Adiabatic ProcessesAdiabatic Processes

Created By:Created By:

Mr. KreegerMr. Kreeger

Homework and Page Homework and Page ReferencesReferences

Textbook-Page 484, Review Book-Page Textbook-Page 484, Review Book-Page 576576

HW #1- Explain why there is a difference HW #1- Explain why there is a difference between the dry adiabatic lapse rate and between the dry adiabatic lapse rate and the moist adiabatic lapse rate.the moist adiabatic lapse rate.

Explain the conditions responsible for Explain the conditions responsible for Absolute stabilityAbsolute stability Absolute instabilityAbsolute instability Conditional instabilityConditional instability

Table of ContentsTable of Contents

1.1. Adiabatic changes in temperatureAdiabatic changes in temperaturea)a) Rising and Subsiding airRising and Subsiding air

b)b) Dry airDry air

c)c) Moist airMoist air

d)d) Types of stabilityTypes of stability1.1. Absolute stabilityAbsolute stability

2.2. Absolute instabilityAbsolute instability

3.3. Conditional instabilityConditional instability

2.2. Lapse RateLapse Rate

1. Adiabatic changes in 1. Adiabatic changes in temperaturetemperature

Adiabatic temp change Adiabatic temp change is any change in temp is any change in temp of a system with out of a system with out any heat being added any heat being added or removed from that or removed from that system.system. Letting air out of tire-Letting air out of tire-

Gas expands temp goes Gas expands temp goes downdown

Filling tire with air-Gas Filling tire with air-Gas compressed and heatedcompressed and heated

Rising and Subsiding AirRising and Subsiding Air

1. RISING AIR EXPANDS AND COOLS

Higher P

Lower P

High P

High P

2. SUBSIDING AIR IS COMPRESSED AND WARMSLower P

Lower P

Higher P (surface)Low P

1b. Dry Air1b. Dry Air

When dry air rises When dry air rises or descends, it’s or descends, it’s temp changes temp changes adiabatically at a adiabatically at a rate of 10C per km. rate of 10C per km. (Dry adiabatic (Dry adiabatic Lapse Rate)-DALRLapse Rate)-DALR

1c. Moist Air1c. Moist Air

When moist air rises When moist air rises and cools to dew point and cools to dew point condensation occurs condensation occurs and clouds form.and clouds form. Until clouds form parcel Until clouds form parcel

follows DALR(10C/km)follows DALR(10C/km) Because latent heat is Because latent heat is

released during released during condensation, moist air condensation, moist air cools at a slower rate cools at a slower rate 6C/km(moist adiabatic 6C/km(moist adiabatic lapse rate) MALRlapse rate) MALR

Diagram showing what occurs Diagram showing what occurs to air as it moves over a to air as it moves over a

mountainmountain

Dry and Moist Adiabatic Lapse Dry and Moist Adiabatic Lapse RateRate

The DALR is The DALR is steeper than the steeper than the MALRMALR When dewpoint and When dewpoint and

temp not equal temp not equal parcel follows DALRparcel follows DALR

When dewpoint and When dewpoint and temp are equal temp are equal parcel follows MALRparcel follows MALR

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Temperature (C)

Alt

itu

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bove s

urfa

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Moist adiabatic Rate (-6°C / km)

Dry adiabatic Rate (-10°C / km)

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Temperature (C)

Altitude (above surface, m

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Types of stabilityTypes of stability

DistinctionsDistinctions Environmental lapse rate-Environmental lapse rate- Observed Observed

temp change with height, measuredtemp change with height, measured DALR, MALR-DALR, MALR- the rates at which a the rates at which a

unsaturated / saturated parcel of air is unsaturated / saturated parcel of air is expected to cool as it rises in the expected to cool as it rises in the atmosphereatmosphere

Absolute StabilityAbsolute Stability

When When Environmental lapse Environmental lapse rate is less than the rate is less than the moist adiabatic moist adiabatic lapse ratelapse rate

Rising parcel always Rising parcel always cooler than cooler than surrounding air, has surrounding air, has tendency to fall tendency to fall back to groundback to ground

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Absolute InstabilityAbsolute Instability

Environmental lapse Environmental lapse rate is greater than rate is greater than dry adiabatic lapse dry adiabatic lapse rate.rate.

Ascending air Ascending air always less dense always less dense than surrounding than surrounding air, wants to air, wants to continue to risecontinue to rise

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Conditional InstabilityConditional Instability

When When environmental environmental lapse rate is lapse rate is between DALR and between DALR and MALR.MALR.

Unsaturated parcel Unsaturated parcel is stableis stable

Saturated parcel is Saturated parcel is unstableunstable

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In GeneralIn General

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UnstableStable

2. Lapse Rate2. Lapse Rate

Parcel of air risesParcel of air rises cools cools capacity to hold water capacity to hold water vapor decreasesvapor decreases RH RH increases.increases.

Moist air rises and Moist air rises and condenses, releasing latent condenses, releasing latent heat (540cal/gm)heat (540cal/gm)slows slows rate of cooling. Keeps rate of cooling. Keeps rising air low in density and rising air low in density and warmer than surrounding warmer than surrounding airair sustains rising motion sustains rising motion

Tops of T-storms can Tops of T-storms can penetrate stratospherepenetrate stratosphere