The formation of the channel is initiated when electrons surge from the cloud base toward the ground.

当电子从云层底部涌向地面时，通道就开始形成了。

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The day dawned sunless and with a low cloud base.

黎明时天气阴沉，云层压得很低。

《柯林斯英汉双解大词典》

FYI, one aircraft has landed and reported cloud base 80m, visibility 1km. What is your intention?

通知你，一架飞机降落并报告，云高80米，能见度1公里，你的意图是什么？

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As a parcel of dry air rises, it has to rise farther before it saturates with enough water to form the cloud base.

CNN: Clouds' role in global warming studied

Funnel clouds look like cone-shaped or thin rope-like protuberances which hang down from the cloud base, and often do not last very long.

BBC: Funnel clouds, twisters, tornados: What are they?

Colin Le Ray said the system allowed planes to land in lower visibility by giving guidance to pilots, particularly when the cloud base was low.

BBC: Fog 'causes disruption' at Guernsey Airport