Why can charges move from a cloud in the sky downwards the ground?

I know the principle of it, but I don't know the difference between it and the things about induced emf in a conductor.

There's an emf induced when a conductor cuts magnetic field lines generally and emf is induced.

But, taking lightning to be considered, both of them are not involved in a complete circuit, so why there's a difference?

The magnitude of the emf induced?

The cloud becomes electrostatically charged.

 

This creates a potential difference between the cloud and the ground, which when great enough causes a spark aka lightning.

Isn't the distribution of charges in a conductor(open circuit)also uneven causing an emf?

In a conductor charges will generally evenly distribute themselves across the conductor. This is because the electrons are free to move and if they were all in one area they would repel each other until they are as far away from each other as possible ie. spread across the whole conductor.

 

It is because of this that if you have a charged sphere then the charge will tend to accumulate on the surface of the sphere. Because the charge repels itself until it is as far away from itself as possible, ie. at the surface of the sphere. But that's kinda irrelevant now.

 

Clouds are not conductors they are insulators anyway.