Meteo 3: Chapter 2 Radiation and other forms of energy transfer Read Chapter 2

What Causes Weather?  Uneven distribution of energy from the sun on the earth  Attempt to redistribute energy evenly in the atmosphere is the cause of weather (and ocean currents)  Sun transmits energy via RADIATION

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

How is radiation created?  Negatively charged electrons oscillate across local magnetic fields, generating electromagnetic radiation –Travels as waves of energy of varying wavelengths and amounts of energy –Wavelength- distance from crest of 1 wave to crest of next –Electromagnetic spectrum- composed of all wavelengths of radiation

Wave Terminology

Electromagnetic Spectrum

Temperature and Radiation  Every object has a wavelength of maximum emission –Depends on temperature –The hotter an object, the shorter the wavelengths of radiation it emits, the shorter the wavelength at which peak emission occurs  Wein’s Law –λ max = 2897 / T, where λ max is in μm and T is in Kelvin

Stefan-Boltzmann Law  The higher the temperature of an object, the more energy it emits  E = σT 4  where σ = 5.67x10 -8 W/(m 2 K 4) (Stefan-Boltzmann Constant)  E is in W/m 2  T is in Kelvin

Radiation  Solar Radiation- radiation emanating from the sun –Heats the earth and drives weather –Solar radiation heats up ground first, which then transfers warmth to atmosphere  Terrestrial Radiation- radiation emitted by the clouds, atmosphere, and earth

The Three Fates of Radiation

Absorption  Amount of energy absorbed depends on object’s absorptivity & intensity of radiation striking it –Absorptivity depends on radiation’s wavelength…darker colored objects absorb more visible radiation than lighter colored objects…light colored objects have higher albedo (fraction of incident radiation reflected) –Intensity of radiation striking an object depends on  The intensity of the radiation emitted by the energy source  The distance from the energy source  The angle at which radiation strikes an object

Transmission & Scattering  Transmission- energy passes through an object without interacting with the object’s molecules or atoms –intensity of radiation unchanged as it passes through  Scattering- a redirection of radiation into other directions –known as back-scattering if radiation scattered back toward source…important for radar applications  Absorption, transmission & scattering can all occur at the same time!

Radiative Transfer in a Thunderstorm

Green Thunderstorm

Path of Radiation from Sun to Earth  Since air molecules back-scatter radiation, the longer the path that solar radiation must travel to reach earth, the greater the chance its intensity will be diminished before striking earth.  However, angle at which solar radiation hits the earth is most important in determining solar input!(see CD) is most important in determining solar input! (see CD)

Radiation Budget  Objects that absorb more energy than they emit undergo a net warming  Objects that emit more energy than they absorb undergo a net cooling  Objects that absorb and emit equal amounts usually experience no temperature change

Equatorial Surplus, Polar Deficit  Uneven heating sets the stage for weather & ocean currents

What happens to solar radiation after entering the atmosphere?

The Sun Warms the Ground, the Ground Warms the Air

Conduction  Conduction- Transfer of energy from the ground to air –During day, ground warmed, so its molecules move faster with more kinetic energy than air molecules…when these two molecules collide, kinetic energy transferred to slower (cooler) air molecules, and air is warmed –At night, ground cools via net emission…cool layer thickens via conduction induced cooling…results in a layer of chill below warmer air (nocturnal inversion)

Convection  Convection- Transfer of energy within the atmosphere by the vertical movement of air –Consider buoyancy, which results from density (mass/volume) differences –Air with a higher temperature is less dense than cold air –Air parcels warmer than their surroundings are positively buoyant, thus tend to rise –Sun heats ground => ground unevenly heats thin layer of air above it => hot spots represent areas of positively buoyant air, which tend to rise –Convection very important…thunderstorms!

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

Clouds and Nighttime Temperature  Clouds efficiently emit infrared radiation that helps heat the Earth’s surface heat the Earth’s surface

The “Greenhouse Effect”  Several gases also absorb (and thus emit) infrared radiation efficiently –These include water vapor (H 2 O), carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) (greenhouse gases) –Along with clouds, lead to greenhouse effect- planetary heating caused by the emission of infrared radiation by several atmospheric gases…ESSENTIAL FOR LIFE ON EARTH

Why does the “Greenhouse Effect” have a bad reputation?  Human burning of carbon-rich fuels (coal, natural gas, oil) since Industrial Revolution is increasing the CO 2 concentration in the atmosphere  Fear that more CO 2 in atmosphere will lead to a warmer planet, an “anthropogenic” greenhouse effect, or “Global Warming”

Increasing Atmospheric CO 2 Concentration