Desert animals like camels and coyotes might have felt at home in places like Kochi, Kottayam and Punalur this year. Day and night temperatures in various parts of Kerala seem to be mimicking desert-like conditions and are drifting apart like never before this January.
The day-night temperature dichotomy in Kerala this January is not exactly like in a desert, not even close. If in a desert the day time temperature touches 50 degree Celsius, at night the temperature can fall to as dramatically low a level as minus 20 degree Celsius. Kerala has still not shown such a freakish difference. Nonetheless, there are indications that tropical Kerala is tending towards such an abnormality.
Take for instance Punalur, where the temperature variation has historically been the highest. Still, the difference has never crossed 13 degree Celsius. But this time the difference has on certain days been as high as 18 degree Celsius. The day-night dichotomy is sharper in Kottayam. Never before has it been more than 11 degree Celsius. This January, the difference has crossed 16 degree Celsius. Notably, it is the minimum temperature that is going down.
Weak cyclonic swirl
Meteorological experts mainly blame what in atmospheric science is called "the weakening of the polar vortex" for this desert-like phenomenon. Now the sun is closer to the southern hemisphere. This means, the north pole will be at its coldest worst. This chillness creates in the north pole what is called a polar vortex, a whirling anti-clockwise cyclone-like circulation.
"At times, like it happened this year, the polar vortex weakens. When this happens there will be a sudden atmospheric warming over the north pole at the level of the stratosphere, the second major atmosphere level some 40 km from the surface of the earth," said Manoj M, a scientist at Cochin University of Science and Technology (CUSAT).
The earth's atmosphere is a connected entity, it is as if the earth is blanketed in a single quilt. Happenings in one place will have its repercussions in other areas as well. If one part of the quilt is pinched or pulled together, the other stretches. "Similarly, when the stratosphere over the north pole warmed, that over the tropical regions cooled. And this coolness has been transferred down to the troposphere in tropical areas," Manoj said. Result: winter in tropical places like Kerala feels colder.
Genie from the west
There is also something called a "westerly disturbance" set in motion by the polar vortex. This is a westerly wind that whooshes like a genie let loose from the Mediterranean region and brings winter to Northwest India, mainly to Himachal Pradesh and Jammu and Kashmir. "This time, the westerly disturbance has drifted to the peninsular regions in the west of the country, too," Manoj said.
Security breach over earth
This is also the time astronomers consider the most ideal for star gazing. Without a speck of cloud and not much of water vapour in the air, there is virtually nothing that stands between the earth and the cosmos. "When the sky is free of clouds, it is easy for the longwave radiation (the radiation emitted by the earth during the night in the form of infrared waves) to escape without hindrance, leaving the earth colder," said atmospheric scientist S Abhilash. The escape is made easy by an unprecedented low level of humidity in the atmosphere. In places like Kottayam, Kochi and Kannur, the fall in humidity levels is a whopping 25 per cent from the normal.
Conversely, the absence of clouds and humidity allows short-wave radiation from the sun, in the form of ultraviolet rays and visible light, to strike the earth in all intensity, without any inhibition. "As a consequence, day temperatures rise," Abhilash said.
