Understanding Weather and Climate 4th Edition Edward Aguado and James E. Burt

1
Understanding Weather and Climate4th
EditionEdward Aguado and James E. Burt
Take Roll!!!
Energy Balance and Temperature
Geosystems 6e An Introduction to Physical
Geography
Chapters 4 5
Chapter 4
Robert W. Christopherson Charles E. Thomsen

• Anthony J. Vega

2
Introduction

• Solar radiation is the atmospheres heat source
• Most gases are transparent to solar radiation
• They do absorb terrestrial radiation
• Gases also scatter energy
• The global energy budget
• A balance between incoming solar radiation and
  outgoing terrestrial radiation

3
Insolation at Earths Surface
Figure 4.2
4
Atmospheric Influenceson Insolation

• Radiant energy is absorbed, reflected, or
  transmitted when it enters the atmosphere
• Transmission
• Includes scattering and refraction
• Energy transmitted through objects
• Varies diurnally from place to place

5
Atmospheric Influences on Insolation

• Refraction
• Radiant energy (i.e., sunlight) travels through
  the vacuum of space and enters the atmosphere,
  i.e., a medium of different density
• The radiant energy/incoming sunlight experiences
  a change in speed and direction

6
Refraction

• Refraction
• Change in Direction and Speed of Light
• Does not increase heat

http//hyperphysics.phy-astr.gsu.edu/Hbase/geoopt/
refr.html
Bcrowell on en.wikipedia GNU Free Documentation
License, Version 1.2 or any later
7
Refraction
Figure 4.4
8
Atmospheric Influences on Insolation

• Absorption
• Particular gases, liquids, and solids absorb
  energy
• Heat increases
• Gases are poor selective absorbers of energy

9

• Reflection
• Redirection of energy
• Does not increase heat
• Albedo percentage of reflected energy
• Scattering
• Scattered energy diffuses radiation
• Changes direction but not wavelength
• Reduces intensity
• Type determined by size of scattering agents

10
Albedo and Reflection
Figure 4.5
11
July and January Albedos
Figure 4.6
12
Clouds and Albedo
Figure 4.7
13
Scattering

• Rayleigh Scattering
• Scattering agents are smaller than energy
  wavelengths
• Forward and backward scattering
• Partial to shorter wavelengths
• Causes blue sky

14
Rayleigh Scattering
15

• Mie Scattering
• Larger scattering agents (aerosols)
• Interacts with wavelengths across visible
  spectrum
• Hazy, grayish skies
• Sunrise/sunset color enhancement

16
Longer radiation path lengths greater Mie
Scattering and reddish skies
17
(No Transcript)
18

• Nonselective Scattering
• Very large scattering agents (water)
• Scatter across the visible spectrum
• White or gray appearance
• No wavelength especially affected
• Transmission
• Energy transmitted through objects
• Varies diurnally from place to place

19
Energy Pathways
Figure 4.1
20

• The Fate of Solar Radiation
• A constant supply of radiation at top of the
  atmosphere
• Entering energy is transmitted, absorbed, or
  scattered
• A Global Energy Budget
• Assumes global annual insolation 100 units
• Atmosphere absorbs 25 units
• 7 units absorbed by stratospheric ozone

21

• Atmospheric Reflection 25 units
• 19 reflected to space by clouds
• 6 units back-scattered to space
• Remaining 50 units are available for surface
  absorption. Of the 50 Units of Energy to reach
  the surface
• 5 reflected back to space
• Remaining 45 absorbed at surface
• Heats surface and overlying air

22
Incoming Radiation
23

• Surface-Atmosphere Radiation Exchange
• Surface emission (terrestrial/longwave radiation)
  
• Much is absorbed by atmospheric gases
• H2O and CO2
• Increases air temperature
• Some energy is reabsorbed at the surface
• Additional surface heating

24

• Greenhouse gases absorb terrestrial radiation
• The atmospheric window - non-absorption of
  wavelengths between 8-15 µm

The atmospheric window
25
The atmospheric window
26

• Clouds absorb virtually all longwave radiation
• Results in warmer cloudy nights

27

• Net radiation difference between absorbed and
  emitted radiation
• The atmosphere absorbs 25 units of solar
  radiation but undergoes a net loss of 54 units
• net deficit 29 units
• The surface absorbs 45 units of solar radiation
  but has a longwave deficit of 16
• net surplus 29 units
• Net radiation deficit equals net surplus, i.e.,
  the surplus and deficits offset

28

• Conduction
• Energy is transferred from the surface to the
  atmosphere
• Energy transferred to the laminar boundary layer

29
Net radiation
30
Energy surplus/deficit offsets between air and
surface
31

• Convection
• When the surface temperature exceeds the air
  temperature
• Normal during the day
• Convection from
• Free convection
• Warmer, less dense fluids rise
• Forced convection
• Initiated by eddies and disruptions to uniform
  airflow

32
Free Convection
Forced Convection
33

• Sensible Heat
• Readily detected heat energy
• Related to objects specific heat and mass
• 8 units transferred to the atmosphere as sensible
  heat
• Latent Heat
• Energy which induces a change of state (usually
  in water)
• Redirects some energy which would be used for
  sensible heat

34

• Latent heat of evaporation is stored in water
  vapor
• Released during condensation
• Globally, 21 units of energy are transferred to
  the atmosphere as latent heat

35
Heat content of substances
36

• Net Radiation and Temperature
• Incoming radiation balances with outgoing
• If parameters are changed, a new equilibrium
  occurs
• Balances
• Global
• Diurnal
• Local

37

• Latitudinal Variations
• Between 38oN and S net energy surpluses
• Poleward of 38o net energy deficits
• Winter hemispheres
• Net energy deficits poleward of 15o
• Mass advection neutralizes energy imbalances

38
Annual average net radiation
39
Ocean circulation
40

• The Greenhouse Effect
• Gases trapping terrestrial radiation
• H2O, CO2, and CH4
• Without the greenhouse effect
• average Earth temperature -18oC (0oF)
• Human activities play a role

41
A true greenhouse stems convection
42
Insolation Receipt and Global Temperature
Distribution

• Temperatures decrease with latitude
• Strong thermal contrasts occur in winter
• Isotherms shift seasonally
• Greater over continents
• More pronounced in the northern hemisphere

43
Shifting of Isotherms with Seasonal Variation in
Insolation Receipt
44
Shifting of Isotherms with Seasonal Variation in
Insolation Receipt
45
Shifting of Isotherms with Seasonal Variation in
Insolation Receipt
46
Influences on Temperature

• Latitude
• Due to axial tilt
• Solar angles, daylengths, beam depletion, beam
  spreading
• Altitude
• Temperatures decline with altitude
• High altitudes have fairly constant temperatures
• More rapid diurnal fluxes

47
Energy Budget by Latitude
Figure 4.13
48
Temperature Variation with Altitude
49

• Atmospheric Circulation
• Latitudinal temperature and pressure differences
  cause large-scale advection
• Contrasts between Land and Water
• Continentality versus maritime effects

50

• Warm and Cold Ocean Currents
• Western ocean basins are warm
• Eastern ocean basins are cold
• Local Conditions
• Small spatial scale features impact temperatures

51
Ocean circulation
52
South-facing slopes have more vegetation
53
The role of vegetation in a local energy balance
54

• Daily and Annual Temperature Patterns
• Diurnal temperatures lag energy receipt
• Surface cooling rate is lower than the warming
  rate
• Due to stored surface energy
• Winds moderate temperature ranges
• Transfer energy through large mass of air

55
Clear Skies
Diurnal energy
Overcast
56
The Greenhouse Effect and Atmospheric Warming

• Atmosphere absorbs heat energy
• A real greenhouse traps heat inside
• Atmosphere delays transfer of heat from Earth
  into space

57
Clouds and Forcing
Figure 4.11
58
Shortwave and Longwave Energy
Figure 4.11
59
EarthAtmosphere Radiation Balance
Figure 4.12
60
Energy Balance at Earths Surface

• Daily Radiation Patterns  
• Simplified Surface Energy Balance  
• The Urban Environment

61
Daily Radiation Patterns
Figure 4.14
62
Surface Energy Budget
Figure 4.15
63
Simplified Surface Energy Balance

• NET R
• SW (insolation)
• SW (reflection)
• LW (infrared)
• LW (infrared)

Figure 4.16
64
Global NET R
Figure 4.17
65
Global Latent Heat
Figure 4.18
66
Global Sensible Heat
Figure 4.29
67
Solar Cooking Solution
Figure FS 4.1.1
68
Solar Energy
Figure FS 4.1.2
69
Radiation Budgets
El Mirage, CA
Pitt Meadows, BC
Figure 4.20
70
The Urban Environment
Figure 4.21
71
Urban Heat Island
Figure 4.22
72
Urban Heat IslandPilotProject
Figure 4.23