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C. P. Weaver
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X.-Z. Liang
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J. Zhu
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P. J. Adams
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P. Amar
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J. Avise
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M. Caughey
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J. Chen
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R. C. Cohen
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E. Cooter
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J. P. Dawson
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R. Gilliam
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A. Gilliland
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A. H. Goldstein
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A. Grambsch
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D. Grano
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A. Guenther
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W. I. Gustafson
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R. A. Harley
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S. He
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B. Hemming
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C. Hogrefe
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H.-C. Huang
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S. W. Hunt
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D.J. Jacob
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P. L. Kinney
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K. Kunkel
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J.-F. Lamarque
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B. Lamb
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N. K. Larkin
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L. R. Leung
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K.-J. Liao
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J.-T. Lin
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B. H. Lynn
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K. Manomaiphiboon
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C. Mass
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D. McKenzie
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L. J. Mickley
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S. M. O'neill
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C. Nolte
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S. N. Pandis
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P. N. Racherla
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C. Rosenzweig
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A. G. Russell
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E. Salathé
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A. L. Steiner
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E. Tagaris
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Z. Tao
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S. Tonse
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C. Wiedinmyer
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A. Williams
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D. A. Winner
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J.-H. Woo
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S. WU
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D. J. Wuebbles

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the different groups, simulated global climate change causes increases of a few to several parts per billion (ppb) in summertime mean maximum daily 8-h average O3 concentrations over substantial regions of the country. The different modeling experiments in general do not, however, simulate the same regional patterns of change. These differences seem to result largely from variations in the simulated patterns of changes in key meteorological drivers, such as temperature and surface insolation. How isoprene nitrate chemistry is represented in the different modeling systems is an additional critical factor in the simulated O3 response to climate change.

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Thomas C. Peterson
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Richard R. Heim Jr.
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Robert Hirsch
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Dale P. Kaiser
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Harold Brooks
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Noah S. Diffenbaugh
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Randall M. Dole
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Jason P. Giovannettone
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Kristen Guirguis
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Thomas R. Karl
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Richard W. Katz
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Kenneth Kunkel
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Dennis Lettenmaier
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Gregory J. McCabe
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Christopher J. Paciorek
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Karen R. Ryberg
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Siegfried Schubert
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Viviane B. S. Silva
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Brooke C. Stewart
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Aldo V. Vecchia
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Gabriele Villarini
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Russell S. Vose
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John Walsh
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Michael Wehner
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David Wolock
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Klaus Wolter
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Connie A. Woodhouse
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Donald Wuebbles

Weather and climate extremes have been varying and changing on many different time scales. In recent decades, heat waves have generally become more frequent across the United States, while cold waves have been decreasing. While this is in keeping with expectations in a warming climate, it turns out that decadal variations in the number of U.S. heat and cold waves do not correlate well with the observed U.S. warming during the last century. Annual peak flow data reveal that river flooding trends on the century scale do not show uniform changes across the country. While flood magnitudes in the Southwest have been decreasing, flood magnitudes in the Northeast and north-central United States have been increasing. Confounding the analysis of trends in river flooding is multiyear and even multidecadal variability likely caused by both large-scale atmospheric circulation changes and basin-scale “memory” in the form of soil moisture. Droughts also have long-term trends as well as multiyear and decadal variability. Instrumental data indicate that the Dust Bowl of the 1930s and the drought in the 1950s were the most significant twentieth-century droughts in the United States, while tree ring data indicate that the megadroughts over the twelfth century exceeded anything in the twentieth century in both spatial extent and duration. The state of knowledge of the factors that cause heat waves, cold waves, floods, and drought to change is fairly good with heat waves being the best understood.

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Bjorn Stevens
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Donald H. Lenschow
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Gabor Vali
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Hermann Gerber
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A. Bandy
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B. Blomquist
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J. -L. Brenguier
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C. S. Bretherton
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F. Burnet
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T. Campos
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S. Chai
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I. Faloona
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D. Friesen
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S. Haimov
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K. Laursen
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D. K. Lilly
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S. M. Loehrer
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Szymon P. Malinowski
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B. Morley
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M. D. Petters
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D. C. Rogers
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L. Russell
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V. Savic-Jovcic
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J. R. Snider
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D. Straub
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Marcin J. Szumowski
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H. Takagi
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D. C. Thornton
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M. Tschudi
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C. Twohy
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M. Wetzel
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M. C. van Zanten

The second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field study is described. The field program consisted of nine flights in marine stratocumulus west-southwest of San Diego, California. The objective of the program was to better understand the physics a n d dynamics of marine stratocumulus. Toward this end special flight strategies, including predominantly nocturnal flights, were employed to optimize estimates of entrainment velocities at cloud-top, large-scale divergence within the boundary layer, drizzle processes in the cloud, cloud microstructure, and aerosol–cloud interactions. Cloud conditions during DYCOMS-II were excellent with almost every flight having uniformly overcast clouds topping a well-mixed boundary layer. Although the emphasis of the manuscript is on the goals and methodologies of DYCOMS-II, some preliminary findings are also presented—the most significant being that the cloud layers appear to entrain less and drizzle more than previous theoretical work led investigators to expect.

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Qing Wang
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Denny P. Alappattu
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Stephanie Billingsley
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Byron Blomquist
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Robert J. Burkholder
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Adam J. Christman
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Edward D. Creegan
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Tony de Paolo
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Daniel P. Eleuterio
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Harindra Joseph S. Fernando
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Kyle B. Franklin
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Andrey A. Grachev
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Tracy Haack
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Thomas R. Hanley
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Christopher M. Hocut
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Teddy R. Holt
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Kate Horgan
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Haflidi H. Jonsson
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Robert A. Hale
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John A. Kalogiros
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Djamal Khelif
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Laura S. Leo
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Richard J. Lind
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Iossif Lozovatsky
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Jesus Planella-Morato
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Swagato Mukherjee
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Wendell A. Nuss
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Jonathan Pozderac
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L. Ted Rogers
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Ivan Savelyev
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Dana K. Savidge
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R. Kipp Shearman
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Lian Shen
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Eric Terrill
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A. Marcela Ulate
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Qi Wang
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R. Travis Wendt
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Russell Wiss
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Roy K. Woods
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Luyao Xu
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Ryan T. Yamaguchi
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Caglar Yardim

Abstract

The Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER) project aims to better quantify atmospheric effects on the propagation of radar and communication signals in the marine environment. Such effects are associated with vertical gradients of temperature and water vapor in the marine atmospheric surface layer (MASL) and in the capping inversion of the marine atmospheric boundary layer (MABL), as well as the horizontal variations of these vertical gradients. CASPER field measurements emphasized simultaneous characterization of electromagnetic (EM) wave propagation, the propagation environment, and the physical processes that gave rise to the measured refractivity conditions. CASPER modeling efforts utilized state-of-the-art large-eddy simulations (LESs) with a dynamically coupled MASL and phase-resolved ocean surface waves. CASPER-East was the first of two planned field campaigns, conducted in October and November 2015 offshore of Duck, North Carolina. This article highlights the scientific motivations and objectives of CASPER and provides an overview of the CASPER-East field campaign. The CASPER-East sampling strategy enabled us to obtain EM wave propagation loss as well as concurrent environmental refractive conditions along the propagation path. This article highlights the initial results from this sampling strategy showing the range-dependent propagation loss, the atmospheric and upper-oceanic variability along the propagation range, and the MASL thermodynamic profiles measured during CASPER-East.

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