close to the ground

Consequently, as they are close to the ground - which is also below zero - the next time they hit a surface the droplet will freeze creating a layer of ice.

And they’re flying perilously close to the ground, sometimes no higher than 100 feet.

Even relatively minor damage could prove fatal because, flying so close to the ground, the pilots would have almost no time to react.

This is a recurring problem in northern India every winter, where low temperatures between December and January trap pollutants close to the ground - which affects visibility - making travel difficult and the air hazardous.

This is because hydroxyl radicals form in the atmosphere close to the ground during the day when the sun shines.