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/Antarctic150 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 energyPartially compensated by absorption of longwave energyemitted 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 tooWarm 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

Tropics Energy surpluses due to high solar altitude (incoming energy exceeds outgoing loss)

Mid-latitudes Surpluses and deficits occur seasonallyDeficits dominate (annual balance at 36° latitude)

Polar regionsDeficit (outgoing loss exceeds incoming energy gain)

Result: Net poleward transport of energy surplus through atmospheric and oceanic currents

Latitudinal Energy Balance Distribution(Fig 3-10)

Net Radiation

Q* = K - K + L - L (Fig. 3-9)

K is solar radiation incident upon the surfaceK is solar radiation reflected from the surfaceL is infrared radiation reradiated to the surfaceL is infrared radiation emitted from the surface

Net radiation, Q* is expended from a non-vegetated surfacethrough one of three pathways:

1. Latent heat of evaporation (stored as water vapour)2. Sensible heat3. Ground heating and cooling (zero annually)

A lake

Notice the low Kvalues

What do youthink the surface type is for this plot ?

Why ?

Energy at Earth's Surface Daily radiation pattern is symmetricalTemperature lags behind insolation curveWhen would you expect the coolest/warmest part of the day?

0

5

10

15

20

25

0 4 8 12 16 20 24

0

200

400

600

800

1000

1200Temperature

Potential Kdown

So far today…(Sept 10, 2003)

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 expendedSensible heat (convection and conduction)Latent heat of evaporation Ground heating at depth

Source: NOAA

ABSORPTION

K TO SPACE=31

L<K !!

Heat transfer7+24=31 !Compensatesfor radiationimbalance atsurface

L

46+19+4=69

L TO SPACE=69

100

46-15=31

100-31-69=0

Temperature

•Measured in degrees Celsius or Kelvin Types of ThermometersThermistersThermocouplesAlcohol ThermometersMercury Thermometers

Global Climate Observing System15,400 known weather stations worldwideDaily mean temperature (average of min and max)Monthly mean temperature (average of daily means)

Gill Radiation Shield

Basis: temperature alterselectrical resistance

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/orprecipitation)

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 evaporationHeat energy absorbed (latent heat of phase change)Land: (more heating expended as sensible heat)

2. Water is transparent; ground is opaqueGround 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