Radiation Flashcards
name 3 things that happens to the solar radiation as its transmitted through earths atmosphere between the atmosphere and ground?
scattering
reflection and absoption of short wave radiation
emittance of long wave radiation
what is solar energy?
radiant light and heat energy emitted by the sun
What is short wave radiation?
UV - visible light
shorter wavelength
how much energy does SWL have?
lots
where does SWL come from?
The sun emits SWL radiation which is directly diffused/ scattered , reflected or absorbed
What is Long wave radiation?
infrared
longer wavelength
how much energy does LW radiation have?
less energy than SW
Where does LW radiation come from?
the ground heats up and re emits as long wave radiation as infrared
define albedo
the reflectivity of a material
how can albedo be calculated?
ratio of outgoing radiation and incoming SW radiation
what does it mean by reflected?
bounces off something and goes in another direction eg a tree
everything we see has light reflecting off it - thats why we cant see very well in dark room
what things cause reflection
reflection by ground surface
reflected by clouds
diffuse reflection
what type of reflection do natural surfaces get?
diffuse reflection as they are rough and energy scattered away from surface
(smooth surfaces have purer reflection when angle of incidence approaches angle of reflection)
what is the albdeo of a perfectly black surface?
zero
no reflection
absorbing
what is the albedo of a perfectly white surface?
1
complete reflection
no absorbing
do smooth surfaces increase or decrease albedo ?
increase albedo (rough surfaces decrease albedo)
how many grey tones can the eye detect?
20
When will liquid water have a high albedo?
when suns angle is very low eg sunrise
the angle is low and radiation will be reflected by water
this is why high latiudes reflect more sola radiation (also due to albedo)
When will liquid water have a low albedo?
when sun is above horizon
it absorbs SR
snow and cloud albedo??
high albedo as white and smooth (clouds vary)
0.4-0.9
sand, dry soil and ice albedi???
darker surface and less smooth so lower albedo than snow
0.3-0.4
vegetation and water albedo???
darker and rough surfaces so have low albedo
0.0 - 0.25
what places have the highest albedo?
snow covered areas like antarctica
cloud cover
(high albedo correlates to places with highest Sw radiation being reflected back to space)
what could scatter radiation into atmosphere ?
gases
particulates - dust
water droplets - clouds
what is diffuse insolation?
shortwave radiation that has been scattered without altering wave length
what % of reflectivity or albedo does scattering account for?
7%
depends on size of molecules being scattered
what determines the colour of light?
the wavelength
Define scattering
the process which electromagnetic radiation or particles are deflected or diffused
it depends upon the size of molecules/particles it encounters
what happends when light encounters molecules in atmosphere ?
Shorter WL (blue) - more scattering Longer WL (red) - less scattering
this is called rayleigh scattering
define rayleigh scattering?
when particle sizes are smaller than the wavelength of incident energy
scattering by small particles
define mie scattering?
particles and wavelengths around the same size
larger particles >0.5 um
eg smoke paricles/ very fine dust
scattered equally though in a more forward direction
atmosphere appears white
define non-selective scattering
associated with large particles all wavelengths affected equally
eg raindrops/cloud droplets/ice
what wavelength is scatterred more? red or blue?
shorter blue wavelength scattered more than long red wavelength
(alost 10 times more)
scattering creates blue skies and red sunsets
what 2 things absorbs solar output?
clouds
gases and dust in atmosphere
what makes up a hazy sunshine?
mie scattering - white around sun
rayleigh scattering - blue sky away from sun
what happens to the fraction of energy that makes it to the surface?
its radiated back to space
(longwave radiation)
if it wasnt radiated back to space then the earth would warm
energy balance important but earth is warming now so energy isnt balanced
how much insolation is lost back to space as shortwave radiation?
~31% reflected
meaning ~69% absorbed
what is the average planetary albedo?
~31%
this is high as moons albedo is 8%
how much LW energy is radiated back to space?
~69%
Name 3 ways insolation is remitted?
absorbed by ground and reemitted as longwave radiation
emitted from ground directly to space
emitted from ground and absorbed by atmosphere, then remmitted by atmosphere to space or the ground
what regions radiate the most longwave radiation??
hot locations
they receive higher input of SW radiation
describe 3 latitudinal variations in the energy balance?
more energy absorbed in tropics
more reflection emitted in polar regions
energy into earths surface balances energy out of earth ~36%
what location receives the most energy?
tropics
desert areas have less cloud so less scattering and lots of radiation reaches the surface
over jungle theres clouds so more scattering and less radiation reaches the ground
what location receives the least energy?
poles
greater sun angle, greater distance through atmosphere, more scattering, greater seasonal variations insolation.
