1. Weather Notes Weather is the condition of Earth’s
atmosphere at a particular
time and place.
Atmosphere the envelope of gases that surrounds the planet.
Composition of the Atmosphere
A. Earth’s atmosphere is made up of the following:
1. Nitrogen 78%
2. Oxygen 21%
3. Carbon Dioxide .03%
4. Water Vapor
5. Particles

2. B. Earth’s atmosphere makes conditions on Earth suitable for living things.
C. The atmosphere keeps most of Earth’s surface warm enough for water to exist as a liquid.
D. Earth’s atmosphere protects living things from dangerous radiation from the sun.
II. Properties of Air
A. Air is made up of atoms and molecules.
B. The amount of mass in a given volume of
air is called density.
Density = Mass/Volume
C. The force pushing on an area is called pressure.

3. D. Air pressure is the result of the weight of a column of air pushing down on an area. The column of air extends upward through the atmosphere.
E. Denser air exerts more pressure than less dense air.
Measuring Air Pressure
A. Barometer instrument that
measures air pressure.
1. Mercury barometer
2. Aneroid barometer
Altitude and the Properties of Air
A. Altitude or elevation is the distance above sea level.
1. Air pressure decreases as altitude increases.

4. 2. Air pressure decreases as density decreases.
3. Fewer oxygen molecules to breathe at a high altitude than at sea level.
Layers of the Atmosphere
Scientists divide Earth’s atmosphere into 4 main layers classified by changes in temperature.
They are the: 1. troposphere
2. stratosphere
3. mesosphere
4. thermosphere
A. The troposphere is the layer of the atmosphere in which Earth’s weather occurs. As altitude increases in the troposphere, the temperature decreases.

5. B. The stratosphere is the second layer of the atmosphere and contains the ozone layer. The ozone layer is important because it protects Earth’s living things from ultraviolet radiation from the sun.
C. The mesosphere is the third layer of the atmosphere. It protects Earth’s surface from being hit by most meteoroids.
D. The thermosphere is the outermost layer of Earth’s atmosphere. It extends outward into space.
1. Ionosphere – the lower layer of the thermosphere. Energy from the sun causes gas molecules in the ionosphere to become electrically charged particles called ions.
2. Exosphere – the outer portion of the thermosphere.

6. Thermal Energy and Temperature
A. Temperature is a measure of how hot or cold a substance is. It is the average amount of energy of motion in the particles of a substance.
B. Thermal energy is the total energy of motion in the particles of a substance.
C. Thermometers measure temperature. They work because liquids expand when they are heated and contract when they are cooled.
1. Celsius scale – used by scientists
2. Fahrenheit – used by US
D. Radiation, conduction and convection work together to heat the troposphere.

7. E. Convection currents, the upward movement of warm air and the downward movement of cold air, move heat throughout the troposphere.
Wind and Water in the Atmosphere
A. Wind the horizontal movement of air from an area of high pressure to an area of lower pressure.
1. Winds are caused by differences in air pressure.
2. Anemometer measures wind speed.
3. Wind-chill factor is the increased cooling a wind can cause.
4. Local winds blow over short distances. They are caused by the unequal heating of Earth’s surface within a small area.

8. 5. Global winds are winds that blow steadily from specific directions over long distances. They occur over a large area.
B. Humidity measure of the amount of water vapor in the air.
C. Relative humidity is the percentage of water vapor that is actually in the air compared to the maximum amount of water vapor the air can hold at a particular temperature.
1. Psychrometer measures relative humidity using two thermometers, a wet-bulb and a dry-bulb.
Clouds and Precipitation
A. Clouds form when water vapor in the air condenses to form liquid water or ice crystals.

9. B. Molecules of water vapor in the air become liquid water in the process of condensation.
C. Three main types of clouds based on shape:
1. Cirrus – wispy, feathery cloud formed at high levels.
2. Cumulus – look like fluffy rounded piles of cotton; form less than 2 km above.
3. Stratus – flat layers of clouds that cover most of the sky and are dull, gray in color.
D. Precipitation include the following 5 types:
1. rain
2. sleet
3. freezing rain
4. snow
5. hail

10. E. Scientists measure precipitation with various instruments including rain gauges and measuring sticks.
Air Masses and Fronts
A. Air Mass a huge body of air that has similar temperature, humidity, & air pressure at any given height.
B. Front – the boundary where air masses meet.
1. cold front – a fast-moving cold air mass overtakes a warm air mass.
2. warm front – a warm air mass overtakes a slow-moving cold air mass
3. stationary front – cold and warm air masses meet, but neither can move the other.
4. occluded front – a warm air mass is caught between two cooler air masses.

11. Storm – violent disturbance in the atmosphere.
A. A thunderstorm is a small storm often accompanied by heavy precipitation and frequent thunder and lightning.
1. Lightning – is a sudden spark as electrical charges jump between clouds.
2. Thunder – is the sound of the air expanding suddenly and explosively.
3. You see lightning before you hear thunder because light travels faster than sound.
Click here to view lightning
B. A tornado is a rapidly whirling, funnel- shaped cloud that reaches down from a storm cloud to touch Earth’s surface.

12. 1. Wind speeds up to 500 km/h.
2. May only touch ground for 15 minutes.
3. Develop in thick cumulonimbus clouds, just like thunderstorms.
C. A hurricane is a tropical cyclone that has strong winds of 120 km/h.
1. Begins over warm ocean water as a low pressure area.
2. Draws energy from the warm, humid air at ocean’s surface.
3. Can last one week or longer.
Click here to view hurricanes
tornado video
Joplin tornado
Hurricane Katrina
Hurricane Sandi