十万个为什么·科学阅读30篇（2）

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为什么某些云层在暮色中会发出明亮光芒？

Noctilucent clouds form high in the mesosphere, about 80–85 km above Earth’s surface.
They appear only during summer months near polar regions when sunlight reflects off ice crystals.
These tiny ice particles grow on meteoric dust that enters our atmosphere from space.
Unlike lower clouds, noctilucent clouds remain sunlit long after sunset due to their extreme altitude.
Their electric-blue glow results from scattering of blue wavelengths by nanoscale ice grains.
Scientists monitor them closely because increasing frequency may signal changes in upper-atmosphere chemistry.
They are visible only when the Sun is 6–12 degrees below the horizon and the sky is otherwise dark.
Ground observers must face north in the Northern Hemisphere to spot these delicate, wavy structures.
Radar and satellite data confirm their composition includes water ice, not frozen carbon dioxide or ammonia.
Studying them helps us understand how atmospheric gravity waves influence cloud formation far above weather systems.

听 → 读 → 学表达 → 懂 → 今天会说这一句 → 跟读录音 → 自己说一句。

Noctilucent clouds form high in the mesosphere, about 80–85 km above Earth’s surface. 夜光云形成于中间层高空，距地球表面约80–85公里。
Their electric-blue glow results from scattering of blue wavelengths by nanoscale ice grains. 其电蓝色辉光源于纳米级冰粒对蓝光波长的散射。
Scientists monitor them closely because increasing frequency may signal changes in upper-atmosphere chemistry. 科学家密切监测它们，因其出现频率上升可能预示高层大气化学变化。

这篇中文题目最接近哪一句？为什么某些云层在暮色中会发出明亮光芒？一次学校运动会的通知一份超市购物清单

课文第一句的意思更接近？夜光云形成于中间层高空，距地球表面约80–85公里。今天学校放假了。请把窗户打开。

这一课主要在讲什么？（看英文标题） Why Do Certain Clouds Glow Brightly at Twilight? How to cook noodles A maths worksheet

Noctilucent clouds form high in the mesosphere, about 80–85 km above Earth’s surface.

Noctilucent clouds form high in the mesosphere, about 80–85 km above Earth’s surface.

第一版：录下来、回听、再听标准音。系统打分以后再加。

用今天的表达，自己说一句。

例子：Noctilucent clouds form high in the mesosphere, about 80–85 km above Earth’s surface.