What Is the Jet Stream, and How Does It Work?

Trapped between two big high-pressure systems, Hurricane Harvey has stalled over Houston, to devastating effect. As the Washington Post notes, if the jet stream were to dip far enough south, it could push Harvey out. Unfortunately, that's not in the forecast.

But what is the jet stream?

A jet stream is a swift current of air that encircles the globe right around the cruising altitude of a commercial airplane. It's easy to forget that there are vast rivers of wind whooshing just a few miles above our heads at speeds that could put most hurricanes and tornadoes to shame, but jet streams affect us every day without our realizing it. These speedy winds drive or influence just about every weather system that we have the pleasure—or misfortune—of experiencing. Planes even use it to cut down on fuel consumption and travel times.

There are usually two jet streams in each hemisphere, the polar jet and the subtropical jet. When we talk about "the jet stream," we're generally talking about the stronger polar jet stream, because most of our weather is driven by it. It's typically found at the same latitude as the U.S.-Canadian border.

We're often guilty of oversimplifying weather events by blaming everything on a clash between warm air and cold air, but temperature gradients really do have an enormous impact on where the jet stream forms and how strong it is. Jet streams form as air in the upper atmosphere moves from south to north and gets deflected to the east by the Coriolis effect. The jet stream will get stronger if the warmer temperatures are to the south and the colder the air is to the north. This is why the jet stream strengthens and dips over the United States during the winter, while it weakens and retreats north into Canada during the heat of the summer.

The jet stream drives our weather through phenomena called troughing, ridging, and jet streaks. Troughs and ridges are curves in the jet stream that are analogous to low pressure (troughs) and high pressure (ridges). In the northern hemisphere, a trough is a southward dip in the jet stream and a ridge is a northward hump in the wind current. You can expect active weather ahead of a trough and quiet weather beneath a ridge.

A jet streak is an area of much faster winds within the jet stream itself. Winds in a jet stream routinely climb above 100 mph, but the wind in a jet streak can clock speeds of more than 200 mph in a boisterous weather pattern. Troughs and jet streaks often team up to create low-pressure systems at the surface, and that's what gives birth to most of our interesting weather. Winds don't flow in a straight line as they twist around a trough or speed in and out of jet streaks. Air collides going into a trough and diverges as it leaves a trough. The same goes for jet streaks.

The process of winds exiting a trough or a jet streak, known as divergence, creates a void in the upper atmosphere. Nature hates imbalance and will do just about anything to balance something that's out of whack. When winds diverge coming out of certain parts of the jet stream, air will rush up from lower altitudes to fill the void. This upward rush of air from the surface leaves lower air pressure at the surface, creating a low-pressure system that can trigger all sorts of nasty weather.

The jet stream is also one of those weather features that could feel the effects of climate change over the coming decades and centuries. Since these wind currents rely on sharp temperature gradients in order to form, a warmer atmosphere will lessen the temperature difference between north and south and possibly create weaker jet streams. A weaker jet stream could act more erratically, creating longer stretches of quiet weather—but also more frequent weather extremes.

Bombshell, Victoria’s Secret’s Bestselling Fragrance, Also Happens to Repel Mosquitoes

Dids, Pexels
Dids, Pexels

People love Bombshell, the best-selling fragrance at Victoria’s Secret, for its summery blend of fruity and floral notes. Not everyone is a huge fan, though: As Quartz reports, the perfume is surprisingly good at warding off mosquitoes. In fact, it’s almost as effective as DEET insect repellent, according to the results of a 2014 experiment by researchers at New Mexico State University.

Researchers took 10 products that are commercially available and tested their ability to repel two different species of mosquitoes: the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus), both of which are known to transmit diseases like dengue fever, chikungunya, and yellow fever. In doing so, volunteers subjected their own flesh to the test by placing their hands on either side of a Y-shaped tube containing the blood-sucking critters. One hand was covered in a synthetic rubber glove, while the other hand was sprayed with one of the products but otherwise left bare. Researchers recorded which tunnel the mosquitoes flew to, and how long they avoided the other end.

Three of the products contained DEET, while four products didn’t. In addition, there were two fragrances (including Bombshell) and one vitamin B1 skin patch. The DEET products were the most effective, but Bombshell proved to be nearly as good, keeping mosquitoes at bay for roughly two hours.

“There was some previous literature that said fruity, floral scents attracted mosquitoes, and to not wear those,” Stacy Rodriquez, one of the study’s authors, said in a statement. “It was interesting to see that the mosquitoes weren’t actually attracted to the person that was wearing the Victoria’s Secret perfume—they were repelled by it.”

This isn’t the first time a perfume has had an unintended effect on the natural world. It turns out that tigers are obsessed with Calvin Klein’s Obsession for Men cologne, partly because it contains a synthetic version of civetone, a pheromone that's secreted by glands located near a civet’s anus. This substance was once used to create musky fragrances, but nowadays the scent is mostly reproduced in a lab. Still, the fake stuff must be pretty convincing, because big cats go crazy when they catch a whiff of it.

[h/t Quartz]

Mystery Solved: Scientists Have Figured Out Why Some Squirrels Are Black

Rena-Marie/iStock via Getty Images
Rena-Marie/iStock via Getty Images

It can be something of a surprise to see an animal sporting a fresh coat of paint. Blue lobsters occasionally surface after being caught in traps. A pink dolphin was spotted in Louisiana in 2007 (and several times since). In the Chinese province of Shaanxi, a cute brown and white panda greets zoo visitors.

Another anomalous animal has joined their ranks. Black squirrels have been spotted in both the United States and the UK, and now scientists believe they know why.

Like many animals with unusual color schemes, black squirrels are the result of a genetic detour. Researchers at Anglia Ruskin University, Cambridge University, and the Virginia Museum of Natural History collaborated on a project that tested squirrel DNA. Their findings, which were published in BMC Evolutionary Biology, demonstrated that the black squirrel is the product of interspecies breeding between the common gray squirrel and the fox squirrel. The black squirrel is actually a gray squirrel with a faulty pigment gene carried over from the fox squirrel that turns their fur a darker shade. (Some fox squirrels, which are usually reddish-brown, are also black.)

A black squirrel is pictured
sanches12/iStock via Getty Images

Scientists theorize a black fox squirrel may have joined in on a mating chase involving gray squirrels and got busy with a female. The black fur may offer benefits in colder regions, with squirrels able to absorb and retain more heat, giving them a slight evolutionary edge.

In North America, black squirrels are uncommon, with one estimate putting them at a rate of one in every 10,000 squirrels. In 1961, students at Kent State University in Ohio released 10 black squirrels that had been captured by Canadian wildlife authorities. The squirrels now populate the campus and have become the school’s unofficial mascot. Their coloring might help them hide from predators, which might come in handy at Kent State: The campus is also home to hawks.

[h/t The Guardian]

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