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A. H. Weber, M. R. Buckner, and J. H. Weber

Abstract

Seventeen mesoscale dispersion models were statistically evaluated with data from krypton-85 emissions from the Savannah River Plant, Aiken, SC. Widely accepted statistical parameters were used for the statistical evaluation. The models were able to predict concentrations more accurately for longer periods of time (yearly) than for shorter periods (twice-daily). The correlations between predictions from different models were approximately the same as correlations between predictions and measurements.

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A. H. Weber and R. J. Kurzeja

Abstract

This paper summarizes the results of meteorological and dispersion measurements during Savannah River Laboratory's Project STABLE (Stable Boundary Layer Experiment) field program. The field program took place at the Savannah River site on three nights during 12–17 April 1988. Meteorological data were collected from a 304-m tower, an array of eight 60-m towers, two sodars, a tethersonde, and a sonic anemometer.

Based on the classification scheme of Kurzeja et al. (1991) the first and third nights were classified as unsteady type IV nights because of the passage of microfronts on each night. The second night exhibited a continuous level of high turbulence with a weak surface-based inversion and was classified as a steady type III night.

The third night was especially interesting because of the considerable directional wind shear with height and the occurrence of two turbulent episodes. The directional shear may have been related to the passage of a high pressure center during the night.

The turbulent episodes lasted from 5 to 30 min and had a horizontal extent of at least 30 km. They were preceded by cooling near the surface and a shift to lower frequencies of the Brunt-Väisälä frequency NBV. It is suggested that a decrease with time of NBV or an increase in the standard deviation of the vertical component of velocity (σw) or σw/NBV might be used to forecast the onset of turbulent episodes reaching the surface.

Sulfur hexafluoride (SF6) tracer was released continuously during the experiments and measured 10–20 km downwind by a mobile continuous analyzer. The tracer transport was shown to be consistent with low-level winds on the 304-m tower, except on the third night. It was hypothesized that on the third night the spatial variability of the wind field was much more extreme than on the other nights and, hence, the winds from the 304-m tower did not reflect the true plume movement. A spatially averaged mean wind was more successful in explaining the observed horizontal plume movement. The wider-than-expected across-are concentration distribution on the third night was attributed to continuously varying shear; whereas the occasional secondary maxima in the tracer pattern were due to discontinuities in the vertical wind shear.

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A. H. Weber and J. O. Blanton

Abstract

A total of 339 389 marine weather observations have been analyzed to Produce Monthly mean wind fields for the South Atlantic Bight. The results of plotting wind vectors on a 1/2° latitude by 1/2° longitude grid yields four traditional seasonal flow regimes (winter, spring, summer and fall) and an additional regime designated as mariners’ fall. These seasonal wind regimes are discussed and related to the monthly mean ocean circulation in the Bight.

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A. H. Weber, J. S. Irwin, W. B. Peterson, J. J. Mathis Jr., and J. P. Kahler

Abstract

Wind measurements from the Savannah River Laboratory-WJBF-TV tower in Beech Island, South Carolina were used to compute turbulence parameters which were then compared with similarity theory predictions summarized by Hanna (1981a). The parameters computed were standard deviations of the fluctuating velocity components σu, σv and σw, and spectral scales λm and lE.

The correlation coefficients were highest for the standard deviations of the velocity components σu, σv and σw. The averaged correlation coefficients for all three components were 0.60, 0.45 and 0.72 for unstable, stable and neutral conditions, respectively.

The averaged correlation coefficients between computed and measured spectral maxima λmu, λmv and λmw were 0.66 for stable conditions and 0.65 for neutral conditions. Very low correlations of −0.11 and 0.01 were obtained for λmu and λmv in unstable conditions. The vertical wavelength λmu., however, had a correlation coefficient of 0.59 between measured and predicted values.

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Jason J. Sharples, Graham A. Mills, Richard H. D. McRae, and Rodney O. Weber

Abstract

Bushfires in southeastern Australia are a serious environmental problem, and consistently cause loss of life and damage to property and other assets. Understanding synoptic processes that can lead to dangerous fire weather conditions throughout the region is therefore an important undertaking aimed at improving community safety, protection of assets, and fire suppression tactics and strategies. In southeastern Australia severe fire weather is often associated with dry cool changes or coastally modified cold fronts. Less well known, however, are synoptic events that can occur in connection with the topography of the region, such as cross-mountain flows and foehn-like winds, which can also lead to abrupt changes in fire weather variables that ultimately result in locally elevated fire danger. This paper focuses on foehn-like occurrences over the southeastern mainland, which are characterized by warm, dry winds on the lee side of the Australian Alps. The characteristics of a number of foehn-like occurrences are analyzed based on observational data and the predictions of a numerical weather model. The analyses confirm the existence of a foehn effect over parts of southeastern Australia and suggest that its occurrence is primarily due to the partial orographic blocking of relatively moist low-level air and the subsidence of drier upper-level air in the lee of the mountains. The regions prone to foehn occurrence, the influence of the foehn on fire weather variables, and the connection between the foehn and mountain waves are also discussed.

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C. von Savigny, A. Rozanov, H. Bovensmann, K.-U. Eichmann, S. Noël, V. Rozanov, B.-M. Sinnhuber, M. Weber, J. P. Burrows, and J. W. Kaiser

Abstract

An unprecedented stratospheric warming in the Southern Hemisphere in September 2002 led to the breakup of the Antarctic ozone hole into two parts. The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) on the European Environmental Satellite (ENVISAT) performed continuous observations of limb-scattered solar radiance spectra throughout the stratospheric warming. Thereby, global measurements of vertical profiles of several important minor constituents are provided with a vertical resolution of about 3 km. In this study, stratospheric profiles of O3, NO2, and BrO retrieved from SCIAMACHY limb-scattering observations together with polar stratospheric cloud (PSC) observations for selected days prior to (12 September), during (27 September), and after (2 October) the ozone hole split are employed to provide a picture of the temporal evolution of the Antarctic stratosphere’s three-dimensional structure.

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B. L. Weber, D. B. Wuertz, R. G. Strauch, D. A. Merritt, K. P. Moran, D. C. Law, D. van de Kamp, R. B. Chadwick, M. H. Ackley, M. F. Barth, N. L. Abshire, P. A. Miller, and T. W. Schlatter

Abstract

The first wind profiler for a demonstration network of wind profilers recently passed the milestone of 300 h of continuous operation. The horizontal wind component measurements taken during that period are compared with the WPL Platteville wind profiler and the NWS Denver rawinsonde. The differences between the network and WPL wind profilers have standard deviations of 2.30 m s−1 and 2.16 m s−1 for the u- and v-components, respectively. However, the WPL wind profiler ignores vertical velocity, whereas the network radar measures it and removes its effects from the u- and v-component measurements. The differences between the network wind profiler and the NWS rawinsonde (separated spatially by about 50 km) have standard deviations of 3.65 m s−1 and 3.06 m s−1 for the u- and v-components, respectively. These results are similar to those found in earlier comparison studies. Finally, the new network wind profiler demonstrates excellent sensitivity, consistently reporting measurements at all heights msl from 2 to nearly 18 km with very few outages.

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R. J. Stouffer, J. Yin, J. M. Gregory, K. W. Dixon, M. J. Spelman, W. Hurlin, A. J. Weaver, M. Eby, G. M. Flato, H. Hasumi, A. Hu, J. H. Jungclaus, I. V. Kamenkovich, A. Levermann, M. Montoya, S. Murakami, S. Nawrath, A. Oka, W. R. Peltier, D. Y. Robitaille, A. Sokolov, G. Vettoretti, and S. L. Weber

Abstract

The Atlantic thermohaline circulation (THC) is an important part of the earth's climate system. Previous research has shown large uncertainties in simulating future changes in this critical system. The simulated THC response to idealized freshwater perturbations and the associated climate changes have been intercompared as an activity of World Climate Research Program (WCRP) Coupled Model Intercomparison Project/Paleo-Modeling Intercomparison Project (CMIP/PMIP) committees. This intercomparison among models ranging from the earth system models of intermediate complexity (EMICs) to the fully coupled atmosphere–ocean general circulation models (AOGCMs) seeks to document and improve understanding of the causes of the wide variations in the modeled THC response. The robustness of particular simulation features has been evaluated across the model results. In response to 0.1-Sv (1 Sv ≡ 106 m3 s−1) freshwater input in the northern North Atlantic, the multimodel ensemble mean THC weakens by 30% after 100 yr. All models simulate some weakening of the THC, but no model simulates a complete shutdown of the THC. The multimodel ensemble indicates that the surface air temperature could present a complex anomaly pattern with cooling south of Greenland and warming over the Barents and Nordic Seas. The Atlantic ITCZ tends to shift southward. In response to 1.0-Sv freshwater input, the THC switches off rapidly in all model simulations. A large cooling occurs over the North Atlantic. The annual mean Atlantic ITCZ moves into the Southern Hemisphere. Models disagree in terms of the reversibility of the THC after its shutdown. In general, the EMICs and AOGCMs obtain similar THC responses and climate changes with more pronounced and sharper patterns in the AOGCMs.

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R. M. Cionco, W. aufm Kampe, C. Biltoft, J. H. Byers, C. G. Collins, T. J. Higgs, A. R. T. Hin, P.-E. Johansson, C. D. Jones, H. E. Jørgensen, J. F. Kimber, T. Mikkelsen, K. Nyrén, D. J. Ride, R. Robson, J. M. Santabarbara, J. Streicher, S. Thykier-Nielsen, H. van Raden, and H. Weber

The multination, high-resolution field study of Meteorology And Diffusion Over Non-Uniform Areas (MADONA) was conducted by scientists from the United States, the United Kingdom, Germany, Denmark, Sweden, and the Netherlands at Porton Down, Salisbury, Wiltshire, United Kingdom, during September and October 1992. The host of the field study was the Chemical and Biological Defence Establishment (CBDE, now part of Defence Evaluation and Research Agency) at Porton Down. MADONA was designed and conducted for high-resolution meteorological data collection and diffusion experiments using smoke, sulphurhexaflouride (SF6), and propylene gas during unstable, neutral, and stable atmospheric conditions in an effort to obtain terrain-influenced meteorological fields, dispersion, and concentration fluctuation measurements using specialized sensors and tracer generators. Thirty-one days of meteorological data were collected during the period 7 September–7 October and 27 diffusion experiments were conducted from 14 to 23 September 1992. Puffs and plumes of smoke and SF6 were released simultaneously for most of the experiments to gauge the resultant diffusion and concentration behavior. Some 44 meteorological and aerosol sensors and four source generators were used during each day of the field study. This array of sensors included 14 towers of wind cups and vanes, 10 sonic anemometer/thermometers, one boundary layer sonde, two lidar, one ion sensor, the CBDE Weather Station, and several one-of-a-kind sensors. Simulations of airflow and diffusion over the MADONA topography (a 9 km by 7.5 km area) were made with a variety of models. Wind fields and wind-related parameters were simulated with several high-resolution (microalpha scale) wind flow models. A tally of the various data-gathering activities indicates that the execution of MADONA was highly successful. Preliminary use of the datasets shows the high quality and depth of the MADONA database. This well-documented database is suitable for the evaluation and validation of short-range/near-field wind and diffusion models/codes. The database was originally placed on CD-ROM in a structured way by CBDE, Porton Down. The database is now available from the Risø National Laboratory, Denmark.

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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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