Dan Dawson, assistant professor in the
Department of Earth, Atmospheric, and
Planetary Sciences, unleashed his weather
machines this semester.
No, Dawson is not an old-school super-villain. His machines, disdrometer probes
to be exact, were essential in research as
part of the VORTEX-SE project, in which
several members of the department participated in March in northern counties of
Alabama near Huntsville.
Funded by the National Oceanic and
Atmospheric Administration, the project
— Verification of the Origins of Rotation in
Tornadoes Experiment-Southeast — looked
at changing patterns in tornado devastation
and why fatality rates increased in this area.
The data collected could have implications
Dawson’s probes were developed by
his former colleagues at the University of
Oklahoma and are equipped to measure
rain and hail particles. An infrared laser
sheet measures the size of the particles,
fall speed and frequency. The mobile meteorological units also feature pressure sensors, temperature and humidity gauges, and
a sonic anemometer, which measures wind
speed. The instruments are loaded with
global positioning systems and sophisticated data collection technology.
“We think there might be some sys-
tematic differences in the details between
how tornadoes are produced in different
environments. That’s where the
microphysics comes into play and where
the raindrop sizes matter,” Dawson says.
“Those differences are critical for how cold
the outflow and rippling downdraft are in
Dawson and fellow EAPS professor
Robin Tanamachi were part of a previous
VORTEX study in Oklahoma in 2009 and
2010. By then, tornado-warning signs could
be found a week in advance through fore-
casting. But better predicting how tornadoes
will travel once they arrive could save lives.
In fact, Dawson’s disdrometer probes
encountered some heavy drama in the
earlier study. Like a scene from the movie
“Twister,” a lighter weight probe was
smashed by high winds. According to the
last bit of data received, the wind gust was
clocked at more than 80 mph.
“A tornado tossed it,” Dawson says.
“That was not what we wanted to happen
but we did get good data from it. It was not
the strongest gust of wind in that storm but
it was the one that did it in.”
The lighter probes, which were more
stationary and weighed only 100 pounds,
were meant to be picked up and follow the
storms. The probes in VORTEX-SE were
cast in a broader net and allowed the storms
to come to the technology itself.
The work helped explain some of the
devastation in the Moore, Oklahoma, storm
in 2013 and the Joplin, Missouri, tornado of
2011, which killed 153 people.
“We thought a tornado like that would
never happen again,” Dawson says.
“Obviously we were wrong. It became severe
and produced a tornado very quickly.”
So why did VORTEX move several
states away in just six years? Data collected
in that time has shown devastation moving
to the southeast because the topography,
climate and population distribution is much
different than in areas like Oklahoma.
Compared to the earlier study, VORTEX-SE
occurred in an area with trees, a river and
more remote roads. Societal factors weighed
in as well — poverty rates and higher popu-
lations of elderly.
These details fueled a paper led by
EAPS professors Michael Baldwin and
Ernest Agee. Dawson, Tanamachi and EAPS
assistant professor Dan Chavas also contributed to the research that looks to explain
why tornado devastation has had a dramatic
“It’s shifting,” Agee says. “We still want
to understand why. There are more torna-
does in that region per year than the tradi-
tional area of the Plains and Oklahoma. The
statistics available say something major has
Baldwin adds that 30 years of data
wasn’t enough to prove why, not to mention
sketchy recordkeeping beyond those 30
years. But as the EAPS researchers sift
through the VORTEX-SE data, the team
should understand tornado behavior more,
why they form where they do and how to
understand the events better.
Many of these weather events occur
when conditions aren’t “optimal” and all of
the ingredients that create tornadoes are
not evident. VORTEX-SE wanted to help
“We want to forecast short time scales
— a day or a couple hours — better and the
climate side,” Chavas says. “How does climate change affect these things? It all ties
in to understanding the phenomena
forecasting the future