ATMOSPHERE

1. ATMOSPHERE Chapter 11

2. Section 11.1 Atmospheric Basics Atmospheric Composition The Earth’s atmosphere extends from Earth’s surface to outer space. It is a blanket of gases that surround the Earth The atmosphere is composed of gases: 78% Nitrogen 21% Oxygen 1% Other Gases (Argon, Hydrogen, Carbon Dioxide, Water Vapor) The amount of water vapor in the atmosphere is constantly changing based on the season, altitude, and features on the ground Solids (dust and salt) combine with water vapor to create clouds Ozone (O3) is a gas formed by the addition of a third oxygen atom to the diatomic oxygen that we breathe. It absorbs ultraviolet radiation from the Sun.

3. Structure of the Atmosphere Troposphere Stratosphere Mesosphere Thermosphere Exosphere

4. Troposphere… Lower Atmospheric Layer • Layer closest to the Earth • Contains most of the mass of the atmosphere • Weather takes place here • Air pollution collects here • Temperatures decrease as you go up, the highest point is between 9-16km (Tropopause)

5. StratosphereLower Atmospheric Layer • Contains the ozone layer • Absorbs most of the ultraviolet radiation • Temperature increases from bottom up • Highest point is 50km (Stratopause)

6. MesosphereUpper Atmospheric Layer • There is no ozone in this layer • Temperature decreases as you rise within the level • The top of the layer is at 80km (Mesopause)

7. ThermosphereUpper Atmospheric Layer • Has only a tiny portion of the mass • Extremely hot – more than 1000o C • You can’t feel the temperatures because the molecules are so far apart (so it wouldn’t feel warm to humans) • The Ionosphere is found within this layer, which contains electrically charged particles and layers of progressively lighter gases.

8. ExosphereUpper Atmospheric Layer • Outermost layer of the atmosphere • Layer where Hydrogen and Helium are found • This layer will gradually turn into outer space • There is no clear boundary between the atmosphere and space, there are fewer and fewer molecules as you increase in altitude until eventually, there are none.

9. Solar Fundamentals • The Sun is the source of all energy in the atmosphere • Energy transfers to Earth in one of three ways: • 1. Radiation • 2. Conduction • 3. Covection

10. Radiation • The transfer of energy through space by visible light, ultraviolet radiation, and other forms of electromagnetic waves • All substances that have temperatures above absolute zero emit radiation • The Higher the temperature of a substance, the shorter the wavelength it emits

11. Conduction • The transfer of energy that occurs when molecules collide • For conduction to occur, substances must be in contact with one another • Energy is transferred from particles of air near the Earth’s surface to the particles of air in the lowest layer of the atmosphere • Conduction affects only a thin atmospheric layer near the Earth’s surface

12. Convection • The transfer of energy by the flow of a heated substance • Pockets of air are heated, become less dense than surrounding air, and rise. As the war air rises, it expands and starts to cool. When it cools, it increases in density and sinks. The process then continues with constant rising and falling of air. • These convection currents are responsible for vertical motions of air, which causes weather.

13. Section 11.2State of the Atmosphere When people discuss the weather, they’re describing the current state of the atmosphere. Atmospheric properties are given to describe weather conditions, such as: Temperature Air Pressure Wind speed Amount of moisture in the air

14. Temperature vs. Heat Temperature Heat • A measurement of how rapidly or slowly molecules move around • Faster molecules have a higher temperature • Slower molecules are cooler • Can be measured in degrees Fahrenheit, degrees Celsius, or Kelvin. • The transfer of energy that occurs because of a difference in temperature between substances • Heat flows from higher temperatures of an object to areas of lower temperature

15. Dew Point • The dew point is the temperature to which air must be cooled at constant pressure to reach saturation • Saturation is when the air holds as much water vapor as possible. • Without saturation, condensation cannot occur. • Condensation occurs when matter changes state from a gas to a liquid.

16. Vertical Temperature Changes • In general, as you go up in the troposphere, the temperature goes down 10 degrees C for ever 1000m increase in altitude. • Lifted Condensation Level (LCL) is the height at which condensation occurs. • The height of LCL often corresponds to the base of clouds.

17. Air Pressure and Density • Temperature is proportional to pressure • Higher temperature  higher pressure • Lower temperature  lower pressure • Temperature is inversely proportional to density • Higher temperature  lower density • Lower temperature  higher density • There is an exception to this rule, known as temperature inversion, because the temperature increases with heigth in an atmospheric layer

18. The concepts of Wind and Relative Humidity Wind Relative Humidity • Cool air is more dense than warm air so it sinks, forcing warm air upward. The differences in density and pressure causes wind • Ultimately, wind is a rush of air that makes an attempt to relieve an imbalance between warm (less dense) air and cool (more dense) air • Wind is faster and stronger at higher altitudes where there are fewer structures to provide friction • The ratio of water vapor in a volume of air relative to how much water vapor that volume of air is capable of holding • Expressed as a percentage • 100% is holding all of the water vapor it can (saturated) • 50% is holding half of the water vapor it can • Varies with temperature • The warmer the air, the more moisture it can hold because there is more space between the air molecules

19. Section 11.3Moisture in the Atmosphere

20. Cloud Formation • Warm (less dense) air rises and cold (more dense) air sinks. Clouds will form when warm, moist air rises, expands, and cools in a convection current. • As the air reaches its dew point, the water vapor in the air condenses around condensation nuclei (small particles in the atmosphere around which cloud droplets can form), they combine with millions of others to form a cloud. • Clouds can also form when wind encounters a mountain and has no choice but to go up. This is referred to as orographic lifting. • When two different air masses meet, this too can create uplift and clouds will form (warm air is pushed up).

21. How quickly an air mass cools is based on its resistance to rising (stable air stays put). This is referred to as stability. • The energy that is transferred to the gas during the change of state is stored in the water vapor and will not be released until condensation occurs. This is referred to as latent heat. • Within a cloud, the process by which cloud droplets collide and join together to form a larger droplet is called coalescence. As this process continues, the droplets become too heavy and gravity eventually takes over… leading to precipitation.

22. Types of Clouds • Clouds are generally classified according to a system developed in 1803. • Low clouds form below 2000m • Middle clouds form between 2000m and 6000m • High clouds form above 6000m

23. Types of Clouds Clouds are named based on their shape: • Cirrus – Wispy, stringy clouds • Cumulus – white, puffy clouds • Stratus – layered sheets of clouds • Nimbus – gray rain clouds, low in the sky • Fog – cloud that forms in contact with Earth’s surface

24. Precipitation When cloud droplets collide and join together to form a larger droplet it is referred to as coalescence Once droplets become too heavy, they fall to the Earth as precipitation. Precipitation is all forms of water that fall from the clouds. Four main types: • Rain • Snow • Sleet • Hail