Water in the Atmosphere

Earth’s surface is covered mainly by water. Oceans cover about 70% of our planet’s surface.

What is the Water Cycle? Earth has been recycling its water supply for 3 billion years. The Water Cycle is the continuous process by which water moves from Earth’s surface to the atmosphere and back. Driven by energy from the SUN.

2 33

Processes of the Water Cycle 1.The Sun heats up the water in Earth’s oceans and lakes.

Processes of the Water Cycle 2. Evaporation: liquid water changes to a gas called water vapor.

Processes of the Water Cycle Transpiration: water vapor is released by plants.

Transpiration Water vapor is released through stomata found in plants..

Humidity The amount of water vapor in the air is humidity. The warmer the air, the more water vapor that the air can hold. The cooler the air, the less water vapor that air can hold.

Relative Humidity The ratio of the amount of water vapor in the air to the maximum amount of water vapor the air can hold at a set temperature.

Relative Humidity When air holds all of the water that it can at a given temperature, it is said to be saturated. Saturated air has a relative humidity of 100%. Relative humidity can be measured using a psychrometer.

Processes of the Water Cycle 3. Condensation: Warm air carries water vapor upward. The air cools and condenses into liquid water. Tiny droplets of water clump together around tiny dust particles in the air, forming clouds.

Dew Point Dew Point is the temperature at which a gas condenses into a liquid. At its dew point, air is saturated.

Clouds A cloud is a collection of millions of tiny water droplets or ice crystals. Formed through condensation when warm air rises and cools. Classified by form and by altitude.

Three Forms of Clouds Three forms of clouds include cumulus, stratus, and cirrus.

Cumulus Clouds Puffy, white clouds that tend to have flat bottoms. Usually indicate fair weather.

Stratus Clouds Clouds that form in layers. Cover large areas of the sky and often block out the sun. Fog is a stratus cloud that has formed near the ground.

Cirrus Clouds Thin feathery white clouds found at high altitudes. Formed when wind is strong and if they get thicker indicate that a change in the weather is coming.

Clouds and Altitude The prefix Cirro- is used to describe clouds that form at high altitudes. The prefix Alto- is used to describe clouds that form at middle altitudes. The prefix Strato-is used to describe clouds that are layered. Cloud names that include nimbo or nimbus are likely to produce precipitation.

Clouds and Altitude

Processes of the Water Cycle 4. Precipitation: As more water vapor condenses, the drops of water grow larger and heavier. The heavy droplets fall as precipitation (rain, snow, sleet, hail).

Processes of the Water Cycle 5. The precipitation that falls on land may: soak into the soil and become groundwater OR Run off the land, eventually flowing back into the ocean.

Water that falls on the surface may run off into rivers and streams, eventually flowing back to a lake or ocean.

How is Earth’s Water Distributed? About 97% of Earth’s water is salt water found in oceans. Only 3% is freshwater.

How is Earth’s Water Distributed? Ice: most of Earth’s freshwater is locked in thick sheets of ice near the Earth’s poles.

How is Earth’s Water Distributed? Rivers and Lakes: Only 0.02% of Earth’s water, but an important source of freshwater for people who live near them. The Great Lakes contain almost 20% of all the water in Earth’s freshwater Lakes