Disclaimer: This post has some really cool photos
A bad weather, storm, thunder and lightning-the perfect recipe to scare the senses off the person unlucky enough to be out during such weather. But behind all this chaos, is a lot of physics, and art. Despite the fact that thunder and lightning might scare you away, there is no denying the beauty and astonishing scene of these events, especially when they are in their full glory. A few days ago, a friend of mine in my hometown Dehradun, made a really amazing time-lapse video of an hour-long thunderstorm, and the 5 second long video was a treat to the eyes. The moment I saw it I had to share it on my blog, so I took screen shots of all the seven lightnings that happened(Each unique in its own way!), and posted them below. But before moving to them, let’s learn some science(Just 5 minutes read, c’mon!).
A brief physics of thunderstorms: It would be wise to mention here that we still don’t know a lot(seriously!) about the actual processes behind the event, so I will skip the details, and try to paint a very basic picture to you. There exists a voltage difference of 1 volt/cm between the surface of earth and the top most level of atmosphere. This 0.4 million volt electric field is constant throughout the planet, varying globally with time, peaking at 7 p.m London time. The total current due to this field is around 1800 amperes! The reason you don’t feel it is because you are grounded to the earth, and so at the zero potential, this equipotential prevents any movement of current in you. This current is mostly due to light ions fromed due to various chemical processes and cosmic rays from outer space, and their presence in the air is what makes it conducting. But calculations show this field should be discharged within an hour! So what has kept it here for so long? Answer: Thunder storms. When lightning strikes the surface of earth, it delivers huge amount of charge which is enough to maintain an average of 1800 amperes of current. To understand lightning, we need to start from the beginning, the creation of a thunderstorm. Thunderstorm clouds are made of individual areas, called ‘cells’. These thunderstorm cells evolve owing to the same processes in different times. A cell consists of bottom hot air, which keeps rising up, continually being displaced by the sinking heavy and cold air. The rising hot air is also accompanied by air from the sides of the cell.When this process continues for long, after a certain time, the cell’s bottom is sufficiently cold, and the updraft is somewhat balanced by the downdraft. This is signalled by the cold weather before the storm. Till now the water drops and ice particles were small and light enough to prevent from falling, but has they bundle up, their weight increases and they begin to fall down. Now brave pilots who have flown through a thunderstorm, say that the top of the cloud is positively charged while the bottom is negatively charged with the accumulation of positive charge in a locally region. Why and how this positive charge is their among the negative charges is a mystery, perhaps because of the downdraft from the higher regions, we don’t know. The positive charge extends upto 6-5 kilometres while the negative charge extends upto 3-4 kilometres. The charge is sent down through the water and ice particles falling down, but how exactly this happens is still unknown. But scientists predict this might be due to the interactions with the ehavy and light ions present in the air, discussed above. The final result of the process is that negative charge through the water (which is a dipole itself) is delivered down, while the updraft carries the slow moving heavy ions and the positive charge back up. Now, we talk about the main attraction, the lightning. We now know that a build up of charge has taken place and is delivered down. Using Boys Camera, we found out that lightning actually takes place in two parts. The first part is the ‘step-ladder’, which is seen as a bright dot originating in the bottom of the cloud extending downwards(but is very dim compared to the actual lightning), but it pauses for around 50 microseconds after every 50 metres or so, and falls in ‘steps’. This path formed is actually a network of negative charge, a conducting wire between the cloud and the Earth. As soon as the step-ladder touches the surface of Earth, the negative charge is drained into the Earth, and this movement of negative charges cause a current to flow in the opposite direction. This current is the flash of lightning, the main lightning that you see. It actually travels from down to up, and so is called a ‘Return Stroke’. Clearly you and I thought the other way round. This bright stroke results in the powerful discharge and heating up of surrounding air, ionizing it, which is seen as a brightly coloured flash of light. A few moments later, another stroke, called the dark ladder, this time from cloud to the surface of Earth runs down the exactly same path as the previous stroke using the remaining debris charge which is enough. There can be sometimes upto 5 to 10 dark ladders! More than often it happens that the step ladder branches off into two or more separate step ladders, and the one to touch the ground first is responsible for the return stroke, but if in this time another of the new step ladders reaches the surface, the dark ladder is takes this new wire path, and hence sometimes the dark ladder is seen distinctly from the step ladder. In the pictures below you can clearly see these happening! These lightnings deliver upto 20-30 coloumbs of charge, of thousands of ampere current, in a potential difference of 30, 40 and sometimes even 100 million volts, which is obviously far high than the 0.4 million volts between our Earth and the upper atmosphere. Nature is truly incredible!
Since now you know the science, its time to admire the art. So here are the pictures from her video that she posted in her instagram, in order of their occurrence(These are screenshots so the quality isn’t as good as the original pics) :
And all this time I thought lightning was supposedly bluish in colour, and I was honestly shocked to find out that here it is magenta, or a shade of pink. If you compare the last pic when everything subdued, with other pictures, you can see how the lightning lit up the houses and especially the area with street lights on the right. When it’s too cloudy to stare at the stars, hope for thunderstorms and learn to admire the beauty in one of natures most scary phenomenons! Happy reading.
-The Cosmogasmic Person