Science – Lightning up

I suspect humanity consists of two types of human beings – those who find major lightning storms strangely fascinating and the remainder that find them slightly terrifying. A few weeks ago, the Auckland region experienced an exceptional electrical storm and being a member of the former type of human, my immediate reaction was to set up my camera mounted against a living room window overlooking the Kaipara Valley.

Contemporary scientists (2021) believe that zillions of lightning strikes over billions of years could have unlocked phosphorus, which is an element essential to life on our planet and on other planets. Phosphorus plays a vital role in the origin of life as a key element in amino acids that make up the complex building blocks of life: DNA, RNA, proteins and ATP. The mineral schreibersite, which consists of iron, nickel and phosphorus, is considered an essential source of phosphorus for the emergence of life on the early earth.

The science of a lightning strike to earth can be understood in stages – storm clouds exhibit separated electrostatic charges arising from the up and down movement of water droplets and ice crystals, with the lowest part of the clouds carrying negative charges and the upper parts positive charge. The increasing negative charges on the cloud base induces the formation of a positive layer of charge on the land surface below. This induced land layer charge becomes concentrated at the tips of those features that project towards the negatively charged bottom of the clouds such as tall buildings, church towers and large trees.

When the potential difference (voltage) between the bottom of the cloud and projecting land features reaches a threshold, an ionized channel is formed in the atmosphere between cloud and ground. Then a stepped leader (a small zone of charged molecules, invisible to the eye) moves in 50 to 100 metre steps between the cloud and the ground creating an ionized pathway for the lightning flash to follow. It is possible for a visible second and third flash to follow the first flash down the charged channel within 200 milliseconds. In the case of a single lightning strike to earth, that strike has a duration of 0.2 second and is made up of many faster flashes of about 0.060 second duration.

The apparent colours of some lightning flashes are thought to arise from one of two causes. Firstly, the two molecules that are the main components of our atmosphere emit colours (blue and deep red for nitrogen; red and green for oxygen) when they shed energy after being energised (for example, by lightning). This is related to the origin of colours in an aurora. Secondly, the white light of a lightning strike can also be refracted by rain droplets which behave like a prism, into the colours of the visible spectrum.

Finally, here are some situations to avoid if lightning is around – do not use a land line phone, remove yourself from elevated areas, avoid lying flat on the ground, do not shelter under a tree, avoid taking shelter in a cave or rocky overhang and get away from bodies of water. In summary, go indoors fast or, if that is not possible, get into your car. Do not take lightning lightly!