The default condition is a combination of cumulus and stratus clouds.

默认状态的组合是积云和层云。

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Simulation results show that targets can be found more easily in cumulus or stratus than in undulance cloud, because undulance cloud is more abrupt change in its intensity.

结果显示，在积状云和层状云背景中的目标识别较容易，在波状云中的目标识别较难。

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Low in the sky there's the classic cotton wool Cumulus, the Stratus, a layer of "rather dull" cloud, and higher up Cirrus - "a translucent delicate streak as if a watercolour brush has been stroked across the blue".

BBC: Weather talk: Is there a way to make it interesting?