Excerpt: 'Weather's Greatest Mysteries Solved!' by Randy Cerveny

Most aircraft crashes involving microbursts occur when planes are attempting to land. As the aircraft makes its final approach to the runway, the pilots are slowing the plane to an appropriate speed. When the blasting winds of the microburst hit the plane, the pilots would experience a marked reduction in their forward airspeed, caused by ramming into the ferocious headwinds created by the microburst.

I once encountered the same situation as those unfortunate pilots when I was driving a high-profile storm chase van on the ground. We were traveling on a bridge at sixty miles per hour when we encountered the headwinds of a microburst -- and literally came to a sudden stop as we smashed into the hundred-plus-mph winds of the microburst.

What I did at that time is exactly what a pilot before Fujita's research would have done: I let up on the accelerator and tried to slow down. And that instinctive impulse could be fatal for a pilot. What we know now is when an aircraft encounters a microburst, a pilot inexperienced with these odd weather events usually tries to compensate the massive headwinds by suddenly decreasing the plane's airspeed. But as the aircraft proceeds to travel through the microburst, abruptly it no longer encounters a headwind but instead is pushed by an incredibly strong tailwind. This causes a sudden decrease in the amount of air flowing across the wings -- the critical principle to maintaining flight. Consequently, the sudden loss of air moving across the wings causes the aircraft to literally drop out of the air.

Following Fujita's groundbreaking discovery of these microburst events, we now know that the best way to deal with a microburst in an aircraft is to increase speed as soon as the abrupt drop in airspeed is noticed. This will allow the aircraft to remain in the air when traveling through the tailwind portion of the microburst and also pass through the microburst with less difficulty. One thing that we have discovered since Fujita's time is that commercial jet aircraft are much more vulnerable to a microburst than small planes. In particular, we have learned that a single-engine prop plane can more quickly speed up or maneuver to avoid the consequences of a microburst, while a jet will have a slower response lag that will make it especially vulnerable to the winds of a microburst.

But what causes these microbursts -- Fujita's small-scale air bombs -- to occur in the first place?

Microbursts are the result of air being rapidly accelerated down from the mid- and upper parts of the thunderstorm to the ground. That downflow can occur due to several factors: by air being pulled down by rain or hail, by the increases in air density as the air is cooled by rain, and by the cooling produced with melting ice crystals. These three forces, if strong enough, can create massively intense and sudden downward movements of air.

One aspect of microbursts that we have learned since Fujita's initial work is their strikingly short lifetime. Most microbursts last only five to fifteen minutes. Such limited duration, coupled with their small spatial extent, makes microburst detection and prediction very difficult. But we have made significant progress in detecting microbursts through the use of Doppler radar.

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