Closed loop problem for lighting in thunderstorm?

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Discussion Overview

The discussion revolves around the nature of electrical circuits in the context of lightning during thunderstorms. Participants explore whether the flow of current in lightning can be considered a closed circuit, particularly focusing on the role of displacement current and charge neutrality in clouds.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asserts that a closed circuit is necessary for current flow and questions how this applies to lightning, where a clear closed loop is not immediately evident.
  • Another participant introduces the concept of displacement current, suggesting it completes the circuit and relates lightning to an RC circuit model.
  • A participant appreciates the inclusion of displacement current and likens the cloud and Earth to a charged capacitor, with lightning acting as current through a resistor.
  • A question is raised about how clouds regain charge neutrality after electrons escape during lightning, indicating a gap in understanding regarding cloud charge restoration.
  • One participant admits uncertainty about the process of how clouds become charged again, suggesting that expertise from meteorologists might be needed.

    • Areas of Agreement / Disagreement

    Participants generally agree on the importance of displacement current in understanding lightning as a closed circuit, but there is no consensus on how clouds restore charge neutrality after lightning strikes.

    Contextual Notes

    The discussion highlights the complexity of electrical phenomena in thunderstorms, with assumptions about charge dynamics and the role of displacement current remaining partially unresolved.

    Who May Find This Useful

    This discussion may be of interest to those studying atmospheric physics, electrical engineering, or anyone curious about the electrical properties of thunderstorms.

goodphy
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Hello.

As far as I know, every circuit capable to flow current must be closed. In other word, open circuit can not flow the current, obviously. Right now, I would like to know this is also true for lighting in bad weather.

When bottom of the dark and heavy cloud get more and more electron by convectional flow inside the cloud (positive charges are accumulated at the top of the cloud), air breakdown occurs once voltage between cloud and ground overruns breakdown voltage of the air. Then current flows from the cloud to ground. I believe majority carrier of this current is electrons from cloud.

In circuit theory, this current must be within closed circuit. But I don't see what is closed loop in this case. It looks like current flow doesn't requires closed loop at first glancing.

How can I overcome this apparent contradiction?
 
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Don't forget the displacement current. This is the same "current" that goes through a capacitor and was one of the key concepts in the development of Maxwell's equations. As the conduction current goes one direction, the displacement current goes the other direction, completing the closed loop.

From a circuit standpoint you can think of lightning as closing a switch in a RC circuit where the capacitor (cloud/earth) is initially charged and the lightning is the current through the resistor.
 
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Oh thanks. Yes. displacement current must be included to complete the circuit. Equivalent circuit that charged cloud and Earth acts as a charged capacitor and lighting as a current through resistor is just beautiful.

Can I have one more question? Once electrons are escaping from the cloud, cloud has to be charge-neutrality again. How cloud get electrons to restore charges?
 
That is a good question, but unfortunately, I don't know the answer to that part. Maybe some meterologist or weather enthusiast here can describe how the cloud becomes charged.
 

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