4. SOLAR TERRESTRIAL RADIATION
G109:4. Solar and Terrestrial Radiation14. S OLAR & T ERRESTRIAL R ADIATIONP ART I:R ADIATIONReading Assignment: A&B:Ch. 2(p. 43-53) LM:Lab. 51. Introduction Radiation Mode of Energy transfer by electromagnetic waves only mode to transfer energy without thepresence of a substance (fluid or solid) works best in a vacuum (empty space)Î Radiation the only way for Earth to receiveenergy from the Sun Weather systems are powered by radiation From Earth-Sun geometry we know: spatial and temporal variations of receipt ofradiation at the top of the atmosphere From Atmospheric Composition: important forradiation at the surface O3 UV radiation, shortwave H2O & CO2 IR radiation, greenhouse, longwaveÎ need to consider different types of radiationRadiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation22. Electromagnetic Radiation radiation waves exhibit characteristics of both electricfields and magnetic fields(from A&B, Figure 2-5 a) Electromagnetic radiation moves at “speed of light” radiation spreads in all directions and moves instraight lines(from A&B, Figure 2-9)Radiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation3 Electromagnetic radiation is described by threeinterdependent variables: wavelength λ“lambda”[m, µm] frequencyν“nu”[s-1, Hz] velocityc[m s-1](c “speed of light” 3 108 m s-1)λ·ν c3. Radiation SpectrumDefinition:The Radiation Spectrum is the distribution of radiativeenergy over different wavelengths, or frequencies.In meteorology: only small part of EM-spectrum ofinterest.Î three important ranges: ultraviolet radiation (UV) visible radiation infrared radiation (IR)Radiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation4Radiation in the Earth-Atmosphere SystemWavelengthEffectUltraviolet RadiationUV10-2 – 0.4 µmSunburnClasssun outputEarth output shortwave radiation: longwave radiation:Radiation.docVisible Radiation0.4 – 0.7 µm“sunlight”0.4 µmvioletblue0.5 µmgreenyellow0.6 µmorange0.7 µmredInfrared RadiationIR0.7 – 100 µmheat-radiationnear IRfar IR0.7-1.5 1.5 – 100[µm][µm]Shortwave radiation7%0%43 %0%37 % 0 %only solar radiationIR radiation emitted by the E/A-system9/12/03longwaveradiation11 % 100 %
G109:4. Solar and Terrestrial Radiation54. Radiation LawsRead: A&B Chapter 2, p 35-39(i)General Principles all things emit radiationo the amount and wavelengths depend primarily onthe emission temperatureo higher the T faster the electrons vibrate shorter wavelength λ more total radiation emitted when any radiation is absorbed by an object: increase in molecular motion increase in temperature(ii) Black Bodies and Gray Bodiesan object or body that absorbs all radiation incidenton it is termed a black body idealization: perfect black bodies do not exist often a good approximation for absorption in agiven range of wavelengths many natural substances behave nearly like blackbodiesRadiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation6 a black body is also an ideal emitter emission spectrum follows a general law(Planck’s curve) describing the maximumpossible emission for a given temperature is often used as comparison standard foremission spectrum a black body has an ideal emission efficiency,termed emissivity:ε 1 an object or body with a less than ideal emissionefficiency (same at all wavelengths) is termed agray body: a gray body has a non-ideal emissionefficiency: emissivityε is often a good approximation for emissionspectra of real objects or bodies1(iii) Reflection – Absorption – Transmission only three things can happen, when radiation with awavelength, λ, hits an object or substance:1. part or all can be reflected:αλ fraction reflected: reflectivity, this part does not interact with the object, it isrejected2. part or all can be absorbed: fraction absorbed: absorptivity, aλ this part raises the temperature of the objectRadiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation7 radiative energy is converted to heat3. part or all can be transmitted:tλ fraction transmitted: transmissivity, this part does not interact with the object, it justgoes through it.Since these are the only possibilities, it follows from theprinciple of conservation:αλ aλ tλ 1(iv) Stefan-Boltzmann Law:the total emitted energy fluxAll objects or substances emit radiation at a rateproportional to the 4th power of their absolutetemperatureTotal energy flux emitted: Ftot [W m-2] :Ftot ε σ T ε4emissivity (0 1); depends on quality of material(see Lab Manual #5 for list of values) σ Stefan-Boltzmann constant 5.67 10-8 [W m-2 K-4] T absolute temperature of emitting object [K] T4 fourth power: faster than linear increase withtemperature.Radiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation8180004th power16000Ftot [W/m2]1400012000416 x ( 2 00T [K]Example Problem(see web under this topic for more exercise problems)If a cloud bottom has a temperature of –10 C, how muchenergy would it be emitting if the emmissivity were 1.0?Solution convert temperature to SI-unit:[ C] [K]T (-10 C) 273.15 263.15 K use Stefan-Boltzmann law for ε 1 (black body):Fcloud ε·σ·T4 1 x 5.67·10-8 x (263.15)4 271.9 W m-2 Check units: units okay – physics okay.[ε·σ·T4] [1] x [W m-2 K-4] x [K4] [W m-2] 9Radiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation(v)Wien’s Displacement Law:9the wavelength of maximum emittanceA rise of temperature in an object not only increasesthe total radiant output, but also shifts this energyoutput to shorter wavelengths, in inverseproportion to the absolute temperatureWavelength of maximum emmittance: λmax [m] :λ maxa a T 1T104010385800 K4000 K2000 K1000 K500 K255 KTempe1036ratu1034reBlackbody Irradiance x [W.m-2]λ λmax wavelength [µm] aconstant: 2898 [µm K] Tabsolute temperature [K]103210-710-610-510-410 -3Wavelength [m]Radiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation10Example Problem(see web under this topic for more exercise problems)If a cloud bottom has a temperature of -10 C what is thewavelength of the peak energy emission? What part ofthe electromagnetic spectrum is this in?Solution convert temperature to SI-unit:[ C] [K]T (-10 C) 273.15 263.15 K use Wien’s law:λmax a·T-1 2898 263.15 11.0 µm Check units: units okay – physics okay.[a·T-1] [µm·K] x [K-1] [µm] 9Radiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation11P ART II: A TMOSPHERIC I NFLUENCESON R ADIATIONReading Assignment: A&B:Ch. 3(p. 68-76) LM:Lab. 51. IntroductionGlobal Shortwave Radiation Balance (overview) 30 % of solar radiation is reflected by clouds,atmospheric gases and the surface 25 % of solar radiation is absorbed by theatmosphere (clouds, atmospheric gases, aerosol) 45 % of solar radiation is absorbed by the surface(oceans, land surface)Influence of Clouds on Shortwave Radiation Balance Clear conditions (no clouds):o 70 % of solar radiation is absorbed by the surface(55% direct, 15% diffuse sky radiation)o only 13 % of solar radiation is reflected Cloudy conditions (overcast):o 25 % of solar radiation is absorbed by the surfacesky radiation)(4% direct,o 51 % of solar radiation is reflectedRadiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation122. Reflection and Scattering of Radiation Reflection: redirection of radiation by a surfaceSpecular Reflection(Mirror)Diffuse Reflection orScattering Scattering by gas molecules or small particles/droplets(from A&B, Figures 3-2, and (Phys.Princ. 2-2) 1)Radiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation Blue Sky and:Rayleigh and13Scattering(from A&B, Figure (Spec. Int. 3-1) 1)oAir Molecules tend to scatter Short Wavelengthsmore, and in all directions the blue end of the visible range diffuse (sky) radiation appears as blueoParticles (droplets, aerosol) tend to scatter AllWavelengths equally, and more forwards thanbackwards (backscatter reflection) mixture of all wavelengths: white light clouds, fog, haze appear as white, gray or milkyoshort-wave reflectance: the albedo ( whiteness)Radiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation143. Transmission of Radiation through theAtmosphere Transmission: the amount of radiation that is left,after going through the atmosphere(from A&B, Figure (Spec. Int. 3-1) 3)a) At the top of the atmosphere white (sun-) light isstarted to be scattered: mostly the blue portionb) As radiation proceeds through the atmosphere, moreof the blue portion is scattered away from the directbeam (further transmitted as diffuse radiation) multiple scatteringc) At the surface mostly the red light is left in thedirect beam sun appears red at sunset/sunriseRadiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation154. Absorption of Radiation in the Atmosphere Absorption: conversion of radiation to heat raises the temperature of theabsorbing substance Kirchoff’s law: if a substance is an efficient emitter in agiven wavelength range, it is also anefficient absorber at the same wavelengthrange:ελ αλ Selective absorption: the absorptivities of atmosphericgases are highly specific to certain spectral bands orwavelength ranges solar radiation (shortwave) absorbers:o UV-absorbers: ozone (O3), oxygen (O2)o visible range (0.4 - 0.7 µm): almost none( window) terrestrial radiation (longwave) absorbers:o IR absorbers: H2O, CO2, N2O, O3, O2o peak terrestrial radiation (8 - 12 µm):almost none( window)The atmosphere is transparent for solar radiation,but nearly opaque for terrestrial radiation:greenhouse radiation trapRadiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation16Atmospheric Windows for Radiation Window:something that lets light (radiation) through Atmospheric Window: a spectral range where theatmosphere is nearly transparentThere are two atmospheric windows: visible range window (0.4 - 0.7 µm): lets most solar radiation through to the surface enables solar radiation to “deliver” the bulk of itsenergy to the surface (for use in climate processes) longwave window (8 - 12 µm): lets some terrestrial radiation through to space enables Earth to “vent off” some of its energy back tospace(from A&B, Figure 3-6a)Radiation.doc9/12/03
G109:4. Solar and Terrestrial Radiation17What happens if the windows are closed? visible range window (0.4 - 0.7 µm):o increased cloud cover, and/or reflective aerosolo increase in global albedoo reduction of energy input into E/A systemo cooling effect longwave window (8 - 12 µm):o increased H2O, CO2 or other greenhouse gaseso increased IR-absorption in atmosphereo warming effect The Greenhouse Effect(more accurately: the enhanced Greenhouse change/globalclimate whatis.html(Jan. 22, 2001)Radiation.doc9/12/03
G109: 4. Solar and Terrestrial Radiation 2 Radiation.doc 9/12/03 2. Electromagnetic Radiation radiation waves exhibit characteristics of both electric fields and magnetic fields (from A&B, Figure 2-5 a) Electrom
4. Solar panel energy rating (i.e. wattage, voltage and amperage). DESIGN OF SYSTEM COMPONENTS Solar Panels 1. Solar Insolation Solar panels receive solar radiation. Solar insolation is the measure of the amount of solar radiation received and is recorded in units of kilowatt-hours per square meter per day (kWh/m2/day). Solar insolation varies .
There are three types of solar cookers, solar box cookers or oven solar cookers, indirect solar cookers, and Concentrating solar cookers [2-10]. Figure 1 shows different types of solar cookers namely. A common solar box cooker consists of an insulated box with a transparent glass or plastic cover that allows solar radiation to pass through.
Non-Ionizing Radiation Non-ionizing radiation includes both low frequency radiation and moderately high frequency radiation, including radio waves, microwaves and infrared radiation, visible light, and lower frequency ultraviolet radiation. Non-ionizing radiation has enough energy to move around the atoms in a molecule or cause them to vibrate .
Medical X-rays or radiation therapy for cancer. Ultraviolet radiation from the sun. These are just a few examples of radiation, its sources, and uses. Radiation is part of our lives. Natural radiation is all around us and manmade radiation ben-efits our daily lives in many ways. Yet radiation is complex and often not well understood.
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Figure 3 shows a plot of solar radiation, according to ASTM G159-98 and ASTM E-490 standards. Solar radoiation includes high levels of visible and NIR radiation, in spite of water absorption bands, but due to strong atmospheric VUV absorption, terrestrial solar collectors cannot
Advanced Engineering Mathematics E Kreyszig; Wiley; 2001 4. Calculus, R A Adams; Pearson; 2002. Calculus (6th Edition) E W Swokowski, M Olinick, D Pence; PWS; 1994. MT1007 Statistics in Practice Credits 20.0 Semester 2 Academic year 2019/20 Timetable 11.00 am Description This module provides an introduction to statistical reasoning, elementary but powerful statistical methodologies, and real .
