GEOG 111 Lecture Notes www sercc com perspectives Fronts divide air masses with different properties Solar and Terrestrial Radiation The electromagnetic spectrum wide spectrum of different types of radiation The sun radiates all bodies radiate radiate energy all bodies emit radiation over a range of wavelengths within the electromagnetic spectrum radiator radiates infrared the hotter it gets the more it radiates length of wavelength period height of wavelength period Gamma X rays ultraviolet violet blue green yellow orange red visible light infrared microwaves radio waves goes from 10 6 nm to 100km wavelength We are interested in UV VIS shortwave K IR longwave L terrestrial ROYGBV Anything to the left of ultraviolet radiation is dangerous to humans Most objects emit infrared TWO RADIATION LAWS Stefan Boltzman Law the hotter a body is the more it radiates E T4 Weins Law the wavelength that a body emits is inversely related to its temperature wavelength of max emission 3 x 107 T the sun emits much more energy than the earth sun emits mostly in the middle range yellowish the earth emits mostly in the infrared range because the earth is much cooler longer wavelength hot vs cold stars reddish blueish white stars red stars are large but they re cool emit at longer wavelength blue stars are small but are very hot in a fire the blue part of the flame is hotter than the red part of the flame Infrared Satellite Temperatures generally decrease with increasing height above the earth therefore higher clouds are colder than lower clouds on earth dark blue parts indicate the longest infrared wavelengths orange color indicates the shortest infrared wavelengths earth is warmer than clouds so its red bluest clouds are the coldest as altitude increases temperature decreases degrees of shading are equated with temperature Earth atmosphere influences on radiation Three processes are important 1 absorption the absorbing medium mostly gas or sometimes particulate matter warms in this process the energy is taken in ex ozone very effective at absorbing ultraviolet radiation lets visible light pass through You are exposed to more ultraviolet at higher altitudes because there is less room for the ozone to absorb ultraviolet fog and smog also absorb UV light clouds absorb made up of billions of microscopic water droplets clouds also reflect light as well greenhouse gasses ex CO2 and water vapor 2 reflection the temperature of the reflecting object is unchanged if its reflecting its implicitly not absorbing anything Albedo a measure of the reflectivity of a material A out going K incoming K x 100 for a mirror 1 1 x100 100 for a black body small number large number x 100 Typical Albedo Values forest 5 10 grass 20 25 sand 20 40 snow new 80 90 old 50 80 snow gets darker from simple particulate matter in the atmosphere water 3 5 overhead to 50 80 near horizon thin clouds 25 30 think clouds 70 85 after it snows snow inhibits temperature rising because it reflects the infrared light back so the ground doesn t warm up 3 Scattering Sunlight comes off and reflects off of atmospheric particles more particles in air more scattering why does volcanic dust make sunsets red orange volcanic dust particles are bigger than most particles bad air quality more particles more scattering sun looks like orange ball in sky forest fires smoke cause more particles orange sun poor visibility global cooling can occur due to volcanic erruptions Solar Radiation direct beam radiation comes directly from sun down to surface diffuse light sky light blue light from sky Inverse relationship between direct beam and diffuse less scattering direct beam increases diffuse light decreases dark blue sky more scattering direct beam decreases diffuse light increases light blue sky Three Controlling Factors 1 Clouds no direct beam all diffuse light 2 Haze concentration if haze increases direct beam decreases diffuse light increases 3 Elevation as elevation increases direct beam increases diffuse light decreases why You re only seeing scattering of violet and blue in space there s no atmosphere and the sky is black Summary on Radiation Transmission Transmissivity Shortwave Factors clouds atmospheric thickness haze Longwave Factors clouds atmospheric thickness greenhouse gasses Earth Sun symmetry Two independent motions 1 The Earth rotates overtime the Earth has been slowing down in rotation temperatures didn t heat up as much during the day and didn t cool down as much at night earth slowing down because friction air over mountains and all the water on earth sloshing around 2 Elliptical Revolution takes 365 25 days on the plane of the elliptical Earth tilted 23 5 degrees January 4th earth and sun are closest together perihelion 91 5 million miles July 4th earth most distant from sun aphelion 94 5 million miles Solar Declination the latitude that the suns direct rays are hitting equinox when suns direct rays hit equator equal days equal nights Solar Elevation angle of sun above horizon if on horizon elevation is zero Sun is elevated higher in June than it is in December SE 90 degress latitude SD Note that SD is negative positive if it occurs in the opposite same hemisphere as the location As solar elevation increases transmissivity decreases seasonal changes in the length of day are related to solar elevation the rate of change in the day length is positively related to the rate of change of solar elevation greatest changes are in later winter and early spring the intensity of solar radiation is related to solar elevation direct ray one energy unit oblique ray half energy unit solar insulation insulation that gets added up over a period of time Summer Solstice longest day in Northern Hemisphere as latitude increases day length increases 24 hour day above arctic circle Winter Solstice shortest day in NH latitude increases day length decreases 24 hour day above Antarctic circle Spring and Fall Equinox equal day equal night Links between solar radiation and earth sun geometry 1 The intensity of solar radiation is related to solar elevation direct indirect like a flashlight 2 The intensity of solar radiation is also affected by atmospheric transmissivity which is related to solar elevation Solar elevation increases Transmissivity increases Energy Transfer Basic warmer regions radiate more energy than cooler regions Thus there is a net transfer from warmer to cooler regions Radiation Transfer Net radiation Q Local Radiation Budget Q K K L L K shortwave L