🌧️ 降水：云长大到托不住就下雨🌧️ Precipitation: When Clouds Can't Hold On
上一片里，小水汽跟着🌍蓝色星球向导变成了云。云越长越大，有一天气流托不住了——这一片看它掉下来。Last leaf, little Vapor became a cloud with the 🌍 blue-planet guide. Clouds keep growing until one day the updraft can't hold them — this leaf watches them fall.
第 1 步：雨雪冰雹三兄弟Step 1: The three falling brothers
云里的小水滴越长越大，气流终于托不住——掉下来时会变成谁？Droplets grow until the updraft gives up — who do they become on the way down?
掉下来时是水，就是雨；冻住了，就是雪；被上升气流抛上抛下、越冻越大，砸下来的就是冰雹。山坡挡住云逼它上升，下的叫地形雨；地面晒热、空气自己往上冲，下的叫对流雨，夏天的暴雨多是它。Falling as water — rain. Falling frozen — snow. Tossed up and down by updrafts, freezing bigger each round — hail smashing down. Hills forcing clouds uphill make relief rain; sun-baked ground sending air rushing up makes convective rain, the usual summer downpour.
雨有大有小，怎么量？拿尺子量天吗？Rain comes big and small — how do we measure it? With a ruler pointed at the sky?
第 2 步：雨量器量毫米Step 2: The gauge counts millimeters
雨量器就是一个带刻度的杯子，量一天接了多少毫米：不到 2 毫米不算下，10 毫米以下是小雨，25 毫米以上就是大雨。A rain gauge is just a marked cup — how many millimeters fall in a day: under 2 barely counts, under 10 is light rain, over 25 is heavy rain.
如果云迟迟不下雨，人能帮一把吗？If a cloud refuses to rain, can people lend a hand?
第 3 步：飞机帮忙下雨Step 3: Airplanes help it rain
能。飞机飞进云里播撒碘化银，给小水滴送“抱抱核”，水滴长得更快，雨就掉了下来。这叫人工增雨，干旱时帮庄稼解渴。Yes. Airplanes seed clouds with silver iodide — extra hugging nuclei so droplets grow faster and fall. That is cloud seeding, quenching thirsty crops in droughts.
🎮 你来当分级员（30 秒）🎮 Your turn: rainfall grader (30 seconds)
道理讲完了。先转水汽和气流旋钮，看降水类型和毫米数怎么变；再接下面 4 道分级题。Theory done. First turn the vapor and updraft knobs and watch the type and millimeters change; then take 4 grading quizzes below.
一句话记住它：降水 = 云里的水滴长大到托不住而掉落；温度定类型（雨 / 雪 / 冰雹），水汽和气流定毫米数。Remember it in one line: precipitation = droplets growing too heavy for the cloud to hold; temperature sets the type (rain / snow / hail), vapor and updraft set the millimeters.
雨是水、雪是冰晶、冰雹是被抛上抛下冻大的冰球Rain is water, snow is ice crystals, hail is ice tossed and frozen big雨量器量毫米：小雨 / 中雨 / 大雨看数字说话The gauge counts millimeters: light / moderate / heavy, numbers decide地形雨靠山坡，对流雨靠晒热；人工增雨靠碘化银帮忙Relief rain needs hills, convective rain needs baked ground; seeding needs silver iodide
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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