Unit 3 Presentation 1 July 10, 2015 Solar radiation Energy Global radiation balance Sun in local sky

SOLAR RADIATION The Earth intercepts 1.5 quadrillion megawatt-hours per year or 28,000 times the power consumed by the entire population of the planet each year.

Strahler & Strahler 2003 i.e., low frequencies i.e., high frequencies Shortwave vs. longwave radiation Ruddiman 2001

Important principles regarding emission of electromagnetic radiation. (1)There is an inverse relationship between wavelength and the temperature T of the object emitting it (e.g. the Sun emits very short wavelength energy because it is so hot). Planck ’ s Law: E = (2  c 2 h /   e [hc/k T - 1] where the speed of light c = 3x10 8 m/s, Boltzmann's constant k = 1.38 x J/ o K, and Planck's constant h = 6.64 x J s. Radiation and Temperature NOTE:  is reported in length units:  m = m (micrometers) nm = m (nanometers) Å = m (Ångstroms)

Important principles regarding emission of electromagnetic radiation. (2) Integrating E over all wavelengths gives the total energy flux emanating from the surface of the radiating body: Stefan ’ s Law: E =   T 4 where  = emissivity of the radiator (= 1 for a blackbody radiator),  = the Stefan-Boltzmann constant (= x W/(m 2 o K 4 )), and T is the absolute temperature of the radiator's surface in o K. (3) The Wien Displacement Law explains wavelength shift of peak E with change in T: max = b/T With b= ×10 −3 m ºK (Wien displacement constant) and T in o K. Radiation and Temperature used in all Earth system and climate models

Shortwave Radiation Ultraviolet –short wavelength (0.2 to 0.4 micrometers), high energy. Does not penetrate atmosphere easily. Visible light –shorter wavelengths are perceived as violet, longer wavelengths as red (0.4 to 0.7 micrometers); penetrates atmosphere easily. Near-infrared radiation –in the wavelengths from 0.7 to 1.2 micrometers. Shortwave infrared radiation –wavelengths from 1.2 to 3 micrometers, invisible to the eye. Penetrates atmosphere easily. THE SUN ~0.5  m E = 2  c 2 h /  e [hc/k T - 1] with T=5800 o K

Longwave radiation Thermal infrared radiation –Wavelengths greater than 3 micrometers –This form of radiation is emitted by cooler bodies. –It is perceived as heat. THE EARTH ~10  m E = 2  c 2 h /  e [hc/k T - 1] with T=288 o K

Wavelengths of Sun and Earth Radiation Earth Energy –Earth’s output peaks in the thermal infrared portion of the electro- magnetic spectrum Strahler & Strahler 2003 Solar Energy –Sun’s output peaks in the visible light portion of the electro- magnetic spectrum.

Effects of solar radiation on the ecosystem:

The Sun's surface has an energy flux density of 70 x 10 6 W/m 2. (Note: W/m 2 = J/s m 2, where J = kg m 2 /s 2). As this radiates out into space, the density diminishes as a function of distance 2 ; by the time it reaches the Earth the density is only on the order of 1370 W/m 2. Path of Radiation from Sun to Earth (or other planet)

From Ruddiman 2001 At top-of-atmosphere (TOA), solar radiation is I=1368 W/m 2. I affects an area equivalent to a disk of dimension  2. Averaging I over a 24-hour period gives  2 I/4  2 =I/4= 342 W/m 2. Incoming solar radiation on Earth  2  2

The Global Radiation Balance The Sun transmits shortwave radiation into space where it is intercepted by Earth. The absorbed radiation is ultimately emitted by Earth as longwave radiation to space

T Earth = ( (1-  ) 343 W m -2 / 5.67 x W m -2 K -4 ) 1/4 = 279 K (+6 ºC) Earth blackbody radiator model But we know T earth = 288K! T Earth = ( ( 0.7) 343 W m -2 / 5.67 x W m -2 K -4 ) 1/4 = 255 K (-18 ºC) No albedo (  =0): With albedo (  =0.3): Input = output (1-  )E=  T 4 T=[(1-  ) E/(  )] 1/4, where  =1

T BR = +6ºC T BR = -47ºC T BR = +55ºC

The Seasonal Cycle Summer

Sun in the local sky Equator Celestial Equator Baltimore Olin Hall

Northern Summer Solstice At 40ºN solar altitude A=73.5º At 40ºN sunrise in NE At 40ºN sunset in NW Note: Zenith angle z = 90º-A

Path of the Sun in the sky at selected latitudes for summer, winter solstices and equinox From Strahler & Strahler 2003 Note: “ 8 ” = “ º ”

EARTH ALBEDO Albedo (Latin for “ white ” ) is the average reflection coefficient of an object (1=white; 0=black). “ Bond albedo ” is the total radiation reflected from an object compared to the total incident radiation from the Sun. “ Geometric albedo ” is the amount of radiation relative to that of a flat Lambertian surface which is an ideal reflector at all wavelengths. De Pater & Lissauer 2010

Trees and grasses

Rocks and Soils

Water and Snow

Broadband Albedo (Oct. 1986)

Baltimore MD Oct. 1986

END OF PRESENTATION