Bulletin of the American Meteorological Society
Tornadoes in the Central United States and the "Clash of Air Masses"
--Manuscript Draft-Manuscript Number:
BAMS-D-13-00252
Full Title:
Tornadoes in the Central United States and the "Clash of Air Masses"
Article Type:
Article
Corresponding Author:
David M. Schultz, Ph.D.
University of Manchester
Manchester, UNITED KINGDOM
Corresponding Author's Institution:
University of Manchester
First Author:
David M. Schultz, Ph.D.
Order of Authors:
David M. Schultz, Ph.D.
Yvette P. Richardson
Paul M. Markowski
Charles A. Doswell
Manuscript Classifications:
2.252: Fronts; 2.464: Tornadogenesis; 3.168: Fronts; 3.440: Tornadoes
Abstract:
After tornado outbreaks or individual violent tornadoes occur in the central United
States, media stories often attribute the location, number, or intensity of tornadoes to
the "clash of air masses" between warm tropical air and cold polar air. This article
argues that such a characterization of tornadogenesis is oversimplified, outdated, and
incorrect. Airmass boundaries and associated temperature gradients can be important
in tornadogenesis, but not in the ways envisioned on the synoptic scale with the clashof-air-masses conceptual model. In fact, excessively strong horizontal temperature
gradients (either on the synoptic scale or associated with a storm's own cool outflow)
may be detrimental to tornadogenesis. Where adjacent air masses are relevant is
through their vertical distribution that produces the requisite instability for the
convective storm, but that instability is not directly related to the formation of tornadoes.
Therefore, this article recommends that a greater effort be made to communicate
accurately to the public the current scientific understanding of the conditions under
which tornadoes are formed.
Author Comments:
We have attached a figure that might be used for the cover of BAMS if desired.
Best regards,
Dave
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[email protected]
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USA Today
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Tornadoes in the Central United States and
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the “Clash of Air Masses”
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DAVID M. SCHULTZ
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Centre for Atmospheric Science, School of Earth, Atmospheric and Environmental Sciences,
University of Manchester, Manchester, United Kingdom
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YVETTE P. RICHARDSON AND PAUL M. MARKOWSKI
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Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania
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Doswell Scientific Consulting, Norman, Oklahoma
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CHARLES A. DOSWELL III
An Article for the Bulletin of the American Meteorological Society
Submitted 26 November 2013
Revised 20 January 2014
Revised 9 March 2014
Corresponding author address: Prof. David M. Schultz; Centre for Atmospheric Science; School
of Earth, Atmospheric and Environmental Sciences; University of Manchester; Simon Building,
Oxford Road; Manchester M13 9PL, United Kingdom.
E-mail: [email protected]
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ABSTRACT
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After tornado outbreaks or individual violent tornadoes occur in the central United States, media
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stories often attribute the location, number, or intensity of tornadoes to the “clash of air masses”
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between warm tropical air and cold polar air. This article argues that such a characterization of
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tornadogenesis is oversimplified, outdated, and incorrect. Airmass boundaries and associated
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temperature gradients can be important in tornadogenesis, but not in the ways envisioned on the
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synoptic scale with the clash-of-air-masses conceptual model.
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horizontal temperature gradients (either on the synoptic scale or associated with a storm’s own
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cool outflow) may be detrimental to tornadogenesis. Where adjacent air masses are relevant is
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through their vertical distribution that produces the requisite instability for the convective storm,
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but that instability is not directly related to the formation of tornadoes. Therefore, this article
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recommends that a greater effort be made to communicate accurately to the public the current
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scientific understanding of the conditions under which tornadoes are formed.
In fact, excessively strong
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CAPSULE
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Media reports that clashing air masses produce tornadoes mischaracterize the abundant new
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observational and modeling research on how tornadoes form.
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The central United States is home to the most frequent violent tornadoes on Earth (Fig.
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1). When major outbreaks of such tornadoes occur, the media often explains their
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occurrence as the result of the “clash of air masses.” Consider the following example:
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Oklahoma provides a fertile breeding ground for tornadoes because of the clash
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between the warm, moist air from the Gulf and cold air from the Rockies and
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Canada: One of the main keys to tornado formation … is “a large temperature
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spread over a short distance.” “Water holds its heat more than land or air.... So
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Oklahoma's proximity to the Gulf of Mexico means there is a source of very
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warm, moist air. As cold air comes from Canada, you can get temperatures of 80
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degrees [F] in the body of the state while it is in the 20s in the Panhandle.” [The
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interviewee says this provides] the power to fuel severe thunderstorms.
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http://www.usatoday.com/story/news/nation/2013/06/08/oklahoma-tornadoes-
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ef5-moore/2401885/
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Other examples of media reporting that the clash of the air masses is responsible for tornadoes
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may be found at http://www.independent.co.uk/news/tornado-disaster-clash-of-air-masses-in-
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tornado-alley-1091490.html,
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tornado-rotation,
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(http://ngm.nationalgeographic.com/2013/11/biggest-storm/tornado-formation), and in Fig. 2.
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There is no intention to single out any particular person or media source with this list, but rather
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to exemplify the type of storyline that appears in the media. Therefore, the consistent message in
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the media is that tornadoes form along the boundaries between air masses, such as cold fronts or
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drylines, with tornado formation being directly linked to the intensity of the “clashing” between
in
the
http://www.myfoxaustin.com/story/21871999/weather-factsNovember
2013
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National
Geographic
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adjacent air masses. Such clashing could perhaps be thought to provide the lift in the three
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ingredients of deep, moist convection: lift, instability, and moisture (Johns and Doswell 1992).
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The reality is that air masses “clash” all the time, but frontal zones only produce tornadoes on
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relatively few occasions. Further, as we will discuss, many tornadoes occur outside of regions
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where air masses are “clashing.”
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occurrence of tornadoes is at best a gross oversimplification.
Therefore, using this canard as an explanation for the
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Why and when the specific phrase “clash of the air masses” was introduced to explain tornadoes
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in the central United States is not clear. One possible origin may be this 1942 quote from
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Sylvester E. Decker, the climatologist for the Weather Bureau Office in Des Moines, Iowa,
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describing tornadoes in Iowa over the past 15 months (House 1963, p. 141):
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Usually more than two air masses are present. There is first of all the original
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cold air mass to the north of the front, a warm [air] mass to the south of the front
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with a stable air mass that is drier and warmer aloft over the warm air mass.
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Reference in the above quote is made to a front. The concept of fronts as airmass boundaries
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originates from the Norwegian cyclone model (Bjerknes 1919; Bjerknes and Solberg 1921,
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1922), which describes the formation of low-pressure systems along the polar front, a region
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where cold polar air is adjacent to warm tropical air. That World War I had recently ended at the
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time of the introduction of this frontal terminology (think All Quiet on the Western Front) is no
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coincidence (Friedman 1989, pp. 187–188).
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In the relatively flat central United States, continental polar, continental tropical, and maritime
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tropical air masses meet easily, a factor in creating the baroclinic environments that favor
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extratropical cyclones. The extratropical cyclones that bring together the ingredients for severe
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convective storms (moisture from the Gulf of Mexico, steep lapse rates coming off the high and
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dry terrain of the Rocky Mountains, and vertical wind shear) are closely tied to the pole-to-
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equator thermal gradients, but the mere presence of those gradients on the synoptic scale is no
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guarantee that these ingredients will be brought together to produce tornadoes in any specific
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extratropical cyclone.
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Horizontal temperature gradients also exist on the storm scale. Temperature gradients associated
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with downdrafts and outflow are likely important in tornadogenesis in supercells (the most
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violent tornadoes are almost always associated with rotating convective storms called supercells,
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Fig. 3), but, as we will discuss, “airmass clashing” is not the best way to describe the role of such
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storm-scale temperature gradients in tornadogenesis. In fact, excessively strong storm-scale
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temperature gradients are associated with nontornadic supercells (e.g., Markowski and
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Richardson 2009).
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MOVING BEYOND THE “CLASH OF THE AIR MASSES” ON THE SYNOPTIC
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SCALE. If the clash of the air masses has any validity as an explanation for tornadoes, there are
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two ways that synoptic-scale horizontal temperature contrasts can be thought to have some
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relevance in tornado development. One is through their link to vertical wind shear (essential to
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supercell storms), and the other through their link, at times, to storm initiation.
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With regard to vertical shear, the vertical derivative of the geostrophic wind is directly related to
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the horizontal temperature gradient, which is why it is called the thermal wind shear. Thus, for
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example, a north–south temperature contrast implies an increasing westerly wind component
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with height. Another part of the wind shear is that associated with the ageostrophic wind, which
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is not directly related to the horizontal temperature gradient. Moreover, whatever the source of
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the shear, it must be located where there is buoyant instability to feed a storm. Tornadic storms
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are not necessarily collocated with the maximum vertical shear; rather, they are located where
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there is sufficient shear and that shear overlaps with buoyant instability. So, although there is a
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loose connection between temperature gradients and vertical wind shear, the connection is even
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looser between temperature gradients and tornadic storms. Indeed, Diffenbaugh et al. (2013)
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showed that under expected climate change, while vertical shear at midlatitudes decreases in
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general as a result of weakening meridional thermal gradients, the number of days with
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conditions favorable for severe weather increases, owing to the greater overlap of regions of
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favorable shear and instability.
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With regard to the initiation of storms, all convective storms are initiated when air parcels with
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convective available potential energy (CAPE) reach their level of free convection (LFC), with
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one of the most common mechanisms for storm initiation being ascent associated with airmass
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boundaries (e.g., fronts, drylines) or other subsynoptic-scale boundaries (e.g., outflow
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boundaries, sea-breeze fronts). Thus, the frequent proximity of low-level temperature gradients
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to developing convective storms is not unique to supercells.
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convective storms initiated along airmass boundaries become tornadic.
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Only a small percentage of
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In addition, the strength of the temperature gradient along a synoptic-scale airmass boundary has
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no precise relationship to the potential for storms initiated along the boundary to spawn
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tornadoes (often supercells have moved a significant distance away from a synoptic-scale
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initiating boundary by the time they reach maturity and pose a tornado threat).1 If anything, there
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is some indication that squall lines, not supercells, are more likely when the temperature gradient
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associated with an airmass boundary is intense (e.g., Roebber et al. 2002; Arnott et al. 2006;
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Stonitsch and Markowski 2007; Dial et al. 2010; Duda and Gallus 2010; Schumann and Roebber
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2010). In other words, strong horizontal temperature gradients may actually pose a decreased
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risk of significant tornadoes (EF2 or greater tornadoes; Hales 1988), given that squall lines are
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less likely to produce significant tornadoes than are discrete supercells (Trapp et al. 2005a;
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Thompson et al 2012; Smith et al. 2012).
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One instance in which an airmass boundary can influence tornadogenesis may be the interaction
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of an ongoing supercell with a pre-existing airmass boundary. Some supercell storms move
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along or across airmass boundaries such as warm fronts, stationary fronts, or outflow boundaries
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produced by other storms, where the likelihood of tornado formation may be locally increased
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owing to enhanced wind shear and moisture near the boundary (e.g., Maddox et al. 1980;
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Markowski et al. 1998; Rasmussen et al. 2000; Wurman et al. 2007). So, in some cases, the
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temperature gradient along a front may be a component of a favorable environment for tornadic
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supercells, although certainly not in all cases. Supercells produce tornadoes in the absence of
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such storm–boundary interactions, and many storm–boundary interactions result in weakening of
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In contrast, nonsupercell tornadoes are favored in storms that have a slow forward motion relative to the initiating
airmass boundary. Nonsupercell tornadoes (e.g., Wakimoto and Wilson 1989) also seem to require that the
initiating boundary be associated with misocyclones at the surface (i.e., cyclonic vorticity at the surface that
precedes the tornadoes) (e.g., Lee and Wilhelmson 1997).
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the supercell and decreased tornado potential (Markowski et al. 1998; Doswell et al. 2002).
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These interactions are not well understood and, moreover, are not essential for tornado
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formation. If anything, storm-boundary interactions seem least likely to trigger tornadogenesis
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when the boundary is accompanied by a large temperature gradient, which usually implies a
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rapid increase in the convective inhibition (as well as decreasing surface-based CAPE)
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encountered by a storm moving across the boundary (Doswell et al., 2002).
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Not only is the strength of the temperature gradient associated with clashing air masses of
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questionable relevance to tornadic supercell initiation, many tornadic supercells are not even
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initiated along fronts. Three examples follow. First, tornadic storms commonly form along or
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near a dryline, a zone of strong moisture contrast but only a modest temperature gradient,
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depending on the time of day (e.g., Rhea 1966; Schaefer 1974; Ziegler and Rasmussen 1998).
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Second, tornadic supercells commonly develop as a result of moist, unstable air flowing gently
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upslope (i.e., toward the west) on the High Plains, especially in regions where such orographic
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lifting is enhanced (e.g., Palmer Divide of eastern Colorado, Cheyenne Ridge of southeastern
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Wyoming). Such upslope severe weather regimes typically are found on the cool side of (not
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along) a synoptic-scale front or outflow boundary produced by an antecedent mesoscale
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convective system (e.g., Doswell 1980). Third, supercells may even form along rainbands in
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hurricanes (e.g., McCaul 1987; Baker et al. 2009; Molinari and Vollaro 2010; Green et al. 2011;
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Edwards et al. 2012). Thus, there are diverse situations in which strong tornadoes could form
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with no strong temperature gradient present.
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If there is any clashing of air masses associated with supercell tornadoes, perhaps it is in the
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vertical, rather than the horizontal. But, media explanations typically do not refer to this vertical
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distribution of air masses. Specifically, deep moist convective storms, including supercells, form
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as a result of the release of buoyant instability, and this instability in the central United States
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frequently comes from the vertical collocation of maritime tropical air underneath continental
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tropical air at midlevels from the southwest, the so-called elevated mixed layer (e.g., Carlson et
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al. 1983). Critically, this vertical distribution of air masses must also be associated with deep-
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layer shear over several kilometers in depth to allow storm-scale rotation to occur within
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supercells. As described above, although a part of this wind shear is associated with horizontal
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temperature gradients due to thermal wind balance, the area of greatest “clashing between two
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air masses” is not necessarily the area of greatest tornado development. Moreover, this vertical
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distribution of air masses occurs much more frequently in this region than the occurrence of
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tornadoes, so the concept has limited predictive ability for tornadogenesis (as discussed in the
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next section).
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To summarize, the clash of air masses on the synoptic scale may be associated with strong
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horizontal temperature gradients, but these situations tend not to be particularly favorable for
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supercells and tornadoes. Instead, the clash of the air masses most relevant for supercells may be
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in the vertical as warm moist air from the Gulf of Mexico underlies the steep lapse rates within
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the elevated mixed layer, producing buoyant instability and vertical wind shear, environmental
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conditions favorable for supercellular convection, but not specifically tornadogenesis.
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MOVING BEYOND “CLASH OF THE AIR MASSES” ON THE STORM SCALE.
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Existing understanding of tornadogenesis on the scale of a convective storm is far from
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complete. Only around 25% of supercells with radar-detected mesocyclones (rotation of a
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broader scale than a tornado) become tornadic (Trapp et al. 2005b), so the key issue is what
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conditions permit tornado formation in only a minority of supercells.
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Observations with airborne and mobile radars have suggested that strong rotation, down as low
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as several hundred meters above the ground, can be present in a supercell without the potentially
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damaging rotation of a tornado ever developing at the surface (e.g., Trapp 1999; Markowski et
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al. 2011). Unlike the rotation at midlevels, rotation at the surface cannot develop with only an
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updraft and environmental shear (horizontal vorticity) because parcels will be moving away from
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the ground as the vorticity is tilted into the vertical (e.g., Davies-Jones and Brooks 1993). Thus,
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the downdrafts in a supercell are essential to tornadogenesis.
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Leading hypotheses for tornadogenesis suggest that vertical vorticity develops as air descends
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within a storm-scale temperature gradient within the outflow (e.g., Davies-Jones et al. 2001;
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Markowski and Richardson 2009; Wurman et al. 2013). If the near-surface circulation produced
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in this manner within the outflow moves into a region of strong ascent, the circulation can be
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accelerated upward and contracted to tornadic strength via conservation of angular momentum.
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Although the degree of storm-scale baroclinity available to produce the tornadic circulation
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increases as the outflow temperature decreases, the low-level temperature decrease makes it
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difficult to carry out the final contraction because the low-level vertical accelerations required to
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contract the circulation are inhibited by negatively buoyant air. Therefore, there is a “sweet
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spot” in the temperature contrast that allows the development of significant circulation while still
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allowing the final contraction to take place. This situation is in contrast to the hypothesis that
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tornado likelihood increases with the intensity of the temperature contrast. In addition, there is
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some indication that colder outflow in nontornadic supercells may be shunted away from the
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location of maximum updraft, such that the final contraction does not occur (Snook and Xue
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2008; Markowski and Richardson 2014).
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Two empirical factors seem to be helpful in discriminating between tornadic and nontornadic
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supercells: the lifting condensation level (LCL) and the vertical wind shear in the lowest
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kilometer (e.g., Rasmussen and Blanchard 1998; Brooks et al. 2003; Thompson et al. 2003;
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Grams et al. 2012; Thompson et al. 2012). A low LCL is related to high low-level relative
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humidity and, presumably, warmer downdrafts (Markowski et al. 2002; Shabbott and Markowski
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2006). Strong low-level shear enhances and lowers the base of the midlevel mesocyclone
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(formed through tilting of environmental horizontal vorticity as described above), which is then
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associated with greater ability to lift (and contract) the outflow air due to vertical pressure
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gradients associated with changes in rotation with height (Markowski and Richardson 2014).
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Therefore, the two empirical factors favored for tornado environments refute the concept that a
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colder downdraft (i.e., “greater clashing”) is better on the storm scale. Thus, there appears to be
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little support for clashing air masses on the storm scale being responsible for tornadogenesis.
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CONCLUSION. Based on our arguments above, we conclude that the notion of tornadogenesis
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being directly related to the “clash of air masses” has limited utility as an explanation on both the
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synoptic scale and storm scale. Therefore, repeating this myth in the media does the public a
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disservice and does not reflect the science of severe storms as it has developed in recent decades.
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If there is any value in retaining the airmass concept, it is in the vertical collocation of air masses
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that produce the instability requisite for intense convective storms, but this explanation does not
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pertain to tornadoes specifically, just to the environment of convective storms in the central
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United States.
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Therefore, we recommend that the weather enterprise work with the media to adopt a new
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explanation for tornadic storms. Instead of “Yesterday's storms were the result of a clashing of
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air masses,” we believe that an explanation along these lines would be more appropriate for a lay
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audience in the vast majority of cases [with parenthetical information included if applicable to
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the specific case].
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“Yesterday's storms occurred when warm humid air near the surface lay under drier
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air aloft with temperature decreasing rapidly with height [originating from higher
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terrain to the west or southwest], providing energy for the storms through the
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production of instability. Large changes in wind with height (“wind shear”) over both
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shallow (lowest 1 km) and deep (lowest 6 km) layers—combined with the instability
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and high humidity near the surface—created a situation favorable for tornadoes to
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form.”
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This explanation, albeit longer than the clashing explanation, is pithy and accurate, describing
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both the ingredients that make the synoptic environment favorable for convective storms and the
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known factors that favor tornado formation.
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Given the large investment in tornado research by the National Science Foundation (e.g., over
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$10 million on VORTEX2 alone; Wurman et al. 2013) and the rapid progress in understanding
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of tornadoes that has resulted, we hope that future information provided to the public can better
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reflect that growth in scientific understanding.
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Acknowledgments. We thank Editor Jeff Waldstreicher, Greg Forbes, and three anonymous
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reviewers for their comments that have improved this manuscript. Partial funding for Schultz
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was provided by the U.K. Natural Environment Research Council to the University of
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Manchester for the Diabatic Influences on Mesoscale Structures in Extratropical Storms
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(DIAMET) project (grant NE/I005234/1) and the Tropopause Folding, Stratospheric Intrusions
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and Deep Convection (TROSIAD) project (grant NE/H008225/1). Funding for Richardson and
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Markowski was provided by the U.S. National Science Foundation (AGS-1157646).
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FIGURE CAPTIONS
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Figure 1. Shaded contours (see the key) showing the number of days per century a violent
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tornado (EF4 to EF5) touched down within 25 miles (40 km) of a point during the period 1921–
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2010 (inclusive) (Fig. 1 in Doswell et al. 2012).
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Figure 2: British Broadcasting Corporation (BBC) Science Editor David Shukman’s tweet the
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day after the 20 May 2013 Moore, Oklahoma, tornado.
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http://www.bbc.co.uk/weather/feeds/22608236.
The link points to
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Figure 3. Photo of a previously tornadic supercell storm on 10 June 2010 near Last Chance,
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Colorado (copyright C. A. Doswell III).
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19
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Figure 1. Shaded contours (see the key) showing the number of days per century a violent
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tornado (EF4 to EF5) touched down within 25 miles (40 km) of a point during the period 1921–
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2010 (inclusive) (Fig. 1 in Doswell et al. 2012).
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20
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Figure 2: British Broadcasting Corporation (BBC) Science Editor David Shukman’s tweet the
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day after the 20 May 2013 Moore, Oklahoma, tornado.
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http://www.bbc.co.uk/weather/feeds/22608236.
430
21
The link points to
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Figure 3. Photo of a previously tornadic supercell storm on 10 June 2010 near Last Chance,
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Colorado (copyright C. A. Doswell III).
22
Response to Reviewers
Click here to download Response to Reviewers: Responses to Editor-R2.docx
Responses to Editor
We have received two reviews of your revised manuscript. The reviewers'
comments are appended below. The manuscript is quite improved. I would like
you to consider a couple of minor revisions before final acceptance of the
paper.
Jeff, thank you for your shepherding our manuscript through the peer-review
process. Also, thanks for your suggestions that have resolved the differences
between us and the reviewers.
Reviewer 3 is still concerned about the highlighting of the USA Today article
(lines 56-66), and its reflection on Mike Smith. While the revised version is
improved in this regard, I am still a little uncomfortable with this situation. I would
like to propose an alternative that I think would improve this situation and still
effectively make your intended point.
We now include a statement after the quote: “There is no intention to single out
any particular person or media source, but rather to exemplify the type of
storyline that appears in the media." This quote simply provides evidence that
there is a problem with the explanations in the media.
This week there was a national story about a physicist, Rongjia Tao from Temple
University who was proposing (in a presentation at the American Physical
Society's Annual Meeting) that a series of enormous walls be constructed in
tornado alley to diminish the tornado threat in this region. His argument
essentially is that the walls would prevent the clash of air masses in this
region. Ironically, the experts quoted in the USA Today story
(http://www.usatoday.com/story/weather/2014/02/25/giant-walls-tornadoalley/5808887/) refuting this proposal are Mike Smith and Harold Brooks. I
suggest utilizing this article as the one highlighted in the text. The current article
could be included among the other examples cited (lines 67-71) if you strongly
believe that is necessary.
We don’t believe it is necessary.
Perhaps you could also include a comment (perhaps a footnote) regarding the
potential for experts to be mis-quoted, quotes utilized out of context, or incorrect
paraphrasing due to not-experts in the media attempting to merge expert
comments into their use of this incorrect concept.
We reiterate our concern that the issue of whether people are being quoted
accurately or not is a distraction. Clearly, most stories are the result of the
media’s simplified understanding of tornadic storms. Thus, accurate reporting is
not relevant to our point.
Reviewer 4 still has questions and concerns about the intended audience for this
article. Aside from the original comments from Greg Forbes that you have
addressed, I do not see any indication that the other reviewers share this
concern, and neither do I. As a BAMS article, this piece addresses the various
members of the weather enterprise, including but not limited to the "experts"
within the media. As you have acknowledged in your response to Dr. Forbes,
reaching the non-expert component of the media will have to be done via other
forums. While the latter is the majority of the real problem, the former (the
Weather Enterprise) needs to be cognizant of this issue and be prepared to help
refute the mis-conceptions (and not fall into the easy sound-bite trap).
We agree.
However, I do think that line 259 needs a little rewording. This comes across like
you are speaking directly to the non-expert media and not necessarily the
weather enterprise. I think your recommendation of having "the media adopt a
new explanation for tornadic storms" is the desired end goal, but for the purpose
of the BAMS venue, I think the key point is having the weather enterprise (e.g.,
the experts) help make this happen. I suggest a rephrasing along the lines of
"Therefore, we recommend that the weather enterprise encourage [alt. work with]
the media to adopt a new explanation for tornadic storms."
Thank you. That is a good suggestion. That change has been implemented.
Regarding Reviewer 4's second point I do not believe the BAMS audience needs
a comprehensive analysis of the climatology of horizontal temperature gradients
and their relationship to tornadoes to be convinced of this argument. Yes,
perhaps such a study might put this issue to bed for good. This could be a good
future project for a student (or maybe an undergraduate class). I do not think this
is necessary for this article. Such a study could be its own future technical
journal submission.
We agree. Such a study goes well beyond what is needed at this stage for this
article in BAMS.
Responses to Reviewer 3:
Thank you again for your further suggestions on improving our manuscript.
Reviewer #3: The revised version is generally acceptable to me, but I think that
the authors are still (unfairly, for points that I made before regarding the tendency
of reporters to misrepresent and/or misunderstand their interviewees) singling out
Mike Smith, and still could make their point well enough without providing links to
specific articles. Please consider simply paraphrasing this article and the others,
including key misuses of 'air mass clashing'. The BAMS readership should be
sufficiently savvy to use internet search engines to find articles with such
phrases.
We have proposed a suggested revision that Editor Waldstreicher has agreed
will address this concern: “There is no intention to single out any particular
person or media source, but rather to exemplify the type of storyline that appears
in the media."
We reiterate our concern that the issue of whether people are being quoted
accurately or not is a distraction. Clearly, most stories are the result of the
media’s simplified understanding of tornadic storms. Thus, accurate reporting is
not relevant to our point.
Responses to Reviewer 4:
Reviewer #4: The authors have addressed a number of concerns with this
second revision. These changes are sufficient for this reviewer to modify the
previous recommendation from "reject" to "accept with major revision". There
remain two significant areas of concern with respect to this work.
Thank you for your comments.
The first concern is one of confusion over who the intended audience is for the
information contained within the manuscript. The readership of AMS BAMS may
include those categorized as mass media communicators but this demographic
must be a small percentage of total subscribers. Yet, this appears to be the
target audience as stated on page 12, line 259: "Therefore, we recommend that
the media adopt a new explanation for tornadic storms." Another reviewer has
already noted: "When it comes to correcting media behavior, however, this article
would need to be published in a trade journal or an on-line forum read by nonmeteorologists in the broadcast industry."
We have followed the recommendation of Editor Waldstreicher with the following
addition to the text: "Therefore, we recommend that the weather enterprise work
with the media to adopt a new explanation for tornadic storms."
We will pursue the trade journal recommendation once this work is online and
can be referenced.
While that approach (publishing in a trade journal) is one way of highlighting and
possibly correcting the inaccuracies of the "clash" interpretation with respect to
tornadoes, what the authors actually wish to accomplish by publishing in BAMS
is the establishment of scientific evidence supportive of their argument, primarily
for other meteorologists. It is meteorologists who will then be called upon to
expertly convey the complexities of tornadoes and tornado outbreaks to the mass
media. The manuscript's target audience includes the authors themselves who
claim they have worked with the media and recognize the difference between the
media and scientific literature. The peer-review process lends credence to, and
provides support for, debunking the "clash" message amongst fellow
meteorologists who are the conduits of this improved information to the media,
and ultimately the masses.
The article is for the entire weather enterprise: students who are learning how the
atmosphere works, scientists as a reminder not to fall into slick-sounding but
inaccurate soundbites, and the members of the broadcast media to not allow
themselves to use these soundbites either. Each different component of our
audience will take away from our article what they want and what they need. No
change.
The second issue is related to the first and presents a bit more work. To more
fully support the hypothesis that the "clash" interpretation in the horizontal plane
is patently false with respect to tornado outbreaks, additional evidence should be
provided to the reader. In particular, a couple claims in the manuscript need
references: On page 4, line 78: "The reality is that air masses "clash" all the time,
but such a situation rarely produces tornadoes." And on page 5, line 102: "...the
mere presence of those gradients on the synoptic scale is no guarantee that
these ingredients will be brought together to produce tornadoes in any specific
extra-tropical cyclone."
If the intention of the authors is to convince other meteorologists reading BAMS
that "clash of the air masses" (at least in the horizontal plane) should be sent to
the dustbin of poor scientific explanation, then there is a need to define and
investigate a climatology of horizontal temperature gradients and their
relationship to tornado outbreaks. At a minimum, the authors should provide
examples of horizontal temperature gradients analyzed for tornado outbreak
cases and then use that analysis to show the relatively frequency of those
gradients existing in the absence of tornado outbreaks. The evidence against the
"clash" claim (in the horizontal) should be provided in sufficiently technical detail
to establish a more convincing argument that will resonate with the
meteorological community.
Such a piece of research is outside the scope of this article. Although an
interesting study, that would take this article well away from its intended purpose.
No change.
With a better description of who the information in the manuscript is directed at
(meteorologists instead of "the media"), and the inclusion of detailed analyses of
horizontal temperature gradients, their frequency, and their association with
tornado outbreaks, the manuscript will be far more appropriate for the readership
of AMS BAMS.
Thank you for your comments. They have improved our manuscript.
Figure 1
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