Atmosphere and Weather

Science, Grade 6


Table Of Contents: Atmosphere and Weather

1. Atmosphere Overview

2.1. Composition of the Atmosphere
The layer of gases that surrounds our planet is called the atmosphere. The atmosphere is composed of 78% nitrogen, 21% oxygen and 1% other gases. Water vapor and tiny particles of dust, smoke and other chemicals are also found in the atmosphere.
2.2. Importance of the Atmosphere
The Earth is unique because it has an atmosphere that can support life. Oxygen and gases in the air are necessary for survival. The atmosphere also traps the sun’s energy to maintain moderate temperatures and forms a protective layer from the sun’s radiation.
2.3. Atmospheric Pressure
The force that atmospheric gases exert on a surface is called air pressure, or atmospheric pressure. This pressure is highest near sea level because gravity pulls the air molecules close to the Earth’s surface. As the altitude increases, the air pressure decreases.
2.4. Air Pollution
Humans add pollutants into the atmosphere every day. Natural sources of air pollution include volcanic ash, pollen and wildfire smoke. Air pollutants can travel great distances and impact environments around the globe.

2. Layers of the Atmosphere

3.1. Five Atmospheric Layers
The atmosphere is composed of five main layers—the troposphere, stratosphere, mesosphere, thermosphere and exosphere. Each layer has different characteristics.
3.2. Troposphere
We live in the troposphere. This is the densest layer, containing gas, water vapor, pollution and most weather elements. As altitude increases in the troposphere, the temperature gets colder.
3.3. Stratosphere
The stratosphere is above the troposphere. Higher altitudes of the stratosphere are warmer because they are heated by the sun’s radiation. The ozone layer that filters harmful ultraviolet radiation is found in the stratosphere.
3.4. Mesosphere
The mesosphere is the coldest layer of atmosphere, with some temperatures as low as minus 100 degrees Celsius. Meteoroids burn up in this layer and leave behind trails of glowing gases known as shooting stars.
3.5. Thermosphere
The thermosphere is located in the upper atmosphere, and the temperature gets warmer as the altitude increases. Air particles in this layer are not dense, but they move very quickly. The ionosphere is a part of the thermosphere that contains charged gas particles that create natural light displays called auroras.
3.6. Exosphere
The exosphere is the outermost layer of the atmosphere. Only very light gases, like hydrogen, helium and individual oxygen molecules are found here.

3. Pause and Interact

4.1. Review
Use the whiteboard tools to complete the activity.

4. Weather

5.1. What is Weather?
The condition of the atmosphere at a specific time in a specific place is known as the weather. The weather includes and is affected by temperature, wind, water and air pressure.
5.2. Weather and the Sun
Weather is driven by the energy from the sun. Energy reaches the Earth as electromagnetic radiation. Molecules in the atmosphere and on the Earth absorb this radiation and begin to vibrate, creating heat energy.
5.3. Global Winds
Global winds are created by the differences in temperature and air pressure between the poles and the equator. The curved direction of these winds is caused by the Earth’s rotation and is called the Coriolis effect.
5.4. Water Cycle
The water cycle is the movement of water from the Earth’s surface to the atmosphere and back. The sun’s energy heats water, causing it to evaporate and form water vapor. When water vapor accumulates, clouds will form. Eventually water precipitates out of the clouds and falls back to Earth.
5.5. Humidity
The amount of water vapor in the air is called humidity. Relative humidity is the percentage of water vapor in the air as compared to the maximum possible humidity at a certain temperature. The dew point is the temperature at which the water vapor will condense to form water droplets or ice crystals.

5. Clouds and Precipitation

6.1. Cloud Formation
Clouds form when water vapor condenses and droplets of water or ice crystals accumulate in the atmosphere. Clouds are categorized by their shape and altitude. The three main types of clouds are cirrus, stratus, and cumulus. Each cloud type is associated with different weather.
6.2. Three Main Types of Clouds
Cirrus clouds are thin, wispy clouds that form at high altitudes and are composed of ice crystals. Stratus clouds form in layers that spread across the sky and often bring continuous rain or snow. Cumulus clouds are large, puffy clouds that are typical of fair weather.
6.3. Other Types of Clouds
A cumulonimbus cloud is a very large cumulus cloud that is responsible for thunderstorms and extreme weather. Altocumulus and altostratus clouds form in the middle of the atmosphere, above 6,000 feet. Stratus clouds that form close to the ground are called fog.
6.4. What is Precipitation?
Precipitation is water that has condensed in the atmosphere and falls to the Earth. Rain, sleet, snow and hail are different forms of precipitation. The type that falls depends on the temperature.
6.5. Rain, Sleet, Snow and Hail
Rain typically falls from stratus clouds in the form of a drizzle or mist. Sleet is a mixture of water and ice, while snow is basically water that has crystallized. Hail forms during a thunderstorm when water droplets move through a cycle of rising, freezing and falling inside a cumulonimbus cloud.

6. Weather Patterns

7.1. Air Masses
Air masses are large bodies of air that have similar temperatures and water content throughout. Air masses and their movements determine the regional weather.
7.2. Types of Air Masses
Air masses are named and characterized by the regions where they come from—arctic, polar or tropical. Continental air masses are typically dry and originate over continents. Maritime air masses are wet and originate over oceans.
7.3. Movement of Air Masses
In the United States, wind belts called the westerlies move air masses from west to east. When air masses move and interact with each other, the weather changes. Warm air is less dense, and it will rise when it meets cooler air.
7.4. Cold and Warm Fronts
A weather front is the boundary where two different air masses meet. A cold front occurs when a cold air mass runs into a warm air mass and creates clouds, rain and storms. A warm front occurs when warm air moves into a cold region, causing drizzly rain or light snow and an increase in the humidity.
7.5. Stationary and Occluded Fronts
A stationary front forms when two different air masses meet and show little movement. This can cause several days of precipitation. An occluded front occurs when a warm air mass is caught between two cold air masses. The warm air that moves upward is cut off from the ground and may form clouds.

7. Pause and Interact

8.1. Review
Use the whiteboard tools to complete the activity.
8.2. Cloud Types
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.

8. Severe Weather

9.1. Thunderstorms
Thunderstorms are small high-energy weather systems that create heavy rain, wind and lightning. These storms form when rapidly rising warm air condenses into an electrically charged cumulonimbus cloud. Lightning occurs when electricity is discharged from the cloud.
9.2. Tornadoes
Tornadoes are funnels of high-speed, rotating winds that often develop in cumulonimbus clouds. Tornadoes form when there is a drastic change in wind direction with increasing altitude.Tornado alley is a region in the central United States that has a high frequency of tornadoes.
9.3. Hurricanes
A hurricane is a large, tropical rotating weather system. A hurricane forms when winds moving in different directions collide over warm ocean water. As long as a hurricane is over open water, it has the potential to grow in strength.
9.4. Winter Storms
Winter weather occurs when moisture-rich air masses encounter cold, polar air masses. A snow belt exists in the northern United States along the Great Lakes, where warm water vapor mixes with cold air masses and creates lake-effect snow.

9. Pause and Interact

10.1. Types of Severe Weather
Follow the onscreen instructions.

10. Predicting Weather

11.1. Forecasting the Weather
Meteorologists are scientists who study and predict weather. They use charts, images, computers and weather instrument data to prepare weather forecasts. In the United States, most weather information comes from the National Weather Service.
11.2. Weather Technology
Advances in technology have improved the accuracy of weather forecasting. Doppler radar allows meteorologists to track the location, movement and intensity of precipitation in a region. Weather balloons and satellites provide large amounts of information that is quickly processed by sophisticated computers.
11.3. Weather Maps
Meteorologists use symbols on maps to indicate weather fronts, air pressure, precipitation, and more. Fronts are indicated with a line that has a triangle or half circle pattern. Areas of equal atmospheric pressure are shown using isobar lines and the symbol H or L.

11. Vocabulary Review

12.1. Atomsphere and Weather Vocabulary Matching
Meteorologists are scientists who study and predict weather. They use charts, images, computers and weather instrument data to prepare weather forecasts. In the United States, most weather information comes from the National Weather Service.

12. Virtual Investigation

13.1. Weather Forecasting
In this virtual investigation you will collect weather information, write a weather report and make a weather forecast. To gather weather data, you will explore and read instruments found at a weather station. Observations of the sky and cloud types will also be used as predictors of the weather.

13. Assessment

14.1. Atmosphere and Weather