Tornadoes - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 313

Figure 6.8. Cyclonic-anticyclonic tornado pair, April 24, 2006, near El Reno, OK. (Top left)
Anticyclonically rotating tornado, part of pair; (top right) cyclonically rotating tornado, part
of pair, before anticyclonically rotating member had formed; (bottom) anticyclonic tornado to
the south (left), dissipating, cyclonic tornado with ropelike condensation funnel to the north
(right). Dashed white line marks approximate location of cloud base associated with the rear-
flank gust front (photographs by the author).
Tornadoes that appear over the water are called ''waterspouts'' ( Figure 6.13 ).
Waterspouts sometimes make landfall and by definition become tornadoes, while
tornadoes sometimes pass over bodies of water and by definition become water-
spouts. There is nothing fundamentally different dynamically about tornadoes and
waterspouts, except perhaps for the characteristics of surface friction and their
effect on the character of the vortex in the boundary layer. Tornadoes have been
observed over all types of terrain, including mountainous areas ( Figure 6.14 ).
Tornadoes do not avoid complex terrain, but certainly high-elevation locations
over mountainous terrain typically are drier than low-elevation locations,
especially those sites that have access to air that has had contact with warm water
surfaces. Also, the effects of surface friction are different over complex terrain and
these might affect the nature of the tornadoes that form over them. Channeling
and other terrain-induced features could affect vertical wind shear locally and
increase or decrease vertical shear, thus possibly increasing or decreasing,
respectively, the chances for tornado formation.
Related to tornadoes and waterspouts are dust devils ( Figure 6.15 ), steam
devils ( Figure 6.16 ), and fire whirls, which are all driven by surface heating, which