• 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/m 2 in frequently cloudy portions of Arctic/Antarctic

150 W/m 2 in Lethbridge (greatest # of hours of sunshine in Canada)
>280 W/m 2 in subtropical deserts

• 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

Gas molecules, dust particles, pollutants, ice and cloud droplets scatter incoming solar radiation.
This results in diffuse radiation
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
• 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

Earth Re-radiation (longwave)
The Earth and its atmosphere emit longwave radiation
Greenhouse Effect:
•Some
L
 is absorbed by CO
2
, H
CFC’s in the lower atmosphere
2
O, CH
4
, NO x and
•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

(Fig 3-10)
Energy surpluses due to high solar altitude
(incoming energy exceeds outgoing loss)
Surpluses and deficits occur seasonally
Deficits dominate (annual balance at

36° latitude)
Deficit (outgoing loss exceeds incoming energy gain)
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.
Latent heat of evaporation (stored as water vapour)
2.
Sensible heat
3.
Ground heating and cooling (zero annually)



What do you think the surface type is for this plot ?
Why ?

25
Daily radiation pattern is symmetrical
Temperature lags behind insolation curve
When would you expect the coolest/warmest part of the day?
20
15
10
5
0
0
Temperature
Potential Kdown
4 8 12
So far today…
(Sept 10, 2003)
16 20 24
0
400
200
1200
1000
800
600

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
46-15=31
L

<K

!!
Heat transfer
7+24=31 !
Compensates for radiation imbalance at surface
Source: NOAA

•Measured in degrees
Celsius or Kelvin
Types of Thermometers
Thermisters
Basis: temperature alters
Thermocouples
Alcohol Thermometers electrical resistance
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)

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 warming)
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