Warm Up 3/19/07

1. Warm Up 3/19/07 • What is true about warm, saturated air? • It contains less water vapor than cold air. • It contains more water vapor than cold air. • It contains the same amount of water vapor as cold air. • It does not contain any water vapor. • Which term describes the conversion of a solid directly to a gas, without passing through the liquid state? • Evaporation • Sublimation • Condensation • Deposition • Rain, snow, sleet, and hail are all examples of ____. • Evaporation • Condensation • Precipitation • Deposition

2. Cloud Formation Chapter 18. Section 2

3. Air Compression and Expansion • Temperature changes that happen even though heat isn’t added or subtracted are called adiabatic temperature changes • When air is allowed to expand, it cools, and when it is compressed, it warms • Any time a volume of air moves upward, it passes through regions of successive lower pressure • Dry Adiabatic Rate – the rate of adiabatic warming or cooling in unsaturated air (1ºC/100 m) • Wet Adiabatic Rate – the rate of adiabatic temperature change in saturated air; it is always less than the dry adiabatic rate

4. Cloud Formation by Adiabatic Cooling

5. Orographic Lifting and Frontal Wedging • Four mechanisms that can cause air to rise are orographic lifting, frontal wedging, convergence, and localized convective lifting • Orographic Lifting – mountains acting as barriers to the flow of air, forcing the air to ascend • Many of the rainiest places on Earth are located on windward mountain slopes • By the time the air has reached the leeward side of the mountain, much of its moisture has been lost • Front – the boundary between two adjoining air masses having contrasting characteristics • The cooler denser acts as a barrier over which the warmer, less dense air rises

6. Orographic Lifting

7. Frontal Wedging

8. Convergence and Localized Convective Lifting • Whenever air in the lower atmosphere flows together, lifting results, this is called convergence • This leads to adiabatic cooling and possibly cloud formation • On warm summer days, unequal heating of Earth’s surface may cause pockets of air to be warmed more than the surrounding air • Consequently, this warmer, less dense packet will move upward • These rising parcels of warmer air are called thermals • The process that produces rising thermals is localized convective lifting • When warm parcels rise above the condensation level, clouds form

9. Convergence

10. Localized Convective Lifting

11. Stability • Stable air is any air which resists vertical movement due to density differences • Stable air tends to remain in its original position, while unstable air tends to rise • Air stability is determined by measuring the temperature of the atmosphere at various heights • The rate of change of air temperature with height is called the environmental lapse rate • Temperature Inversion – a layer where the temperature increases with height; the most stable conditions for air • Clouds associated with the lifting of unstable air are towering and often generate thunderstorms and tornados

12. Stable Atmosphere and Adiabatic Rate

13. Absolute Stability

14. Absolute Instability

16. Condensation • Recall that condensation happens when water vapor in the air changes to a liquid in the form of dew, fog, or clouds • For any of the forms of condensation to occur, the air must be saturated • Generally, there must be a surface for water vapor to condense on • Condensation Nuclei – tiny bits of particulate matter that serve as surfaces on which water vapor condenses • When condensation takes place, the initial growth rate of cloud droplets is rapid • It diminishes quickly because the excess water vapor is absorbed by numerous competing particles • This results in the formation of a cloud consisting of millions upon millions of tiny water droplets

17. Cloud Condensation Nucleus

18. Assignment • Read Chapter 18, Section 2 (pg. 510-516) • Do Section 18.2 Assessment #1-7 (pg. 516)