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query and generate a mean center for only the F4 and higher torna-
does. Compare the locations of the two mean centers. The location of
the mean center of the F4 and higher tornadoes is also in Missouri but
about 90 miles northeast of the mean center for all of the tornadoes.
8. Clear the definition query. Create a standard deviational ellipse con-
sidering all the tornadoes. Approximately how many states are cov-
ered wholly or in part by this ellipse? It appears that most states,
about 35, are covered at least partly by this ellipse, which extends
from Virginia to Colorado. This reflects the widespread distribution
of tornadoes in the United States. Repeat for the F4 and higher torna-
does, and compare the two ellipses. The standard deviational ellipse
for the F4 and higher tornadoes is centered in Missouri but has a
much smaller size, reflecting the Great Plains and central lowlands
of the country as the focal point for intense tornadoes; this ellipse
covers about 20 states from Ohio to Kansas, and from Wisconsin to
Louisiana.
9. Generate a mean center and a standard deviational ellipse for January,
April, July, and October's tornadoes. Compare these ellipses in terms
of shape and size. Name two reasons why the ellipses vary so much
during each season. The ellipses vary so much because of the air
masses, driven by seasonal change and prevailing winds, that change
the pattern of the tornadoes from winter to summer and back to win-
ter again.
10. Zoom into Ann Arbor, Michigan, and select the tornadoes that have
occurred in that area. Generate a set of buffers around the torna-
does in that area. Identify areas that are outside of a distance that
you choose, say 1000 feet or 1000 meters, from a tornado having
occurred there over the span of this data set. Do any such areas exist?
Yes, depending on where you select the tornadoes, some areas will
be outside the buffer distance. Then, answer the following question:
Do such areas that exist outside the buffers mean that those areas
are relatively safe, or does it simply mean “it's due for a big one?”
Contrary to popular belief with regard to tornadoes, earthquakes, or
other natural hazards, every area that is subject to the same climate
or tectonic forces is equally susceptible to another event. In other
words, the areas that have not experienced a tornado in the past are
not “overdue” for a tornado occurring there. Mother Nature has no
“tally sheet” or GIS of past touchdowns!
8.8 Related theory and practice: Access through QR codes
Theory
Persistent archive:
University of Michigan Library Deep Blue:
http://deepblue.lib.umich.edu/handle/2027.42/58219
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