What Are Microbursts?

NOAA Legacy Photo ERL/WPL, Flickr // CC BY 2.0
NOAA Legacy Photo ERL/WPL, Flickr // CC BY 2.0

It's monsoon season in the American Southwest. Daily thunderstorms popping up over a dry landscape provide countless opportunities for passersby to take pictures and videos of the torrents as they bring an annual dose of rain to the otherwise parched desert. One of the more striking features of these desert thunderstorms is a term you see all over social media: microbursts. These destructive wind events can be terrifying to live through, but beautiful to watch from afar.

A microburst is a downward burst of damaging winds, rain, and hail that literally drops out of the bottom of a thunderstorm. A microburst occurs over a relatively tiny area; the extent of the strong winds is usually only a mile or two wide. From a distance, a microburst can look like a water balloon falling toward the ground, splashing outward upon impact like a mushroom cloud unfolding in reverse. Pictured above is a microburst with a classic water balloon appearance, spotted by NOAA scientists around 1980.

Meteorologists didn't give much thought to this phenomenon until the 1970s, when Dr. Ted Fujita—famous for his pioneering research into tornado intensity that led to the creation of the Fujita Scale—started to study the distinct pattern of damage that these windstorms leave behind.

You don't want to find yourself beneath a microburst. Just as with other destructive thunderstorms, some folks who experience these damaging winds insist that they really lived through a tornado. These winds come on suddenly, often going from a gentle breeze to a nightmarish windstorm within seconds, and can blow away anything not nailed down to the ground. Winds in a microburst can easily exceed 60 mph—but the strongest microbursts mimic the intensity of weak tornadoes, with winds peaking above 100 mph in some spots.

Microburst, circa 1980
Well-developed thunderstorm with microburst, circa 1980
NOAA Legacy Photo ERL/WPL, Flickr // CC BY 2.0

Different parts of the United States are prone to different types of microbursts. A wet microburst occurs with heavy rain or hail; these are common in humid areas like the southeast. A dry microburst, on the other hand, isn't accompanied by any precipitation at all; blowing dust and debris at the surface is often the only indication one of these events is occurring. Dry microbursts are common in places where there's not much humidity, like higher elevations or the desert.

Microbursts form due to two factors: evaporation and the weight of rain and hail. Evaporation is a cooling process; when liquid water turns to water vapor, it absorbs heat and cools the air around it. If dry air starts to invade the environment in or around a thunderstorm, it can cause rain to evaporate and leave behind large sections of air that are suddenly cooler than their surroundings. This less dense air sinks toward the ground, falling faster and faster until impact. The weight of the rain and hail also contributes to the speed of a microburst. Water is heavy, and that weight plays a big role in dragging cool air down from a thunderstorm. The two processes combined help create microbursts.

The biggest danger posed by microbursts is their sudden, sneaky formation. Microbursts happened with almost no notice at all until just the last decade or two. You didn't know it was happening until it happened. This surprise downward burst of winds and resulting wind shear can be potentially lethal to aircraft that are taking off and landing during thunderstorms. Microbursts have contributed to numerous airplane crashes over the years, killing hundreds of people.

We've gotten much better at detecting microbursts. The prevalence of Doppler weather radar across the United States, including smaller radars installed near most major airports, allows meteorologists to give people on the ground and in airplanes a little bit of advance notice before a microburst occurs. Wind shear detection systems both on the ground and installed in aircraft have also helped tremendously when pilots are flying into nasty weather.

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Why Are Barns Often Painted Red?

iStock/Ron and Patty Thomas
iStock/Ron and Patty Thomas

Beginning with the earliest American settlements and continuing into the 18th century, most barns weren't painted at all. Early American barn builders took sun exposure, temperature, moisture, wind, and water drainage patterns into account when placing and building barns, and they seasoned the wood (that is, they reduced the moisture content) accordingly. The right type of wood in the right environment held up fine without any paint.

Toward the end of the 1700s, these old-school methods of barn planning and building fell by the wayside. People sought a quicker, easier fix for preserving their barns—a way to coat and seal the wood to protect it from sunlight and moisture damage. Farmers began making their own coating from a mix of linseed oil (a tawny oil derived from the flax seeds), milk, and lime. It dried quickly and lasted a long time, but it didn't really protect the wood from mold and wasn't quite like the "barn red"we know today—it was more of a burnt orange, really.

Turning Red

The problem with mold is that it decays wood and, in large quantities, can pose health risks to people and animals. Rust, it turns out, kills mold and other types of fungi, so farmers began adding ferrous oxide (rusted iron) to the linseed oil mix. A little bit of rust went a long way in protecting the wood, and it gave the barn a nice red hue.

By the late 19th century, mass-produced paints made with chemical pigments became available to most people. Red was the least expensive color, so it remained the most popular for use on barns, except for a brief period when whitewash became cheaper and white barns started popping up. (White barns were also common on dairy farms in some parts of Pennsylvania, central Maryland, and the Shenandoah Valley, possibly because of the color's association with cleanliness and purity.)

Throughout Appalachia (a historically poorer region), many barns went unpainted for lack of money. In the tobacco regions of Kentucky and North Carolina, black and brown barns were the norm, since the dark colors helped heat the barn and cure tobacco.

Today, many barns are still painted the color traditionally used in a given region, with red still dominating the Northeast and Midwest.

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This story was updated in 2019.

Is There An International Standard Governing Scientific Naming Conventions?


Jelle Zijlstra:

There are lots of different systems of scientific names with different conventions or rules governing them: chemicals, genes, stars, archeological cultures, and so on. But the one I'm familiar with is the naming system for animals.

The modern naming system for animals derives from the works of the 18th-century Swedish naturalist Carl von Linné (Latinized to Carolus Linnaeus). Linnaeus introduced the system of binominal nomenclature, where animals have names composed of two parts, like Homo sapiens. Linnaeus wrote in Latin and most his names were of Latin origin, although a few were derived from Greek, like Rhinoceros for rhinos, or from other languages, like Sus babyrussa for the babirusa (from Malay).

Other people also started using Linnaeus's system, and a system of rules was developed and eventually codified into what is now called the International Code of Zoological Nomenclature (ICZN). In this case, therefore, there is indeed an international standard governing naming conventions. However, it does not put very strict requirements on the derivation of names: they are merely required to be in the Latin alphabet.

In practice a lot of well-known scientific names are derived from Greek. This is especially true for genus names: Tyrannosaurus, Macropus (kangaroos), Drosophila (fruit flies), Caenorhabditis (nematode worms), Peromyscus (deermice), and so on. Species names are more likely to be derived from Latin (e.g., T. rex, C. elegans, P. maniculatus, but Drosophila melanogaster is Greek again).

One interesting pattern I've noticed in mammals is that even when Linnaeus named the first genus in a group by a Latin name, usually most later names for related genera use Greek roots instead. For example, Linnaeus gave the name Mus to mice, and that is still the genus name for the house mouse, but most related genera use compounds of the Greek-derived root -mys (from μῦς), which also means "mouse." Similarly, bats for Linnaeus were Vespertilio, but there are many more compounds of the Greek root -nycteris (νυκτερίς); pigs are Sus, but compounds usually use Greek -choerus (χοῖρος) or -hys/-hyus (ὗς); weasels are Mustela but compounds usually use -gale or -galea (γαλέη); horses are Equus but compounds use -hippus (ἵππος).

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