Lecture 6: Chapter 4The passage of shortwave and longwave energy through the atmosphere or water is called:transmissionSolar irradiance measures the amount of electromagnetic energy striking asurface perpendicular to the sun’s rays at the top of the Earth’s atmosphere.Solar Constant the amount of energy received at the top of the Earth's atmosphere (top of the thermosphere) on a surface that is perpendicular tothe Sun’s rays (at the average distance of the Earth from the Sun).The generally accepted solar constant is 1368 W/m2, which is a satellite measured yearly average.Insolation may be transmitted several ways:1. Scattering2. Diffusion3. Refraction4. ReflectionScattering is: gases and dust in the atmosphere redirecting radiation.Small gas molecules in the air scatter shorter wavelengths of light. The shorter the wavelength, the greater the scattering; the longer the wavelength, the less the scattering.The sky is blue because: during the day, the shorter wavelengths – the blues and the violets – are scattered more, and dominate the atmosphere.During the day, the rays are also more direct, and experience less scattering than low-angle rays, which have to travel farther.Sunsets are red and orange because in the evening, when the sun’s angle is greater, the rays are traveling farther through the atmosphere, and the blues and violets get scattered out (redirected) sooner, before reachingour eyes, leaving longer-waved reds and oranges to be reflected.Smog appears white because the large particles associated with air pollutionscatter all wavelengths of visible light.Some insolation is diffused by clouds and atmosphere and transmits to earth as diffuse radiation – which is: the downward component of scattered light.Refraction is a: bending actionAs insolation enters the atmosphere, it passes from one medium to another, from virtually empty space into atmospheric gases, or from air into water. This subjects the insolation to a change of speed, which also shifts its direction.Refraction of sunset: light from the Sun when it is low in the sky must penetrate more air than when the Sun is high: it is refracted through air layers of different densities on its way to the observer.Refraction adds about 8 minutes of daylight that we wouldn’t have if we didn’t have an atmosphere. This is because sunlight gets refracted through the atmosphere. So, at sunrise, we see the Sun’s image about 4 minutes before the Sun peaks over the horizon, and the same thing happens at night – we see the refracted image about 4 minutes after sunset.Mirages are images that appear near the horizon where light waves: are refracted by layers of air at different temperatures, (and so of different densities) on a hot day. Matching:1. Radiation being bent C2. Radiation being scattered downward A3. Radiation being redirected by gases and dust G4. Passage of energy through the atmosphere and water E5. Shorter visible lightwaves being scattered B6. Mirages C7. Longer visible lightwaves being scattered D8. All visible lightwaves being scattered F9. Eight additional minutes of daylight Ca) Diffuse radiationb) Sky is bluec) Refractiond) Sunsetse) Transmissionf) Smogg) ScatteringReflection is: insolation that bounces directly back into space.Albedo is: the % of insolation that is reflected0% albedo means all of the insolation is absorbed; 100% albedo means all of the insolation is reflected.The albedo of an object is determined by color, texture and sun altitude.The earth’s albedo is called: EarthshineEarth’s average albedo is a combination of 21% reflected by clouds, 3% reflected by the ground (land and ocean), and 7% reflect scattered by the atmosphere.The earth has an albedo that is 4 times brighter than moonshine.1. COLORIn the visible wavelengths, darker colors have lower albedos (they absorb more insolation) and lighter colors have higher albedos (they absorb less insolation).2. TEXTURESmooth surfaces increase albedo, rougher surfaces decrease it.As the snow in the Arctic Ice Cap melts, less light is reflected, so thearea gets warmer, so more snow melts, so still less light is reflected.An example of positive feedback.Tropical forests have low albedo (15%). They have a rougher texture, a darker color.Cloudless deserts have high albedos (35%). They have a smoother texture, alighter color.3. ALTITUDEOn water surfaces, the angle of the solar rays (altitude) affects albedo: low angles produce a greater reflection than higher angles.How solar cookers work: albedo and heat traps.Albedo involves:A. refractionB. reflectivityC. diffuse radiationD. scattering of thermal energy Which has the highest albedo?A. White sandB. Water where the sun is directly overheadC. A forestD. dark asphalt highwayWhich is not true regarding albedo?A. Darker colors absorb more insolationB. Low sun angles over water produce higher albedos than high sun anglesC. Smooth surfaces have higher albedo than rough surfacesD. The Earth’s albedo is sometimes called EarthshineE. The Earth has a lower albedo than the moon doesClouds and AlbedoClouds reflect insolation. So they are cooling the earth’s surface, because less energy is reaching the surface.Cloud-albedo forcing: an increase in albedo caused by clouds.BUT clouds can also act as insulation, trapping longwave radiation from earthand so raising temperatures (more on that later.) Cloud-greenhouse forcing is: an increase in greenhouse warming caused by clouds..When Mount Pinatabu exploded, releasing many aerosols into the air, albedo increased, and there was an average cooling of almost one degree F.Pollution haze is increasing the reflectivity (albedo) of the atmosphere, and reducing the amount of insolation reaching the surface by 10%.Global dimming is: is the term for the reduced amount of light reaching the surfaceBUT, even as they decrease the amount of insolation reaching the surface, human pollutants are increasing the amount of energy being retained: they increase energy absorption in the atmosphere by 50%.Do aerosols affect the solar constant?- No, because they not at the top of the atmosphere, which is where the solar constant is measured.T/F When clouds prevent insolation from reaching the ground, it is known as cloud-albedo forcing. T/ F When clouds trap longwave radiation from earth, which raises temperatures, it is known as cloud-greenhouse forcing.T/F After Mount Pinatabu exploded, global temperatures went up.When reduced amount of light reaches the earth’s