section E:

electromagnetic energy: (3)

• form of energy that propagates as both electric and magnetic waves

• travel in packets of energy called photons

• includes light, radiation, electromagnetic waves/radiation

electromagnetic energy can be described by what 3 things?

wavelength, frequency and energy

wavelength:

measured crest to crest or trough to trough; is the distance between one wave crest to another one or one wave trough to the next

frequency:

is the number of waves that pass in a given time

energy:

the ability to do work

what emits electromagnetic energy?

everything above absolute zero (0*K or -273*C) emits electromagnetic energy

2 electromagnetic radiation principles:

1. Wein’s law

2. Stefan-Boltzmann law

Wein’s law:

describes the INVERSE relationship between temperature of an object and the wavelength that it emits

• hotter objects emit shorter wavelengths

• colder objects emit longer wavelengths

hotter objects emit…

shorter wavelengths and more total amounts of radiation

cooler objects emit…

longer wavelengths and less total amounts of radiation

sun mostly emits _____ energy:

shortwave

earth emits mostly ______ energy:

longwave

Stefan-Boltzmann law:

describes the direct relationship between the absolute temperature and the amount of radiation

• hotter objects emit more total amounts of radiation than cooler objects

• cooler objects emit less total amounts of radiation than hotter objects

who emits more radiation? the sun or the earth?

the sun

electromagnetic spectrum:

is a classification system that describes the entire wavelength of electromagnetic energy

micrometer:

1 (mew)m = 1/1,000,000m (1×10^-6)

nanometer:

1nm = 1/1,000,000,000m (1×10^-9)

visible light wavlength:

0.4 micrometers to 0.7

what 3 parts of the electromagnetic spectrum are of particular interest to geographers?

• infrared radiation

• visible light

• ultraviolet

infrared wavelength:

0.7 micrometers to 1000

ultraviolet wavelength:

0.01 micrometers to 0.4

visible light and ultra violet are on what end of the electromagnetic spectrum?

short wave

infrared is on what end of the electromagnetic spectrum?

long wave

infrared radiation: (2)

• earth radiation is entirely thermal infrared (longwave!)

• ~45% of the solar energy infrared (short wave)

visible light: (3)

• 47% of the solar energy

• ~ short wave

• where indigo is the shortest wavelength of visible light and red is the longest wavelength of visible light

ultraviolet: (3)

• ~8% of the solar energy

• most is filtered by the ozone layer

• short wave

the sun: (4)

• nuclear fusion (H—>He) creates electromagnetic (solar) radiation

• temperatures; surface - 6000*C, internal - 16 million*C

• 150 million km from earth

• earth intercepts a very small portion of all solar radiation

what is the speed of light and how long does it take light from the sun to reach earth?

speed of light 300,000km/s

• ~8 mins to reach earth

does the sun’s emitted electromagnetic energy lose energy on its journey to earth?

NO! electromagnetic energy emitted by the sun does not lose any energy it just is going in all directions and therefore the earth only absorbs a small portion of the total solar output

• rays aren’t losing energy - we just receive a small portion as the rays diverge/spread across space

solar radiation: (3)

• travels through space without loss of energy

• intensity diminishes with distance from the sun (more diffusely spread)

• small fraction intercepted by the sun (0.000,000,000,45)

inverse square law of intensity:

I/d²

• where I is the intensity if radiation at 1 unit of distance

• D is distance travelled in those units

insolation:

incoming solar radiation

solar constant: (3)

is the total solar irradiance

• almost constant amounts of solar insolation received at the top of atmosphere per square meter

• ~1367 W/m²

universe is made up of what 2 things?

energy and matter

matter:

solids, liquids, gases and their atomic particles with which all things are made up of

energy: (assigned reading)

the ability to do work; anything that has the ability to change the state or condition of matter - can neither be created nor destroyed

types of energy:

kinetic, chemical, gravitational, potential, radiant

work:

refers to force acting over distance

power:

another way to look at energy, by measuring how much energy is transferred per unit of time

• unit is watt (W)

internal energy:

where the state of a substance (solid, liquid, gas, plasma) depends on how vigorously the molecules jiggle in place - in constant movement, where internal energy is a form of kinetic energy

kinetic energy:

energy of movement

temperature:

a description of the average kinetic energy of the molecules in a substance; the more vigorously the molecules jiggle (and therefore the greater the internal/kinetic energy) the higher the temperature of a substance

• popular terms; a measure of the degree of hotness or coldness of a substance

3 temperature scales:

• fahrenheit (*F)

• celsius (*C)

• kelvin (K)

heat:

aka thermal energy; is energy that transfers from one object or substance to another because of a difference in temperature

radiation: (AR)

process in which electromagnetic energy is emitted from a body; the flow of energy in the form of electromagnetic waves

absorption: (AR)

the ability of an object to assimilate energy from electromagnetic waves that strike it

reflection: (AR)

the ability of an object to repel waves without altering the object or the waves

albedo: (AR)

the reflectivity of a surface - the fraction of total solar radiation that is reflected back, unchanged, into space

scattering: (AR)

the deflection of light waves in random directions by gas molecules and particulates in the atmosphere; shorter wavelengths of visible light are more easily scattered than longer wavelengths

transmission: (AR)

the ability of a medium to allow electromagnetic waves to pass through it

greenhouse effect: (AR)

the warming in the lower troposphere causes by the differential transmissivity of radiation through the greenhouse gases in the atmosphere; the atmosphered easily transmits incoming shortwave radiation from the sun but inhibits the transmission of outgoing longwave radiation from the surface

greenhouse gases: (AR)

gases that can transmit incoming shortwave radiation from the sun but absorb outgoing longwave terrestrial radiation; the most important natural greenhouse gases are water vapour and carbon dioxide

conduction: (AR)

the movement of energy from one molecule to another without changing the relative positions of the molecules - it enables the transfer of heat between different parts of a stationary body

convection: (AR)

energy transfer through the vertical circulation and movement of fluids, such as air, due to density differences

convection cell: (AR)

a closed pattern of convective circulation

advection: (AR)

horizontal transfer of energy, such as through the movement of wind across earth’s surface

the flow of solar radiation in the atmosphere:

as solar radiation flows through earth’s atmosphere it may flow unimpeded (transmission) or it may be modified by absorption, reflection or scattering

UV region covers the wavelength range of…

100-400nm

UV is subdivided into 3 bands:

UVA, UVB, UVC

UVA:

most reaches earth - transmits through window glass

UVB:

~10% reaches earth - blocked by window glass

UVC:

all absorbed by atmosphere

absorption:

gases & particulates interrupt the flow of radiation by absorbing specific wavelengths and gain heat - note different colours have different absorption abilities!

reflection:

redirected radiation returning to space and has no heating effect - ability of an object to repel waves

scattering:

solar radiation bounces off an object in a variety of directions and has no heating effect - shorter wavelengths more easily scattered

blue skies: (2)

• thanks to rayleigh scattering

• shorter wavelengths (blues/violets) are scattered more easily than longer wavelengths hence why we observe a blue sky

why is the sky not purple?

there are more blue wavelengths and our eyes readily observe blue light much easier than violet light

red sunsets:

sun is low in the sky and light passes through so much atmosphere that all the blues are scattered away, leaving longer wavelengths (reds, oranges, yellows)

portion of direct solar radiation:

25% - uninterrupted straight through the atmosphere to the surface with no interference

portion of reflection/scattering of solar radiation:

31% - attributed to clouds and dust, other particulates scatter away radiation - do not reach the surface/lost

portion of solar radiation absorbed by the atmosphere:

24% - not reaching the surface; absorbed by atmosphere or ozone

portion of indirect/diffuse solar radiation:

20% - went through a journey but still made it to the surface ultimately

what percent of solar radiation reaches the surface?

45% - 25% direct and 20% diffuse/indirect

greenhouse effect: (4)

• shortwave radiation from the sun is more transmissible through the atmosphere compared to long wave

• shortwave is absorbed at the surface and long-wave (thermal infrared) is emitted by the earth

• thermal infrared long-wave emitted by the earth is radiated into the atmosphere which is warms the earth (note that the waves cannot pass through window/glass and is trapped)

• warms the atmosphere!

counterradiation:

long wave radiation emitted by the surface, absorbed by greenhouse gases, and re-radiated back towards the surface as long wave (the process which keeps the earth at an average of 15*C)

does the sun directly warm the earth?

no! the greenhouse effect from the suns radiation warms the atmosphere

absorbed radiation:

of the 45% of solar radiation that reaches the surface of the earth 96% of energy is absorbed by the land and water bodies and stored as heat (latent or sensible)

2 kinds of heat:

sensible or latent

sensible heat:

can be sensed and measured

latent heat:

is hidden and cannot be measured

latent heat definition:

latent heat is energy stored or released when a substance changes state

stored energy is lost in several ways: (3)

• through conduction to gases in the atmosphere

• removed by evaporation and stored as latent heat

• radiation into atmosphere or lost to space

albedo: (3)

• the reflectivity of an object; how much insolation will bounce off it

• proportion of solar radiation reflected upward from a surface

• earth’s average albedo: 29-34%

albedo depends on what 2 things:

1. surface characteristics (colour, roughness)

2. angle of incidence (example of rock skipping changing the angle to have more skips)

example of something with low albedo:

black asphalt paving

water body albedo:

variable! sometimes lots of reflectivity and other times not so much - because the angle of incidence

global albedo patterns: what is this showing?

• purple/blue areas have relatively low albedo (concentrated in oceans where radiation is absorbed)

• poles have high albedo (ice reflects most of the radiation) and there is a low angle of incidence

net radiation:

difference between incoming shortwave and outgoing long wave radiation

variations in earth’s net radiation is due to what 3 things?

latitude (aka angle of incidence), seasonality, length of day

variations in net radiation due to latitude:

• low latitudes have a surplus - more incoming than outgoing because the high angle of incidence

• high latitudes have a deficit - more energy is lost/outgoing than incoming because the consistent low angle of incidence

angle of incidence:

the main determinant of the intensity of solar radiation received on earth

• if a ray comes in at 90* it is very concentrated, if it comes at a low angle its distributed more across the surface

why don’t the tropics get hotter and hotter and the poles get colder and colder (angle of incidence)?

the surplus in the low latitudes is moved through atmospheric circulation (75-80%) and ocean currents do the remaining heat/energy transfer

variations in net radiation due to seasonality:

• northern hemisphere; net radiation drops in January and spikes in july

• therefore southern hemisphere - reverse

annual variations in insolation: (4)

daily insolation over a year (at the top of the atmosphere) changes at different latitudes

• higher latitudes have a single peak on the summer solstice

• the equator has two daily peaks in a year (most stable)

• on the summer solstice the north pole receives more total daily insolation than the equator

what is being shown? label the various colours:

annual variations insolation

• yellow 90* N (pole)

• orange 60* N (mid latitudes)

• green 30* N (low latitudes)

• blue equator (most stable with two characteristic peaks)

the global radiation budget refers to…

variations in annual insolation at different latitudes

air and surface temperature measures…

the amount of SENSIBLE heat (heat you can feel)

surface temperature:

measure of kinetic energy contained in a region very close to earth’s surface

atmospheric temperature:

measure of kinetic energy in unit of geographical space within the air - measured at 1.2m above the ground (as this can differ greatly from surface / think asphalt driveways)

temperature determinant:

determined by energy balance of a substance