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E. M. Agee
,
J. T. Snow
, and
P. R. Clare

Abstract

Analyses are presented of the tornado tracks for four tornado families affecting Indiana and neighboring states on 3 April 1974. The study by Agee et al.(1975)on the occurrence of multiple suction vortices in the tornado has been used by further extending Ward's (1972) multiple vortex phenomenon to the scale of the tornado cyclone. This has allowed an interpretation of multiple tornado events by means of which consecutive tornado damage paths may be frequently recognized as segments of cycloidal tracks for multiple vortices occurring within the larger tornado cyclone.

A tornado cyclone, most likely within the right rear quadrant of the severe thunderstorm, may contain two, three, or more smaller scale vortices (mini tornado cylones) that revolve cyclonically about the center of the. parent tornado cyclone as the entire system translates along with the thunderstorm. It is shown that these centers of action have cycloidal tracks that can be matched with the damage paths of tornado families. Tornadoes are observed to be left-turners or right-turners, depending on what portion along the cycloidal track touchdown and demise occur. A tornado family may he associated with a single vortex parent tornado cyclone which tends to produce longer tornado tracts that do not undergo appreciable turning. Tornado families, however, may be generated by multiple vortex tornado cyclone systems, and in this case tornado tracks follow a curtate cycloid, eventually turning into the cold air and dissipating. Another tornado can reappear, however, as the parent vortex caster returns cyclonically (along the cycloidal path) to more favorable environmental conditions for redevelopment. Finally, a summary is presented depicting the scales of possible multiple vortex systems associated with the tornado producing thunderstorm.

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E. M. Agee
,
J. T. Snow
,
F. S. Nickerson
,
P. R. Clare
,
C. R. Church
, and
L. A. Schaal

Abstract

An observational study of the West Lafayette, Ind., tornado of 20 March 1976 has been made that presents photographic evidence of tornado formation accompanied by suction “debris” vortices in the surface boundary layer that produced a cycloidal debris pattern. Furthermore, four case studies of cycloidal debris analysis form this pattern using aerial photography support the multiple-suction vortex model proposed by Agee et al. (1975). Average values of the tangential speed of a suction vortex according to loop shift estimates ranged from 26.4 to 44 m s−1 and maximum values according to loop width estimates ranged from 44.0 to 61.6 m s−1 as the tornado grew to its most intense stage. The aerial and ground surveys of the damage track also showed that the cycloidal debris pattern corresponded to a region of F3 and F4 wind-speed damage.

Photographic evidence also documented a tail-cloud formation similar to the Fargo tornado (Fujita, 1959) that rotated cyclonically through the northeast to northwest sector of the tornado cyclone with a tangential speed of 16 m s−1 at a distance of 3 km from the tornado funnel.

Analysis of cloud photography further showed the features of the tornado system at various stages of intensity. Notable was the formation of a broad descending bowl-shaped cloud accompanied by multiple “condensation” funnels that corresponded to the region of strongest tornado intensity with F4 structural damage. This study also illustrates that multiple-suction debris vortices in the surface boundary layer can occur with only one condensation funnel present. This event is recognized as a similar but slightly different and smaller multiple-vortex phenomenon than that required for multiple-condensation funnels that fully extend through the planetary boundary layer.

Features unique to cyclodial debris patterns and the role of suction vortices in producing certain types of damage are also brought out in this study. Also a concentrated region of damage along a pathline of the southerly flow into the multiple-vortex region may be associated with a strong vorticity feeder band similar to that reported by Golden and Purcell (1975). Several such feeder bands may concentrate the vorticity into the core of the tornado cyclone. The tail-cloud phenomenon appears to be related to this flow feature in the tornado cyclone wind field.

Radar data from Marseilles, Ill., and Grissom Air Force Base, Ind., were analyzed for a portion of the lifetime of the parent thunderstorm system to determine the relationship between the path of the tornado cyclone and the Sadorus, Ill., and West Lafayette tornado tracks. Finally, a pressure drop of 44.6 mb was recorded in the path of the tornado cyclone at the time the West Lafayette tornado funnel was developing.

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Chelsea R. Thompson
,
Steven C. Wofsy
,
Michael J. Prather
,
Paul A. Newman
,
Thomas F. Hanisco
,
Thomas B. Ryerson
,
David W. Fahey
,
Eric C. Apel
,
Charles A. Brock
,
William H. Brune
,
Karl Froyd
,
Joseph M. Katich
,
Julie M. Nicely
,
Jeff Peischl
,
Eric Ray
,
Patrick R. Veres
,
Siyuan Wang
,
Hannah M. Allen
,
Elizabeth Asher
,
Huisheng Bian
,
Donald Blake
,
Ilann Bourgeois
,
John Budney
,
T. Paul Bui
,
Amy Butler
,
Pedro Campuzano-Jost
,
Cecilia Chang
,
Mian Chin
,
Róisín Commane
,
Gus Correa
,
John D. Crounse
,
Bruce Daube
,
Jack E. Dibb
,
Joshua P. DiGangi
,
Glenn S. Diskin
,
Maximilian Dollner
,
James W. Elkins
,
Arlene M. Fiore
,
Clare M. Flynn
,
Hao Guo
,
Samuel R. Hall
,
Reem A. Hannun
,
Alan Hills
,
Eric J. Hintsa
,
Alma Hodzic
,
Rebecca S. Hornbrook
,
L. Greg Huey
,
Jose L. Jimenez
,
Ralph F. Keeling
,
Michelle J. Kim
,
Agnieszka Kupc
,
Forrest Lacey
,
Leslie R. Lait
,
Jean-Francois Lamarque
,
Junhua Liu
,
Kathryn McKain
,
Simone Meinardi
,
David O. Miller
,
Stephen A. Montzka
,
Fred L. Moore
,
Eric J. Morgan
,
Daniel M. Murphy
,
Lee T. Murray
,
Benjamin A. Nault
,
J. Andrew Neuman
,
Louis Nguyen
,
Yenny Gonzalez
,
Andrew Rollins
,
Karen Rosenlof
,
Maryann Sargent
,
Gregory Schill
,
Joshua P. Schwarz
,
Jason M. St. Clair
,
Stephen D. Steenrod
,
Britton B. Stephens
,
Susan E. Strahan
,
Sarah A. Strode
,
Colm Sweeney
,
Alexander B. Thames
,
Kirk Ullmann
,
Nicholas Wagner
,
Rodney Weber
,
Bernadett Weinzierl
,
Paul O. Wennberg
,
Christina J. Williamson
,
Glenn M. Wolfe
, and
Linghan Zeng

Abstract

This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here.

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