Upward Lightning

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    • Brazilian researchers recently succeeded in taking pictures of positive upward discharges of electricity from lightning conductor rods in São José dos Campos.

    What is 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.

    Lightening and its Strike Procedure

    • Definition:
      • Lightning is a very rapid — and massive — discharge of electricity in the atmosphere, some of which is directed towards the Earth’s surface. 
      • These discharges are generated in giant moisture-bearing clouds that are 10-12 km tall. 
      • The base of these clouds typically lies within 1-2 km of the Earth’s surface, while their top is 12-13 km away. 
      • Temperatures towards the top of these clouds are in the range of minus 35 to minus 45 degrees Celsius.
    • Procedure: 
      • As water vapour moves upward in the cloud, the falling temperature causes it to condense. Heat is generated in the process, which pushes the molecules of water further up.
      • As they move to temperatures below zero degrees celsius, the water droplets change into small ice crystals. 
      • They continue to move up, gathering mass — until they are so heavy that they start to fall to Earth.
      • This leads to a system in which, simultaneously, smaller ice crystals are moving up and bigger crystals are coming down.

    • Collision: 
      • Collisions follow, and trigger the release of electrons — a process that is very similar to the generation of sparks of electricity. 
      • As the moving free electrons cause more collisions and more electrons, a chain reaction ensues.
      • This process results in a situation in which the top layer of the cloud gets positively charged, while the middle layer is negatively charged. 
    • Electrical difference between two layers: 
      • The electrical potential difference between the two layers is huge — of the order of a billion to 10 billion volts. 
      • In very little time, a massive current, of the order of 100,000 to a million amperes, starts to flow between the layers.
    • Enormous heat release: 
      • An enormous amount of heat is produced, and this leads to the heating of the air column between the two layers of the cloud. 
      • This heat gives the air column a reddish appearance during lightning. As the heated air column expands, it produces shock waves that result in thunder.
    • Reaches Earth:
      • While the Earth is a good conductor of electricity, it is electrically neutral. 
      • However, in comparison to the middle layer of the cloud, it becomes positively charged. As a result, about 15%-20% of the current gets directed towards the Earth as well. 
      • It is this flow of current that results in damage to life and property on Earth.
    • Lightning strikes more on: 
      • There is a greater probability of lightning striking tall objects such as trees, towers or buildings. 
      • Once it is about 80-100 m from the surface, lightning tends to change course towards these taller objects. 
      • This happens because air is a poor conductor of electricity, and electrons that are travelling through air seek both a better conductor and the shortest route to the relatively positively charged Earth’s surface.

    Source: IE