Solar Radiation: The driving factor • Radiation (energy transmitted as waves, rays and particles) released, absorbed & reflected by all things • travels as both a particle and a wave • is affected by - gravity, magnetism, and atmosphere composition, distance, angle of incidence • provides Earth with an external source of energy
The sun produces most of its electromagnetic energy in intermediate wavelengths / frequencies. True False
Sources of radiation • Sun and other stars are dominant source - Sun is closest so it has a greater influence • Earth emits some energy as well - Solar radiation is absorbed by Earth and transformed into longwave radiation • Many other planets emit radiation as well - e.g., Jupiter and Saturn - source is from the planet itself not all is absorbed and re-emitted like Earth
The Sun • 93 million miles from Earth • It rotates once every 600 hrs (25 days) • Has hot spots and "cool" spots - sunspots are relatively "cool" Produces electro- magnetic radiative energy • - concentrated in UV, Visible & IR spectral classes
Sunspots - cyclical magnetic “storms” that occur in 11 year cycles are lower in temperature, but increase solar output. Solar Max = lots of sunspots and increased energy output Solar Min = few to no sunspots and decreased energy output
Long Short Electromagnetic Spectrum (l) Frequency (mHz) refers to vibration of particles Wavelength ( ) = distance between wave crests l
Position affects radiation • • Far away=less radiation Far away=less radiation; Closer=more radiation • • Titled toward= more radiation Titled away=less radiation; Tilted toward = more
The northern hemisphere experiences winter because the Earth is farther away from the Sun than it is during the summer months. True False
Eccentricity 100 kyr cycle Earth’s orbit aphelion
Obliquity 41 kyr cycle Axis 20 kyr ago Axis at present Axis at 20 kyr in future Perpendicular to the ecliptic
Precession of Equinox 22 kyr cycle Conditions 11 kyr ago sun Earth at perihelion Earth at aphelion sun Conditions now Path of Earth’s orbit around the sun
Precession 22 kyr cycle
Milankovitch cycles- pacemaker to the ice ages * fromO18 ice and deep sea sediment cores
The atmosphere acts as a mirror, prism and a trap • Scatters some of the radiation Ozone & dust - why the sky is blue prism • Reflects some of the radiation Dust & clouds - clouds, snow, water etc. mirror • Absorbs some of the radiation Clouds & gases - ground, ozone, dust, etc. trap
Albedo = ________________ reflected radiation Albedo = ________________ incident radiation ･ A measure of the amount of reflected radiation ･ Some things reflect radiation better than others - "dry" or "cold" Snow & Ice = high albedo - water = moderate for visible, low for infrared - plants= moderate for visible ･ Land absorbs and releases radiative energy quicker than water
Albedo of land surfaces on Earth Warm colors are higher; cool are lower; white no data available Data collected by NASA’s MODIS satellite, April 2002
IR output from Earth K
Effects of cloud type on radiation budget • different types of interference have different effects on Earth's energy budget