Power to the Looney toons OCNG 251 Oceanography Tuesday Sept 30th 2008 Part 1 i The Earth heat budget ii Wind Patterns Oceans and Climate Systems What do we have left before Mid Term 1 The structure of the Oceans a The Earth heat budget b Wind patterns 2 Filling up the Ocean a Physical Properties of Water b TS Diagram Density Structure of Oceans 3 The Ocean in motion a Horizontal and vertical circulation b Global circulation 4 Climate Variability a Climate Change Past Future b El Ni o Southern North Atlantic Oscillations Radiation and temperature Any object with a temperature above absolute 0 1 Emits radiation 2 At a wavelength directly proportional to its temperature the higher the temperature the faster the electrons vibrate Stefan Boltzmann Law E T4 E is the maximum emitted energy per m2 is a constant 5 67x10 8 W m2 k4 T is the object object s surface temperature in Kelvin Earth s Radiative equilibrium temperature The state at which absorption of solar radiation emission of IR radiation 255 K 18 C But the actual T of Earth is much higher than that 288 K 15 15 C How can we explain the 33 33 difference Radiation The basics about electromagnetic radiation The shorter the wavelength the more energy it carries from X rays and Gamma rays to radio waves E h or hc E is the energy of a photon is the frequency of the corresponding electromagnetic wave is its wavelength h is a constant known as Planck Planck s constant 6 63 10 34 Joules per second Radiation and temperature Any object with a temperature above absolute 0 3 Emits radiation at a wavelength inversely proportional to its temperature the higher the energy the shorter the wavelength Wien Wien s Law max Constant T max is the maximum wavelength emitted The constant is 3000 m K Radiation Spectra of Sun and Earth max Sun 3000 mK 6000 K 0 5 m max Earth 3000 mK 300 K 10 m Fate of Radiation Dependent on the medium it is meeting 44 of the sun sun s radiation in the visible region 0 4 0 7 m 7 as UV and 37 as near IR 88 of the sun energy is radiated at wavelength 1 5 1 5 m While the Earth emits in the far IR IR 10 m Radiation absorption and emission Radiation may be absorbed by many types of materials It turns out that all objects are able to emit radiation at all wavelengths and similarly absorb all types of radiation Radiation absorption and emission So the sun shines shines and the Earth bakes bakes but really really The Earth also looses looses its energy as fast as it gains it so it shines in its own right shines The energy is not lost but rather converted to some type of internal energy within the absorbing medium Any object that is a perfect absorber and perfect emitter is called a blackbody The Sun and Earth both absorb and emit radiation close to 100 efficiency blackbodies Radiating in the IR portion of the spectrum Long wavelength low radiation energy Radiation absorption and emission Not all substances on Earth behave as blackbodies Most substances are selective absorbers i e glass UV and IR Selective absorption of radiation in the Atmosphere O2 and O3 absorb almost 100 of the UV radiation of 0 3 m Objects that selectively absorb radiation also selectively re emit radiation at the same wavelength Kirchhoff Kirchhoff s Law Good absorbers are good emitters at a particular Specifically for gases 0 1 0 3 0 5 0 7 H2O and CO2 are strong absorbers of IR radiation and poor absorbers of visible radiation 0 1 0 3 0 5 0 7 1 5 10 15 20 0 1 0 3 0 5 0 7 1 5 10 15 20 1 5 10 15 20 CH4 and N2O and O3 are also strong absorbers of IR radiation As these gases absorb IR emitted by the Earth Earth s surface remember that most of it comes from Earth they gain kinetic energy Kinetic energy transferred to O2 and N2 temperature Atmospheric greenhouse effect Atmos window H2O CO2 CH4 NO2 CFC Earth Energy Balance Solar constant 1370 W m2 caught by a disc disc facing the Sun and retransmitted to the whole Earth sphere Sc x r2 4 4 r2 Sc 4 340 W m2 The Earth s heat budget Do we have a surplus Is it going to Social Security Q Qs Qb Qh Qe Qv 0 Qb back radiation Qh Thermal Cond Qv Advection Qe Evaporation Qs Solar radiation Earth Energy Balance Although average T vary seasonally and spatially the Earth Earth s overall T changes only slightly over the years must must return to space the same amount of energy it absorbed Total energy input 100 units per unit time The Heat Budget The wavelength of energy radiated from a body is inversely proportional to the temperature of the body Sun radiates at shorter wavelengths 0 5 m visible than the Earth 10 m infrared The average temperature of Earth s surface and the lower layer of atmosphere is 15 C However if the atmosphere contained no water vapor CO2 or CH4 the temperature of the Earth would be about 18 C The greenhouse effect H2O vapor 73 or 24 C CO2 21 or 7 C CH4 6 or 2 C Earth Energy Balance More details Where are the other 30 Balanced Budget Incoming 65 of Qs 35 bounce off Earth surface and Atmosphere albedo 17 are absorbed by the atmosphere 48 are absorbed by Earth Outgoing 8 are emitted directly as Earth s back radiation 27 are emitted directly by the atmosphere 19 transferred by conduction 46 transferred by evaporation Global Radiation Balance Equation Solar Constant short wave radiation radiation Solar 2 constant 1370 W m caught by a disc disc facing the Sun and retransmitted to the whole Earth sphere Sc x r2 4 4 r2 Sc 4 340 W m2 Reflection albedo albedo Reflective quality of Earth Earth s surface and atmosphere Short wave radiation is reflected back to space without being absorbed Absorption and back radiation back radiation Assimilation Assimilation of short wave radiation energy and its conversion to long wave radiation displacement from short energetic wavelength to longer less energetic wavelengths Global Radiation Solar Short Wave Radiation SW Reflection Albedo Absorption and back radiation LW If the total system here Earth does not gain or lose energy then SW Albedo LW 0 Or SW Albedo LW 1 Sphericity 2 Seasonality If the Earth were a disk with its surface perpendicular to the rays of sunlight each point on it would receive the same amount of radiation However the Earth is a sphere and its surface tilts with respect to the incoming rays of energy with the regions furthest away aligned in parallel to the radiation and thus receiving no energy at all The Earth Earth s axis is tilted in relation to the plane of the ecliptic the Sun Earth plane that cuts through both centers Global Radiation Balance Equation