Cyclone karma

Chennai is located in the tropical zone of the planet and, as such, doesn’t experience a stiff difference between the high temperatures of summer and the lower temperatures of winter. All year long, its location ensures that sufficient quantities of heat are available for the continuous evaporation of water from the seas, which then blow inland resulting in high humidity. During winter, however, a drop in atmospheric temperature – however small – ensures that the ocean is slightly warmer than itself. At this stage, when the water saturated with water vapour rises upward, it moves from a warmer environment to a much cooler one, and condenses.

When water exists in its gaseous form as vapour, the water molecules moved around erratically. This motion is represented as potential energy of the gas. When the vapour turns into liquid because of the colder temperature, its motion through the air can no longer be erratic. Therefore, the potential energy is lost into the upper atmosphere as heat. As more and more saturated water rises from the sea to a higher altitude, more heat is lost, eventually resulting in the formation of a heated “ball”. Because it is warmer, it has a lower density than its surroundings, causing winds blowing in its vicinity to start spiraling into it.

When this process has happened over the span of a few days, the spiralling vortex of air becomes so forceful that it assumes a cyclonic nature. The heat core becomes what is called the “eye of the storm”, which is constantly fed by air currents rising from the sea, whereas the winds blowing around it become the arms of the cyclone. Now, a tiny fraction of the heat lost upon condensation of water vapour is converted to mechanical energy. In other words, the air current rises, cools, loses heat, speeds up, and gathers more water vapour – like a positive feedback loop. In this manner, once a cyclone is born, it sustains itself at a faster and faster rate until the temperature rises and the heat core is forced to collapse.

The reasons cyclones are getting more erratic in the tropical belt, and especially around the Indian subcontinent, are of two kinds.

The first reason is global warming. Since global warming has caused an increase in the temperature of the oceans, more cyclones can form irrespective of what seasons it is, summer or winter. Consequently, the intensity of the cyclone increases as more water is evaporated from the warmer seas, making them dense and slow. When a cyclone stays in the same region for too long, the cyclonic winds tend to cool the water body beneath, sometimes up to a depth of 60 metres. Even a temperature drop of 5 degrees Celsius can kill the cyclone raging above by starving the heat core in a matter of hours.

The second reason, and one more relevant to us, is dust. Because of the fast winds that a cyclone generates, sometimes up to 15 m/s, dust on the ground is whipped up into the atmosphere. Dust particles have a grainy, coarse surface that scatters sunlight in different directions, reducing the amount of direct heat that can be absorbed by oceans to warm up. When the ocean isn’t warm enough, a cyclone is prevented from forming. Another outcome is that when the dust particles reach the heat core of the storm, they absorb the heat and cool the core down. When the temperature in the core drops, despite still being warm enough, the cyclone partially weakens. However, the weakening process is usually at an accelerated pace, which means once a cyclone starts to weaken, it goes all the way and kills itself.

While still being one of the greener cities of India, deforestation is excessive in the city, and its consequences are appearing directly in the amounts of rain we receive: sometimes too much, sometimes too little. If there were more trees, the soil that would have supported it wouldn’t have become loose and turned into dust, in the process causing havoc in the airs.