1. Today’s Agenda Quick In-class Practice Quiz
Review up to material in the last lecture

2. Temperature Questions
What causes annual and diurnal temperature variations?
Do hottest/coldest temperatures occur during maximum/minimum input of solar radiation?
What physical processes modulate temperature variations?

3. Atmospheric Composition Mass, Density, Pressure Vertical Structure
The Blue Marble
ATMO Lecture
Atmospheric Composition Mass, Density, Pressure Vertical Structure
Photo from Apollo 17

4. What is air made of? N2 and O2 are most abundant
variable
N2 and O2 are most abundant
Concentrations (except O3) are constant up to ~80 km
N2 and O2 are chemically active, continuously cycled
Ar, Ne, He, and Xe are chemically inert trace gases
H2O, CO2, CH4, N2O and O3 important greenhouse gases

5. Aerosols Natural and Anthropogenic Sources

6. Fundamental Concepts Three properties that characterize the air
Mass – amount of matter; inertia
Density – mass/volume
Pressure – force per area

7. How Pressure Changes with Height
1 mb
48 km - 1 mb
32 km - 10 mb
16 km mb
0 km mb
log 100 = 0
log 101 = 1
log 102 = 2
log 103 = 3
48 km
±16 km
10x change
10 mb
32 km
±16 km
10x change
100 mb
16 km
±16 km
10x change
This relationship can be easily quantified by noting for
For every 16 km in altitude ☞ pressure decreases by a factor of ten.

8. Barometer and Altimeter
Android App
iPhone App

9. Vertical Temperature Change Defines layers of the atmosphere
inversion
isothermal
6.5oC/km
Environmental Lapse Rate
Rate at which observed temperature decreases with height
Inversion
Temperature decreases with height
Isothermal
Temperature constant with height
Ahrens

10. ATMO 170 Lecture Weather and Climate
Surface analysis for Z

11. What is Weather? Weather – The state of the atmosphere:
at a specific location
for a moment in time
Weather Elements
1) Temperature
2) Pressure
3) Humidity
4) Wind
5) Visibility
6) Clouds
7) Significant Weather
Automated Surface Observing System
Tucson International Airport

12. Responsible for underlined parameters
Surface Station Model
Responsible for underlined parameters
Temperatures
Plotted °F in U.S.
Sea Level Pressure
Leading 10 or 9 is not plotted
Only the 3 rightmost digits are plotted w/o decimal point
Example above:
mb plotted as 107
common wx
rain snow fog
thunderstorms
Decoding Station Model
Practice from CIMMS

13. Weather vs. Climate
Weather - atmospheric conditions at specific time and place
Think Snapshot
Climate - average weather and the range of extremes compiled over many years
Think Statistics

14. ATMO 170 Lecture Temperature vs. Heat Heat Transfer
A boiling pot of water illustrates all modes of heat transfer

15. Energy and Heat Transfer
Energy can only
converted from one form to another or transferred from one place to another
Total energy is conserved
1. Energy can only be converted from one form to another or transferred from one place to another. It cannot be created or destroyed.
2. Energy transfer is done from hot to cold

16. Energy and Heat Transfer
Temperature – a measure of the average speed of molecules
Internal Energy – energy an object has due to the movement of its atoms and molecules
Heat (Transfer) – energy transfer due to temperature differences
Heat flows from warmer => colder
Equilibrates temperature differences

17. Modes of Heat Transfer Three primary modes of heat transfer
Conduction – molecule to molecule
Convection – vertical transport of fluid
Advection => horizontal transport +
Latent Heat – energy of phase changes
Large for H2O Vapor <=> Liquid
Works with fluid motions
Radiation – electromagnetic waves

18. ATMO 170 Lecture Laws of Radiation
Depiction of Van Allen belt that protects earth from harmful radiation from the sun

19. Radiation
All mass that has a temperature greater than 0 K, emits radiation.
This radiation is in the form of electromagnetic waves, produced by the acceleration of electric charges.
These waves do not need matter in order to propagate; they move at the “speed of light” (3x108 m/sec; 186,000 miles/sec) in a vacuum
Radiation -
Any object that has a temperature greater than absolute zero (0 K), emits radiant energy. The radiation is in the form of waves that have both electric and magnetic properties. Thus, they are called electromagnetic wave.
The waves are produced by electric charges moving.
This means of energy transfer does not involve matter, but instead electro-magnetic waves that travel at 300,000 km/sec. This is the major method of transferring energy from the sun to the earth, and at this rate it takes about 8 minutes for radiation to travel from the sun to the earth.

20. Electromagnetic Waves
Important aspects of waves are:
Wavelength: Distance between peaks.
Amplitude: Height of crests
Frequency: # waves that pass a point in one second
Period: Time it takes one wave to pass a point
The picture of electromagnetic waves passing through the atmosphere is much like that of the waves on the surface of the water. There are threeimportant aspects about the waves:
What kind of wave is it? Wavelength or distance between the peaks of the waves.
How fast is the wave moving? Measured by how many crests pass a fixed location in one second.
How big is it? Amplitude or distance between peaks and valley. When more radiation is emitted, the amplitude increases.
Wavelength
Distance
btw peaks
Amplitude Height of crests/troughs
Frequency # crests per unit time

21. Electromagnetic Spectrum
WAVELENGTH
FREQUENCY
meteorological significance
The electromagnetic waves can occurs with any size of wavelength. In meteorology, however, the unit of measure commonly for the EM waves is the micrometer.

22. Plank’s Law: Emission Spectrum Wien’s and Stefan-Boltzmann Laws
Energy from an object is spread unevenly over all wavelengths.
Emission spectrum of Sun
Planck’s Law
Energy Emitted
Wavelength
Ahrens

23. Planck’s Laws
Ahrens 7th ed.
Wien’s => Hotter the object, shorter the wavelength of max emission. Stefan-Boltzmann => Hotter the object, the more radiation emitted.

24. Take Home Points All objects above 0K emit radiation
Hotter the object, shorter the wavelength of maximum emission: Wien’s Law Know it
Hotter objects radiate more energy than colder objects: Stefan-Boltzmann Law Know it
Objects that are good absorbers of radiation are also good emitters.

25. Radiative Equilibrium
Radiation absorbed / emitted by an object increases / decreases the energy of the object.
Increase / Decrease in energy absorbed causes temperature warm / cool
When the energy absorbed equals energy emitted, this is called Radiative Equilibrium.
Corresponding temperature is constant Radiative Equilibrium Temperature.

26. ATMO 170 Lecture Selective Absorption Greenhouse Effect Global Energy Balance
View as Slide Show
An artist’s rendition of the greenhouse effect. What’s wrong with this picture?
Picture link

27. Properties of Radiation
Radiation has four possible fates
Absorbed
Transmitted
Reflected
Scattered
All four are important in the atmosphere

28. A “Grey Body” = Not all wavelengths absorbed Some are. Some are not
A “Grey Body” = Not all wavelengths absorbed Some are. Some are not. This is How the Atmosphere Behaves
SUNLIGHT
(SHORTWAVE)
INFRARED
(LONGWAVE)
EMISSION
GREY BOX
SOME
TRANSMISSION
OF SUNLIGHT
THROUGH BOX
REFELECTION
SCATTERING
FROM BOX
SOME ABSORPTION
OF SUNLIGHT BY BOX

29. To explain selective absorption, we turn to Quantum Mechanics

30. Energy States for Atoms
Electrons can orbit only in permitted states
Each state corresponds to a specific energy level
Only quantum transitions occur between states
Each quantum interval corresponds to a specific wavelength of electromagnetic radiation as electrons accelerate between levels
eV=1.25/λ
microns
Hydrogen Atom
Gedzelman 1980, p 104
0.12
0.66

31. Energy States of Molecules
H2O vibrational modes
Energy States of Molecules
Stretching Scissoring Stretching
Molecules also rotate and vibrate
But at specific frequencies or energy levels only
Quantum intervals between energy levels correspond to specific wavelengths of electromagnetic radiation as electrons accelerate between levels
CO2 vibrational mode

32. Atmospheric Spectrum UV VIS IR UV (<0.3 μm) absorbed by O2 and O3
Visible ( μm) NOT absorbed
Infrared (5-20 μm) selectively absorbed mostly by H2O and CO2

33. Greenhouse Explanation
Greenhouse Effect
0°F
59°F
The presence of the gases in our atmosphere that absorb and emit infrared radiation helps maintain the Earth’s average temperature at about 59°F.
Greenhouse Explanation

34. Atmospheric Energy Balance Complex Balance
Solar
70 in = 70 out 30 reflected
mostly by clouds
Incoming
100
Atmosphere 160 in = 160 out
Infrared
95% absorbed
by air
Ground
147 in = 147 out
Ahrens

35. Primary reason for seasons
Tilt of the Earth’s axis. Affects two things
How “high in the sky” the sun is
Length of daylight
Earth-Sun Relationship (animation)

36. Chicago - hottest time of year occurs one month after summer solstice
Consider Average MAX Temperature for Chicago IL
warming
warming
equilibruim
cooling
USA Today WWW Site

37. Warmest and coldest days of year occur at points of radiative equilibrium
comet.ucar.edu

38. Warmest-Coldest Days Temperature Difference
Lutgens and Tarbuck
Continents undergo larger changes than oceans
High latitudes undergo larger changes than low latitudes

39. Daily Range of Temperatures
Ahrens 6th ed.
MAX-MIN difference decreases with height
Cycle is “felt” up to ~1 km

40. Why do daily MAX-MIN occur when they do?
When incoming Solar exceeds outgoing IR
Temperature rises
When outgoing IR exceeds incoming Solar
Temperature falls
When outgoing IR equals incoming Solar
Radiative equilibrium
Temperature peaks
MAX occurs
Late afternoon
MIN occurs
After sunrise
Ahrens

41. Controls of Temperature
Elevation
Latitude
Land vs. Ocean
Prevailing Wind

42. Take Home Points
Balance between incoming and outgoing energy controls temperature changes. We typically observe…
Warmest Day in July; Coldest Day in January
MAX is late afternoon; MIN is just after sunrise
Diurnal temp. changes are largest at ground.
Affected by wind, cloud cover, land type
Winter-Summer differences
Largest over interior of continents and high latitudes
Temperature controls
Elevation; Latitude; Land-Sea; Prevailing Wind