GEOG 303
Earth’s Energy Balance
- What is heat?
o Sensible heat (what we feel) is a measure of kinetic energy of molecules
- Radiation
o Energy travels in waves
o Wavelengths can vary and are classified into different spectrums
o Defn: the flow of electromagnetic energy
o Wavelength Spectra
§ Visible light, X-ray, UV light, Gamma rays, Infrared, Microwaves, Radio
- Electromagnetic Radiation (EMR)
o Similar to the waves of the ocean – energy can be transferred
o Wavelength is inversely related to frequency
§ Small waves high frequency
o Energy is related to frequency – high frequency = high energy
o All objects emit radiation
- Key Equations and Laws
o Planck’s Law
§ For a given object the energy at any specific wavelength (λ) is dependent on temperature (K)
§ A black body is an object that completely absorbs all radiation hitting it and emits the maximum possible radiation for its temperature
o Stefan-Boltzmann Law – Quantifying Energy
§ There is a direct relationship b/w an object temperature and the radiation it emits
§ Emissivity is a coefficient which identifies what proportion of radiation that is received is emitted
· 1 (100%) is a black body – 100% of the radiation absorbed is emitted
o Wien’s Law
§ The wavelength at which maximum energy emission occurs
· 2897 µm K
- Wavelengths
o Shortwave
§ Originating from the sun – Gamma rays, X-rays, UV radiation, Visible light, near Infrared
§ Measured using a pyranometer
o Longwave
§ Originating form the Earth – Thermal infrared (heat)
§ Measured using a pyrgeometer
- How EMR interacts with materials
o Absorbed (a λ) – energy is transferred to the material
o Reflected (Alpha λ) – energy bounces off and back out
o Transmitted (t λ) – energy passes through the material
§ All three process combine to equal 1 – conservation of energy
- EMR in the Atmosphere
o Scattering
§ Depends on:
· Wavelengths of EMR compared to particle size
· Amount of particles/gases
· How far the EMR travels through the atmosphere
§ Rayleigh Scattering
· Shorter wavelengths of the visible spectrum are scattered by particles smaller than the wavelengths of light – dust, NO2 and O2 (Why the sky is blue)
· Clear days
§ Mie Scattering
· Occurs when the wavelength of EMR is similar to the particles in the atmosphere (or the particles are larger) – driven by the presence of aerosols
§ Non selective (Geometric) Scattering
· The particles are much larger than the wavelength (water vapour and clouds)
· Cloudy/Dark days
o Diffuse Radiation
§ Radiation can either be direct of diffuse – straight to us or can bounce around first
§ This is a result of the different kinds of scattering above
M3 Lecture 2
The Greenhouse Effect
- What is it?
o The trapping of Earth’s surface heat by the atmosphere (like a blanket)
o Visible light passes through and Infrared radiation is absorbed
- What makes a greenhouse gas?
o The atomic structure lends itself to absorbing energy
o Residence time in the atmosphere (how long it stays in the atmosphere)
- Longwave radiation emissions and emission window
o Radiation emitted over a range of wavelengths (under the red line)
o Blue: where the energy is effectively transmitted through the atmosphere
o The bottom graphs show where the energy is absorbed by different greenhouse gases at specific wavelengths.
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Greenhouse Gases
o Major ones include
§ Water vapour, Carbon dioxide, Methane, Ozone, Nitrous oxide
o Why do we care about methane emissions?
§ The direct effect of methane is about 60x stronger than carbon dioxide over 20 years
o Why is carbon dioxide the focus?
§ It has higher concentrations and a long lifetime = more long term effects
- Forcing vs Feedback
o Forcing: an external or internal driver that causes a change in climate
§ Needs to change solar output, albedo or GHG’s
§ Examples: solar variability, changes in carbon dioxide, aerosols
o Feedback: a response to climate forcing that amplified or buffers the initial change
§ Examples: albedo, cloud and water vapour feedback
- Water vapour
o Why don’t we have to worry about this?
§ Short residence, doesn’t build up
§ It is a feedback due to forcing
- Local Energy Balances
o There are more flows of energy than just radiation
o Locally solar radiation that is absorbed is converted to thermal (sensible) or latent heat
o There is a conservation of energy here:
§ A given input from the sun is partitioned: 100
· 15 reflected back to the atmosphere
· 25 to sensible heat – the object warms
· 60 to latent heat of evaporation
- Energy Flow Terms
o Kinetic Energy – energy of movement (E = ½ m • v2)
o Potential Energy – energy associated with gravity or chemistry (E = mgh)
o Internal Energy – total energy within a system
o Heat – the transfer of energy from one object to another
§ Conduction and Convection
- Conduction
o Transfer of energy when touching – solids are better conductors
o Occurs in the laminar layer – layer closest to the ground
o Gradient of temperature influences the rate of conduction – the bigger the difference the quicker conduction occurs
o QC = -k ∆T
§ k (thermal conductivity coefficient (W/mK))
§ ∆T (difference in temperature (K) over distance (m))
- Convection
o Transfer of energy to due the movement of fluid – also occurs more rapidly with a greater ∆T
o QH = -K ∆T
§ K (Eddy diffusivity (transfer of energy due to eddy/mixing motion)
§ ∆T (difference of temperature between two points
- Sensible Heat
o Energy transfer that can be measured with a thermometer
- Specific Heat
o The amount of heat required to raise the temperature of 1kg of substance by 1K
o Compared to other water due to hydrogen bonds require a lot of energy
- Latent Heat
o Heat associated with a phase change
o Cannot be measured with a thermometer
o Melting or evaporation requires heat : Freezing or condensing releases heat
M3 Lecture 3
- Inverse Square Law
o An object twice the distance from the light source receives a quarter of the illumination
o Can be used to calculate the solar content
- Angle of the Sun
o The angle of the suns rays determines the seasonality of a region
§ The equator countries are warmer because they receive more direct sunlight and countries like Canada have seasons due to periods of direct (90˚) and periods of indirect sunlight (at an angle)
Earth’s Energy Balance
- What is heat?
o Sensible heat (what we feel) is a measure of kinetic energy of molecules
- Radiation
o Energy travels in waves
o Wavelengths can vary and are classified into different spectrums
o Defn: the flow of electromagnetic energy
o Wavelength Spectra
Visible light, X-ray, UV light, Gamma rays, Infrared, Microwaves, Radio
- Electromagnetic Radiation (EMR)
o Similar to the waves of the ocean – energy can be transferred
o Wavelength is inversely related to frequency
Small waves high frequency
o Energy is related to frequency – high frequency = high energy
o All objects emit radiation
- Key Equations and Laws
o Planck’s Law
For a given object the energy at any specific wavelength (λ) is dependent on temperature (K)
A black body is an object that completely absorbs all radiation hitting it and emits the maximum possible radiation for its temperature
o Stefan-Boltzmann Law – Quantifying Energy
There is a direct relationship b/w an object temperature and the radiation it emits
Emissivity is a coefficient which identifies what proportion of radiation that is received is emitted
• 1 (100%) is a black body – 100% of the radiation absorbed is emitted
o Wien’s Law
The wavelength at which maximum energy emission occurs
• 2897 µm K
- Wavelengths
o Shortwave
Originating from the sun – Gamma rays, X-rays, UV radiation, Visible light, near Infrared
Measured using a pyranometer
o Longwave
Originating form the Earth – Thermal infrared (heat)
Measured using a pyrgeometer
- How EMR interacts with materials
o Absorbed (a λ) – energy is transferred to the material
o Reflected (Alpha λ) – energy bounces off and back out
o Transmitted (t λ) – energy passes through the material
All three process combine to equal 1 – conservation of energy
- EMR in the Atmosphere
o Scattering
Depends on:
• Wavelengths of EMR compared to particle size
• Amount of particles/gases
• How far the EMR travels through the atmosphere
Rayleigh Scattering
• Shorter wavelengths of the visible spectrum are scattered by particles smaller than the wavelengths of light – dust, NO2 and O2 (Why the sky is blue)
• Clear days
Mie Scattering
• Occurs when the wavelength of EMR is similar to the particles in the atmosphere (or the particles are larger) – driven by the presence of aerosols
Non selective (Geometric) Scattering
• The particles are much larger than the wavelength (water vapour and clouds)
• Cloudy/Dark days
o Diffuse Radiation
Radiation can either be direct of diffuse – straight to us or can bounce around first
This is a result of the different kinds of scattering above
M3 Lecture 2
The Greenhouse Effect
- What is it?
o The trapping of Earth’s surface heat by the atmosphere (like a blanket)
o Visible light passes through and Infrared radiation is absorbed
- What makes a greenhouse gas?
o The atomic structure lends itself to absorbing energy
o Residence time in the atmosphere (how long it stays in the atmosphere)
- Longwave radiation emissions and emission window
o Radiation emitted over a range of wavelengths (under the red line)
o Blue: where the energy is effectively transmitted through the atmosphere
o The bottom graphs show where the energy is absorbed by different greenhouse gases at specific wavelengths.
- Greenhouse Gases
o Major ones include
Water vapour, Carbon dioxide, Methane, Ozone, Nitrous oxide
o Why do we care about methane emissions?
The direct effect of methane is about 60x stronger than carbon dioxide over 20 years
o Why is carbon dioxide the focus?
It has higher concentrations and a long lifetime = more long term effects
- Forcing vs Feedback
o Forcing: an external or internal driver that causes a change in climate
Needs to change solar output, albedo or GHG’s
Examples: solar variability, changes in carbon dioxide, aerosols
o Feedback: a response to climate forcing that amplified or buffers the initial change
Examples: albedo, cloud and water vapour feedback
- Water vapour
o Why don’t we have to worry about this?
Short residence, doesn’t build up
It is a feedback due to forcing
- Local Energy Balances
o There are more flows of energy than just radiation
o Locally solar radiation that is absorbed is converted to thermal (sensible) or latent heat
o There is a conservation of energy here:
A given input from the sun is partitioned: 100
• 15 reflected back to the atmosphere
• 25 to sensible heat – the object warms
• 60 to latent heat of evaporation
- Energy Flow Terms
o Kinetic Energy – energy of movement (E = ½ m • v2)
o Potential Energy – energy associated with gravity or chemistry (E = mgh)
o Internal Energy – total energy within a system
o Heat – the transfer of energy from one object to another
Conduction and Convection
- Conduction
o Transfer of energy when touching – solids are better conductors
o Occurs in the laminar layer – layer closest to the ground
o Gradient of temperature influences the rate of conduction – the bigger the difference the quicker conduction occurs
o QC = -k ∆T
k (thermal conductivity coefficient (W/mK))
∆T (difference in temperature (K) over distance (m))
- Convection
o Transfer of energy to due the movement of fluid – also occurs more rapidly with a greater ∆T
o QH = -K ∆T
K (Eddy diffusivity (transfer of energy due to eddy/mixing motion)
∆T (difference of temperature between two points
- Sensible Heat
o Energy transfer that can be measured with a thermometer
- Specific Heat
o The amount of heat required to raise the temperature of 1kg of substance by 1K
o Compared to other water due to hydrogen bonds require a lot of energy
- Latent Heat
o Heat associated with a phase change
o Cannot be measured with a thermometer
o Melting or evaporation requires heat : Freezing or condensing releases heat
M3 Lecture 3
- Inverse Square Law
o An object twice the distance from the light source receives a quarter of the illumination
o Can be used to calculate the solar content
- Angle of the Sun
o The angle of the suns rays determines the seasonality of a region
The equator countries are warmer because they receive more direct sunlight and countries like Canada have seasons due to periods of direct (90˚) and periods of indirect sunlight (at an angle)