Gabriel Daniel Farenheit Dutch Physicist 1724 developed a

• Gabriel Daniel Farenheit - Dutch Physicist (1724) developed a temperature scale – Ice Point = 32 o. F – Steam Point = 212 o. F • Anders Celsius - Swedish Astronomer (1742) - developed a metric temperature scale. – Ice Point = 0 o. C – Steam Point = 100 o. C • William Thomson Kelvin - British Mathematician (1800’s) developed the Kelvin (or absolute scale). – 0=absolute zero – Ice Point = 273 K – Steam Point = 373 K

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The sun is the major source of energy for all atmospheric processes. On a global scale, the motions of the atmosphere are mainly a direct response to seasonal and latitudinal differences in the amount of radiation reaching the surface. Solar Constant - the amount of solar radiation reaching the top of a planet’s atmosphere at its average distance from the sun.

Solar Constant = Total Solar Emission 4 p (distance 2) For Earth: Solar Constant = 3. 86 X 1026 W = 1367 W/m 2 4 p (1. 5 X 1011 m) For Mars: Solar Constant = 3. 86 X 1026 W = 445 W/m 2 4 p (2. 25 X 1011 m)

• Energy - ability to do work. • Units of energy: – Calorie – Joule (J) • 1 joule = 0. 239 calories = 1 Kg m 2/s 2 • Power - rate at which energy is released • Unit of power – Watt (W) 1 W = 1 J/s • Any activity requires a transfer of energy!

• Three forms of energy transfer: 1. Convection 2. Conduction 3. Radiation

1. Convection Transfer of energy (heat) by mixing of a fluid. Accomplished by displacement of the fluid.

2. Conduction Transfer of energy (heat) by movement through a material. No displacement - accomplished by electrons.

3. Radiation - form of energy that can be propagated without a transfer medium. • Electromagnetic Radiation - Energy emitted due to the temperature of an object. • Energy emitted from the sun is transferred to earth as electromagnetic radiation. • Electromagnetic radiation from the sun is the main source of energy for our atmosphere.

Wave length = type of radiation Wave height = Amount - intensity

Electromagnetic Radiation • • • Visible light Microwaves Ultraviolet Radio waves X-rays

• Electromagnetic radiation may be described in terms of quantity and quality. – Quantity (Intensity) - how much - proportional to wave height (or amplitude) – Quality - type of radiation - wavelength

Stephan - Boltzman Law I = s T 4 I - Intensity s - Stefan - Boltzman Constant 5. 67 X 10 -8 watts/m 2/K 4 T - Temperature The single factor that determines how much energy a (black) body radiates is temperature. Hotter bodies emit more energy than cooler ones.

Intensity and Emissivity I = e s T 4 I - Intensity s - Stefan - Boltzman Constant 5. 67 X 10 -8 watts/m 2/K 4 T - Temperature - Emissivity how efficient a substance is at emitting radiation.

Wein’s Law l(max) = constant/T l - wavelength T - Temperature Constant - 2900 µm/K The single factor that determines the maximum wavelength a body radiates is temperature. Hotter bodies emit smaller wavelengths than cooler ones.

Wein’s Law l - wavelength l(max) = constant/T T - Temperature Constant - 2900 For Earth at 290 K l(max) = constant/T = 2900/290 = 10 µm For the Sun at 6000 K l(max) = constant/T = 2900/6000 = 0. 48 µm

Hotter bodies (like the sun) emit more radiation with peaks at shorter wavelengths. SW - shortwave radiation. (mostly ultraviolet) Cooler ones bodies (like the earth) emit less radiation with peaks at longer wavelengths. LW - longwave radiation. (mostly infrared)

• Ecliptic plane - imaginary surface that earth sweeps as it orbits around the sun. • Perihelion - Earth’s nearest approach to the sun. (~Jan. 3) - 91, 000 miles • Aphelion - Earth’s furthest distance from the sun. (~July 3) 94, 000 • Rotation - Earth makes one complete spin on its axis every 24 hours. • Axis - imaginary line connecting the north and south poles.

The tilt of earth on its axis is o 23. 5 and is constant, point toward the north star Polaris. This is the major cause of seasons on earth!

Tilt of Earth on its Axis • • The tilt of earth on its axis means that half the year the Northern Hemisphere faces the sun and the other half of year the Southern Hemisphere faces the sun. The tilt affects: 1. Angle at which sunlight intersects the surface. 2. Length of day. 3. Amount of atmosphere that solar radiation must penetrate to reach the surface.

June Solstice • Summer solstice ~ June 21 • Northern Hemisphere has its maximum tilt toward the sun. • First day of summer • Maximum solar radiation in the NH – Higher solar angles – Longer days – Less atmosphere depletion

December Solstice • Winter solstice ~ December 21 • Northern Hemisphere has its maximum tilt away from the sun. • First day of winter in NH • Minimum solar radiation in the NH – Lower solar angles – Shorter days – More atmosphere depletion

March Equinox • Spring Equinox ~ March 21 • The Hemispheres do not tilt toward or away from the sun. • First day of spring • Equal solar radiation in both hemispheres – Solar angles are the same for both hemispheres – Every location on earth receives 12 hours daylight – Atmosphere depletion is the same in both hemispheres

September Equinox • Autumnal Equinox ~ September 21 • The Hemispheres do not tilt toward or away from the sun. • First day of Fall • Equal solar radiation in both hemispheres – Solar angles are the same for both hemispheres – Every location on earth receives 12 hours daylight – Atmosphere depletion is the same in both hemispheres

Latitude - E -W trending lines (great circles) that change N and S of the equator • Subsolar point - the point on Earth where the sun’s rays meet the surface at a right angle. The noonday sun will appear directly overhead. • Solar declination - latitudinal position of the subsolar point.

• Tropic of Cancer - a line of latitude at 23. 5 o N and is the Northern limit of solar declination. • Tropic of Capricorn - a line of latitude at 23. 5 o S and is the Southern limit of solar declination.

• Arctic Circle - a line of latitude at 66. 5 o N. – All points north of this latitude receive 24 hours of daylight during the summer solstice and 24 hours darkness during the winter solstice. • Antarctic Circle - a line of latitude at 66. 5 o S. – All points south of this latitude receive 24 hours of daylight during the summer solstice and 24 hours darkness during the winter solstice.

Factors that affect the amount of solar radiation reaching the surface 1. Solar Angle 2. Length of Day 3. Atmosphere penetration