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.

Does the Full Moon Really Make People Act Crazy?

iStock.com/voraorn
iStock.com/voraorn

Along with Mercury in retrograde, the full moon is a pretty popular scapegoat for bad luck and bizarre behavior. Encounter someone acting strangely? Blame it on the lunar phases! It's said that crime rates increase and emergency rooms are much busier during the full moon (though a 2004 study debunked this claim). Plus, there's that whole werewolf thing. Why would this be? The reasoning is that the Moon, which affects the ocean's tides, probably exerts a similar effect on us, because the human body is made mostly of water.

This belief that the Moon influences behavior is so widely held—reportedly, even 80 percent of nurses and 64 percent of doctors think it's true, according to a 1987 paper published in the Journal of Emergency Medicine [PDF]—that in 2012 a team of researchers at Université Laval's School of Psychology in Canada decided to find out if mental illness and the phases of the Moon are linked [PDF].

To test the theory, the researchers evaluated 771 patients who visited emergency rooms at two hospitals in Montreal between March 2005 and April 2008. The patients chosen complained of chest pains, which doctors could not determine a medical cause for the pains. Many of the patients suffered from panic attacks, anxiety and mood disorders, or suicidal thoughts.

When the researchers compared the time of the visits to the phases of the Moon, they found that there was no link between the incidence of psychological problems and the four lunar phases, with one exception—in the last lunar quarter, anxiety disorders were 32 percent less frequent. "This may be coincidental or due to factors we did not take into account," Dr. Geneviève Belleville, who directed the team of researchers, said. "But one thing is certain: we observed no full-moon or new-moon effect on psychological problems."

So rest easy (or maybe not): If people seem to act crazy during the full Moon, their behavior is likely pretty similar during the rest of the lunar cycle as well.

This story was updated in 2019.

NASA Reveals How Living in Space for a Year Affected Scott Kelly’s Poop

NASA, Getty Images
NASA, Getty Images

When you agree to be part of a yearlong space study, you forfeit some right to privacy. In astronaut Scott Kelly’s case, the changes his body endured while spending a year at the International Space Station (ISS) were carefully analyzed by NASA, then published in a scientific journal for all to see. Kelly submitted blood samples, saliva samples, and cheek swabs. Even his poop was subjected to scrutiny.

As PBS reports, Scott Kelly’s fecal samples revealed that his gut microbiome underwent significant but reversible changes during his time in orbit. In what was surely good news for both Kelly and NASA, his gut bacteria didn’t contain anything “alarming or scary,” according to geneticist Martha Hotz Vitaterna, and it returned to normal within six months of landing on Earth.

Even after being subjected to the challenging conditions of space, “Scott’s microbiome still looked like Scott’s microbiome, just with a space twist on it,” said Vitaterna, who was one of the study’s authors.

The fecal probe was one small part of a sweeping NASA study that was just published in the journal Science, more than three years after Kelly’s return. Dubbed the Twins Study, it hinged on the results of Kelly’s tests being compared with those of his identical twin, retired astronaut Mark Kelly, who remained on Earth as the control subject.

NASA’s goal was to gain insight into the hazards that astronauts could face on proposed long-term missions to the Moon and Mars. The agency has gone to great lengths to get this information, including offering to pay people $18,500 to stay in bed for two months in order to replicate the conditions of anti-gravity.

It also explains why NASA was willing to launch unmanned rockets into space to collect samples of Kelly’s poop. On four different occasions at the ISS, Kelly used cotton swabs to pick up poo particles. When the rockets arrived to drop off lab supplies, they returned to Earth with little tubes containing the swabs, which had to be frozen until all of the samples were collected. The process was tedious, and on one occasion, one of the SpaceX rockets exploded shortly after it launched in 2015.

The study also found that his telomeres, the caps at the ends of chromosomes, had lengthened in space, likely due to regular exercise and a proper diet, according to NASA. But when Kelly returned to Earth, they began to shorten and return to their pre-spaceflight length. Shorter telomeres have a correlation with aging and age-related diseases. “Although average telomere length, global gene expression, and microbiome changes returned to near preflight levels within six months after return to Earth, increased numbers of short telomeres were observed and expression of some genes was still disrupted,” researchers wrote.

Researchers say more studies will be needed before they send the first human to Mars. Check out NASA's video below to learn more about what they discovered.

[h/t PBS]

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