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Charles H. Pierce
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Charles H. Pierce
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CHARLES H. PIERCE

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CHARLES H. PIERCE

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CHARLES H. PIERCE

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CHARLES H. PIERCE
and
LEWIS C. NORTON

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Samuel Penn
,
Charles Pierce
, and
James K. McGuire

Some features of the squall line situation of June 9, 1953 and accompanying tornadoes in central and eastern Massachusetts are discussed. From radarscope photographs, it is pointed out (1) that the Worcester tornado and the Franklin-Wrentham tornado each occurred in the right-rear quadrant of a squall-line thunderstorm cell, and (2) that this relative position, with an associated tail or hook in the radar echo, is similar to that of the Illinois tornado of April 9, 1953. A tentative explanation is suggested for tornado formation in this position.

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Timothy J. Wagner
,
Alan C. Czarnetzki
,
Megan Christiansen
,
R. Bradley Pierce
,
Charles O. Stanier
,
Angela F. Dickens
, and
Edwin W. Eloranta

Abstract

Ground-based thermodynamic and kinematic profilers were placed adjacent to the western shore of Lake Michigan at two sites as part of the 2017 Lake Michigan Ozone Study. The southern site near Zion, Illinois, hosted a microwave radiometer (MWR) and a sodar wind profiler, while the northern site in Sheboygan, Wisconsin, featured an Atmospheric Emitted Radiance Interferometer (AERI), a Doppler lidar, and a High Spectral Resolution Lidar (HSRL). Each site experienced several lake-breeze events during the experiment. Composite time series and time–height cross sections were constructed relative to the lake-breeze arrival time so that commonalities across events could be explored. The composited surface observations indicate that the wind direction of the lake breeze was consistently southeasterly at both sites regardless of its direction before the arrival of the lake-breeze front. Surface relative humidity increased with the arriving lake breeze, though this was due to cooler air temperatures as absolute moisture content stayed the same or decreased. The profiler observations show that the lake breeze penetrated deeper when the local environment was unstable and preexisting flow was weak. The cold air associated with the lake breeze remained confined to the lowest 200 m of the troposphere even if the wind shift was observed at higher altitudes. The evolution of the lake breeze corresponded well to observed changes in baroclinicity and calculated changes in circulation. Collocated observations of aerosols showed increases in number and mass concentrations after the passage of the lake-breeze front.

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Céline Bonfils
,
Benjamin D. Santer
,
David W. Pierce
,
Hugo G. Hidalgo
,
Govindasamy Bala
,
Tapash Das
,
Tim P. Barnett
,
Daniel R. Cayan
,
Charles Doutriaux
,
Andrew W. Wood
,
Art Mirin
, and
Toru Nozawa

Abstract

Large changes in the hydrology of the western United States have been observed since the mid-twentieth century. These include a reduction in the amount of precipitation arriving as snow, a decline in snowpack at low and midelevations, and a shift toward earlier arrival of both snowmelt and the centroid (center of mass) of streamflows. To project future water supply reliability, it is crucial to obtain a better understanding of the underlying cause or causes for these changes. A regional warming is often posited as the cause of these changes without formal testing of different competitive explanations for the warming. In this study, a rigorous detection and attribution analysis is performed to determine the causes of the late winter/early spring changes in hydrologically relevant temperature variables over mountain ranges of the western United States. Natural internal climate variability, as estimated from two long control climate model simulations, is insufficient to explain the rapid increase in daily minimum and maximum temperatures, the sharp decline in frost days, and the rise in degree-days above 0°C (a simple proxy for temperature-driven snowmelt). These observed changes are also inconsistent with the model-predicted responses to variability in solar irradiance and volcanic activity. The observations are consistent with climate simulations that include the combined effects of anthropogenic greenhouse gases and aerosols. It is found that, for each temperature variable considered, an anthropogenic signal is identifiable in observational fields. The results are robust to uncertainties in model-estimated fingerprints and natural variability noise, to the choice of statistical downscaling method, and to various processing options in the detection and attribution method.

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Annmarie G. Carlton
,
Joost de Gouw
,
Jose L. Jimenez
,
Jesse L. Ambrose
,
Alexis R. Attwood
,
Steven Brown
,
Kirk R. Baker
,
Charles Brock
,
Ronald C. Cohen
,
Sylvia Edgerton
,
Caroline M. Farkas
,
Delphine Farmer
,
Allen H. Goldstein
,
Lynne Gratz
,
Alex Guenther
,
Sherri Hunt
,
Lyatt Jaeglé
,
Daniel A. Jaffe
,
John Mak
,
Crystal McClure
,
Athanasios Nenes
,
Thien Khoi Nguyen
,
Jeffrey R. Pierce
,
Suzane de Sa
,
Noelle E. Selin
,
Viral Shah
,
Stephanie Shaw
,
Paul B. Shepson
,
Shaojie Song
,
Jochen Stutz
,
Jason D. Surratt
,
Barbara J. Turpin
,
Carsten Warneke
,
Rebecca A. Washenfelder
,
Paul O. Wennberg
, and
Xianling Zhou

Abstract

The Southeast Atmosphere Studies (SAS), which included the Southern Oxidant and Aerosol Study (SOAS); the Southeast Nexus (SENEX) study; and the Nitrogen, Oxidants, Mercury and Aerosols: Distributions, Sources and Sinks (NOMADSS) study, was deployed in the field from 1 June to 15 July 2013 in the central and eastern United States, and it overlapped with and was complemented by the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. SAS investigated atmospheric chemistry and the associated air quality and climate-relevant particle properties. Coordinated measurements from six ground sites, four aircraft, tall towers, balloon-borne sondes, existing surface networks, and satellites provide in situ and remotely sensed data on trace-gas composition, aerosol physicochemical properties, and local and synoptic meteorology. Selected SAS findings indicate 1) dramatically reduced NOx concentrations have altered ozone production regimes; 2) indicators of “biogenic” secondary organic aerosol (SOA), once considered part of the natural background, were positively correlated with one or more indicators of anthropogenic pollution; and 3) liquid water dramatically impacted particle scattering while biogenic SOA did not. SAS findings suggest that atmosphere–biosphere interactions modulate ambient pollutant concentrations through complex mechanisms and feedbacks not yet adequately captured in atmospheric models. The SAS dataset, now publicly available, is a powerful constraint to develop predictive capability that enhances model representation of the response and subsequent impacts of changes in atmospheric composition to changes in emissions, chemistry, and meteorology.

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