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R. T. Ryan

Abstract

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Anthony W. Lyza
,
Todd A. Murphy
,
Barrett T. Goudeau
,
Preston T. Pangle
,
Kevin R. Knupp
, and
Ryan A. Wade

Abstract

The Sand Mountain and Lookout Mountain Plateaus in northeastern Alabama have been established as a regional relative maximum in tornadogenesis reports within the southeastern United States. Investigation of long-term surface datasets has revealed (i) stronger and more backed winds atop Sand Mountain than over the Tennessee Valley, and (ii) measured cloud-base heights are lower to the surface atop Sand Mountain than over the Tennessee Valley. These observations suggest that low-level wind shear and lifting condensation level (LCL) height changes may lead to conditions more favorable for tornadogenesis atop the plateaus than over the Tennessee Valley. However, prior to fall 2016, no intensive observations had been made to further investigate low-level flow or thermodynamic changes in the topography of northeastern Alabama. This paper provides detailed analysis of observations gathered during VORTEX-SE field campaign cases from fall 2016 through spring 2019. These observations indicate that downslope winds form along the northwest edge of Sand Mountain in at least some severe storm environments in northeastern Alabama. Wind profiles gathered across northeastern Alabama indicate that low-level helicity changes can be substantial over small distances across different areas of the topographic system. LCL height changes often scale to changes in land elevation, which can be on the order of 200–300 m across northeastern Alabama.

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Ryan T. Walker
,
David M. Holland
,
Byron R. Parizek
,
Richard B. Alley
,
Sophie M. J. Nowicki
, and
Adrian Jenkins

Abstract

Thermodynamic flowline and plume models for the ice shelf–ocean system simplify the ice and ocean dynamics sufficiently to allow extensive exploration of parameters affecting ice-sheet stability while including key physical processes. Comparison between geophysically and laboratory-based treatments of ice–ocean interface thermodynamics shows reasonable agreement between calculated melt rates, except where steep basal slopes and relatively high ocean temperatures are present. Results are especially sensitive to the poorly known drag coefficient, highlighting the need for additional field experiments to constrain its value. These experiments also suggest that if the ice–ocean interface near the grounding line is steeper than some threshold, further steepening of the slope may drive higher entrainment that limits buoyancy, slowing the plume and reducing melting; if confirmed, this will provide a stabilizing feedback on ice sheets under some circumstances.

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R. T. Ryan
,
H. H. Blau Jr.
,
P. C. von Thüna
,
M. L. Cohen
, and
G. D. Roberts

Abstract

An improved single-particle light scattering instrument for measurement of cloud microstructure has been built and used in field studies. Cloud particle size and number information is measured over 12 sizing intervals, in the range 4 to 85 μ diameter. The microstructure can be observed in real time and with a spatial resolution not previously reported. The general features of water cloud droplet size and number distributions are consistent with previous direct capture and replication studies. The transition from water to ice phase regions in cumuliform clouds can be inferred from dramatic changes observed in the distribution features. Results are also presented for stratus and cirrus cloud penetrations.

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EXECUTIVE COMMITTEE2
,
Donald R. Johnson
,
Robert T. Ryan
,
William D. Bonner
,
James R. Mahoney
,
Kristina B. Katsaros
,
Ronald D. McPherson
,
Richard E. Hallgren
, and
Kenneth C. Spengler
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Ryan M. May
,
Kevin H. Goebbert
,
Jonathan E. Thielen
,
John R. Leeman
,
M. Drew Camron
,
Zachary Bruick
,
Eric C. Bruning
,
Russell P. Manser
,
Sean C. Arms
, and
Patrick T. Marsh

Abstract

MetPy is an open-source, Python-based package for meteorology, providing domain-specific functionality built extensively on top of the robust scientific Python software stack, which includes libraries like NumPy, SciPy, Matplotlib, and xarray. The goal of the project is to bring the weather analysis capabilities of GEMPAK (and similar software tools) into a modern computing paradigm. MetPy strives to employ best practices in its development, including software tests, continuous integration, and automated publishing of web-based documentation. As such, MetPy represents a sustainable, long-term project that fills a need for the meteorological community. MetPy’s development is substantially driven by its user community, both through feedback on a variety of open, public forums like Stack Overflow, and through code contributions facilitated by the GitHub collaborative software development platform. MetPy has recently seen the release of version 1.0, with robust functionality for analyzing and visualizing meteorological datasets. While previous versions of MetPy have already seen extensive use, the 1.0 release represents a significant milestone in terms of completeness and a commitment to long-term support for the programming interfaces. This article provides an overview of MetPy’s suite of capabilities, including its use of labeled arrays and physical unit information as its core data model, unit-aware calculations, cross sections, skew T and GEMPAK-like plotting, station model plots, and support for parsing a variety of meteorological data formats. The general road map for future planned development for MetPy is also discussed.

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EXECUTIVE COMMITTEE2
,
Warren M. Washington
,
David D. Houghton
,
Robert T. Ryan
,
Donald R. Johnson
,
Margaret A. LeMone
,
Alexander E. MacDonald
,
Richard E. Hallgren
, and
Kenneth C. Spengler
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EXECUTIVE COMMITTEE
,
Robert T. Ryan
,
Warren M. Washington
,
Donald R. Johnson
,
William D. Bonner
,
Margaret A. LeMone
,
Ronald D. McPherson
,
Richard E. Hallgren
, and
Kenneth C. Spengler
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P. J. Webster
,
E. F. Bradley
,
C. W. Fairall
,
J. S. Godfrey
,
P. Hacker
,
R. A. Houze Jr.
,
R. Lukas
,
Y. Serra
,
J. M. Hummon
,
T. D. M. Lawrence
,
C. A. Russell
,
M. N. Ryan
,
K. Sahami
, and
P. Zuidema

The methods and initial results of an extensive pilot study, the Joint Air–Sea Monsoon Interaction Experiment (JASMINE) held in the Indian Ocean during the summer of 1999, are described. The experimental design was based on the precept that the monsoon sways back and forth from active to inactive (or break) phases and that these intraseasonal oscillations are coupled ocean–atmosphere phenomena that are important components of the monsoon system. JASMINE is the first comprehensive study of the coupled ocean–atmosphere system in the eastern Indian Ocean and the southern Bay of Bengal. Two research vessels, the NOAA ship Ronald H. Brown and the Australian research vessel Franklin, totaled 52 days of surveillance in April–June and September, with 388 conductivity–temperature–depth (CTD) casts and 272 radiosonde ascents. In addition, both ships carried identical flux systems to measure the ocean–atmosphere interaction. The Brown had five radar systems and profilers, including a cloud radar and a Doppler C-band rain radar.

Active and break periods of the monsoon, and the transitions between these phases, and the onset of the 1999 South Asian summer monsoon occurred during JASMINE. The undisturbed and disturbed periods had vast differences in the net heating of the ocean, ranging from daily averages of +150 W m−2 during the former to −100 W m−2 in the latter. Accompanying these changes in the monsoon phase were distinct states of the upper ocean and the atmosphere, including complete reversals of the near-equatorial currents on the timescales of weeks. Diurnal variability occurred in both phases of the monsoon, particularly in near-surface thermodynamical quantities in undisturbed periods and in convection when conditions were disturbed. The JASMINE observations and analyses are compared with those from other tropical regions. Differences in the surface fluxes between disturbed and undisturbed periods appear to be greater in the monsoon than in the western Pacific Ocean. However, in both regions, it is argued that the configuration of convection and vertical wind shear acts as a positive feedback to accelerate low-level westerly winds. Outstanding questions and tentative plans for the future are also discussed.

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Kevin R. Knupp
,
Todd A. Murphy
,
Timothy A. Coleman
,
Ryan A. Wade
,
Stephanie A. Mullins
,
Christopher J. Schultz
,
Elise V. Schultz
,
Lawrence Carey
,
Adam Sherrer
,
Eugene W. McCaul Jr.
,
Brian Carcione
,
Stephen Latimer
,
Andy Kula
,
Kevin Laws
,
Patrick T. Marsh
, and
Kim Klockow

By many metrics, the tornado outbreak on 27 April 2011 was the most significant tornado outbreak since 1950, exceeding the super outbreak of 3–4 April 1974. The number of tornadoes over a 24-h period (midnight to midnight) was 199; the tornado fatalities and injuries were 316 and more than 2,700, respectively; and the insurable loss exceeded $4 billion (U.S. dollars). In this paper, we provide a meteorological overview of this outbreak and illustrate that the event was composed of three mesoscale events: a large early morning quasi-linear convective system (QLCS), a midday QLCS, and numerous afternoon supercell storms. The main data sources include NWS and research radars, profilers, surface measurements, and photos and videos of the tornadoes. The primary motivation for this preliminary research is to document the diverse characteristics (e.g., tornado characteristics and mesoscale organization of deep convection) of this outbreak and summarize preliminary analyses that are worthy of additional research on this case.

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