Title: NATS 101 Intro to Weather and Climate Lecture 5 TR Greenhouse Effect Seasons Temperature Variations
1NATS 101Intro to Weather and ClimateLecture 5
TRGreenhouse EffectSeasonsTemperature
Variations
2Absorption
Visible
- Visible (0.4-0.7 ?m) is absorbed very little
- O2 an O3 absorb UV (shorter than 0.3 ?m)
- Infrared (5-20 ?m) is selectively absorbed
- H2O CO2 are strong absorbers of IR
- Little absorption of IR around 10 ?m
atmospheric window
IR
Ahrens, Fig. 2.9
3Total Atmospheric Absorption
Ahrens, Fig. 2.9
- Visible radiation (0.4-0.7 ?m) is not absorbed
- Infrared radiation (5-20 ?m) is selectively
absorbed, but there is an emission window at 10
?m
4Simple Example of the Greenhouse Effect(0 Solar
absorbed, 100 IR absorbed)
Radiative Equilibrium
1 Unit Outgoing IR to Space
1 Unit Incoming Solar
1/2
1/4
1/8
1/16
½ emitted to space ½ emitted to ground
1/16
1
1/2
1/4
1/8
2 Units IR Emitted by Ground
Take Home Point Surface is warmer with
selectively absorbing atmosphere than it would be
without it.
5Global Solar Radiation Balance (Not all Solar
Radiation SR reaches the surface)
30 SR reflects back to space
Albedo percent of total SR reflected
20 absorbed by atmosphere
70 SR absorbed by earth-atmosphere
Ahrens, Fig. 2.13
50 SR absorbed by surface
6Atmosphere Heated from Below
Ahrens, Fig. 2.11 old ed.
Air above ground heats by convection and
absorption of some IR from ground
Net Effect Atmosphere is Heated From Below
Air contacting ground heats by conduction
Ground heats further through absorption of IR
from atmosphere
Solar radiation heats the ground
7Global Atmo Energy Balance
Ahrens, Fig. 2.14
Solar
Atmosphere
Ground
8Summary
- Greenhouse Effect (A Misnomer)
- SFC Warmer than Rad. Equil. Temp
- Reason selective absorption of air
- H2O and CO2 most absorbent of IR
- Energy Balance
- Complex system has a delicate balance
- All modes of Heat Transfer are important
9Supplemental References for Todays Lecture
- Aguado, E. and J. E. Burt, 2001 Understanding
Weather Climate, 2nd Ed. 505 pp. Prentice Hall.
(ISBN 0-13-027394-5) - Danielson, E. W., J. Levin and E. Abrams, 1998
Meteorology. 462 pp. McGraw-Hill. (ISBN
0-697-21711-6) - Gedzelman, S. D., 1980 The Science and Wonders
of the Atmosphere. 535 pp. John-Wiley Sons.
(ISBN 0-471-02972-6) - Lutgens, F. K. and E. J. Tarbuck, 2001 The
Atmosphere, An Intro-duction to the Atmosphere,
8th Ed. 484 pp. Prentice Hall. (ISBN
0-13-087957-6) - Wallace, J. M. and P. V. Hobbs, 1977 Atmospheric
Science, An Introductory Survey. 467 pp. Academic
Press. (ISBN 0-12-732950-1)
10Reasons for Seasons
- Eccentricity of Earths Orbit
- Elongation of Orbital Axis
- Tilt of Earths Axis - Obliquity
- Angle between the Equatorial Plane and
the Orbital Plane
11Eccentricity of Orbit
Perihelion
Aphelion
Ahrens (2nd Ed.), akin to Fig. 2.15
Earth is 5 million km closer to sun in January
than in July.
Solar radiation is 7 more intense in January
than in July.
Why is July warmer than January in Northern
Hemisphere?
12147 million km
152 million km
Ahrens, Fig. 2.17
13Solar Zenith Angle
- Depends on latitude, time of day season
- Has two effects on an incoming solar beam
- Surface area covered or Spreading of beam
- Path length through atmosphere or Attenuation of
beam
Long Path
Large Area
Equal Energy
23.5o
Small Area
Short Path
Ahrens, Fig. 2.19
14Beam Spreading
- High Sun Power Spread over Smaller Area
Low Sun Power Spread over Larger Area
15Quantifying Beam Spreading
16Atmospheric Path Length
17Length of Day
Lutgens Tarbuck, p33
18Day Hours at Solstices - US Sites
- Summer-Winter
- Tucson (32o 13 N) 1415 - 1003
- Seattle (47o 38 N) 1600 - 825
- Anchorage (61o 13 N) 1922 - 528
- Fairbanks (64o 49 N) 2147 - 342
- Hilo (19o 43 N) 1319 - 1046
Arctic Circle
Gedzelman, p67
19Path of Sun
- Hours of daylight increase from winter to summer
pole - Equator always has 12 hours of daylight
- Summer pole has 24 hours of daylight
- Winter pole has 24 hours of darkness
- Note different Zeniths
Danielson et al., p75
20Solar Declination
Solstice
Equinox
Solstice
Aguado Burt, p46
21Noon Zenith at Solstices
- Summer-Winter
- Tucson AZ (32o 13 N) 08o 43 - 55o 43
- Seattle WA (47o 38 N) 24o 08 - 71o 08
- Anchorage AK (61o 13 N) 37o 43 - 84o 43
- Fairbanks AK (64o 49 N) 41o 19 - 88o 19
- Hilo HI (19o 43 N) 3o 47 (north) - 43o
13
Aguado Burt, p46
22Incoming Solar Radiation (Insolation) at the Top
of the Atmosphere
C
W
C
W
http//web.geog.arizona.edu/comrie/nats101/wa/wa1
insol.jpg
23Is Longest Day the Hottest Day?
Consider Average Daily Temperature for Chicago IL
warming
warming
cooling
equilibruim
USA Today WWW Site
24Annual Energy Balance
Radiative Warming
Radiative Cooling
Radiative Cooling
NH
SH
Ahrens, Fig. 2.21
- Heat transfer done by winds and ocean currents
Differential heating drives winds and currents
We will examine later in course
25Summary
- Tilt (23.5o) is primary reason for seasons
- Tilt changes two important factors Angle at
which solar rays strike the earth Number of hours
of daylight each day - Warmest and Coldest Days of Year Occur after
solstices, typically a month later - Poleward Heat Transport Requirement Done
by Atmosphere-Ocean System
26Assignment for Lecture
- Ahrens
- Pages 55-71
- Problems 3.1, 3.2, 3.5, 3.6, 3.14