Lectures 2-3 week 1-2 2009: HAS222d Solar radiation, the - PowerPoint PPT Presentation

Lectures 2-3 week 1-2 2009: HAS222d Solar radiation, the greenhouse, global heat engine http://en.wikipedia.org/

The 4 streams of this 2.Global Environment course (see syllabus) 1.Energy physical, chemical, biological atmosphere, ocean, land surface forms of energy energy, air, water, ice, carbon concetrated, diluted the sun-atmosphere-ocean heat engine conservation transmission/movement fluid circulations in which protective transformation ‘niches’ of life develop efficiency of transformation heat engines degradation (and entropy) 4.Arctic populations storage ‘utilization’ by plants and animals carbon cycle, photosynthesis natives: settlement Europeans: exploration 3.Humans and energy assimilation, exploitation history of energy demand shaping of their lives and development by energy and food ….fossil fuels resources in a harsh environment connections with evolution amplified global alternative energies warming in the Arctic

Let’s start with the sun diameter: 1.38 million km disc of the distance from Earth (mean): 149.6 million km (93 million miles)* sun tilt of Earth’s rotation axis relative to its orbit round the sun: 23.5 0 Earth the orbit is an ellipse, but only about 2% different from a circle: the oribital eccentriciy**= 0.017 angle Θ rotation period: 23.9 hours length of day: 24 hours On July 4 this year the Earth is farthest from the sun (aphelion); on Jan 4 it was closest (perihelion); about 7% more sunlight (rate of energy falling on Earth) in Jan than in July. As Northern Hemisphere goes, so goes climate! The eccentricity shifts with 100,000 year period from 0.05 to nearly zero. perihelion shifts with 21,000 year period obliquity (tilt of axis) shifts with 41,000 year period …..all these slight changes alter the amount of sunshine and its distribution at the Earth’s surface, somehow leading to ice ages….cycles of cold and warm climate. Averaged over the globe, sunlight falling on Earth in July (aphelion) is indeed about 7% less intense than it is in January (perihelion)." That's the good news. The bad news is it's still hot. "In fact," says Spencer, "the average temperature of Earth at aphelion is about 4o F (2.3o C) higher than www.cwru.edu, it is at perihelion." Earth is actually warmer when we're farther from the Sun ! http://science.nasa.gov/headlines/y2001/ast03jul_1.htm ========================================================================================= * (these two numbers together tell us how big the disc of the * (these two numbers together tell us how big the disc of the sun appears in the sky … sun appears in the sky ….the relationship is .the relationship is ½ Θ Θ = tan ½ tan = ½ ½ diameter/distance (see diagram above) diameter/distance (see diagram above) For small angles tan Θ Θ us approximately us approximately Θ Θ , measured in radians. For small angles tan , measured in radians. So, Θ Θ = 1.38/149.6 = 0.00922 radians or .00922 x 360/2 = 1.38/149.6 = 0.00922 radians or .00922 x 360/2 Л Л So, degrees. This is 0.53 degrees degrees. This is 0.53 degrees… ….roughly .roughly ½ ½ degree,almost degree,almost the same the same angular size as the moon, which is why we have such perfect ec angular size as the moon, which is why we have such perfect eclipses) lipses) = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = * * the eccentricity of an ellipse is defined as the ratio √ √ (1 b 2 2 /a /a 2 2 ) * * the eccentricity of an ellipse is defined as the ratio (1- -b ) where a is the where a is the largest diameter (the major axis) and b is perpendicular to it, the smallest the smallest largest diameter (the major axis) and b is perpendicular to it, diameter diameter

The sun’s radiation reaches the Earth with an intensity of about 1368 watts per square meter…that would be like 13.68 one-hundred watt light bulbs illuminating a one- meter square surface, except that light bulbs put their 100 watts of power into other forms of heat as well as visible and infrared radiation. Given the distance of the sun from the Earth (149.6 million km) and the diameter of the sun (1.38 million km), how much power (energy per unit time) is radiating from one square meter of the bright outer surface of the sun? http://commons.wikimedia.org/wiki/File:Solar-cycle-data.png

Visible light has wavelengths between 400 and 700 nanometers (0.4/1000 to 0.7/1000 of a millimeter) (often we will also use the length unit of “micron”… a millionth of a meter a “nanometer” is a billionth of a meter. In yet other units, this is 4000 to 7000 Angstroms: 1 Angstrom is about the diameter of a hydrogen atom.)

• The wavelength ( l ) is the distance between one peak of the wave and the next peak. It's a distance so can be measured in metres, centimetres etc. It is sometimes given the Greek letter (lambda). It's also the distance between one part of the wave and the next part which is at exactly the same stage of vibration - but 'peak-to-peak' is easier to remember. • The frequency ( f ) is the number of complete waves passing a point each second. It's a 'number per second' so it's measured in / s or s-1 ; usually called hertz ( Hz ) after a German physicist. • 1 kilohertz = 1 kHz = 1000 Hz 1 megahertz = 1 MHz = 1,000,000 Hz For example: 100 complete sound waves enter your ear in a second (you'd hear a deep hum). f = 100 per second = 100 /s = 100 s-1 = 100Hz • The speed of a wave ( v ) is just what it says. It's the speed at which the vibrations in the wave move from one point to the next. Wave speed is measured in metres per second (m/s, ms-1). • For example: speed of sound in air = 330 m/s (approximate) speed of light in space = 300,000,000 m/sec = 3 x 10 8 meters per second http://www.bbc.co.uk/schools/gcsebitesize/physics/waves/waveequationsrev2.shtml

www.andor.com/image_lib

The incoming solar radiation (in watts per square meter, per micron of wavelength) outside the atmosphere (upper solid curve) and at the ground (lower solid curve) under typical atmospheric conditions. The horizontal axis is wavelength of the light in microns (millionths of a meter).

Wien’s law: peak radiation occurs at a wavelenth of 2897/T (in microns...10 -6 m, and T in degrees Kelvin) (this comes from Planck’s law for radiation of a ‘black body’ as a function of wavelength and temperature)

The total of this radiation, summed over all frequencies is equal to σ T 4 where σ is called the Stephan Boltzmann constant, and the peak of the curve B occurs at a wavelength which varies inversely with the temperture as you see in the figure at right. Here σ = 5.67 x 10 -8 watts per meter squared, per degree Kelvin w m -2 K -1 written as To make some plots from Planck’s law (previous page) you can go to http://csep10.phys.utk.edu/guidry/java/planck/planc k.html and select a temperature by sliding the slide-bar.

The temperature of a hot object determines the color (wavelength) of its radiation. Here the colors of various stars correspond to the peak in these curves of radiation intensity (note that the twinkling of stars in the night sky is due to irregularities in the air temperature…refraction).

solar radiation …. arriving at the top of the atmosphere and at the Earth’s surface W. Connelly HADCM3 data Wikipedia

Notice that sunlight observed at the ground has some dark lines in its spectrum… some specific colors (wavelengths) are blocked by water vapor, ozone… short waves long waves 400 nm 500 nm 700 nm Isaac Newton’s experiment with a glass prism showed sunlight splitting into a rainbow of colors. This is because the speed of light is slower inside the glass. Wavefronts of light slow down in glass, bending the rays. The amount of slowing varies with wavelength. Hence light rays with different wavelengths (i.e.,different colors) are split apart, making a rainbow as above. http://bass2000.obspm.fr/solar_spect.php

Earth radiates at a lower temperature and hence at sunlight enters longer the atmosphere wavelength…in with much energy visible infrared in the visible or ‘heat’ wavelenghts radiation Hartmann, Global Physical Climatology, Academic Press 1994

Infrared radiation upward from the Earth, assuming a 280K temperature red+yellow+blue = total radiation of the earth at +7° C in the range between 400 and 1800 cm -1 . 10 microns (10 millionth of a meter) appears here as 1000 cm -1 blue = radiation that is absorbed by greenhouse gases. yellow = radiation that is allowed to pass by greenhouse gases. (red = absence of an absorption spectrum due to technical reasons concerning the measurements.) http://www.espere.net/Unitedkingdom/water/uk_watervapour.html

contributions of various gases to the greenhouse effect (other than water vapor which has the greatest effect)

solar radiation (kilowatt-hours per square meter, per day) varies with latitude and season (here neglecting the great effect of cloudiness) www.fao.org/DOCREP/003/X6541E/X6541E03.htm

Australia, with few mountains, cannot catch the moisture from the sea and has been experiencing severe drought. This is expected to worsen with global warming