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Helicopter pilot Jerry Ferguson was cruising through the skies above Phoenix on Monday as thunderstorms erupted around the desert city.

While filming the weather for a local television station, Ferguson took a picture that ranks among the best photos ever captured of a dangerous meteorological phenomenon known as a microburst.

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Microbursts occur when a rush of rain cooled air collapses toward the ground from a parent thunderstorm, crashing to the ground and spreading out at speeds above 100 miles per hour.

The microburst in this image, and in a related timelapse video shot by Bryan Snider from the vantage point of Phoenix's Sky Harbor International Airport.

As Angela Fritz of the Capital Weather Gang blogwrote on Tuesday, microbursts "form within the main downdraft of the storm, and are triggered by two main physical processes — the drag that’s created by falling rain and hail, and evaporation."

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"When water evaporates it cools the air, which makes it more dense and accelerates the descent," she wrote.

Zoomed in image of the rain shaft associated with the microburst.Credit: Jerry Ferguson

Microbursts are a major hazard for aircraft that are landing or departing an airport at relatively low rates of speed, since such winds can cause significant airspeed fluctuations and even cause a plane to stall and crash.

For example, the crash of Delta Flight 191 in Dallas in 1985 was blamed on a microburst, as was Pam Am flight 759, a Boeing 727, in New Orleans in 1982.

These crashes and others led to the development of radar technology and warning systems that give pilots early warning of such weather conditions.

One of the leading scientists who investigated microbursts and helped lead the way toward these lifesaving systems was Tetsuya (Ted) Fujita, whose subsequent tornado studies led to the development of the Fujita Tornado Damage Scale.

(责任编辑：娛樂)