十万个为什么·科学阅读30篇（2）

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为什么某些雷暴中闪电会从地面向上分叉？

Most lightning appears to strike downward, but it actually begins with invisible upward 'leaders' from tall objects.
When storm clouds build negative charge, the ground below becomes positively charged by induction.
Sharp structures like towers or trees launch positive streamers that reach up to meet descending negative leaders.
The first connection point determines the main lightning path, which then carries massive current downward.
High-speed cameras show upward branching occurs when multiple streamers rise simultaneously from different points.
Tall buildings and wind turbines frequently initiate upward lightning, especially in winter storms.
This type is more common in mountainous regions where terrain enhances electric field concentration.
Scientists install triggered lightning towers to study upward discharges safely and repeatedly.
Upward flashes last longer and transfer more charge than typical cloud-to-ground strikes.
Recognizing this behavior improves lightning protection design for critical infrastructure worldwide.