万物简史 第368期:进入对流层(9)（在线收听） |
Jet streams, usually located about 30,000 to 35,000 feet up, can bowl along at up to 180 miles an hour and vastly influence weather systems over whole continents, yet their existence wasn't suspected until pilots began to fly into them during the Second World War. Even now a great deal of atmospheric phenomena is barely understood. A form of wave motion popularly known as clear-air turbulence occasionally enlivens airplane flights. About twenty such incidents a year are serious enough to need reporting. They are not associated with cloud structures or anything else that can be detected visually or by radar. They are just pockets of startling turbulence in the middle of tranquil skies. In a typical incident, a plane en route from Singapore to Sydney was flying over central Australia in calm conditions when it suddenly fell three hundred feet—enough to fling unsecured people against the ceiling. Twelve people were injured, one seriously. No one knows what causes such disruptive cells of air. 急流通常位于大约9O0O—10000米高空，能以每小时将近300公里的速度动，极大地影响着所有大陆的天气系统。然而，直到第二次世界大战期间飞行员开始飞进里面，我们才发现它的存在。即使到了现在，还有大量的空气现象我们知道得很少。有一种波动通常被称之为“晴空端流”，它偶尔会造成飞机剧烈颠簸。每年大约有20次这样的事故严重到了需要报道的程度。它们与云团结构或其他任何可以用肉眼或雷达测到的现象没有关系。它们是晴空中小范围的端流。举个典型的例子，一架从新加坡飞往悉尼的飞机正在平静的条件下飞越澳大利亚中部，突然间下降了90米——足以把没有系安全带的人甩到天花板上。12个人受了伤，有一个伤势还很严重。谁也不清楚怎么会有这种制造混乱的小气流。
The process that moves air around in the atmosphere is the same process that drives the internal engine of the planet, namely convection. Moist, warm air from the equatorial regions rises until it hits the barrier of the tropopause and spreads out. As it travels away from the equator and cools, it sinks. When it hits bottom, some of the sinking air looks for an area of low pressure to fill and heads back for the equator, completing the circuit.
空气在大气层里到挫流动的过程，与地球内部机器转动的过程，二者是一样的，即对流。潮湿的热空气从赤道地区升起，碰着了对流层顶就向外扩展。随着远离赤道，它渐渐冷却，渐渐下沉。碰到底都以后，有一部分下沉的空气向低压地方流动，掉头返回赤道，完成了那个环流。 |
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