上一片里，小水汽跟着🌍蓝色星球向导升上天空。这一片看它的变身：从看不见的水汽，变成天上的云。Last leaf, little Vapor rose into the sky with the 🌍 blue-planet guide. This leaf watches the makeover: from invisible vapor to clouds.
第 1 步：三朵云，三种脾气Step 1: Three clouds, three moods
先认识天上的三位常客——长相不同，脾气也不同。Meet the three regulars up there — different looks, different moods.
积云像棉花糖，又白又胖，预示好天气；层云像灰布，盖住太阳就是阴天；卷云是高空的丝缕，又薄又透，全是小冰晶。Cumulus looks like cotton candy — white and chubby, fair weather ahead. Stratus is a gray cloth — hide the sun and the day turns gloomy. Cirrus is a high thin wisp, sheer and see-through, all tiny ice crystals.
你可能会问：看不见的水汽，怎么变成看得见的云？You might ask: how does invisible vapor become a visible cloud?
第 2 步：抱住灰尘，就成云了Step 2: Hug some dust, become a cloud
水汽上升，越往上越冷。冷到一定程度，小水滴就想抱团——抱住空气里的灰尘（凝结核），越聚越多，一朵云就拼出来了。高空太冷，抱成的就是冰晶。Vapor rises and cools. Cold enough, droplets want to clump — hugging dust specks in the air (nuclei), gathering more and more until a cloud takes shape. Way up high it is freezing, so the clumps are ice crystals.
认出三种云有什么用？能帮你看明天的天气。What good is telling the three apart? It reads tomorrow's weather.
第 3 步：看云识天气Step 3: Read the sky
满天小棉花糖，多半是好天气；灰布盖顶，出门带伞；丝缕弯成钩钩云，老人说“天上钩钩云，地上雨淋淋”——雨可能在路上了。Cotton balls everywhere, fair skies likely. Gray cloth overhead, bring an umbrella. Wisps curling into hooks — as the old saying goes, “Hook clouds above, rain is coming.”
🎮 你来当造云师（30 秒）🎮 Your turn: cloud maker (30 seconds)
道理讲完了。先拖湿度和温度滑块，亲手造一朵云；再接下面 4 道认云题。Theory done. First drag the humidity and temperature sliders to make a cloud by hand; then take 4 cloud quizzes below.
一句话记住它：云 = 水汽上升遇冷，抱住灰尘聚成的水滴或冰晶；积云报好天气、层云报阴天、卷云是高空丝缕。Remember it in one line: a cloud = vapor rising and cooling, hugging dust into droplets or ice crystals; cumulus means fair, stratus means gloomy, cirrus is the high wisp.
云是抱团的水滴或冰晶，配方 = 水汽 + 凝结核（灰尘）+ 遇冷Clouds are clumped droplets or ice crystals: vapor + dust nuclei + cooling积云棉花糖 = 好天气；层云灰布 = 阴天；卷云丝缕 = 最高最冷Puffy cumulus = fair; gray stratus = gloomy; wispy cirrus = highest, coldest天上钩钩云，地上雨淋淋——卷云变厚，雨在路上了Hook clouds above, rain on the way — thickening cirrus means rain is coming
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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