Warm Up 3/14Warm Up 3/141) Which gas is most important for understanding atmospheric

processes?a. water vapor c. carbon dioxideb. oxygen d. ozone

2) What is true about warm, saturated air?a. It contains less water vapor than cold air.b. It contains more water vapor than cold air.c. It does not contain any water vapor.d. It contains the same amount of water vapor as cold air.

3) If the water-vapor content of air remains constant, lowering air temperature causes a(n) ____.a. decrease in relative humidityb. increase in relative humidityc. increase in evaporationd. temperature inversion

Answers: 1) a. 2) b. 3) b.Answers: 1) a. 2) b. 3) b.

Cloud FormationCloud Formation

Chapter 18. Section 2Chapter 18. Section 2

Air Compression and ExpansionAir Compression and Expansion Temperature changes that happen even though Temperature changes that happen even though

heat isn’t added or subtracted are called heat isn’t added or subtracted are called adiabatic adiabatic temperature changestemperature changes

When air is allowed to expand, it cools, and when When air is allowed to expand, it cools, and when it is compressed, it warmsit is compressed, it warms

Any time a volume of air moves upward, it passes Any time a volume of air moves upward, it passes through regions of successive lower pressurethrough regions of successive lower pressure

Dry Adiabatic Rate –Dry Adiabatic Rate – the rate of adiabatic the rate of adiabatic warming or cooling in unsaturated air (1warming or cooling in unsaturated air (1ºC/100 m)ºC/100 m)

Wet Adiabatic Rate –Wet Adiabatic Rate – the rate of adiabatic the rate of adiabatic temperature change in saturated air; it is always temperature change in saturated air; it is always less than the dry adiabatic rateless than the dry adiabatic rate

Cloud Formation by Adiabatic Cloud Formation by Adiabatic CoolingCooling

Concept CheckConcept Check

What happens to heat stored in water vapor What happens to heat stored in water vapor when it is cooled to its dew point?when it is cooled to its dew point?

Latent heat is released.Latent heat is released.

Orographic Lifting and Frontal WedgingOrographic Lifting and Frontal Wedging Four mechanisms that can cause air to rise are Four mechanisms that can cause air to rise are

orographic lifting, frontal wedging, convergence, orographic lifting, frontal wedging, convergence, and localized convective liftingand localized convective lifting

Orographic Lifting –Orographic Lifting – mountains acting as barriers mountains acting as barriers to the flow of air, forcing the air to ascendto the flow of air, forcing the air to ascend

Many of the rainiest places on Earth are located Many of the rainiest places on Earth are located on windward mountain slopeson windward mountain slopes

By the time the air has reached the leeward side By the time the air has reached the leeward side of the mountain, much of its moisture has been of the mountain, much of its moisture has been lostlost

Front –Front – the boundary between two adjoining air the boundary between two adjoining air masses having contrasting characteristicsmasses having contrasting characteristics

The cooler denser air acts as a barrier over which The cooler denser air acts as a barrier over which the warmer, less dense air risesthe warmer, less dense air rises

Orographic LiftingOrographic Lifting

Frontal WedgingFrontal Wedging

Convergence and Localized Convective LiftingConvergence and Localized Convective Lifting Whenever air in the lower atmosphere flows Whenever air in the lower atmosphere flows

together, lifting results, this is called together, lifting results, this is called convergenceconvergence This leads to adiabatic cooling and possibly cloud This leads to adiabatic cooling and possibly cloud

formationformation On warm summer days, unequal heating of Earth’s On warm summer days, unequal heating of Earth’s

surface may cause pockets of air to be warmed surface may cause pockets of air to be warmed more than the surrounding airmore than the surrounding air

Consequently, this warmer, less dense packet will Consequently, this warmer, less dense packet will move upward move upward

These rising parcels of warmer air are called These rising parcels of warmer air are called thermalsthermals

The process that produces rising thermals is The process that produces rising thermals is localized convective liftinglocalized convective lifting

When warm parcels rise above the condensation When warm parcels rise above the condensation level, clouds formlevel, clouds form

ConvergenceConvergence

Localized Convective LiftingLocalized Convective Lifting

Concept CheckConcept Check

What are thermals?What are thermals? Thermals are rising parcels of air that are Thermals are rising parcels of air that are

warmer than surrounding air.warmer than surrounding air.

StabilityStability Stable air is any air which resists vertical movement Stable air is any air which resists vertical movement

due to density differencesdue to density differences Stable air tends to remain in its original position, while Stable air tends to remain in its original position, while

unstable air tends to riseunstable air tends to rise Air stability is determined by measuring the Air stability is determined by measuring the

temperature of the atmosphere at various heightstemperature of the atmosphere at various heights The rate of change of air temperature with height is The rate of change of air temperature with height is

called the environmental lapse ratecalled the environmental lapse rate Temperature Inversion –Temperature Inversion – a layer where the a layer where the

temperature increases with height; the most stable temperature increases with height; the most stable conditions for airconditions for air

Clouds associated with the lifting of unstable air are Clouds associated with the lifting of unstable air are towering and often generate thunderstorms and towering and often generate thunderstorms and tornadostornados

Stable Atmosphere and Adiabatic Stable Atmosphere and Adiabatic RateRate

Absolute StabilityAbsolute Stability

Absolute InstabilityAbsolute Instability

Concept CheckConcept Check

What types of weather can result when What types of weather can result when stable air rises?stable air rises?

Clear weather may occur or light-to-Clear weather may occur or light-to-moderate precipitation.moderate precipitation.

CondensationCondensation Recall that condensation happens when water vapor Recall that condensation happens when water vapor

in the air changes to a liquid in the form of dew, fog, or in the air changes to a liquid in the form of dew, fog, or cloudsclouds

For any of the forms of condensation to occur, the air For any of the forms of condensation to occur, the air must be saturatedmust be saturated

Generally, there must be a surface for water vapor to Generally, there must be a surface for water vapor to condense oncondense on

Condensation Nuclei –Condensation Nuclei – tiny bits of particulate matter tiny bits of particulate matter that serve as surfaces on which water vapor that serve as surfaces on which water vapor condensescondenses

When condensation takes place, the initial growth rate When condensation takes place, the initial growth rate of cloud droplets is rapidof cloud droplets is rapid

It diminishes quickly because the excess water vapor It diminishes quickly because the excess water vapor is absorbed by numerous competing particlesis absorbed by numerous competing particles

This results in the formation of a cloud consisting of This results in the formation of a cloud consisting of millions upon millions of tiny water dropletsmillions upon millions of tiny water droplets

Comparative DiametersComparative Diameters

AssignmentAssignment

Read Chapter 18 (pg. 504 – 522)Read Chapter 18 (pg. 504 – 522) Do Chapter 18 Assessment #1-30 (pg. 527-Do Chapter 18 Assessment #1-30 (pg. 527-

528)528)