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TORNADOES

Data show twisters form over Kanto in September

by Jun Hongo

Staff Writer

Damage to people and property by tornadoes made headlines over the past week, with the latest in Tochigi Prefecture injuring three people while destroying houses and other buildings.

Here are some questions and answers regarding twisters:

Are twisters common in Japan?

About 17 were observed each year between 1991 and 2006, according to statistics compiled by the Meteorological Agency.

That number is just a mere fraction of the roughly 1,300 that typically form every year in the United States, but when taking into account the amount of area covered, it would be inaccurate to say tornadoes are rare in Japan, the agency warns.

Although Tochigi, Saitama and Chiba prefectures, all located in the Kanto region, were struck by tornadoes in the past week, twisters have occurred from Hokkaido to Okinawa.

The tally from 1961 and 2006 shows that September is the peak month, with 1 p.m. being the most likely time of day for a tornado to strike.

Geographic and weather conditions in the Kanto region are favorable for tornadoes. The mountainous region to the west, the humid hot air coming in from the Pacific and cooler wind coming in from the north this time of year all help.

The Meteorological Agency has confirmed that weather conditions were nearly identical when the tornado touched down in Saitama and Chiba on Monday and when the Tochigi tornado hit Wednesday.

Have there been more tornadoes in Japan recently?

The Meteorological Agency states it is difficult to tell whether tornado counts have risen in recent years because the survey methods continue to change. Occurrences also vary every year and there are no consistencies.

There were 28 tornadoes and/or microbursts, a strong, localized downdraft also known as wind shear, in 2012, 15 in 2011, 37 in 2010 and 23 in 2009, according to the agency.

How do tornadoes form?

The agency said that because they form so suddenly, the mechanism of how they are created is still not completely known.

A collision of warm, humid air with a cooler, dry front causes a spiral ascension of the wind. Soaring cumulonimbus clouds also play a role in the formation of tornadoes, especially supercells with mesocyclones.

Because atmospheric conditions are the key ingredient, twisters can form not only over open land but also in areas like Tokyo with skyscrapers.

What are supercells?

A supercell, which spawned Monday’s tornado, is a giant cumulonimbus that is capable of causing massive damage.

Supercells are so huge that they differ “from ordinary thunderstorms in that the rotation of their updraft enables them to overcome the self-limiting mechanisms that bring demise to regular storms,” according to the U.S. National Oceanic and Atmospheric Administration.

Has Japan seen any particularly devastating tornadoes?

On November 7, 2006, a tornado touched down in Saroma, Hokkaido, at about 1:30 p.m. It struck buildings near a construction site, lifting some into the air and killing nine people.

What is the Fujita scale?

The Fujita scale is a measurement of tornado intensity created by the late meteorologist Tetsuya Fujita, a Japanese native who did his research at the University of Chicago.

The New York Times wrote in Fujita’s obituary in 1998 that he “devised the standard scale for rating the severity of tornadoes and discovered the role of sudden violent downbursts (microbursts) of air that sometimes cause airplanes to crash.”

Fujita, who died at age 78, was known to many as the Tornado Man or Mr. Tornado, according to the article. Fujita linked the damage caused by a tornado with its wind speed in his scale.

According to his hierarchy, an F0 tornado boasts a wind speed of 17 to 32 meters per second and is strong enough to bend antennas or small branches on a tree. The strongest tornado on the scale is an F5, which can obliterate houses and lift automobiles and train cars with wind speeds that can reach 142 meters per second. The 2006 tornado in Hokkaido that killed nine people was classified as an F3. No F4 or F5 tornado has ever been recorded in Japan, according to the Meteorological Agency.

Can the government issue better and quicker warnings for tornadoes?

Signs that a tornado may be forming include darkening skies, hailstorms and even a jetlike roar. But some reports said fair conditions continued Wednesday until 10 to 20 minutes before the Tochigi tornado formed, so prediction remains difficult.

The Meteorological Agency has been using radars to track wind movements inside clouds and began providing new forecasts for tornadoes and microbursts in 2008.

However, records show that the agency has been able to accurately predict a tornado only 5 to 10 percent of the time.