A fickle, fiery waterfall

AN ephemeral waterfall only flows at certain times. For example, Horsetail Fall in Yosemite National Park appears in winter and early spring. On clear days in mid- to late February, the setting sun hits the waterfall and briefly turns it into a glowing orange ‘firefall.’ n

THE coastal city of Lima, the capital of Peru, is very humid. But its desert climate means it gets hardly any rain. One solution could be ... billboards? An experimental sign equipped with a filtration panel draws water from the air and provides about 25 gallons a day of drinking water.

“FROST flowers” in Arctic and Antarctic seas can form on a calm ocean surface when very dry air is much colder than the water. These crystallised structures draw so much brine from the sea that they can be three to five times saltier than the water.

A CIRCUMHORIZONTAL arc is sometimes called a ‘fire rainbow,’ but it really forms due to ice. When light shines a certain way through the ice crystals in a high-altitude cirrus cloud, it gets bent, like in a prism, creating a colourful halo that lights up the sky.