New research may alter what we know about how tornadoes form

Author: Carolyn Gramling / Source: Science News for Students

WASHINGTON, D.C. — Tornadoes might form from the ground up, rather than the top down.

That could seem unexpected.

Many people picture tornadoes forming from funnel clouds that eventually extend to the ground, said Jana Houser. She spoke December 13 in a news conference, here, at the American Geophysical Union fall meeting. Houser is an atmospheric scientist at the University of Ohio in Athens. She and her colleagues have new data that upend this “top-down” idea of how tornadoes form.

Understanding how tornadoes form is important. That’s especially true in the United States, where the storms seem to be getting more intense.

Thunderstorms that spawn tornadoes are called supercells. These form where powerful currents of warm, moist air get trapped beneath layers of colder, drier air. Forecasters typically scan supercells for telltale signs of that a tornado may be developing.

The other necessary ingredient for tornadoes to form is wind shear. Wind shear occurs when there are differences in wind speed at different levels above the ground. This can cause air masses to rotate horizontally. Air rising through the supercell can then tip the rotation from horizontal to vertical. This creates conditions ripe for a tornado.

Scientists have long debated where the wind rotations begin that will lead to twisters. That’s partly because the moment of twister birth remains a mystery. Tornadoes can form within 30 to 90 seconds. So studying how they start often is limited by not getting to the right place at the right time. Houser’s team was no exception, she said.

But a rapid-scanning Doppler radar helped her team capture…

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