DEPARTMENT OF GEOGRAPHY
Climate
GEOG0005
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Name that Weather System
The 2 synoptic maps above are 24 hours apart. What is the weather system in the panel on the
right off the southeast coast of Greenland?
A. An occluded front
B. An anticyclone
C. A cyclone
D. Blocking
What is the term for the transition from the system on the left to that on the right?
Name that Weather System
The 2 synoptic maps above are 24 hours apart. What is the weather system in the panel on the
right off the southeast coast of Greenland?
A. An occluded front
B. An anticyclone
C. A cyclone
D. Blocking
What is the term for the transition from the system on the left to that on the right? Cyclogenesis
What is climate?
• Average atmospheric conditions
• Averages out weather, but not
necessarily seasons
• The state of climate components or
variables (temperature,
precipitation)
• Climate measurements span
modern to distant past
(paleoclimate)
• Classified by land cover type,
precipitation, temperature (Köppen)
Broad climate classifications
Source:
https://earthhow.co
m/koppen-climate-cl
assification/

WHAT CONTROLS
CLIMATE?
Global Energy Budget
Energy Transfer
• Radiation
• Conduction
• Convection
Radiation
• Transfer of energy as waves or
particles through air
(emission/transmission)
• Called electromagnetic radiation
• Electromagnetic spectrum: range
of frequencies of electromagnetic
radiation and their wavelengths
(or energies)
• Includes longwave (low energy)
and shortwave (high energy)
radiation
Energy inversely proportional to wavelength
Conduction
• Heat (energy) transfers from one molecule to next as
molecules vibrate
• Rate of transfer of heat
depends on temperature
difference (gradient)
• Example: heat moving along
a metal bar
• Occurs in all fluid phases
(gas, liquid, solid)
Convection
• Transfer of heat by movement of
a fluid (mass transfer)
• Caused by buoyancy forces due
to changes in density that arise
from changes in temperature
• Causes turbulence (fluid mixing)
or an instability (uneven heating)
in the atmosphere
• Moist convection leads to
thunderstorms
Heat Transfer in the Atmosphere
Convection Radiation
Conduction
Test Your Understanding
What kind of heat transfer is taking place above the low-pressure system of a cyclone?
A. Conduction
B. Convection
C. Radiation
D. None of these
Test Your Understanding
What kind of heat transfer is taking place above the low-pressure system of a cyclone?
A. Conduction
B. Convection
C. Radiation
D. None of these
Longwave and Shortwave
Radiation from the sun is in the shortwave (UV/visible)
Radiation from the Earth is in the longwave (infrared)
Occupy distinct regions on the electromagnetic spectrum
Sun Earth
Blackbody Radiation
• Radiance: power emitted by a blackbody
radiation flux per unit area per unit solid angle [W/m2/sr]
• Spectral radiance: Radiance per unit wavelength [W/m2/sr/nm]
Radiation
Absorbs all
incoming radiation
Re-emits with equal
intensity in all directions
(isotropic)
Temperature (T)
Blackbody
Blackbody Radiation
• Radiation emitted by a blackbody depends only on its temperature
• Planck’s law of blackbody radiation defines this relationship:
• Tells us how much radiation emitted at a certain wavelength for a body of a
certain temperature
Planck’s Law:
B: spectral radianceh, c, k: constants
n: frequency of lightT: absolute temperature
Stefan-Boltzmann Law
• Relates power radiated from a blackbody to its temperature
• Total energy radiated by a blackbody with temperature T is
proportional to the 4th power of T (T4)
• This spectral intensity (I) over all directions and wavelengths
is:
I = σT4
where σ = 5.67x10-8 W m-2 K-4 is a constant (the Stefan-Boltzmann
Constant)
• I is in power per unit area or Watts per square metre (W/m2)
Test Your Understanding
The Stefan-Boltzmann constant is 5.67x10-8 W m-2 K-4 and the temperature of the sun, a
blackbody, is 5778 K. What is the energy radiated from the surface of the sun?
A. 5778 W/m2
B. 63000 kW
C. 63000 kW/m2
D. 0.0032 W/m2
Test Your Understanding
The Stefan-Boltzmann constant is 5.67x10-8 W m-2 K-4 and the temperature of the sun, a
blackbody, is 5778 K. What is the energy radiated from the surface of the sun?
A. 5778 W/m2
B. 63000 kW
C. 63000 kW/m2
D. 0.0032 W/m2
Radiation Modifiers: Albedo
Incident
radiation
Radiation
reflected
• Ratio of reflected to incident
(incoming) radiation
• Ranges from 0 to 1
• Represent with the symbol
alpha (a) Earth’s surface
Earth’s Albedo
• Clouds, ice, reflective
land surfaces like deserts
increase Earth’s albedo
(a)
Albedo Properties of
Earth’s surface
• Reflectivity is equivalent to albedo
• Earth has a global average albedo
(a) of 0.3
• 30% of incident (incoming) sunlight
reflected
Reflectivity
Radiation Modifiers: Emissivity
• Amount of radiation absorbed by
a body compared with that of a
blackbody
• Ranges from 0 to 1
• Represent with the symbol
epsilon (e)
• Called a grey body if e < 1
• Emissivity of Earth’s atmosphere
is ~0.77
Radiation not absorbed
Earth’s atmosphere
Earth’s surface
Incident radiation
Radiation Modifiers: Transmittance
• Amount of radiation not
absorbed by grey body
• Ranges from 0 to 1
• 1 – e
Radiation not absorbed
Earth’s atmosphere
Earth’s surface
Incident radiation
Transmitted radiation
Incoming radiation
Earth
Shadow area:
Incoming radiation
Sun’s energy is 1366 W/m2 (the solar constant or So)
So
Shadow area:
Incoming radiation
• Area of Earth: 4πR2
• Area of the Earth the sun intercepts: πR2
• Fraction of So received by Earth = (πR2)/(4πR2)
= 1/4
• Amount of sun’s radiation absorbed by Earth: 1 – a
Outgoing radiation
Earth is a blackbody
that emits longwave
radiation
Energy proportional
to its temperature:
σT4
Earth is a
blackbody
Steady State
• Earth’s climate system, unperturbed, is in a
(quasi-) steady state:
Energy In = Energy Out
(Incoming radiation = Outgoing radiation)
• Space is a vacuum, so only energy transferred is
electromagnetic radiation
We have everything we need to calculate temperature
Energy in = Energy out
T = 255 K = -18oC
Too cold to be habitable. Actual temperature is +15oC.
Greenhouse Gases (GHGs)
Earth’s atmosphere is a grey body (e ~ 0.77) due to GHGs
Absorbs upwelling longwave radiation from surface and re-emits in
all directions
sfc. = surface
GHGs maintain
Earth’s surface T at
288 K (15oC)
Longwave and Shortwave Radiation
Majority of
shortwave
passes through
atmosphere
Very little
longwave
escapes
Earth’s atmosphere transparent to sun’s shortwave radiation, but absorbs most
longwave radiation
Absorption of Radiation by Greenhouse Gases
Dominant GHGs:
• water vapour
• carbon dioxide
(CO2)
• methane (CH4)
• nitrous oxide (N2O)
Putting it all together: Earth’s Energy Balance
Equator gets more sun radiation than the Poles
More
Less
Energy Transfer
Sun’s rays
Incoming radiation not uniform
Redistribution of Heat
• Convection plays role
• Not as simple as Hadley’s 1735
suggestion that convection cell
extends from Equator to the Poles Hot air
rises
Cold air sinks
Convection cell
Convection cell
Does not account for the Coriolis effect
Hadley model:
Tropical Cells
• Sun heats Equator
• Hot air rises
• Air masses move toward Poles
• Air masses diverge from north-
south path due to Coriolis
effect
• Cool dry air sinks at about 30o
latitude (deserts)
• Still named Hadley cells
Convection Cells:
• moist, warm air rises, forms clouds
• cold, dry air subsides (warms)
Surface Winds:
• subsiding branch of cell reaches
surface, forms surface winds that
diverge due to Coriolis effect
• poleward and equatorward winds
meet, air forced upward, maintains
convective cells
Global Cells and Surface Winds
Ferrel cell
Ferrel cell
Polar cell
Annual mean surface temperature
• Warmest at the Equator
• Coldest at the Poles
• Antarctic colder than Arctic
(isolated - less land mass
to redistribute head)
• Colder at elevation
• Canada colder than Europe
Annual mean rainfall/precipitation
• Most rain in Intertropical Convergence Zone (ITCZ) (convective uplift)
• Little rain at edge of tropics ~30oN (subsidence)
• More rain over Equatorial
oceans (storm tracks)
Circulation patterns not always stable
• Seasonal variability
• Interannual variability:
– North Atlantic Oscillation
– El Nino-Southern Oscillation
– Extreme weather
• Longer timescale variability of 1000s of years
Climate Summary
1. Climate definition
2. Energy transfer: radiation, convection, conduction
3. Earth’s energy balance: incident sunlight, blackbody
radiation, albedo, greenhouse gases
4. Differential heating and redistribution of heat
5. Annual average climate variables (temperature,
precipitation)
• Next Lecture: Seasons, Climate Change