天文·每日一图——飞机凝结尾的X形影子
文摘
2024-04-24 09:40
广东
Image Credit & Copyright: Fatih EkmenExplanation: What created this giant X in the clouds? It was the shadow of contrails illuminated from below. When airplanes fly, humid engine exhaust may form water droplets that might freeze in Earth’s cold upper atmosphere. These persistent streams of water and ice scatter light from the Sun above and so appear bright from below. On rare occasions, though, when the Sun is near the horizon, contrails can be lit from below. These contrails cast long shadows upwards, shadows that usually go unseen unless there is a high cloud deck. But that was just the case over Istanbul, Türkiye, earlier this month. Contrails occur all over planet Earth and, generally, warm the Earth when the trap infrared light but cool the Earth when they efficiently reflect sunlight. The image was taken by a surprised photographer in the morning on the way to work.
说明: 这朵云上的庞大X形是怎么来的？它是飞机凝结尾受到下方阳光照射所投射的影子。当飞机航行时，引擎排放的潮湿废气，可在地球冰寒的高层大气凝结成水滴，并可进一步凝结成冰。这些滞留良久的线形水和冰迹，会散射上方的太阳光，因此从下方观看时显得相当明亮。然而在较罕见的情况下，当太阳位于地平线附近时，飞机凝结尾会受到下方的阳光照耀。这些凝结尾向上投射的颀长影子，除非遇到高层云，否则通常隐不可见。而这正是本月稍早，在土耳其伊斯坦布尔上空所看到的景观。地球各地都能见到飞机的凝结尾，当它们吸收红外光时，会让地球变暖，但高效率反射阳光时，却能让地球降温。这幅影像是一位颇为惊讶的摄影者，摄于上班的途中。
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