Energy Input: Solar Radiation
•decreases poleward
•reduced in areas of frequent cloud
•total energy input to atmosphere highest at equator,
but highest insolation at surface in subtropical deserts
Global Range in Average Annual Solar Radiation Intensity
<80 W/m2 in frequently cloudy portions of Arctic/Antarctic
150 W/m2 in Lethbridge (greatest # of hours of sunshine in Canada)
>280 W/m2 in subtropical deserts
Short-wave Energy Loss:
Albedo
•Proportion of insolation that is reflected (31% global avg.)
•Energy may reflect back to space without being absorbed
•Darker colours have lower albedo
Water: low albedo for high solar alitude (calm seas)
high albedo for low solar altitude (calm seas)
rough seas moderate this pattern
Cloud-albedo forcing reduces available solar energy
Partially compensated by absorption of longwave energy
emitted by the Earth (cloud-greenhouse forcing)
Albedo of Water
Scattering
Gas molecules, dust particles, pollutants, ice and cloud
droplets scatter incoming solar radiation.
This results in diffuse radiation
Absorption
69% of top-of-atmosphere solar radiation is absorbed
Earth’s surfaces (45%)
Atmosphere (24%)
Heats surface or converted to chemical energy in
photosynthesis
Conduction, Convection and Advection
Conduction
•heat is diffused to cooler material as radiation absorbed
•land heats more quickly than water
Why ? Thermal mixing and higher heat capacity of water
•Solids (land) are better conductors than gases (atmosphere).
Convection
•physical mixing with a strong vertical motion in gaseous or
liquid media
•As land heats up, the air immediately above warms too
Warm air rises (less dense) while cooler air falls (more dense)
Advection
•Lateral heat transfer
Energy Output:
Earth Re-radiation (longwave)
The Earth and its atmosphere emit longwave radiation
Greenhouse Effect:
•Some L is absorbed by CO2, H2O, CH4, NOx and
CFC’s in the lower atmosphere
•Re-radiated in all directions (some toward Earth)
Human-Induced Climate Change:
•Greenhouse gas emissions (eg. fossil fuel burning)
•Increased absorption of L
Effect of Clouds:
•High clouds cause cloud-greenhouse forcing
•Low clouds cause cloud-albedo forcing
Latitudinal Energy Balance Distribution
(Fig 3-10)
Tropics
Energy surpluses due to high solar altitude
(incoming energy exceeds outgoing loss)
Mid-latitudes
Surpluses and deficits occur seasonally
Deficits dominate (annual balance at  36° latitude)
Polar regions
Deficit (outgoing loss exceeds incoming energy gain)
Result:
Net poleward transport of energy surplus through
atmospheric and oceanic currents
Net Radiation
Q* = K - K + L - L (Fig. 3-9)
K is solar radiation incident upon the surface
K is solar radiation reflected from the surface
L is infrared radiation reradiated to the surface
L is infrared radiation emitted from the surface
Net radiation, Q* is expended from a non-vegetated surface
through one of three pathways:
1.
2.
3.
Latent heat of evaporation (stored as water vapour)
Sensible heat
Ground heating and cooling (zero annually)
A lake
Notice the
low K
values
What do you
think the
surface type
is for this
plot ?
Why ?
Energy at Earth's Surface
Daily radiation pattern is symmetrical
Temperature lags behind insolation curve
When would you expect the coolest/warmest part of the day?
25
So far today…
(Sept 10, 2003)
Temperature
Potential Kdown
20
1200
1000
800
15
600
10
400
5
200
0
0
0
4
8
12
16
20
24
September 10, 2003
Temperature
1000
Potential Kdown
800
15
600
10
400
5
200
0
0
0
4
8
12
16
20
24
Hour
January 22, 2004
25
1200
Temperature
20
1000
Potential Kdown
800
15
600
10
400
5
200
0
0
0
4
8
12
Hour
16
20
24
TOA Solar Radiation
(W/m^2)
20
TOA Solar Radiation
(W/m^2)
1200
Temperature (degrees
Celsius)
Temperature (degrees
Celsius)
25
Radiation vs. Energy Balance
Overall, the surface receives more K and L
than it expends as K and L
Why does the surface not just get hotter and hotter ?
Energy is expended
Sensible heat (convection and conduction)
Latent heat of evaporation
Ground heating at depth
K TO SPACE=31
L
L TO SPACE=69
100-31-69=0
100
ABSORPTION
46+19+4=69
L<K !!
Heat transfer
7+24=31 !
Compensates
for radiation
imbalance at
surface
46-15=31
Source: NOAA
Temperature
•Measured in degrees Celsius or Kelvin
Types of Thermometers
Thermisters
Basis: temperature alters
Thermocouples
electrical resistance
Alcohol Thermometers
Mercury Thermometers
Gill Radiation Shield
Global Climate Observing System
15,400 known weather stations worldwide
Daily mean temperature (average of min and max)
Monthly mean temperature (average of daily means)
Temperature Controls
Latitude
•Variation in insolation
Altitude
•temperature decreases with altitude
•‘Parcel’ of air expands as pressure reduced
•Mountainous areas are colder than locations near sea level
•Surfaces gain and lose heat rapidly to atmosphere at high
elevation (air is has less mass per unit area)
•Permanent equatorial icefields and glaciers at high altitude
•Snowline closer to the ground with increasing latitude (and/or
precipitation)
Cloud Cover
Reflect and absorb solar radiation (surface cooling)
Absorb, and (re-)radiate longwave radiation (surface warmin
Overall effect is a slight cooling (mainly low cloud)
Land-Water Heating Differences
1. Ocean: energy lost to evaporation
Heat energy absorbed (latent heat of phase change)
Land: (more heating expended as sensible heat)
2. Water is transparent; ground is opaque
Ground absorbs insolation at Earth-Atmosphere interface
3. Solar insolation distributed to much greater depth
in water (photic layer)
Water has higher specific heat
(same volume can hold more heat)
4. Water movement - mixing spreads heat over a
greater volume
Surface waters and deep waters mix