Changed how tornadoes are born

Surely, many people know that a tornado, is an atmospheric vortex that occurs in a thundercloud (supercell) and spreads down to the surface of the earth. In appearance, this phenomenon resembles a cloud sleeve or a kind of trunk, whose diameter can reach tens and hundreds of meters.

For a long time it was assumed that, a tornado originates as a funnel in a thundercloud. Gradually sucking in air from below, it begins to descend. Visual data "tornado hunters" and eyewitness accounts confirmed this version.

However, the new work of American researchers refutes existing ideas. According to the meteorologist Jana Houser of the University of Ohio and her colleagues, tornadoes do not originate from a cloud funnel. Moreover, even the direction taken by researchers to study tornadoes was still erroneous, because the latter do not originate in the sky at all.

Experts clarify that the key stage of their work was the study of a tornado called El Reno (2013 El Reno tornado) formed on May 31, 2013 in the eponymous region of the US state of Oklahoma.

It was the widest tornado ever recorded: the maximum diameter of the crater reached 4.2 kilometers, and the speed of the air flow in the vortex was more than 480 kilometers per hour (which is the second largest wind speed recorded on Earth).

Houser and her team watched the storm using a mobile radar system - a new type of Doppler radar. The device recorded wind speed in a tornado every 30 seconds.

Meanwhile, colleagues of meteorologists from other scientific centers collected and analyzed photographic and video frames of the epic event.

When the experts compared the data, they noticed something strange. In some of the images, the tornado El Reno was clearly visible on the ground, but these pictures were taken a few minutes before the same whirlwind at a height of 15-30 meters caught the radar.

Then meteorologists again analyzed the radar data and found clear evidence that the crater on the ground was formed earlier, and only then a whirlwind of air was noted at high altitudes.

Then the researchers studied in detail the data sets of three other tornadoes that occurred in the United States in 2011 and 2012. It turned out that in all cases the formation of vortices occurred on the ground or near its surface, and not in thunderstorm clouds. In addition, none of the four tornadoes studied went down from above.

It was also found that the formation of a tornado takes an average of 30 to 90 seconds. This means that it is incredibly difficult to predict with high accuracy where and when the next cataclysm will occur. Yet new data provide a clearer picture of the process of the birth of tornadoes.

"It needs a strong low-level, near-surface rotation that occurs at the right place at the right time, which correlates with the circulation of air masses in larger parental storms in order to form a tornado" explains Jana Houser.

The authors of the paper note that today weather forecasters make forecasts and warnings about tornadoes, based on radar observations. At the same time, they especially closely monitor the rotation of air masses above the ground, at the level of clouds.

In the light of new data, prognostic models will probably need to be changed.

"We need to revise the paradigms that serve to explain the formation of a tornado, and it is especially important to inform the weather forecasters who make the warnings. In fact, you will never find conclusive evidence of the downward movement of the tornado, so we must stop making it a priority for our forecasting strategies" sure Jana Houser.

In her opinion, one of the possible options for more accurate forecasting is the use of complex weather simulations and the compilation of scenarios for each major storm as it develops. To do this, meteorologists will need to launch a "virtual version" of a particular storm several hours before it begins and determine if it can generate a tornado. In addition, as the storm grows, it will be necessary to compare models with real data in search of clues about the probable origin of a tornado.

The team presented a more detailed report on the work done at the annual meeting of the American Geophysical Union.

By the way, earlier, researchers established an interesting fact: it turned out that birds hear approaching tornadoes and other cataclysms.

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