A microburst is an incredible yet very dangerous phenomenon associated with thunderstorms. These localized columns of air burst suddenly from the bottom of thunderstorm clouds. More than just random bouts of rain and strong winds, they are close relatives of tornadoes. Their destructive capabilities threaten human life and property.
Microburst illustration. Photo: NASA
Mr. Tornado
Renowned meteorologist Ted Fujita, aka Mr. Tornado, coined the word microburst, also known as a downburst. In the 1970s, many people died in multiple plane crashes, and the aviation industry risked losing public confidence. Many blamed these catastrophes on pilot error.
Fujita thought differently. He investigated and discovered that the culprit was an unexpected strong downdraft, or downburst, of wind. A column of cool air plunges to the ground and fans out in every direction.
Types of microbursts
There are three main types of this phenomenon. The most common is a wet microburst. It occurs during humid spring or summer conditions. Dry air interacts with what’s called precipitation loading — excessive amounts of moisture. When water droplets or hail meet dry air, they evaporate, thereby cooling the air. This cool air at the base of a thunderstorm cloud sinks to the ground since it is heavier and denser than warm air. Called entrainment, it forces air and either rain or hail to plunge downward at great speeds.
A microburst in a rural area. Photo: Calling Tatu/Shutterstock
A dry microburst follows the same principle but with little precipitation. When the humidity levels or rainfall are less at the base of the thundercloud, the moisture evaporates. The cool air then descends only as wind.
Lastly, hybrid microbursts are combinations of the two. They blend specific conditions like sublimation, high levels of precipitation, dry-air entrainment, and cooling of air beneath the cloud base.
Microburst. Photo: Bruce Haffner/Twitter
Tornado-like wind speeds
Microburst events only last up to 15 minutes and are less than four kilometres in size. On rare occasions, there are macrobursts which exceed four kilometres.
Wind speeds in microbursts can reach a devastating 240kph. No wonder some mistake them for tornadoes. One can distinguish the two by their debris patterns. A microburst flattens trees or infrastructure with a central impact point. A tornado zigzags through the landscape and leaves behind a cyclonic pattern.
Debris from a microburst. Photo: Stacy Hopke/Burnett County Sheriff Department
Scientists can tell if a microburst is likely to occur by monitoring air patterns via radar and DCAPE (Downdraft Convective Available Potential Energy). This model calculates the amount of energy a downdraft may have in a thunderstorm. But technology can only predict the ideal conditions for one to occur, rather than when.
