In the News: http://www.npr.org/templates/player/mediaplayer.html?action=1&t=1&islist=false &id=112755481&m=112805055 1
In the News: http://www.economist.com/scien cetechnology/displaystory.cfm?st ory_id=14302001 2
In the News: http://www.jpl.nasa.gov/videos/airs/carbonmonoxide20090903-640.mov 3
Barometric Pressure: 4
Infrared Imagery: http://www.sciencedaily.com/releases/2008/12/081227214927.htm 5
Causes of Earth s Seasons (ERTH 303, 10 September, 2009) 1. The Seasons: a. Earth Sun geometry 2. Energy Balance and Temperature a. Atmospheric influences on insolation: absorption, reflection, and scattering 6
Seasons: Earth-Sun geometry Why does insolation vary? 2. Earth s axial tilt = 23.5 relative to elliptical plane rotation axis http://upload.wikimedia.org/wikipedia/commons/6/61/axialtiltobliquity.png 7 Early Winters Spire and Blue Peak, North Cascades, WA
Seasons: Earth-Sun geometry Solstice: What is the one Earth-Sun relationship defining a solstice? 8
Seasons: Earth-Sun geometry Solstice: Maximum axial tilt in relation to the Sun Hemispheric p axes inclined toward or away from Sun Causes maximum difference in solar insolation, between hemispheres 9
Seasons: Earth-Sun geometry June Solstice (~ June 21) * Subsolar point = Tropic of Cancer (23.5 o N) 24 h daylight at Arctic Circle = 90-23.5 = 66.5 N * December Solstice (~ Dec. 21) * point = Tropic of Capricorn (23.5 o S) 24 h daylight at Antarctic Circle = 90-23.5 = 66.5 S 10
Seasons: Earth-Sun geometry 11
Seasons: Earth-Sun geometry 11:40 11:30 pm, June 15, 19 st Kotzebue,, Noatak National Alaska, 33 Preserve, miles north Alaska, of the 68.01 N Arctic Circle latitude 12
Seasons: Earth-Sun geometry June Solstice (~ June 21) * Subsolar point = Tropic of Cancer (23.5 o N) 24 h daylight at Arctic Circle = 90-23.5 = 66.5 N * December Solstice (~ Dec. 21) * Subsolar point = Tropic of Capricorn (23.5 o S) 24 h daylight at Antarctic Circle = 90-23.5 = 66.5 S * 13
Seasons: Earth-Sun geometry Equinoxes Subsolar point = 0, insolation evenly distributed between hemispheres Temporally centered between solstices ~ March 21 and ~ Sept 21 14
Seasons: Earth-Sun geometry 15
Seasons: Earth-Sun geometry Bozeman US Naval Obs. Night and Day Across Earth: http://aa.usno.navy.mil/data/docs/earthview.php http://en.wikipedia.org/wiki/image:day_length.jpeg 16
Insolation and axial tilt: At what latitude would the Arctic Circle occur, if Earth s axis was tilted 20 instead of 23.5? (a) 68 (b) 65 (c) 20 (d) 70 (e) NA 17
Insolation and axial tilt: At what latitude would the Arctic Circle occur, if Earth s axis was tilted 20 instead of 23.5? (a) 68 (b) 65 (c) 20 (d) 70 (e) NA 18
Insolation and axial tilt: At what latitude would the Arctic Circle occur, if Earth s axis was tilted 20 instead of 23.5? (a) 68 (b) 65 (c) 20 (d) 70 (e) NA How about the Tropic of Cancer? (a) -15 (b) 23.5 (c) 20 (d) 70 (e) -20 19
Insolation and axial tilt: At what latitude would the Arctic Circle occur, if Earth s axis was tilted 20 instead of 23.5? (a) 68 (b) 65 (c) 20 (d) 70 (e) NA How about the Tropic of Cancer? (a) -15 (b) 23.5 (c) 20 (d) 70 (e) -20 20
Insolation and axial tilt: At what latitude would the Arctic Circle occur, if Earth s axis was tilted 20 instead of 23.5? (a) 68 (b) 65 (c) 20 (d) 70 (e) NA How about the Tropic of Cancer? (a) -15 (b) 23.5 (c) 20 (d) 70 (e) -20 On June 21 st, how many hours of daylight does the equator receive? (a) 16 (b) 12 (c) 24 (d) 8 (e) 10 21
Insolation and axial tilt: At what latitude would the Arctic Circle occur, if Earth s axis was tilted 20 instead of 23.5? (a) 68 (b) 65 (c) 20 (d) 70 (e) NA How about the Tropic of Cancer? (a) -15 (b) 23.5 (c) 20 (d) 70 (e) -20 On June 21 st, how many hours of daylight does the equator receive? (a) 16 (b) 12 (c) 24 (d) 8 (e) 10 22
Seasons: Earth-Sun geometry Why does solar angle matter? 23 Napequa Crater Lake Valley, National Glacier Park, Peak ORWilderness, WA
Seasons: Earth-Sun geometry Why does solar angle matter? 1. Beam spreading 2. Atmospheric beam depletion zenith angle = angle between Sun and vertical solar altitude = angle between sun and horizontal angle (horizon) 24
Seasons: Earth-Sun geometry 25 Bozeman = 45.7 N lat. Zenith angle today? Dec. 21? June 21? Radiation Intensity:???
Seasons: Earth-Sun geometry Interactive effects of solar angle and daylength: 26
Energy Balance and Temperature (ERTH 303, 10 September, 2009) 1. The Seasons: a. Earth Sun geometry 2. Energy Balance and Temperature a. Atmospheric influences on insolation: absorption, reflection, and scattering 27
Earth s Energy Balance Solar radiation is the atmosphere s heat source, but... Most gases are transparent to solar radiation, yet absorb terrestrial radiation Gases also reflect and scatter energy Blue skies and orange sunsets, brought to you by the absorption and reflection of energy by the atmosphere 28
Earth s Energy Balance The global energy budget = a balance between incoming solar radiation and outgoing terrestrial radiation 29 http://geography.uoregon.edu/envchange/clim_animations/gifs/three_rads_web.gif
Absorption of insolation Absorption = energy transfer to the absorber: gases, particulates, droplets absorber gains energy and warms energy delivered to Earth s surface reduced Examples: ultraviolet radiation almost completely absorbed by ozone in stratosphere near-infrared radiation (c. 50% of Sun s radiation) is effectively absorbed by CO 2 and water vapor 30
Reflection and Scattering of insolation Reflection = radiation is redirected away for surface, without being absorb albedo = proportion of visible light reflected by an object (ranges from 0-1 1, from dark to bright) Snow has high albedo, while the burned trees have a low albedo. Yellowstone NP. 31
Reflection and Scattering of insolation Light is reflected in different ways: 1. specular reflection = energy reflected with equal intensity 2. diffuse reflection, or scattering = energy not reflected with equal intensity, but broken down into a number of weaker rays: Incoming solar radiation is scattered back into space, and back to Earth, creating diffuse radiation 32
Reflection and Scattering of insolation Types of Scattering: 1. Rayleigh scattering agents smaller than wavelength of incoming radiation scatters in all directions affects shorter wavelengths (e.g. blue light) 33
Reflection and Scattering of insolation Types of Scattering: 2. Mie larger scattering agents (aerosols) scatters light forward (thus little energy back into space) affects wavelengths across visible spectrum 34 Mie scattering is largely responsible for colorful sunsets, and also hazy, gray days when aerosol concentrations are high
Reflection and Scattering of insolation Types of Scattering: 2. Mie 35
Reflection and Scattering of insolation Types of Scattering: 3. Nonselective scattering Very large scattering agents (water) Scatters across the visible spectrum, thus creating white or gray appearance 36