Water in the Atmosphere

Water never leaves the Earth. It is constantly being cycled through the atmosphere, ocean, and land. This process, known as the water cycle, is driven by energy from the sun. The water cycle is crucial to the existence of life on our planet.

The Water Cycle

During part of the water cycle, the sun heats up liquid water and changes it to a gas by the process of evaporation. Water that evaporates from Earth’s oceans, lakes, rivers, and moist soil rises up into the atmosphere.

The process of evaporation from plants is called transpiration. (In other words, it’s like plants sweating.)

As water (in the form of gas) rises higher in the atmosphere, it starts to cool and become a liquid again. This process is called condensation. When a large amount of water vapor condenses, it results in the formation of clouds.

When the water in the clouds gets too heavy, the water falls back to the earth. This is called precipitation.

When rain falls on the land, some of the water is absorbed into the ground forming pockets of water called groundwater. Most groundwater eventually returns to the ocean. Other precipitation runs directly into streams or rivers. Water that collects in rivers, streams, and oceans is called runoff.

Water Phase and Molecular Speed Review The image above show how water molecules look in all three phases from a microscopic point of view. Notice the speed of the molecules in each of the phases. Increase Temperature and Increase Particle Speed.

Humidity & Relative Humidity Humidity is the amount of water vapor in the air Humidity is the amount of water vapor in the air Relative humidity is a measure of the amount of water vapor that the air is holding, compared to the amount it can hold at a specific temperature Relative humidity is a measure of the amount of water vapor that the air is holding, compared to the amount it can hold at a specific temperature

Humidity & Relative Humidity When the air is holding as much moisture as it can, it’s said to be saturated When the air is holding as much moisture as it can, it’s said to be saturated

Relative Humidity Relative Humidity Example: At 10 degrees Celsius, 1 cubic meter of air can hold a maximum of 8 grams of water vapor. At 10 degrees Celsius, 1 cubic meter of air can hold a maximum of 8 grams of water vapor. If there actually were 8 grams of water vapor in the air, relative humidity would be 100% and the air would be saturated. If there actually were 8 grams of water vapor in the air, relative humidity would be 100% and the air would be saturated. If there were 4 grams of water vapor in the air, relative humidity would be 50%. If there were 4 grams of water vapor in the air, relative humidity would be 50%.

Relative Humidity In the cool of the morning, the air can’t hold as much moisture. We often have dew on a summer morning In the cool of the morning, the air can’t hold as much moisture. We often have dew on a summer morning Once the air has warmed, the relative humidity drops since the air can hold more moisture Once the air has warmed, the relative humidity drops since the air can hold more moisture

You’ve seen water on the outside of a cold drink? The cold air around the glass causes a lower temperature at which the air is saturated The cold air around the glass causes a lower temperature at which the air is saturated

You’ve seen water on the outside of a cold drink? The temperature at which air is saturated and condensation takes place is the dew point The temperature at which air is saturated and condensation takes place is the dew point

Cloud Formations

How do clouds form? Sunlight causes water to evaporate into the atmosphere. Sunlight causes water to evaporate into the atmosphere. This air containing the water vapor is heated at the surface of the earth and rises. This air containing the water vapor is heated at the surface of the earth and rises. As the air rises, it cools and the water vapor condenses on some form of particulate matter such as dust, ash, or smoke to form clouds. As the air rises, it cools and the water vapor condenses on some form of particulate matter such as dust, ash, or smoke to form clouds. The particulate matter are called Condensation Nuclei. The particulate matter are called Condensation Nuclei.

Condensation on spider webs. Views of early morning Condensation on spider webs. Views of early morning Condensation

Importance of Clouds So, what is a cloud?So, what is a cloud? ~ It is a thick mass of suspended water drops or ice crystals. What do clouds tell us?What do clouds tell us? ~ The presence of clouds in the sky is one type of signal to meteorologists that there will be changes in the weather.

Identifying Clouds To better communicate and understand the many cloud forms in the sky, meteorologists identify clouds based on five basic cloud characteristics: 1. The altitude at which they occur 2. Color 3. Density 4. Shape 5. Degree of cover. From this information, we can identify three basic cloud types and many other common cloud types.

Cloud Type by Altitude- Clouds can also be classified based on their altitude There are three general categories of cloud heights: High Clouds = Cirrus Middle Clouds = Alto Low Clouds = Stratus

Cirrus Clouds thin, white clouds with a wispy or feathery appearance. thin, white clouds with a wispy or feathery appearance. Highest of all clouds forming at 30,000 feet or more above the earth's surface. Highest of all clouds forming at 30,000 feet or more above the earth's surface. Formed by ice crystals. Formed by ice crystals. Cirrus clouds are usually the first sign of an approaching storm. Cirrus clouds are usually the first sign of an approaching storm.

Sun Pillar Cirrus Cloud Phenomenon Sometimes, when the sun is just below the horizon, aligned ice crystals reflect light from their crystal faces. We see the cumulative effect of millions of reflections of this sunlight as a sun pillar.

Cumulus Clouds: Cumulus or fluffy cotton ball looking clouds form when air is forced up rapidly and rises higher. Cumulus or fluffy cotton ball looking clouds form when air is forced up rapidly and rises higher. Usually means fair weather when not very tall Usually means fair weather when not very tall Towering cumulus clouds with flat tops often produce thunderstorms and are called “cumolonimbus clouds” Towering cumulus clouds with flat tops often produce thunderstorms and are called “cumolonimbus clouds”

Stratus Clouds Form in flat layers and are a dull gray color Form in flat layers and are a dull gray color “strato” means ‘spread out’ and these clouds usually cover all or most of the sky evenly. “strato” means ‘spread out’ and these clouds usually cover all or most of the sky evenly. Stratus clouds are formed when air is forced up slowly. Stratus clouds are formed when air is forced up slowly. Called Nimbostratus clouds if they produce drizzle, rain or snow Called Nimbostratus clouds if they produce drizzle, rain or snow

Alto Clouds Altocumulus and Altostratus clouds are “middle-level” clouds that are higher than regular cumulus and stratus clouds but lower than cirrus clouds. Altocumulus and Altostratus clouds are “middle-level” clouds that are higher than regular cumulus and stratus clouds but lower than cirrus clouds.

Cloud Type by Rain Nimbus: any cloud that rains Cumulonimbus: taller, towering versions of cumulus clouds. Their height can be from two to five miles. These clouds often form thunderstorms. Nimbostratus: are often associated with steady precipitation and occur in thick, continuous layers and are often dark gray in color. Nimbostratus: low, flat clouds that are often associated with steady precipitation and occur in thick, continuous layers and are often dark gray in color.

Mrs. Douglass’ Favorite Clouds Cumulonimbus Mammatus--- very unstable atmosphere and they mean conditions are right for TORNADOES to form. Often present with thunderstorms as well. Look like cow udder! Cumulonimbus Mammatus--- very unstable atmosphere and they mean conditions are right for TORNADOES to form. Often present with thunderstorms as well. Look like cow udder!

Cumulonimbus Clouds As seen from Apollo 8

Fog Clouds that form at or near ground Clouds that form at or near ground Often forms when the ground cools after a warm, humid day. Often forms when the ground cools after a warm, humid day. The morning sun “burns” the fog off as the water droplets evaporate. The morning sun “burns” the fog off as the water droplets evaporate. In mountainous areas, fog can form as warm, moist air moves up the mountain slops and cools In mountainous areas, fog can form as warm, moist air moves up the mountain slops and cools

Fog Pictures Ocean Fog Mountain Fog

Forms of Precipitation Precipitation (pre-sip-uh- tay-shun) is any form of water that falls to the Earth's surface. Precipitation (pre-sip-uh- tay-shun) is any form of water that falls to the Earth's surface.

Types of Precipitation The type of precipitation that falls to the ground depends upon the formation process and the temperatures of the environment between the cloud and the surface The type of precipitation that falls to the ground depends upon the formation process and the temperatures of the environment between the cloud and the surface

Precipitation Not all clouds produce precipitation Not all clouds produce precipitation For precipitation to occur, cloud droplets or ice crystals must grow heavy enough to fall through the air. For precipitation to occur, cloud droplets or ice crystals must grow heavy enough to fall through the air. Cloud droplet collect and combine with each other Cloud droplet collect and combine with each other As they grow larger, they move faster and collect more small droplets As they grow larger, they move faster and collect more small droplets When heavy enough, they fall out of the cloud. When heavy enough, they fall out of the cloud.

The different types of precipitation? Rain Rain Snow Snow Hail Hail Sleet Sleet Freezing Rain Freezing Rain

Rain Rain develops when growing cloud droplets become too heavy to remain in the cloud and as a result, fall toward the surface as rain Rain develops when growing cloud droplets become too heavy to remain in the cloud and as a result, fall toward the surface as rain

Rain Rain can also begin as ice crystals that collect each other to form large snowflakes Rain can also begin as ice crystals that collect each other to form large snowflakes As the falling snow passes through the freezing level into warmer air, the flakes melt As the falling snow passes through the freezing level into warmer air, the flakes melt

Rain from snow!

Snow Snow is formed when ice crystals form from water vapor that is in the clouds directly above your heads! Snow is formed when ice crystals form from water vapor that is in the clouds directly above your heads! This process is called sublimation This process is called sublimation

Hail Hail is formed when updrafts carry raindrops upwards into extremely cold areas of the atmosphere Hail is formed when updrafts carry raindrops upwards into extremely cold areas of the atmosphere

Hail There the raindrops merge and freeze. When the frozen clumps get too heavy they fall to earth There the raindrops merge and freeze. When the frozen clumps get too heavy they fall to earth

Hail Hail can vary in size, from the size of a small stone to that of a baseball! So be careful Hail can vary in size, from the size of a small stone to that of a baseball! So be careful

Sleet Sleet is frozen raindrops. Sleet begins as rain or snow and falls through a deep layer of cold air that contains temperatures below freezing that exist near the surface. Sleet is frozen raindrops. Sleet begins as rain or snow and falls through a deep layer of cold air that contains temperatures below freezing that exist near the surface.

Sleet Rain that falls through this extremely cold layer has time to freeze into small pieces of ice Rain that falls through this extremely cold layer has time to freeze into small pieces of ice

Freezing Rain Freezing rain is falling rain that cools below 0°C, but does not turn to ice in the air Freezing rain is falling rain that cools below 0°C, but does not turn to ice in the air The water is “supercooled” The water is “supercooled”

When the drops hit anything they instantly turn to ice!

T H E E N D