Section 1
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If we assume radiative balance, we can convert this into an effective radiating temperature by invoking the Stefan-Boltzmann law
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Section 1
(50 cards)
If we assume radiative balance, we can convert this into an effective radiating temperature by invoking the Stefan-Boltzmann law
(total energy = sT4 with s = 5.67x10-8 Wm-2K-4, T in Kelvin [celsius + 273.15]). 240W m2 =sT4
Planck function
objects emit radiation according to their temperature, following the Planck Function
Sea ice
has a higher albedo and affects the amount of sun's energy absorbed by the Earth.
Radiative Balance: the net incoming solar radiation (ISR) equals
the net outgoing terrestrial terrestrial radiation (OTR), That is, ISR=OTR
blackbodies
objects that emit 100% efficiency and have a distribution of wavelengths of emitted radiation is given by the Planck Function
Net solar radiation at the top of the earth's atmosphere =
incoming minus reflected (Energy flux: W/m2)
Solar Flux: Inverse-square law
-The total flux of energy transferred from one object to another varies according to the distance between the two objects. This relationship is known as the inverse-square law
What are some key features of the planet's latent heat flux distribution?
-there is more evaporation (thus latent heat flux) over ocean than land -some land areas such as deserts have almost no latent heat flux - almost all evaporation occurs in the tropics and subtropics -there is generally more evaporation in the subtropics than the tropics -some very wet land surfaces, such as tropical forests, have latent heat flux rates that are comparable to those of the subtropical ocean condensation is sometimes seen over very cold land surfaces
current levels of CO2 are roughly
400 ppm
Another maximum?
mid-latitude storm track
Convection
-macroscopic redistribution of heat, driven by heating at the surface -warm air rises and expands, cold air contracts and sinks -happens in ocean and atmosphere but more common in the atmosphere
Atmospheric circulation
-A fluid heated from below develops convective overturning: rising motion above the heating source, sinking motion where the heating is less.
North Atlantic, salty water cools and become so dense to sink to the deep ocean and spread across ocean basins. This overturning circulation is known as the
thermohaline circulation, and takes 100s to 1000s years to complete a circuit
Solar radiation versus terrestrial radiation
-The difference between how solar radiation and terrestrial radiation interact with molecules of various gases in the air is key to our current climate and to how we are changing it. -Solar radiation is not absorbed strongly* in the atmosphere, so sunlight tends to get through and heat the ground. -Terrestrial radiation is both absorbed and emitted in the atmosphere, leading to the greenhouse effect
Hadley cell
Surface heating at the tropics drives a similar atmospheric circulation known as the Hadley Cell, with raising air near the equator, and sinking air in the subtropics -similar to convective overturning
Characteristics of a latent heat flux
-directly proportional to evaporation -always occurring over the wet ocean, but also occur over the land surface, if moisture is available -latent heat flux is measure in W/m2 -it is generally positive, indicating a loss of water (evaporaton) from the relatively wet surface to the armosphere -rarely negative (only when surface condensation occurs)
Stefan-Boltzmann law
total energy emitted is given by E=σ T^4
Global energy fluxes in the climate system
see picture of solar radiation and longwave radiation with latent heat fluxes
How are the different forms of radiation organized?
according to their wavelengths (and hence energy levels), creating the electromagnetic spectrum
warming and raising motion are assoicated with
low surface pressure
Phase changes
-heat transfer due to evaporation -requires energy and therefore removes heat from the liquid -ex. from the surface when liquid water is present , to the atmosphere, and is also known as a latent heat flux
Conduction
-heat transfer that occurs between warm and cold objects -fast moving molecules of substance 1 collide with neighboring molecules of substance 2 to speed up ex. Earth's surface and atmosphere, and is also known as sensible heat flux
Winds constantly blow...
at the surface from high to low pressures, and is deflected by the coriolis force
the total energy emitted by the sun can be calculated from the Stefan-Bolzmann law
-Imagine this total energy being distributed over a sphere whose center coincides with the sun. Let's say the radius of the sphere is d. The total surface area of the sphere is proportional to d2. As the radius of the sphere increases, the same energy is distributed over a larger and larger area. The energy per unit area, or flux, falls off as 1/d2. -earth is about 150 million km from the sun -The result is about 342 W/m2 of solar radiation reaching the top of earth's atmosphere on average.
Outgoing longwave radiation
-The Earth emit radiation like a blackbody. This emission is in form of infrared or longwave radiation, and depends on the temperature of emission
Our carbon emission have resulted with...
a significant increase in atmospheric CO2
Coriolios force:Objects move to the...... of wind in the Southern Hemisphere
left
We can solve for T by dividing 240 by σ, and taking the fourth root. We find that T=255K (-18oC or 0oF). However, Earth's temp on average is 288K. What is this discrepency?
This discrepancy is a measure of the planet's greenhouse effect
Albedo
-earth also reflects solar radiation -we define the reflectivity or albedo as the ratio of reflected to incident radiation -the albedo of the Earth is about .3, meaning 30% of the incoming solar flux is reflected back to space -certain regions are typically much more reflective than others -incoming solar radiation changes with latitude, season, surface conditions and clouds
Radiation
-transfer of energy due to electromagnetic radiation -the radiation emanting from substance 1 encounters substance 2, which absorbs the radiation -the absorbed radiation heats substance 2 -ex. visible solar radiation, and infared terrestrial radiation from the Earth's surface
terrestrial fluxes key features
-Terrestrial fluxes are largest over the subtropics and deserts, and smallest over the poles in wintertime, and deep tropics, especially rain forests. -Seasonal variation in the terrestrial fluxes follows the seasonal variation of temperature. -Outgoing terrestrial fluxes are distributed more uniformly than net solar fluxes.
Upward Sensible heat fluxes are greatest in which two places?
Hot, drive land surfaces such as deserts and warms oceans in the wintertime
What are some key features of the planet's net solar flux distribution?
-Latitude is the key determinant of how much solar radiation any given location receives -influences of the planet's albedo can be seen in 1. high latitudes 2. deserts 3. deep tropics (note overall importance of clouds (equator, tropics, mid latitudes)) -enormous contrast between solar radiation over the summer hemisphere and the winter pole, which receives almost none
How can air movement be explained?
-in terms of surface pressure, which measures the weight of the entire column of air
Wein's displacement law
the distribution's peak wavelength is inversely proportional to the temperature of the object (=2898/T)
humans added ..... of carbon per year
10.7 Gt
Two main sources of anthropogenic carbon
fossil fuel burning and land use change
ISR calculation
If S is the incoming solar flux, and α is the planet's albedo, then: S(1-a)=342(1-0.3)»240W/m2
Planck functions for temperatures characterstic of the sun and the earth
-wavelength distributions of the radiation emitted by the sun and the earth differ because the sun is much hotter than the earth
solar raidiation
-Because there is little overlap in wavelength between the radiation emitted by the earth and the radiation emitted by the sun, almost all light in the earth's atmosphere with a wavelength less than 3 microns is solar in origin, and is known as solar radiation
Where is precipitation highest?
the rising part of the Hadley cell, lowest in the subtropics
The ocean's heat capacity is high and can absorb
a lot of energy with small changes in temperature
Terrestrial and solar radiation & atmospheric absorption
Most solar radiation can make it all the way through the atmosphere, but very little terrestrial radiation can.
Coriolios force:Objects move to the...... of wind in the Northern Hemisphere
Right
Why does solar flux at the surface vary?
the angle between the surface and the direction of the radiation -a more oblique angle gives a greater area over which the energy is absorbed, hence less energy per unit area -this is one reason the poles receive less energy than the equator
Ekman drift is responsible for:
coastal upwelling and equatorial upwelling
cooling and sinking motions are associated with
high pressures
Wind drives ocean surface citculation organized into:
gyres, which rotate clockwise in the northern hemisphere, and counterclockwise in the southern hemisphere
Downward sensible heat fluxes occur where?
greatest over cold continents in wintertime (ex. north america, Eurasia, and Antartica)
terrestrial radiation
At the same time, almost all light in the earth's atmosphere with a wavelength greater than 3 microns comes from the earth or its atmosphere, and is called terrestrial radiation
Section 2
(13 cards)