climate earth’s radiation balance. solar radiation budget life on earth is supported by energy...
Post on 20-Dec-2015
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Climate
Earth’s Radiation Balance
Solar Radiation Budget
• Life on earth is supported by energy from the sun
• Energy from the sun is not simply absorbed by earth, but also retransmitted
• Without retransmission, all water would boil away & all life would fry
• The balance between absorption and retransmission of the sun’s energy is called the radiation budget
Basic Processes Governing the Radiation Balance
• Insolation measures the amount of energy coming from the sun via short wave radiation.
• Measured in watts/sec• Top graphic is winter• Bottom graphic is
summer
Insolation
Annual Insolation
Albedo
• Degree of reflectivity of the Earth-Atmosphere system (ranges from 0-1)
• Ice and sand are highly reflective (high albedo)
• Oceans and forests don’t reflect much (low albedo)
• top-winter• bottom-summer
Annual Albedo
Short Wave Reflected Radiation
• Measures the amount of the sun’s energy that is reflected due to the albedo
• Measured in watts/m2
• Does not affect processes on earth since it is never absorbed
• Top-winter• Bottom-summer
Annual Short Wave Reflection
Short Wave Absorption
• The energy absorbed by the earth-atmosphere system
• Primary cause of earth’s surface temperature
Annual Short Wave Absorption
Surface Temperature
• Provides a measure of the temperature all over the Earth
• Temperatures measured in Kelvin
• Heat at the surface is translated into long wave radiation
Annual Surface Temperature
Radiation Spectra for Sun & Earth
• The wavelength energy emitted by a body is inversely related to the temperature of the body.
(nm) = 2.9 x 106/T
Outgoing Long Wave Radiation
• Measures the amount of energy leaving the Earth
• Results from the surface temperature
• Also called terrestrial radiation
• Measured in watts/m2
Annual Long Wave Terrestrial Emission
Net Radiation
• Difference between incoming and outgoing radiation
• Over time and space this is zero
Annual Net Radiation
Greenhouse Amount
• Amount of energy retained by Earth’s atmosphere
• This storage of energy is called the Greenhouse Effect
• Necessary for maintaining life on Earth
Greenhouse Percent
• Amount of energy stored in atmosphere
• Shows Greenhouse Effect as a fraction of the total possible energy that could be stored in the atmosphere
• Useful for detecting changes over time
• Annual graphic
Partitioning of Incoming SW Radiation• ~19 units absorbed in
atmosphere to become heat & LW radiation – 2 units by ozone
– 17 units by clouds & gases
• ~23 units scattered & then absorbed as diffused insolation
• ~28 units directly absorbed at surface
• Total absorbed = 70 units
Processes of Retransmission
• Three modes– latent heat (drives
hydrological cycle)
– sensible heat (atmosphere heated by updrafts)
– radiation of IR into space
• Total of 70 units emitted
Comparison of Radiation Budgets of the Terrestrial Planets• Compare Earth, Venus & Mars
• Earth & Venus have similar mass & dimensions; Mars 10% Earth’s mass & half as large
• Temperatures expected to be in the order:Venus > Earth > Mars
• Observed:Earth (255 K) > Venus (234 K) > Mars (217 K)
• The surface temperatures bear little resemblance to their effective temperaturesVenus (427oC) > Earth (15oC) > Mars (-53oC)
• Due to greenhouse effect• Venus
– extensive atmosphere (100x more mass than Earth’s)
– composed mainly of CO2, H2O, SO2
• Mars– atmosphere contains more CO2 Earth’s
– has 100x less water than Earth’s atmosphere