Meteo 3: Chapter 2Meteo 3: Chapter 2

Radiation and other forms of Radiation and other forms of energy transferenergy transfer

Read Chapter 2Read Chapter 2

What Causes Weather?What Causes Weather?

Uneven distribution of energy from the sun Uneven distribution of energy from the sun on the earthon the earth

Attempt to redistribute energy evenly in the Attempt to redistribute energy evenly in the atmosphere is the cause of weather (and atmosphere is the cause of weather (and ocean currents)ocean currents)

Sun transmits energy via RADIATION Sun transmits energy via RADIATION

Radiation is Bad? Good? Radiation is Bad? Good?

Study: No Radiation Level Safe –CBS News

Scientists Claim 'A Little Radiation Is Good For You'!!From Dr. Alan Cantwell, MD

Wireless Worries? New Studies Call for More Research, Some Scientists Say

                  

             

Fundamental PrincipleFundamental Principle

Everything radiates Everything radiates energy at all energy at all wavelengths and at wavelengths and at all times!all times!

How is radiation created?How is radiation created?

Negatively charged electrons oscillate across local Negatively charged electrons oscillate across local magnetic fields, generating electromagnetic magnetic fields, generating electromagnetic radiationradiation– Travels as waves of energy of varying wavelengths and Travels as waves of energy of varying wavelengths and

amounts of energyamounts of energy– Wavelength- Wavelength- distance from crest of 1 wave to crest of distance from crest of 1 wave to crest of

nextnext– Electromagnetic spectrum- Electromagnetic spectrum- composed of all composed of all

wavelengths of radiationwavelengths of radiation

Wave TerminologyWave Terminology

Electromagnetic SpectrumElectromagnetic Spectrum

Temperature and RadiationTemperature and Radiation

Every object has a wavelength of maximum Every object has a wavelength of maximum emissionemission– Depends on temperatureDepends on temperature– The hotter an object, the shorter the wavelengths of The hotter an object, the shorter the wavelengths of

radiation it emits, the shorter the wavelength at which radiation it emits, the shorter the wavelength at which peak emission occurspeak emission occurs

Wein’s LawWein’s Law– λλmaxmax = 2897 / T, where λ = 2897 / T, where λmax max is in μm and T is in Kelvinis in μm and T is in Kelvin

Stefan-Boltzmann LawStefan-Boltzmann Law

The higher the temperature of an object, the more The higher the temperature of an object, the more energy it emitsenergy it emits

E = σTE = σT44

where σ = 5.67x10where σ = 5.67x10-8 -8 W/(mW/(m22KK4)4)

(Stefan-Boltzmann Constant)(Stefan-Boltzmann Constant) E is in W/mE is in W/m22

T is in KelvinT is in Kelvin

RadiationRadiation

Solar Radiation- Solar Radiation- radiation emanating from the radiation emanating from the sunsun– Heats the earth and drives weatherHeats the earth and drives weather– Solar radiation heats up ground first, which then Solar radiation heats up ground first, which then

transfers warmth to atmospheretransfers warmth to atmosphere

Terrestrial Radiation-Terrestrial Radiation- radiation emitted by the radiation emitted by the clouds, atmosphere, and earthclouds, atmosphere, and earth

The Three Fates of RadiationThe Three Fates of Radiation

AbsorptionAbsorption

Amount of energy absorbed depends on object’s Amount of energy absorbed depends on object’s absorptivity & intensity of radiation striking itabsorptivity & intensity of radiation striking it– Absorptivity depends on radiation’s wavelength…darker Absorptivity depends on radiation’s wavelength…darker

colored objects absorb more visible radiation than colored objects absorb more visible radiation than lighter colored objects…light colored objects have lighter colored objects…light colored objects have higher higher albedo albedo (fraction of incident radiation reflected)(fraction of incident radiation reflected)

– Intensity of radiation striking an object depends onIntensity of radiation striking an object depends on The intensity of the radiation emitted by the energy sourceThe intensity of the radiation emitted by the energy source The distance from the energy sourceThe distance from the energy source The angle at which radiation strikes an objectThe angle at which radiation strikes an object

Transmission & ScatteringTransmission & Scattering

Transmission- Transmission- energy passes through an object energy passes through an object without interacting with the object’s molecules or without interacting with the object’s molecules or atomsatoms– intensity of radiation unchanged as it passes throughintensity of radiation unchanged as it passes through

Scattering- Scattering- a redirection of radiation into other a redirection of radiation into other directionsdirections– known as known as back-scattering back-scattering if radiation scattered back if radiation scattered back

toward source…important for radar applicationstoward source…important for radar applications

Absorption, transmission & scattering can all occur Absorption, transmission & scattering can all occur at the same time!at the same time!

Radiative Transfer in a ThunderstormRadiative Transfer in a Thunderstorm

Green ThunderstormGreen Thunderstorm

Path of Radiation from Sun to EarthPath of Radiation from Sun to Earth Since air molecules Since air molecules

back-scatter radiation, back-scatter radiation, the longer the path that the longer the path that solar radiation must solar radiation must travel to reach earth, the travel to reach earth, the greater the chance its greater the chance its intensity will be intensity will be diminished before diminished before striking earth.striking earth.

However, angle at which solar radiation hits the earthHowever, angle at which solar radiation hits the earth is most important in determining solar input!is most important in determining solar input! (see CD)(see CD)

Radiation BudgetRadiation Budget

Objects that absorb more energy than they emit Objects that absorb more energy than they emit undergo a net warmingundergo a net warming

Objects that emit more energy than they absorb Objects that emit more energy than they absorb undergo a net coolingundergo a net cooling

Objects that absorb and emit equal amounts Objects that absorb and emit equal amounts usually experience no temperature changeusually experience no temperature change

Equatorial Surplus, Polar DeficitEquatorial Surplus, Polar Deficit

Uneven heating sets the stage for weather & ocean Uneven heating sets the stage for weather & ocean currentscurrents

What happens to solar radiation after entering the What happens to solar radiation after entering the atmosphere?atmosphere?

The Sun Warms the Ground, the Ground Warms the AirThe Sun Warms the Ground, the Ground Warms the Air

ConductionConduction

Conduction- Conduction- Transfer of energy from the ground Transfer of energy from the ground to airto air– During day, ground warmed, so its molecules move During day, ground warmed, so its molecules move

faster with more kinetic energy than air molecules…faster with more kinetic energy than air molecules…when these two molecules collide, kinetic energy when these two molecules collide, kinetic energy transferred to slower (cooler) air molecules, and air is transferred to slower (cooler) air molecules, and air is warmed warmed

– At night, ground cools via net emission…cool layer At night, ground cools via net emission…cool layer thickens via conduction induced cooling…results in a thickens via conduction induced cooling…results in a layer of chill below warmer air layer of chill below warmer air (nocturnal inversion)(nocturnal inversion)

ConvectionConvection

Convection- Convection- Transfer of energy within the Transfer of energy within the atmosphere by the vertical movement of airatmosphere by the vertical movement of air– Consider buoyancy, which results from density Consider buoyancy, which results from density

(mass/volume) differences(mass/volume) differences– Air with a higher temperature is less dense than cold airAir with a higher temperature is less dense than cold air– Air parcels warmer than their surroundings are positively Air parcels warmer than their surroundings are positively

buoyant, thus tend to rise buoyant, thus tend to rise – Sun heats ground => ground unevenly heats thin layer of Sun heats ground => ground unevenly heats thin layer of

air above it => hot spots represent areas of positively air above it => hot spots represent areas of positively buoyant air, which tend to risebuoyant air, which tend to rise

– Convection very important…thunderstorms!Convection very important…thunderstorms!

Convective EddiesConvective Eddies

Eddies- Eddies- Turbulent Turbulent swirls that move warm swirls that move warm air up and cool air air up and cool air down, thereby down, thereby removing temperature removing temperature gradients near the gradients near the ground via mixingground via mixing

Clouds and Nighttime TemperatureClouds and Nighttime Temperature

Clouds efficiently emit infrared radiation that helpsClouds efficiently emit infrared radiation that helps

heat the Earth’s surfaceheat the Earth’s surface

The “Greenhouse Effect”The “Greenhouse Effect”

Several gases also absorb (and thus emit) infrared Several gases also absorb (and thus emit) infrared radiation efficientlyradiation efficiently– These include These include water vapor (Hwater vapor (H22O), carbon dioxide O), carbon dioxide

(CO(CO22),), methane (CH methane (CH44), and nitrous oxide (N), and nitrous oxide (N22O) O)

(greenhouse gases)(greenhouse gases)– Along with clouds, lead to Along with clouds, lead to greenhouse effect- greenhouse effect- planetary planetary

heating caused by the emission of infrared radiation by heating caused by the emission of infrared radiation by several atmospheric gases…ESSENTIAL FOR LIFE ON several atmospheric gases…ESSENTIAL FOR LIFE ON EARTHEARTH

Why does the “Greenhouse Why does the “Greenhouse Effect” have a bad reputation?Effect” have a bad reputation?

Human burning of carbon-rich fuels (coal, natural Human burning of carbon-rich fuels (coal, natural gas, oil) since Industrial Revolution is increasing gas, oil) since Industrial Revolution is increasing the COthe CO22 concentration in the atmosphere concentration in the atmosphere

Fear that more COFear that more CO22 in atmosphere will lead to a in atmosphere will lead to a

warmer planet, an “anthropogenic” greenhouse warmer planet, an “anthropogenic” greenhouse effect, or “Global Warming”effect, or “Global Warming”

Increasing Atmospheric COIncreasing Atmospheric CO22 Concentration Concentration