风是由热空气上升产生真空而引起的空气流动。
Wind is a current of air caused by a vacuum caused by hot air rising.
一个新的研究表明它们飞得很快并全靠自己产生的气流，没有那预想中的上升气流帮它们提升到天空般的高度。
A new study shows that they do it quickly and under their own steam, without the help of upslope tailwinds thought to loft them over the sky-high peaks.
热空气上升，冷空气补充取代之，就产生了对流气流。
As warm air rises cool air is drawn in to replace it creating a convection current.
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