Raindrops condense around microscopic pieces of material called cloud condensation nuclei CCN. CCN can be particles of dust , salt , smoke , or pollution. Brightly colored CCN, such as red dust or green algae, can cause colored rain. Because CCN are so tiny, however, color is rarely visible. When rain forms around certain types of pollutants, such as sulfur dioxide and nitrogen oxide , the CCN react with water to make the rain acidic.
This is called acid rain. Acid can harm plants, aquatic animals like fish and frogs, and the soil. Sulfur dioxide and nitrogen oxide can be released into the atmosphere naturally, such as through a volcanic eruption.
These pollutants can also be released by human activity, such as the burning of fossil fuel s. Burning fossil fuels can influence rain patterns. In urban area s, where many vehicles are on the road at once, rainfall is more likely during the weekend than during the week. This is because during the week, millions of cars release exhaust into the atmosphere, creating billions of CCN in the clouds.
By the end of the week, clouds are much more likely to be saturated with moisture and CCN. Scientists have developed a process called cloud seeding to "plant" CCNs in clouds to cause rain.
Cloud seeding would reduce drought , although there is very little evidence that it works yet. Although most people think raindrops look like teardrops, they actually look more like chocolate chip cookies. Like raw balls of dough dropped on a cookie sheet, the smallest raindrops, up to 1 millimeter in diameter , are actually spherical. At 2 millimeters raindrops start to flatten, because of the air pressure pushing up on them as they fall to Earth.
This effect is increased at 3 millimeters, and depressions form on the bottom of the drops as the air pushes up on the drops harder. At 4 millimeters raindrops actually distort into a shape that looks like a parachute.
When they get to be about 4. Raindrops measure 0. Drizzle , which is smaller than rain, consists of drops smaller than 0. Most of Earth's precipitation falls as rain. Raindrops often begin as snowflake s, but melt as they fall through the atmosphere. Snow forms in the same way rain does, but in colder conditions. Rain falls at different rates in different parts of the world. Dry desert regions can get less than a centimeter 0. The world record for the most rain in a single year was recorded in Cherrapunji, India, in , when 2, centimeters inches of rain fell.
Animal Rain It may not rain cats and dogs, but sometimes it rains tadpoles and tiny fish. This strange meteorological event is probably caused by waterspouts, basically tornadoes that form over water. Waterspouts start out as vortexes, or columns of rotating, cloud-filled wind.
As the vortex descends over an ocean or lake, small aquatic animals may be swept up in the waterspouts funnel. Changes in pressure and wind force the waterspout to change back into a low-lying cloud, emptying precipitationincluding any creatures swept up in the waterspoutover a nearby landmass. But what makes clouds? Water vapor turns into clouds when it cools and condenses—that is, turns back into liquid water or ice. In order to condense, the water vapor must have a solid to glom onto. In the cloud, with more water condensing onto other water droplets, the droplets grow.
When they get too heavy to stay suspended in the cloud, even with updrafts within the cloud, they fall to Earth as rain. However, if the layers of atmosphere within the cloud, and between the cloud and the ground, alternate between warmer than freezing and colder than freezing, you get other kinds of precipitation.
It can go round and round, adding more and more layers of new ice. If the updrafts in a thunder cloud are strong enough, the hail stones can get pretty big before they become too heavy to stay up. Hail stones can range from pea size to golf ball size, and up! A new record for the largest hailstone ever was set in ! It fell on July 23, in Vivian, South Dakota.
It was 8 inches in diameter, That could put a real dent in your day! They look more like kidney beans when falling to the Earth. Very large rain drops larger than 4. These extra-large drops usually end up splitting into two smaller droplets. The indents on raindrops are caused by air resistance. Precipitation is always fresh water, even when the water originated from the ocean. This is because sea salt does not evaporate with water.
However, in some cases, pollutants in the atmosphere can contaminate water droplets before they fall to the Earth. The precipitation that results from this is called acid rain. Acid rain does not harm humans directly, but it can make lakes and streams more acidic. This harms aquatic ecosystems because plants and animals often cannot adapt to the acidity. Acid rain can be manmade or occur naturally. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
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