The Electrical Storm

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Let us begin by reviewing the generation of a lightning stroke and its interaction with structures and objects on the ground.

In order for lightning to form, the weather must become unstable, which means that a drastic difference between the pressure and the temperature in the atmosphere must develop, thereby allowing the movement of a rising packet of air to become self-sustaining. The condition of this updraft exists in the cumulonimbus, the thundercloud.

Inside the cumulonimbus, the updraft separates the charged by carrying the finer positively-charged precipitation to higher altitudes, while the heavier negatively-charged precipitation falls to the floor of the cloud. most the electrical discharges happen between the negative cloud and the positive earth.

Meanwhile , back on the ground, the atmospheric electric field escalates to rates over 10kV/m, and a corona effect develops on particular structures such as buildings. Within the negative storm cloud, a downward leader form and moves in steps towards the ground.

As the downward leader advances towards earth, the collective action of the high electric field at the ground and the ionization of the corona effect generate a positive upward moving streamer, which emanate from certain structures or objects such as lightning conductors.

When the upward moving streamer connect with the downward leader, the ionized path between the cloud and the earth is complete and the main discharge current, called the return stroke, flow into the ground. The final length of the upward streamer is called the striking distance. (title of Bruce Willis movie ??)