intensifies calculated from the model are scattered about 1.0;, the scatter is the result of receptor location, meander amplitude, period, and instantaneous plume width. The magnitude of the scatter from model runs covering different receptor locations is essentially equal to the magnitude of the matter from the tracer observations. The simple meandering plume model thus provides a straightforward explanation of very complex patterns observed in the tracer concentration fluctuation data in terms of wind meander, receptor location, and instantaneous plume width.

Full access
Julia E. Flaherty, David Stock, and Brian Lamb

Abstract

A 3D computational fluid dynamics study using Reynolds-averaged Navier–Stokes modeling was conducted and validated with field data from the Joint Urban 2003 dispersion study in Oklahoma City, Oklahoma. The modeled flow field indicated that the many short buildings in this domain had a relatively small effect on the flow field, whereas the few tall buildings considerably influenced the transport and diffusion of tracer gas through the domain. Modeled values were compared with observations along a vertical profile located about 500 m downwind of the source. The isothermal base case using the standard k–ε closure model was within 50% of the concentration measurements, and a convective case with ground and building surfaces 10°C hotter than ambient temperatures improved the modeled profile to within 30% of observations. Varying wind direction and source location had a marked effect on modeled concentrations at the vertical profile site. Ground-level concentrations were 6 times the observed values when the approach flow wind direction was changed by +15° and were nearly zero when the wind direction was changed by −15°. Similar results were obtained when the source was moved 50 m to the east and to the west, respectively. All cases underestimated wind speed and turbulent kinetic energy near the surface, although adding heat significantly improved the magnitude of the modeled turbulent kinetic energy. Model results based upon a Reynolds stress closure scheme were also compared with the vertical concentration profiles. Neither the isothermal case nor the thermal buoyancy case resulted in an improvement over the standard k–ε model.

Full access
Steven L. Edburg, Gene Allwine, Brian Lamb, David Stock, Harold Thistle, Holly Peterson, and Brian Strom

Abstract

Bark beetles kill millions of acres of trees in the United States annually by using chemical signaling to attack host trees en masse. As an attempt to control infestations, forest managers use synthetic semiochemical sources to attract beetles to traps and/or repel beetles from high-value resources such as trees and stands. The purpose of this study was to develop a simple numerical technique that may be used by forest managers as a guide in the placement of synthetic semiochemicals. The authors used a one-dimensional, one-equation turbulence model (klm) to drive a three-dimensional transport and dispersion model. Predictions were compared with observations from a unique tracer gas experiment conducted in a successively thinned loblolly pine canopy. Predictions of wind speed and turbulent kinetic energy compared well with observations. Scalar concentration was predicted well and trends of maximum observed concentration versus leaf area index were captured within 30 m of the release location. A hypothetical application of the numerical technique was conducted for a 12-day period to demonstrate the model’s usefulness to forest managers.

Full access
George J. Huffman, David T. Bolvin, Eric J. Nelkin, David B. Wolff, Robert F. Adler, Guojun Gu, Yang Hong, Kenneth P. Bowman, and Erich F. Stocker

Abstract

The Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) provides a calibration-based sequential scheme for combining precipitation estimates from multiple satellites, as well as gauge analyses where feasible, at fine scales (0.25° × 0.25° and 3 hourly). TMPA is available both after and in real time, based on calibration by the TRMM Combined Instrument and TRMM Microwave Imager precipitation products, respectively. Only the after-real-time product incorporates gauge data at the present. The dataset covers the latitude band 50°N–S for the period from 1998 to the delayed present. Early validation results are as follows: the TMPA provides reasonable performance at monthly scales, although it is shown to have precipitation rate–dependent low bias due to lack of sensitivity to low precipitation rates over ocean in one of the input products [based on Advanced Microwave Sounding Unit-B (AMSU-B)]. At finer scales the TMPA is successful at approximately reproducing the surface observation–based histogram of precipitation, as well as reasonably detecting large daily events. The TMPA, however, has lower skill in correctly specifying moderate and light event amounts on short time intervals, in common with other finescale estimators. Examples are provided of a flood event and diurnal cycle determination.

Full access
Sarah J. Doherty, Stephan Bojinski, Ann Henderson-Sellers, Kevin Noone, David Goodrich, Nathaniel L. Bindoff, John A. Church, Kathy A. Hibbard, Thomas R. Karl, Lucka Kajfez-Bogataj, Amanda H. Lynch, David E. Parker, I. Colin Prentice, Venkatachalam Ramaswamy, Roger W. Saunders, Mark Stafford Smith, Konrad Steffen, Thomas F. Stocker, Peter W. Thorne, Kevin E. Trenberth, Michel M. Verstraete, and Francis W. Zwiers

The Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) concluded that global warming is “unequivocal” and that most of the observed increase since the mid-twentieth century is very likely due to the increase in anthropogenic greenhouse gas concentrations, with discernible human influences on ocean warming, continental-average temperatures, temperature extremes, wind patterns, and other physical and biological indicators, impacting both socioeconomic and ecological systems. It is now clear that we are committed to some level of global climate change, and it is imperative that this be considered when planning future climate research and observational strategies. The Global Climate Observing System program (GCOS), the World Climate Research Programme (WCRP), and the International Geosphere-Biosphere Programme (IGBP) therefore initiated a process to summarize the lessons learned through AR4 Working Groups I and II and to identify a set of high-priority modeling and observational needs. Two classes of recommendations emerged. First is the need to improve climate models, observational and climate monitoring systems, and our understanding of key processes. Second, the framework for climate research and observations must be extended to document impacts and to guide adaptation and mitigation efforts. Research and observational strategies specifically aimed at improving our ability to predict and understand impacts, adaptive capacity, and societal and ecosystem vulnerabilities will serve both purposes and are the subject of the specific recommendations made in this paper.

Full access
Manfred Wendisch, Ulrich Pöschl, Meinrat O. Andreae, Luiz A. T. Machado, Rachel Albrecht, Hans Schlager, Daniel Rosenfeld, Scot T. Martin, Ahmed Abdelmonem, Armin Afchine, Alessandro C. Araùjo, Paulo Artaxo, Heinfried Aufmhoff, Henrique M. J. Barbosa, Stephan Borrmann, Ramon Braga, Bernhard Buchholz, Micael Amore Cecchini, Anja Costa, Joachim Curtius, Maximilian Dollner, Marcel Dorf, Volker Dreiling, Volker Ebert, André Ehrlich, Florian Ewald, Gilberto Fisch, Andreas Fix, Fabian Frank, Daniel Fütterer, Christopher Heckl, Fabian Heidelberg, Tilman Hüneke, Evelyn Jäkel, Emma Järvinen, Tina Jurkat, Sandra Kanter, Udo Kästner, Mareike Kenntner, Jürgen Kesselmeier, Thomas Klimach, Matthias Knecht, Rebecca Kohl, Tobias Kölling, Martina Krämer, Mira Krüger, Trismono Candra Krisna, Jost V. Lavric, Karla Longo, Christoph Mahnke, Antonio O. Manzi, Bernhard Mayer, Stephan Mertes, Andreas Minikin, Sergej Molleker, Steffen Münch, Björn Nillius, Klaus Pfeilsticker, Christopher Pöhlker, Anke Roiger, Diana Rose, Dagmar Rosenow, Daniel Sauer, Martin Schnaiter, Johannes Schneider, Christiane Schulz, Rodrigo A. F. de Souza, Antonio Spanu, Paul Stock, Daniel Vila, Christiane Voigt, Adrian Walser, David Walter, Ralf Weigel, Bernadett Weinzierl, Frank Werner, Marcia A. Yamasoe, Helmut Ziereis, Tobias Zinner, and Martin Zöger

Abstract

Between 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON– CHUVA) venture to quantify aerosol–cloud–precipitation interactions and their thermodynamic, dynamic, and radiative effects by in situ and remote sensing measurements over Amazonia. The ACRIDICON–CHUVA field observations were carried out in cooperation with the second intensive operating period of Green Ocean Amazon 2014/15 (GoAmazon2014/5). In this paper we focus on the airborne data measured on HALO, which was equipped with about 30 in situ and remote sensing instruments for meteorological, trace gas, aerosol, cloud, precipitation, and spectral solar radiation measurements. Fourteen research flights with a total duration of 96 flight hours were performed. Five scientific topics were pursued: 1) cloud vertical evolution and life cycle (cloud profiling), 2) cloud processing of aerosol particles and trace gases (inflow and outflow), 3) satellite and radar validation (cloud products), 4) vertical transport and mixing (tracer experiment), and 5) cloud formation over forested/deforested areas. Data were collected in near-pristine atmospheric conditions and in environments polluted by biomass burning and urban emissions. The paper presents a general introduction of the ACRIDICON– CHUVA campaign (motivation and addressed research topics) and of HALO with its extensive instrument package, as well as a presentation of a few selected measurement results acquired during the flights for some selected scientific topics.

Full access