Week 2 Flashcards
(19 cards)
What is radiation? What effect does it have on surface temperatures? How do different gases affect it?
-Radiation is a form of energy
-All objects with a temperature greater than 0 Kelvin emit some type of radiation- this energy is emitted as electromagnetic radiation.
-has a significant effect on surface temperatures
-The Earth receives energy from the sun via incoming solar radiation. This incoming solar radiation is absorbed to warm the Earth’s surface and atmosphere
-Earth, being a warmer object than space, also emits energy, primarily as terrestrial radiation in the infrared part of the spectrum
-gases affect radiation by absorbing it at various points within the atmosphere
-water vapour and carbon dioxide, have strong absorption bands in the infrared radiation part of the spectrum
-different gases absorb radiation in different parts of the spectrum and have different potencies (Global Warming Potential or GWP)
Describe the full greenhouse effect. What influences it?
-full greenhouse effect is the process by which the presence of certain gases in the Earth’s atmosphere causes the planet’s surface temperature to be significantly higher than it would otherwise be
1.Incoming solar radiation is absorbed by the Earth’s surface and atmosphere
2. warmed Earth and atmosphere then emit infrared (longwave) radiation
3. greenhouse gases then re-emit infrared radiation in all directions
4. portion of this re-emitted radiation is directed downwards towards the Earth, which the Earth’s surface absorbs
What influences the green house effect?
-concentration and types of greenhouse gases
-atmosphere’s transmission characteristics= determine how it absorbs, emits, and transmits radiation
-the incoming solar radiation
-Earth’s albedo
What is the electromagnetic radiation? What is the electromagnetic spectrum?
-electromagnetic radiation is the form of energy emitted by all objects with a temperature greater than 0 Kelvin
-electromagnetic spectrum encompasses the entire range of electromagnetic radiation, ordered by wavelength or frequency
-includes various types of radiation, such as radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, x-rays, and gamma rays
What is the equation relating frequency, wavelength and speed of light?
-energy carried per wave or photon increases as wavelength decreases (and frequency increases)
The relationship between frequency (ν), wavelength (λ), and the speed of light (c) is given by the equation:
νλ = c.
The energy of a photon is also related to frequency/wavelength by the equation: E = hν = h/λ, where h is Planck’s constant
What emits radiation?
all objects with a temperature greater than 0 K emit some type of radiation (energy)
What are the radiation laws?
basic radiation laws that govern blackbody radiation are:
-Stefan-Boltzmann Law: states that warmer objects emit more intensely (more total energy per unit area) than cold objects
-Wien’s Law: shows that warmer objects emit a higher proportion of their energy at shorter wavelengths than cold objects. As temperature increases, the peak of the energy distribution shifts to smaller wavelengths
What is black body radiation and equilibrium?
-black body is a theoretical object that absorbs all radiation falling on it and re-emits it as a function of its surface temperature
-Earth also acts as a blackbody radiator in terms of emitting terrestrial radiation
-Black body equilibrium relates to a state where energy inputs are balanced by energy leaving, such as the steady state temperature of the Earth’s atmosphere
What laws govern blackbody radiation?
Stefan-Boltzmann Law: This law relates the total energy emitted per unit area per second (I) by a black body to its absolute temperature (T).
I = σT⁴:
-I= energy per unit area emitted per second (Watts m⁻²)
- T is the equivalent blackbody Temperature (K)
-σ is the Stefan-Boltzmann constant (5.67 x 10⁻⁸ W m⁻² K⁻⁴)
Wien’s Law: This law describes how the wavelength at which the maximum energy is emitted (λmax) by a black body depends on its absolute temperature (T)
λmax * T = B:
-T is in K
-λmax is the peak wavelength
-constant B depends on the units used for wavelength; for example, if λmax is in nanometres (nm), the constant is approximately 2.897 x 10⁶ nm⋅K, or if λmax is in metres, the constant B is 2.897 x 10⁻³ m⋅K
Describe terrestial radiation? What is the peak wavelength according to Wien’s law?
Terrestrial radiation refers to the energy that the Earth emits
-ie the outgoing longwave radiation
Based on the Earth’s average surface temperature of approximately 288K, the emitted terrestrial radiation is primarily in the infrared part of the spectrum
-according to Wien’s Law, the peak wavelength of this terrestrial radiation is around 10 µm, which is significantly longer than the peak wavelength of incoming solar radiation (~0.5 µm)
What is Earth’s energy balance?
Earth’s energy balance= the equilibrium state where the energy entering the top of the atmosphere must be balanced by the energy leaving
-for the planet’s average temperature to remain stable, the total amount of energy absorbed from the sun must equal the total amount of energy radiated back into space as infrared radiation
Balance calculation has to account for things like:
-the Earth’s albedo (reflection of incoming solar radiation)
the greenhouse effect (absorption and re-emission of outgoing terrestrial radiation by the atmosphere)
What is Earth’s albedo? How does the brightness of Earth’s surfaces affect it? (give % values of albedo)
Earth’s albedo (α) is the measure of how much incoming solar radiation is reflected back into space
-approximately 0.3
brightness of Earth’s surfaces directly affects the albedo:
-Very dark colours have an albedo close to zero (or close to 0%) e.g. oceans
-Very light colours have an albedo close to one (or close to 100%) e.g. ice and snow
What is solar radiation reflected by?
Incoming solar radiation is reflected by the earth’s surface, clouds, and the atmosphere
-clouds= around 20%
-air (dust or aerosols)= about 6%
-earth’s surface= approx 5% (depends on surface type- albedo)
In total, about 30% of incoming solar radiation is reflected or scattered back to space
How do we calculate the balance between incoming and outgoing radiation for Earth?
equate the energy entering the top of the atmosphere that is absorbed by the Earth system with the energy leaving as outgoing terrestrial radiation
-ignores greenhouse effect assuming the Earth as simple black body from its “effective” radiating temperature level.
How do we calculate Incoming Solar Radiation?
calculated by taking the solar constant (S₀), multiplying by the cross-sectional area of the Earth (πre²), and accounting for the portion reflected (albedo, α).
Incoming absorbed = (1 - α) * S₀ * πre². Note: S₀ is the solar constant (e.g., 1370 W m⁻², currently ~1361 W m⁻²).
What is the outgoing terrestrial radiation?
Outgoing Terrestrial Radiation from the Earth assumed as a black body is calculated using the Stefan-Boltzmann Law over the Earth’s entire surface area (4πre²) at its effective blackbody temperature (Te).
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Outgoing = σTe⁴ * 4πre².
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For balance, Incoming absorbed = Outgoing: (1 - α) * S₀ * πre² = σTe⁴ * 4πre²
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We can cancel the πre² from both sides: (1 - α) * S₀ = σTe⁴ * 4
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Rearranging to solve for Te⁴: Te⁴ = (1 - α) * S₀ / (4σ)
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Taking the fourth root gives the equivalent blackbody temperature: Te = [((1 - α) * S₀) / (4σ)]¹/⁴
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Using values like α = 0.3, S₀ = 1370 W/m², and σ = 5.67 x 10⁻⁸ W m⁻² K⁻⁴, this calculation yields Te = 255K (-18°C)
Why is the radiation spectra of the Earth and the Sun different?
Wien’s Law= hotter objects emit radiation at shorter wavelengths, and cooler objects emit at longer wavelengths
Sun has a very high surface temperature of approximately 5800 Kelvin. Its radiation spectrum peaks around 0.5 µm
Earth lower average surface temperature of about 288 Kelvin (+15°C), emits radiation that peaks at much longer wavelengths- spectrum peaks in the infrared part of the spectrum, around 10 µm
Fully explain the Earth’s radiation balance?
- Energy enters the system as incoming solar radiation from the Sun
- around 30% of this is immediately reflected back to space by clouds, the atmosphere, and the Earth’s surface
- remaining 70% absorbed by the Earth’s surface and atmosphere
- absorbed solar energy warms the Earth’s surface and atmosphere
- absorbed solar energy warms the Earth’s surface and atmosphere
(While the atmosphere is relatively transparent to incoming solar radiation, it is nearly opaque to outgoing terrestrial infrared radiation) - Greenhouse gases within the atmosphere absorb much of this upward-moving infrared radiation
- re-emit infrared radiation in all directions- a substantial amount directed downwards
- Earth absorbs it causing it to heat further
This is why the surface is warmer (288K) than the simple blackbody calculation (255K)
What are the absorption and emission equations?
Absorption: A molecule can absorb radiant energy if the energy of the incoming photon (hν) is equal to the difference between two energy levels (ΔE = Ef - Ei) in the molecule
Emission: A molecule can emit a photon when it drops from a higher energy state (Ei) to a lower energy state (Ef). The energy of the emitted photon (hν) is equal to the difference in the energy levels (ΔE = Ei - Ef)
energy of a photon is given by the equation: E = hf = h/λ where h is Planck’s constant, f (or ν) is frequency, and λ is wavelength.
