Todays lecture objectives:

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ATMS 305 Atmospheric Thermodynamics and Statics

• Todays lecture objectives
• Adiabatic Processes (WH 3.4)
• How can the First Law of Thermodynamics really
  help me to forecast thunderstorms?

?
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ATMS 305 Adiabatic Processes

• Todays lecture topics
• Adiabatic Processes (WH 3.4)
• Concept of an air (Polly) parcel
• The adiabatic lapse rate
• Potential temperature
• Poissons Equation
• Application of Poissons Equation
• The pseudoadiabatic chart

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First Law of Thermodynamics
change in internal energy
work done
heat added
other forms
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First Law of Thermodynamics

• Types of Processes
• Isochoric (or Isosteric)
• Isobaric
• Isothermal
• Adiabatic (this lecture)

(courtesy F. Remer)
5
First Law of Thermodynamics

• Types of Processes
• Isochoric (or Isosteric)
• Isobaric
• Isothermal
• Adiabatic (this lecture)

(courtesy F. Remer)
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ATMS 305 Adiabatic Processes

• Heat can be added to Polly by many processes
  (radiation, friction, condensation of water vapor
  later, turbulent transfer of heat), however

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ATMS 305 Adiabatic Processes

• These processes are often of secondary importance
  for time periods up to a day

(courtesy F. Remer)
8
ATMS 305 Adiabatic Processes

• Therefore, there is value in applying the First
  Law of Thermodynamics for adiabatic processes

Processes in which no heat (dq) is added or
withdrawn from a system (Polly Parcel), so that
her change in temperature is a result of
expansion and compression
Many processes in the atmosphere are dry
adiabatic
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ATMS 305 Adiabatic Processes
A
B, C
Volume at tf
Volume at ti
10
Poissons Equation

• General form of Poissons Equation
• relates initial conditions of pressure and
  temperature to final pressure and temperature

http//www.hgtv.com/hgtv/ah_personal_care_safety/a
rticle/0,,HGTV_3149_1390664,00.html
NOT poison
(courtesy F. Remer)
11
Application of Poissons Equation

• Example - Cabin Pressurization
• Jet airplanes are pressurized to 8,000 ft (770
  mb). If outside air temperature at a cruising
  altitude of 30,000 ft (300 mb) is -40oF, what
  is the final temperature?

(courtesy F. Remer)
12
Application of Poissons Equation

• Example - Cabin Pressurization
• TInitial -40oF -40oC 233oK
• TFinal ?
• PInitial 300 mb
• PFinal 770 mb

(courtesy F. Remer)
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Application of Poissons Equation

• Example - Cabin Pressurization
• TInitial 233oK
• TFinal ?
• PInitial 300 mb
• PFinal 770 mb

(courtesy F. Remer)
14
Application of Poissons Equation

• Example - Cabin Pressurization
• TInitial -40oF -40oC 233oK
• TFinal 305K 32oC 90oF
• PInitial 300 mb
• PFinal 770 mb

(courtesy F. Remer)
15
Application of Poissons Equation

• Many processes in the atmosphere are dry
  adiabatic
• vertical motions
• thermals

(courtesy F. Remer)
16
ATMS 305 Adiabatic Processes

• Pseudoadiabatic chart
• Area of most relevance is in the portion shown
  within the dotted lines
• Sloping black heavy lines are the dry adiabats
  (lines of constant potential temperature)

Note the actual temperature of the air at 1000
mb is equal to its potential temperature.
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Application of Poissons Equation

• Comparing the temperature at different altitudes
• Relatively warmer or colder?

-37oC
300 mb
2oC
600 mb
(courtesy F. Remer)
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Application of Poissons Equation

• Bring to same level
• Compress 300 mb air to 600 mb

-37oC
300 mb
2oC
600 mb
(courtesy F. Remer)
19
Application of Poissons Equation

• TInitial -37oC 236K
• TFinal ?
• PInitial 300 mb
• PFinal 600 mb

-37oC
300 mb
2oC
600 mb
(courtesy F. Remer)
20
Application of Poissons Equation

• Compare

-37oC
300 mb
15oC
2oC
600 mb
Warmer or Colder
Stable or Unstable
(courtesy F. Remer)
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Potential Temperature

• Compress air to 1000 mb
• Standard
• Avoids using an arbitrary pressure level

1000 mb
(courtesy F. Remer)
22
Potential Temperature

• Example
• Compare the air at two different levels
• 900 mb and 21oC
• 700 mb and .5oC

(courtesy F. Remer)
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Potential Temperature

• 900 mb and 21oC (294K)

(courtesy F. Remer)
24
Potential Temperature

• 700 mb and .5oC (273.5K)

(courtesy F. Remer)
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Potential Temperature

• 900 mb and 21oC
• q 302 K
• 700 mb and .5oC
• q 303 K
• Air is the same!

(courtesy F. Remer)
26
Potential Temperature

• Potential temperature can act as a tag or air
  tracer

(courtesy F. Remer)
27
Potential Temperature

• Potential temperature can act as a tag or air
  tracer

(courtesy F. Remer)
28
Potential Temperature

• Rising Thermal of Air
• Parcel Potential Temperature is Constant

z
Dry Adiabatic Lapse Rate
T
(courtesy F. Remer)
29
Potential Temperature

• Potential temperature is constant in the mixed
  layer

Mixed Layer
q Const.
(courtesy F. Remer)
30
Potential Temperature

• Measure of Stability
• Statically Stable

1000 mb
(courtesy F. Remer)
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