十万个为什么·科学阅读30篇（4）
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Why Do Some Clouds Appear Green Before Severe Thunderstorms?
为什么强雷暴来临前某些云会呈现绿色？
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Green clouds often appear before tornadoes or hailstorms in humid, mid-latitude regions.
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Sunlight passes through thick, water-laden storm clouds that absorb red wavelengths more strongly.
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The remaining blue and green light mixes to produce a distinct emerald or jade hue near the cloud base.
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This effect requires specific lighting angles, cloud depth, and high liquid water content to occur.
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Meteorologists do not consider green clouds a guaranteed tornado sign, but they signal dangerous conditions.
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Photographers and storm chasers use this visual cue to anticipate severe weather development.
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Laboratory experiments confirm that suspended water droplets scatter green light preferentially under certain densities.
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Satellite imagery rarely captures this color because it depends on ground-level viewing geometry.
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Green cloud observations are most common in the US Great Plains during spring and early summer.
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Scientists continue studying how aerosol composition might enhance or suppress this optical phenomenon.