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Why does it rain?
Rain is an important part of the water cycle — evaporation, condensation and precipitation — that distributes water all over the earth. The sun heats the earth causing water in the oceans and the ground to evaporate. This turns water into water vapour that becomes part of the atmosphere. Warm air holds quite a bit of water — you may have heard people complain about high humidity. Next the water vapour cools and condenses to form clouds. If the clouds are big enough and have enough water droplets, the droplets bang together and stick like bubble gum, forming even bigger drops. When the drops get heavy, they fall because of gravity. That’s precipitation, and depending on the temperature, it falls as rain, sleet, snow or hail. Water that falls to the earth soaks into the ground and feeds streams and lakes and the cycle starts all over again.
Rain Facts
India,where as much as 87 feet of rain has fallen in one year.
in 2004 — some as large as 10 mm!
In comparison,electrical wiring in a house carries 20-30 amperes.
This is called ’virga’, a phenomenon often seen in hot, dry desert regions.
The Greeks believedthat it was a sign from the gods foretelling war.
What is that smell when it rains?
You must have noticed a distinctive smell in the air after it rains. That’s not rain you smell, its dirt! The piquant, musky odour that hangs in the air emanates from an odorous chemical buried in the soil called 'geosmin' (literally 'earth smell'). When the soil dries out, Actinomycetes, a type of filamentous bacteria, produces the geosmin spores. The wetness and force of rainfall kicks these tiny spores up into the air where the moisture after a rain acts as an aerosol (just like an aerosol air freshener). The moist air easily carries the spores to us so we breathe them in.The bacteria are extremely common and can be found in areas all over the world, which accounts for the universality of this sweet 'after-the-rain' smell. Since the bacteria thrives in moist soil, but releases the spores once the soil dries out, the smell is most acute after a rain that follows a dry spell.
Why do earthworms come out after a rain?
Most people think that earthworms come out of the ground after a rain because their burrows are flooded with water. But earthworms aren’t afraid of water; they can live completely submerged in water for many months, and in fact, die if their skin becomes dried out. What worms are actually afraid of is waterlogged soil, for it contains a substance called carbonic acid, which forms when water combines with certain chemicals in the soil. Carbonic acid enters the worm’s body through openings in its skin and acts like a drug on the worm, eventually even killing it. So it’s carbonic acid and not water that sends earthworms scurrying out of the ground after a rainstorm.
How is a rainbow formed?
During or immediately after a shower of rain, there are thousands of tiny droplets (raindrops) floating around in the air. When light from the sun encounters a water droplet (spherical in shape), it penetrates the outer boundary of the droplet. As it enters, the light is bent (refracted) and scattered (dispersed) into a continuous band of colours. These colours are reflected off the back of the drop again as they pass through the front of the drop once more, thus being bent some more. The angle of bending is different for different wavelengths of light. Red is refracted the least, and violet the most. You will always see the colours of a rainbow in the following order: Red, Orange, Yellow, Green, Blue, Indigo and Violet.A rainbow always appears in front of the observer, whose back is to the sun. Each falling water droplet (raindrops) flashing its colours to the observer for just an instant, before another drop takes its place letting the rainbow appearance remain constant to the observer.
When we see a rainbow, it usually appears arc shaped. However, rainbows are formed as a circle. The light from the sun is being refracted by the droplets over a certain angle (about 42º). The bow shape is actually part of a circle of light that is cut off by the horizon that obstructs it. The lower the sun is in the sky the more one will be able to see of the rainbow (a larger bow). It is however possible to see the full circle of a rainbow at a high altitude such as in an aeroplane. This is due to the fact that the horizon does not block the observer’s view.
How does lightning work?
Lightning is an electric current, and just like the electricity lurking in the outlets in your house, it can be deadly. Within a thundercloud, many small bits of ice bump into each other as they swirl around in the air. All those collisions create an electrical charge. After a while, the whole cloud fills up with electrical charges (usually with a negative charge closest to the earth). Since opposites attract each other, it causes a positive charge to build up on the ground beneath the cloud. The ground’s electrical charge concentrates around anything that sticks up, such as mountains, lone trees, people, or even blades of grass. The charge streaming up from these points eventually connects with a charge reaching down from the clouds, and — zap! —lightning strikes.
What causes thunder?
Thunder is caused by lightning. When a lightning bolt travels from the cloud to the ground it actually opens up a little hole in the air, called a channel. Once the light is gone, the air collapses back in and creates a sound wave that we hear as thunder. The reason we see lightning before we hear thunder, is because light travels faster than sound!Because a lightning bolt is so hot, it superheats the air around it. The air particles quickly expand and contract, so fast that they break the speed of sound and create sound waves, that is, thunder.
