國立自然科學博物館

春日夜晚大雨前閃電的壯觀景象。雷雲（帶電的雲層）對建築物及大地的自然放電引起雷電，天氣悶熱潮濕時，地面的水受熱變為蒸汽，並且隨地面的受熱空氣而上升，在空中與冷空氣相遇，使上升的水蒸汽凝結成小水滴，形成積雲。雲中水滴受強烈氣流吹襲，分裂為小水滴和大水滴。積雲中負電荷在底部蓄積，雷雲底部帶負電，由於靜電感應，在大地表面感應有正電荷。這樣雷雲與大地間形成了一個大的電容器。當電場強度很大，超過大氣的擊穿強度時，即發生了雷雲與大地間的放電，就是一般所說的雷電。

On a spring night, thunderclouds (cloud layer that carries an electrical charge) and lightning appear. When it is warm and muggy, steam and hot air from the ground rise to encounter cold air. Water drops and, subsequently, cumulus form. The water drops in cumulus are subjected to strong air currents and separate into large and small drops. Negative charge accumulates at the bottom of cumulus or thunderclouds. Due to electrostatic induction, there is reaction with positive charge on the earth’s surface and the formation of a large capacitor. When electric field intensity surpasses electrical breakdown strength, electricity is discharged, creating thunder and lightning.

程周平-家朋春雷1