Source : INDIA TODAY NEWS
On June 23, a wall of dust rolled across Delhi in a matter of minutes, swallowing roads and turning the afternoon sky an eerie brown. The India Meteorological Department (IMD) had warned of it only hours earlier.
For Delhi, such scenes have become an almost yearly summer ritual.
So why does the capital keep choking on dust? The answer lies in a tidy collision of geography, heat and physics.
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THE SCIENCE BEHIND DELHI’S DUST STORMS
Delhi sits downwind of the Thar Desert in Rajasthan. Through the scorching summer, the desert floor bakes into fine, loose sand that strong westerly winds lift and carry hundreds of kilometres towards the northern plains.
For centuries, the Aravalli Range stood as a natural barrier, slowing these gritty winds and trapping much of the sand before it could reach the city.
Decades of mining, tree-felling and unchecked construction have punched gaps in this ancient shield, letting more dust sail straight into the National Capital Region.
HOW A STORM IS BORN
A dust storm is really a high-energy thunderstorm. It begins with fierce surface heating. As the ground in north-west India crosses 40 degrees Celsius, the air just above it turns hot and restless.
This sets up a steep lapse rate, the speed at which air cools as you climb higher. The wider the gap between the hot ground and the cold air aloft, the more unstable the atmosphere becomes.
Scientists measure this stored energy as Convective Available Potential Energy, or CAPE, which is simply the fuel a storm draws on.
WHY THE WIND TURNS VIOLENT
Heat alone is not enough. A trigger is needed, usually a passing weather system such as a cyclonic circulation or a western disturbance, which nudges the hot surface air upwards.
Once a towering cumulonimbus, or rain-bearing cloud, builds up, it begins to release rain. In Delhi’s dry summer air, much of that rain evaporates before it reaches the ground. Evaporation cools the surrounding air and makes it heavy, and this dense air comes crashing down as a downdraft.
When it slams into the surface, it bursts outwards in every direction, lifting topsoil and hurling it across the city as a wall of dust. On June 23, these gusts touched 50 to 60kmph in parts of Delhi-NCR.
IS CLIMATE CHANGE TO BLAME?
Dust storms are natural, yet scientists say a warming planet is sharpening their edges. Hotter summers store more energy in the atmosphere, feeding the very instability that drives these storms.
There is no firm agreement that they strike more often, but the heatwaves and volatile conditions behind their fury are clearly growing more pronounced. The dust then mixes with the city’s own pollution, pushing air quality to dangerous levels.
A SEASON OF DUST
These storms are a pre-monsoon affair, peaking between March and June. They ease once the monsoon sweeps in, settling the dust and cooling the land.
This year, with the rains running nearly two weeks late, Delhi has had to wait longer for relief.
– Ends
SOURCE :- TIMES OF INDIA
