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It’s a perfectly sunny day, with a clear blue sky. The pilot has just announced that your flight has reached cruising altitude, so the seat belt sign is turned off. Passengers move around in the cabin. Suddenly the plane started shaking. You instinctively grab the arm of your chair. The passengers who stood are getting ready. The child starts crying.
After a minute the alarm passes, your body relaxes, and you exhale deeply. Then the plane falls like a rock. Your stomach jumps into your throat. But there is no storm outside, not even clouds. What’s going on?
This clear-air turbulence, as it’s called, is caused by patches of air circulating randomly within the world’s jet streams — powerful air currents that circle the globe from west to east and that we see on weather maps as broad, wavy lines around which centers of low and high pressure curve. . Airlines like to fly within these bands of fast-moving air to increase speeds and reduce travel times if the bands are close enough to the desired flight direction. Whirlpools, invisible to the eye, hit the wings of the aircraft. And when the blow is strong enough, it shakes the plane up or down. The passengers freeze and the flight attendants stumble. Over the past four decades, clear air turbulence has increased by up to 55 percent in different regions around the world. Models project another increase of 100 to 200 percent over the next 30 to 60 years. Every time a strike arrives, it strikes without warning.
Pilots can spot turbulence ahead with relative ease when in a storm or among clouds. Onboard radar can track the movements of raindrops at a distance to detect the turbulent movement of the air. The pilots can then warn passengers and crew members in advance, encouraging them to take their seats and lock up before the aftershock hits. However, in clear air the turbulence is not visible to radar; Pilots usually don’t know it’s there until the plane hits it.
Overcast turbulence is caused by the heating effect of the sun. At dawn, the sun begins to warm the earth, which in turn heats the air near the surface. This warmer air is less dense than the cooler air above it, so it rises. Displaced cold air falls, and the process repeats, which is called convection currents. The up and down drafts of these currents push against the wings of the aircraft, and if the pushes are strong and sudden, the brews begin to deflate.
Clear air turbulence occurs almost exclusively within jet streams. The fast band of air in a jet stream (imagine an oblong tube) clips the slower air immediately above and below it, somewhat destabilizing the upper and lower limits of the jet stream and changing it from stationary to fuzzy. At the same time, however, the density differences between the jet stream air and the air above and below it re-stabilize the boundary.
Most of the time, the stabilization effect overcomes the destabilizing effect, giving you a smooth ride. But if the winds get strong, the destabilizing force can win the tug-of-war. The result is chaotically moving air that suddenly pushes up and down the wings.
Streaming through historical flight and weather data, Paul Williams and colleagues at the University of Reading in England found that turbulence in the North Atlantic jet stream increased in frequency by 17 to 55 percent from 1979 to 2020. The largest increase was in the mostly severe category of Turbulence, defined as having a Tess strength greater than 1 g. At that force, anything that isn’t clamped to the plane, including your stomach, will float temporarily because turbulence causes the plane to accelerate downward faster than gravity. If you don’t twist, you will rise from your seat as the plane will quickly fall a few tens of meters.
What does this increase mean for your average trip? First, severe disorders are relatively rare. In-flight measurements show that approximately 0.1 percent of the atmosphere at cruising altitude contains severe turbulence. “This equates to about 30 seconds for an average eight-hour flight,” says Williams, a professor of atmospheric sciences. The most likely scenario, he says, is that for every 10 flights a person takes, nine will not have severe turbulence, and the flight will take several minutes.
Moderate to mild agitation is more common and what most of us will experience. In moderate disturbance, the jumps and dips in height are usually a few metres. An eight-hour flight today may contain 10 to 15 minutes of clear air turbulence today, Williams says, but projections indicate that the extent of this turbulence will double or triple over the next few decades as warming caused by climate change increases wind shear in the region. The Plane. flow.
Since frequent tremors are more likely to cause more wear and tear on aircraft, airlines may face higher repair costs. Flyers may also encounter more stressed parents, like me, who are tired of trying to keep their little one in their seat every time the seatbelt sign lights up. These lifting buckles are very easy for little hands to operate.
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