Section E: Global Energy System

what is electromagnetic energy

form of energy that propagates as both electric and magnetic waves, travels in packets of energy called photons

electromagnetic energy can be described by

wavelength, frequency, energy

everything above ___ emits electromagnetic energy

absolute zero (0°K=-273°C)

first principle of electromagnetic radiation

inverse relationship between temperature of an object and wavelength that it emits

• wein’s law

• hotter objects emit shorter wavelengths

second principle of electromagnetic radiation

direct relationship between the absolute temperature and the amount of radiation

• stephan-boltzmann law

• hotter objects emit more radiation than cooler objects

• earth emits less radiation than the sun

infrared radiation

(0.7 to 1000µm)

• earth radiation is entirely (thermal) infrared (long wave)

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

visible light

(0.4 to 0.7µm) 47% of the solar energy coming from the sun.

• short wave

ultraviolet

(0.01 to 0.4µm)

• 8% of solar energy

• most filtered by ozone layer

• short wave

what is the temperature of the sun

6000°C at surface, 16 million°C internal

how far is the earth from the sun

150 million km

what is the speed of light

300,000km/s

what creates electromagnetic radiation

nuclear fusion (H→He)

how much solar radiation does earth intercept

a very small amount

solar radiation travels through space with or without loss of energy

without

how does the intensity of solar radiation change with distance from the sun

it diminishes

what is the inverse square law of intensity

I/d² where

• I=intensity of radiation at 1 unit distance

• d=distance travelled in those units

insolation

incoming solar radiation

explain solar constant

total solar irradiance

• almost constant amount of solar insolation received at top of atmosphere per square meter over a year

what is the numerical value of the solar constant

1367 W/m²

what are the three ways solar radiation can be modified

absorption, reflection, scattering

UVA

most reaches earth, transmits through window glass, what sunscreen blocks

UVB

10% reaches earth, blocked by window glass

UVC

all absorbed by atmosphere

absorption

electromagnetic waves assimilated by that object

reflection

ability of an object to repel electromagnetic waves that strike it. no heating effect

scattering

deflection of light waves in a variety of directions. has no heating effect. depends on wavelength.

why is the sky blue

rayleigh scattering. shorter wavelengths are scattered more easily than longer wavelengths. more blue than purple in electromagnetic spectrum

explain 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 like red and orange

how much solar energy reaches the surface of the earth

45% (25% direct and 20% indirect)

how much solar energy doesn’t make it to the earth

55%

explain the greenhouse effect

sun sends shortwave to earth, earth absorbs 45% of it. thermal infrared from earth is radiated back. that longwave from the earth heats up the atmosphere

counterradiation

longwave radiation emitted by the surface absorbed by greenhouse gases and re radiated back towards the surface as longwave

sensible heat

can be sensed (feel and touch) and measured

latent heat

is hidden and cannot be measured. energy stored or released when substance changes state

stored energy lost in several such as

conduction to gases in the atmosphere, removed by evaporation and stored as latent heat, radiation into atmosphere or lost in space

albedo

overall reflectivity of an object or surface

explain it

purple area=low albedo, low latitudes so high angle of incidence. poles have high albedo (ice reflects most of the radiation), low angle of incidence

net radiation

difference between incoming shortwave and outgoing longwave radiation

variations in earth’s net radiation due to

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

explain surplus and deficit

low latitudes=surplus of energy because more incoming than outgoing. high latitudes=deficit because more outgoing than incoming. (low angle of incidence so energy more spread out)

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

angle of incidence

the global radiation budget

variations in annual insolation at different latitudes

surface temperature

measure of kinetic energy contained in a region very close to earth’s surface (hot asphalt)

atmospheric temperature

measure of kinetic energy in unit of geographical space within the air. measured at 1.2m above ground

surface and air temperature

measures the amount of sensible heat

temperature is determined by

energy balance of a substance

average annual temperature

avg temp calculated over the course of the year (mean annual temp)

controlled mainly by elevation and latitude

annual temperature range

difference between the avg max and avg min temps over a year at a location (seasonality)

three main large scale geographic factors that influence air temperatures

latitude, seasons, and length of day

explain latitudes as a factor that influences air temp

different angle of incidence causes energy to be directed in smaller of larger surface areas.

low lats: high amounts of solar energy

high lats: lower angle of incidence = less solar energy

explain seasons and length of day as a factor that influences air temp

axial tilt and migration of subsolar point. influences day light length and daily radiation patterns (mid lats)

day length at equator always the same

what is a local factor that influences air temp

maritimes vs continental locations

maritime

places that are located within or near a very large body of water and are more moderate and humid climate

continental

places surrounded by landmasses. more extreme climates (warmer summers and colder winters)

land cools and heats more rapidly than water due to

specific heat, transmission, mobility, evaporative cooling

specific heat

amount of energy it takes to raise the temp of 1 gram of a substance by 1°C

transmission

heat gets spread out in water better than on land

mobility

water disperses heat down through convection. on land it disperses only by conduction (bad at it)

evaporative cooling

evaporation = cooling process (heat is lost). land has some evaporation but a lot less

it takes _ times more energy to heat water than a land substance

5

other factors that influence air temp

altitude, slope aspect, topographic barriers, wind flow patterns

explain altitude as a factor

as altitude increases, atmospheric pressure, temperature and moisture content decreases. but temperature range increases

slope aspect

direction slope is facing

topographic barriers

divert/funnel wind. windward = side that faces wind (wet side). leeward = side sheltered from wind (warm dry side).

wind flow patterns

direction of wind flow can change air temp depending on source of air, its modification and barriers

urban area temps

dry surfaces = less vegetation and less water, stored heat, dark surface= low albedo, fossil fuels = heat byproduct

rural areas temp

more reflective surfaces, wetter surfaces=more water, evaporation + transpiration = evapotranspiration, cools surface