// lecture 05 Flashcards
factors that influence climate at a given place:
sunshine (and latitude), topography/mountains, proximity to oceans and large lakes, ocean currents, presence of trees/vegetation.
energy from the sun is
electromagnetic radiation. goes through space at the speed of light. either absorbed or reflected once it gets to earth.
radiation with shorter wavelengths are
more energetic.
shortest wavelength to longest wavelength:
gamma rays, x-rays, ultraviolet (UV) radiation, visible light, infrared radiation, microwaves, and radiowaves.
the sun emits:
- visible light.
- near infrared radiation (infrared with very short wavelength, but longer than visible).
- small, but dangerous, amount of ultraviolet radiation.
these three bands together are called “shortwave radiation” or “solar radiation.”
insolation
the amount of solar radiation energy coming in.
by the time it gets to the top of the atmosphere, the sun shines at a strength of
1360 watts per square meter.
1360 W/m^2 is roughly what’s experienced in the
tropics when the sun is directly overhead.
if the area is perpendicular to the solar beam,
then the solar energy per unit area is maximized.
solar x exposure area
sweat x skin area.
the average incoming solar radiation is
340 W/m^2, which is exactly 1/4 of 1,360 W/m^2.
high latitudes get less
direct radiation, which spreads out more.
shadow area of a sphere (a circle) is
1/4 of the surface area of a sphere 4pir^2. shadow area = pir^2.
only ___ of solar radiation gets absorbed in the ____
20%, atmosphere; 50%, surface; and 30%, reflected back to space.
albedo
fraction of incident light that’s reflected away. ranges from 0 (no reflection) to 1 (all gets reflected).
human eye sensitivity is most to
wavelengths around 550 nanometers. when light levels are low, it shifts to around 500 nanometers.
solar emission peaks in the
blue region of visible radiation, which is a big part of the solar emission.
near infrared also constitues an
important energy flux.
albedo values for earth:
- cloud albedo varies from 0.2 to 0.7. thicker clouds have higher albedo.
- snow albedo ranges from 0.4 - 0.9 (depends on age) and ice is about 0.4.
- ocean is < 0.1, forests are 0.15, and deserts are 0.3.
30% of incoming solar radiation is reflected away by:
15% from clouds, 8% from the surface, and 7% by the atmosphere (things like dust from deserts and air pollution are key).
Earth Radiation Budget Experiment
measured Earth’s albedo from a system of orbiting satellites.
total absorbed solar radiation is
70% of the incoming solar radiation because 30% is reflected away. 70% of 340 W/m^2 = 240 W/m^2.
earth loses energy through
infrared radiation (longwave radiation)
everything emits radiation, which depends
partly on the substance, but mostly on temperature.
thermal night vision technology
detects longwave radiation.
higher temperature =
more radiation and more energetic radiation (shorter wavelength).
the earth is heated by tje
sun (shortwave radiation) and it loses energy by longwave radiation (out to space).
if the energy (solar radiation) into a system (Earth) is greater than
the energy out (outgoing longwave radiation), the temperature will increase, which results in an increase of energy out (longwave radiation). this will happen until E in = E out (energy balance).
global warming…
upsets the energy balance of the planet.
if there was no atmosphere for energy balance to occur,
the mean temperature of the earth would be -18 C.
greenhouse effect:
all longwave radiation doesn’t escape directly to space.
Stefan-Boltzmann law
- a body emits as the fourth power of its temperature in Kelvins.
- Kelvin is the absolute temperature scale 0 C = 273 K.
- the hotter an object, the more radiation it emits: blackbody emission = sigma T^4 where sigma = 5.67 x 10^-8 W m^-2 K^-4.
- the basic way earth stabilizes its temperature is by getting hotter and emitting more energy to space.
the temperature of a black body that emits the same amount of longwave radiation that the earth needs to emit to balance its absorbed solar radiation
absorbed solar radiation = emitted longwave radiation 5/4(1 - albedo) = sigma T^4.
greenhouse gases block longwave radiation from
escaping directly back to space. these gases re-radiate both upward and downward. the extra radiation causes additional warming of the surface.
greenhouses gases cause the
outgoing radiation to happen at higher levels (no longer at the surface). air gets colder as you go upward, so the radiation space is much less (colder -> less emission).
atmosphere and surface are black bodies for
terrestrial. atmosphere is transparent to solar.
