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Courtesy of University Corporation for Atmospheric Research

Rain

Rain is precipitation that falls to the Earth in drops of 5mm or more in diameter according to the US National Weather Service. Virga is rain that evaporates before reaching the ground.

Raindrops form when millions of tiny water droplets collide together in clouds to form larger ones. Eventually, they become too heavy and fall out of the clouds as rain.

Nimbostratus clouds and cumulonimbus clouds commonly produce rain. Very small raindrops are called drizzle. Stratus clouds or stratocumulus clouds can sometimes produce a light mist or drizzle.

Although they look like teardrops in cartoons, a raindrop is not really that shape. A raindropís shape is dependent on its size. Typical raindrops are shaped like hamburger buns because of the large air pressure on the bottom of the drop that flattens it. A lower air pressure on the sides of the drop let the raindrop expand in size. The place with the greatest average yearly rainfall in the United States is on the island of Kauai in Hawaii with 40 inches (1 meter).

Have you ever noticed an earthy smell in the air that often comes out before it rains? The odor may be from bacteria in soil that produces an aromatic gas. These gases are pushed into the air as rain falls on the soil. Winds are the reason the smell may hit you before the rain shower.

Acid rain is a mix of water and acidic air pollutants from power plants, factories, houses, and cars. This type of rain can have harmful effects on our ecosystems. Acid rain falls on industrialized areas with large amounts of pollution. It also falls in places that are downwind from air pollution sources.


Last modified October 2, 2008 by Becca Hatheway.

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Evaporation

One process which transfers water from the ground back to the atmosphere is evaporation. Evaporation is when water passes from a liquid phase to a gas phase. Rates of evaporation of water depend on things...more

Nimbostratus

Nimbostratus clouds belong to the Low Cloud (surface to 2000m up) group. They are dark gray with a ragged base. Nimbostratus clouds are associated with continuous rain or snow. Sometimes they cover the...more

Cumulonimbus

Cumulonimbus clouds belong to the Clouds with Vertical Growth group. They are generally known as thunderstorm clouds. A cumulonimbus cloud can grow up to 10km high. At this height, high winds will flatten...more

Drizzle

Drizzle is light precipitation that is made up of liquid water drops that are smaller than rain drops. Drizzle can be so light that only a millimeter of water falls to the Earth's surface in one day. It...more

Stratus

Stratus clouds belong to the Low Cloud (surface-2000m up) group. They are uniform gray in color and can cover most or all of the sky. Stratus clouds can look like a fog that doesn't reach the ground....more

Stratocumulus

Stratocumulus clouds belong to the Low Cloud (surface-2000m) group. These clouds are low, lumpy, and gray. These clouds can look like cells under a microscope - sometimes they line up in rows and other...more

Wind

Wind is moving air. Warm air rises, and cool air comes in to take its place. This movement creates different pressures in the atmosphere which creates the winds around the globe. Since the Earth spins,...more

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