Solar & TerrestrialRadiation

The Electromagnetic Spectrum

• Energy travel as waves and particles• Energy is the capacity to do work• E=MC2

– Where E is energy, M is mass and C is the speed of light (300,000km/sec)

• Energy has electrical AND magnetic properties

• ALL object ABSORB and EMIT EM radiation

EM Radiation

• Described in terms of Wavelength or Frequency• Wavelength distance between successive

crests or troughs in km, m, mm, m• Frequency # wave crest/time (1sec) cycles/sec

or Hertz (Hz)• The longer the Wavelength () the lower the

frequency• Frequency is inversely proportional to , so the

higher the frequency the shorter the

There is a simple relationship between the wavelength (), frequency (), and velocity (c). If you know any 2 of them then you can compute the 3rd using   c =

or, velocity (c) equals wavelength () times frequency ().

EM Radiation

• Travel through space• In a vacuum travel at the speed of light• Pass through liquids, solids, gases• EM radiation can be reflected, refracted when

crossing different mediums as well as absorbed• Solar radiation arrives on Earth primarily as

visible (0.4-0.7 m) and Ultra-violet and is reflected and absorb and re-radiated to space as visible and Infra-red (heat)

Radiation Laws• Perfect radiator- blackbody• Blackbody- at a constant temperature absorbs

ALL radiation that is incident on it and EMITS all radiant energy it absorbs

• All known objects emit and absorb all forms of EM radiation

• The of most intense radiation (max) emitted by a blackbody is inversely proportional to absolute T of the object max=C/T where C is 2897 if is in m and T is in K,

where absolute zero is -273.15oC– This is a statement of Wien’s Displacement Law

Wien’s Displacement Law• Hot objects (stars) emit radiation that

peaks at relatively short wavelength– The blackbody temperature is 6000K– For the Sun it is about 0.5m

• Cold objects (planets, like the Earth-atmosphere system) emit peak radiation at longer wavelengths– The blackbody temperature is 288K (15oC)– For the Earth it is about 10m

Stefen-Boltzmann Law

• The total energy flux emitted by a blackbody across all wavelengths (E) is proportional to the fourth power of the absolute temperature (T4) of the object– E~T4

– A small change in temperature results in a greater change in radiational energy emitted

– Since the sun radiates at a greater temperature than the Earth the law predicts that the energy output per square meter of the sun will be 190,000 times greater than the earth

Input of Solar Radiation• Stellar nuclear synthesis

– 80%hydrogen– Hydrogen fusion alpha particle Helium– Internal temperature 20 million oC

• Photosphere- Visible solar surface 6,000oC• Sunspots- cool areas of the sun’s surface• Chromosphere- outward area, ions of H+ He+

4,000-40,000 oC• Solar corona- highest level of solar atmosphere,

ionized gases, extending millions of kilometers into space, where solar wind originates

Solar Altitude

• Intensity of solar radiation varies with latitude

• Intensity of solar radiation varies with time of day

• Intensity of solar radiation varies with path through atmosphere gases

TROPIC

TEMPERATE

POLAR

Earth’s Motions in Space and the Seasons

• Rotation on its axis every 24hrs (day)• Revolution around the sun every 365.2422 days

elliptical orbit (year)• Closest 3 January (perihelion) farthest 4 July

(aphelion), Earth receives 6.7% more radiation at perihelion than aphelion

• Earth’s tilt at 23.5o

• Summer & Winter Solstice– Tropic of Cancer & Tropic of Capricorn

• Equinoxes (March & September)

Solar Radiation & The Atmosphere

• Solar radiation interacts with gases and aerosols• Scattering & reflection (albedo), absorption

(absorptivity) or transmissivity (amount that reaches earth’s surface) of solar radiation must equal 100%

• In scattering a particle disperses solar radiation in all directions

• Scattering by molecules is wavelength dependent and preferential scattering of blue-violet light by N2 and O2 is the reason for the daytime sky

• Water and ice scatter visible light equally at all wavelengths so that clouds appear white

Albedo• Fraction of total radiation reflected by an

object (surface).• Varies according to:

Cloud cover. Particles in air. Angle of sun’s rays. Types of surface.

Stratospheric Ozone• Ozone is a gas made up of three oxygen atoms (O3).• Ozone is destroyed when it reacts with molecules containing

nitrogen, hydrogen, chlorine, or bromine. (CFCs)• Ozone protects life on Earth from the Sun’s ultraviolet (UV)

radiation. • Ozone screens all of the most energetic, UV-c, radiation, and

most of the UV-b radiation. • Ozone only screens about half of the UV-a radiation.

Excessive UV-b and UV-a radiation can cause sunburn and can lead to skin cancer and eye damage.

• In the lower atmosphere (the troposphere) near the Earth’s surface, ozone is created by chemical reactions between air pollutants from vehicle exhaust, gasoline vapors, and other emissions.

• At ground level, high concentrations of ozone are toxic to people and plants.

The Ozone Layer• The depletion of the ozone (O3) layer was first reported in 1985

by British scientists who said the amount of ozone had been decreasing over Antarctica since the late 1970s

• Depletion of the ozone layer over the poles is most severe in the winter months

• The greatest loss is over Antarctica because Antarctic winters are colder than Arctic winters

• The ozone hole grew to its largest recorded size in 2000, expanding to an area roughly three times the size of the United States

• Satellites carrying total ozone mapping spectrometers (TOMS) have been used to map the zone since 1978

Map of ozone over Antarctica (1997) in Dobson units [0.01mm thickness of ozone at standard P

& T (0oC and 1 atm)]

Ozone Problem• Decreased levels of ozone in the atmosphere will allow

more ultraviolet radiation to reach the surface • A 50% decrease in ozone is estimated to cause a 350%

increase in ultraviolet radiation reaching the surface• Ultraviolet radiation is known to adversely affect growth and

reproduction in organisms and is thought to increase the risk of skin cancer and cataracts

• Research also indicates that increased ultraviolet light may decrease rates of photosynthesis and growth in marine plants, phytoplankton, by about 2–4% under the Antarctic ozone hole

OZONE

• Thanks to the UN Montreal Protocol• The production and consumption of entire

groups of harmful ozone-depleting chemicals has been successfully phased out in developed countries, and the same process is now well under way in developing countries.

• Overall, almost ninety five per cent of all ozone-depleting substances have been phased out

After 20 years of protecting the ozone layer with a new generation of chemicals, governments are now having to confront the fact that these ozone-friendly substitutes for chlorofluorocarbons (CFCs) also happen to be greenhouse gases that contribute to global warming.

Intensity of solar radiation

• The Earth receives solar radiation unequally over its surface

• The intensity per unit area of surface is greatest at the equator

• Intermediate in the middle latitudes• The lowest intensity is at the polar regions

Global Solar Radiation Budget• Reflected 31%• Absorbed by atmosphere 20%• Absorbed by Earth’s surface 49%• Earth’s climate is controlled by a Greenhouse

Effect• Gases in the atmosphere control this effect

– H2Ovapor, CO2, O3, CH4, N2O– The percent of IR radiation absorbed varies with – An Atmospheric Window is a range of over which

little or no radiation is absorbed– A visible window extends 0.3-0.9m and major IR 8-

13 m, the peak IR emission of the planet is at 10m

Absorptivity is very low or near zero in atmospheric window

Greenhouse Gases• CO2 is stored in four reservoirs: three that are active and

one inactive reservoir including – the atmosphere, – the oceans,– the terrestrial system– Earth’s crust

• Most CO2 is stored in the oceans while the smallest amount is found in the atmosphere.

• Short-wavelength incoming radiation is not blocked by CO2, but re-radiated long-wavelength energy is, and this warms the atmosphere causing the greenhouse effect

Greenhouse Gases• Changing atmospheric chemistry can be monitored for past years

by analyzing bubbles trapped in polar ice. • It can be demonstrated that following the Industrial Revolution, the

concentration of CO2 has risen dramatically and continues to rise at an increasing rate.

• The concentration of CO2 in the atmosphere has increased from 280 ppm to 380 ppm since 1850

• Currently, the average increase in concentration is about 1.4 ppm per year

Past Climate in Ice• Polar ice sheets (Greenland and Antarctica)• Ice cores preserve a detail make up of the ocean and

atmosphere• Trapped bubbles contain gases from the past• GRIP (Greenland Ice Core Project) drilled a core 3029m a

record of more than 200,000 yrs• Identify volcanic events, lead production, large scale

pollution• Pre and post industrial revolution levels of sulfate (3X) and

nitrate (2X)• Russian core at Vostok (3623m ~ 450,000 yrs)

– CO2 increased 140K and decreased 100K; 10K increase by 40%

Ice Core

Ice Core

CO2• Scientists have estimated that the greenhouse

effect may produce a global warming of 2–4°C over the next hundred years. – This could melt high latitude ice and raise sea level

by as much as 1 m by the year 2100.• Careful measurements of short term increases

in global temperatures have shown a twenty year warming period which began in 1920 and another period of warming that began in 1977 and continued through the 1980s

CO2

• There is considerable debate over the actual cause or causes of the observed global warming and different mechanisms have been proposed to explain it including:– increasing levels of CO2,– variations in sun spot cycles, and– changing concentrations of dust particles in the air

CO2• Some natural processes actually lead to global cooling. Massive

volcanic eruptions can release enough ash to the air to block incoming solar radiation and cool the planet for a period of time

• The use of fossil fuels and the burning of tropical forests produces about 7 billion tons of CO2 annually.

• Roughly 3 billion tons are stored in the atmosphere, another 2 billion tons enters the oceans and ocean sediments

• At least 1 billion tons are taken up by plants in the re-growth of logged forests

FUTURE

• Sharp reduction in coal & oil consumption• Greater reliance Non fossil fuel energy

resources• Higher energy efficiencies• Halt deforestation

Monitoring Radiation

• Pyranometer measures solar radiation striking horizontal surface

• Transmits total (direct plus diffuse) short wave (< 3.0m) radiation

• Black and white surfaces (differences in absorptivity and albedo) mean a different temperature response (W/m2)

• Infrared Radiometer measures IR emitted by objects

Solar Power• Solar power is a clean, reliable form of

renewable energy generated by converting energy from the sun's radiation into electricity

• Solar cells, also referred to as photovoltaic (PV) cells are grouped and connected together in a single frame called a panel or module

• These cells are comprised of special semi-conductive materials, which is most often a piece of silicon positioned under a layer of thin glass

The world's largest solar electric power plantThe Gut Erlasee Solar Park, a 12-megawatt facility

Located near the Bavarian town of Arnstein, Germany

Solar Power• Concentrating Solar Power (CSP): systems are

based on a series of mirrors or reflectors that focus the sunlight into a central photo receptor

• These systems tend to be very large and produce hundreds of megawatts of power.

• Australia will invest $320 million to construct the world’s largest solar power plant

• The plant, which will be built in Victoria state, will have a capacity of 154 megawatts and will be built over the next several years, with a completion date set for 2013

Australia