If we placed cameras in the path of a tornado, they would either be damaged by the strong winds and swirling debris, or become so caked with mud and water that they wouldn’t produce any useful pictures. And of course, it’s not safe for humans to try to observe tornadoes at close range. It’s important to always seek shelter when tornado conditions develop.
We do have some ideas about the structure of the inside of tornadoes from instruments called mobile Doppler radars. Scientists can drive these instruments to locations near the tornado, but stop at a safe distance.
The radar sends energy toward the tornado, and when it hits the storm, some of the energy is bounced back. Researchers can analyze that reflected energy to detect important characteristics about the tornado. These include where there is and is not rain within the storm, where there is debris, how fast the winds are, and how these properties change moving away from the center of the tornado toward its outer edges and up vertically through the storm cloud above it.
Researchers use mobile radar to study tornadoes and other kinds of storms across the U.S.
From these radar observations, we have learned that tornadoes usually have a clear area in their centers, or at least a zone that is rain- and debris-free. This area also has intense vertical winds that sometimes are strong enough to suck pavement up from roads.
This clear space is surrounded by a ring of heavy rain and debris that is often moving outward, away from the tornado’s center. That’s because the winds are spinning incredibly fast and creating centrifugal force that pulls these objects away from the middle of the storm. Sometimes areas of heavy rain that are a little farther removed from the tornado spiral inward toward the area of rotation, like the spiral bands that extend outward from the eye of a hurricane.
Some tornadoes have only one main funnel cloud. Others have multiple small funnels that rotate around each other. There are even tornadoes that don’t have a funnel cloud at all. As long as winds are rotating in a tight circle all the way from the storm cloud down to the ground, it’s a tornado, even if atmospheric conditions haven’t condensed water vapor in the air into a visible funnel.
Scientists have also learned that many tornadoes don’t actually descend from the cloud to the ground. Rather, they form at the ground and quickly build upward — often in less than a minute.
Tornadoes can form at the ground before radar detects rotating winds at low levels.
When that happens, your eyes may fool you if you’re watching for a funnel cloud coming down from the sky. There could already be tornado-strength winds at the surface, even without that funnel cloud. So be careful — when it comes to tornadoes, looks can be deceiving.
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Jana Houser receives funding from the National Science Foundation.
This article is republished from The Conversation under a Creative Commons license.
Photos: See tornadoes' deadly destruction over the years
May 22, 2011: Joplin, Missouri
April 2011: Southeastern U.S.
Feb. 5, 2008: 'Super Tuesday' outbreak
April 2014: Southeast and Midwest
May 20, 2013: Moore, Oklahoma
March 18, 1925: Missouri, Illinois and Indiana
May 11, 1953: Waco, Texas
Nov. 6, 2005: Evansville, Indiana
May 10, 2008: Southwest Missouri
May 25, 2008: Iowa
Feb. 29, 2012: Illinois
Feb. 11, 2009: Oklahoma
April 28, 2011: Virginia
June 8, 1984: Barneveld, Wisconsin
May 1955: Udall, Kansas
March 2, 2012: Indiana
October 2013: Nebraska
May 4, 2003: Missouri
June 11, 2008: Iowa
July 8, 2014: Upstate New York
Dec. 10-11, 2021: Kentucky, Tennessee, Ohio Valley, southern US