Upward Lightning

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Context

An event known as “upward lightning” or upward flashes, has been known for long, but the researchers succeeded in photographing it with high-speed video cameras at very high resolution.
The researchers captured the electric action in São José dos Campos, a city northeast of São Paulo in Brazil.

About Upward Lightning

Upward lightning is a phenomenon whereby a self-initiated lightning streak develops from a tall object that travels upward toward an overlaying electrified storm cloud.
For this to happen, storm electrification and the resulting presence of a cloud charge region are enabling factors.
The vertical elevation of a tall object accentuates the electric field locally on the ground, resulting in conditions favourable for the initiation of an upward streak (called a leader) from a tall object, which can also develop in response to an electric field change created by a nearby preceding lightning flash.

Process: Stepped ladder trigger

Simply put, this process is triggered by the development of the stepped leader (essentially a channel of negative charge that travels downward in a zigzag pattern from a cloud, nearly invisible to the human eye) traveling to the ground in a millisecond, leading to an intensification of the positive charge on the ground.
As the streaks of the stepped leader keep streaking towards the ground, the electrical charges between the leader tips and the tops of tall objects on the ground keep on increasing. In due course, these forces cause the air above these tall buildings or towers to ionise and thereby turn more conductive.
With the negative charge repeatedly moving toward the ground, the channel of air just above the tall objects turns positively charged, which starts streaking upwards and is called an upward streamer.
In due course, the negatively-charged, downward-moving stepped leader makes contact with one of the developing positively-charged upwards streamers.

PRACTICE QUESTION

Q. What do you understand by the concept of Upward Lightning? How is it different from Lightning? Explain the mechanism in detail.