Recently, British Airways passengers flying from New York to London were pleasantly surprised to arrive at their destination, one and half hours earlier than the scheduled time. No, the aircraft did not have more powerful engines neither did it take a shortcut. It was just lucky enough to ride a powerful jet stream! In spite of all the abuse heaped upon her, mother nature is generous enough to offer this gift to the aviation industry. Jet streams are fast flowing currents or streams of air usually found anywhere between 23000 ft to 52000 ft above sea level. A jet stream is usually thousands of kilometers long, few hundred kilometers wide and few kilometers thick. The most natural question would be how and why they occur. Well, they are formed when two masses of air with substantial temperature contrast meet. Now the air does not flow from the high temperature mass to the low temperature mass. Instead, it flows along the boundary of the air masses due to the Coriolis effect.
There are two types of jet streams. The polar jets are the stronger ones found between altitudes of 23000 ft and 39000 ft. The subtropical jets are the weaker ones found between altitudes of 33000 ft and 52000 ft. The northern and southern hemispheres have their own polar and subtropical jets. The speed of the jet stream depends on the temperature gradient. Greater the temperature difference, greater is the speed. While the average speed is around 110mph, speeds up to 250mph have been recorded. The effects of the jet stream were noticed as early as 1883 when the Krakatoa erupted. The smoke and dust that rose up high into the atmosphere was carried a long way and was tracked over several years. In 1920s, a Japanese meteorologist, Wasaburo Oishi, used balloons to track these winds. The first man to fly solo around the world in 1933, American pilot, Wiley Post, noticed that sometimes his ground speed greatly exceeded his air speed. However, the real understanding of the jet streams is credited to WW II pilots who flew repeated sorties and found tail winds in excess of 100mph.
There is another interesting story about Sir Richard Branson when he and Per Lindstrand successfully attempted flying across the globe in a balloon. When flying across the Pacific, as luck would have it, they had lost two-thirds of the fuel but had another 7000 miles to cover. They had two options, resign to fate and wait to get drowned in the Pacific or try to get into a jet stream and cross the Pacific. Per Lindstrand was an experienced balloonist and they somehow managed to catch a jet stream. However as soon as they got into the Jetstream, the balloon which was more than 6 storeys high rocketed ahead horizontally with the capsule being pulled behind!! The airspeed shot up from 70mph to 230mph! They missed their target landing area, Los Angeles, by 4000 miles and landed up in the Arctic but survived. Also, mountaineers, trying to scale peaks like the Mt. Everest routinely encounter jet streams clocking more than 100mph. They have no option but to stay put in the tents.
The jet stream does affect the climate. In some regions it is known to have caused hurricanes while the Hawaiian Islands have mostly managed to avoid those due to jet streams. While the aviation sector has been using these to cut down on fuel and time, scientists are finding out ways to harness the potential wind energy to generate power. It is estimated that only 1 percent of the wind energy in the jet streams is sufficient to meet the world’s energy needs! However, the technology might take another 15-20 years to develop. The bleak side of the story is, the jet streams are expected to get weaker as a result of global warming. Hope we learn from our past mistakes and stop messing around with mother nature so that we are able to take advantage of this wonderful phenomenon. Long live the jet stream!