Notes

Outline

Lecture 2: Global Energy Cycle

Solar Flux and Flux Density  Solar Luminosity (L)      the constant flux of energy put out by the sun                          L = 3.9 x 1026   W  Solar Flux Density (Sd)      the amount of solar energy per unit area on a sphere centered at the Sun with a distance d                          Sd  = L / (4 p d2)   W/m2

Solar Flux Density Reaching Earth  Solar Constant (S)     The solar energy density at the mean distance of      Earth from the sun (1.5  x 1011 m)         S = L / (4 p d2)            = (3.9 x 1026 W) / [4 x 3.14 x (1.5  x 1011 m)2]            = 1370 W/m2

Solar Energy Incident On the Earth  Solar energy incident on the Earth       =  total amount of solar energy can be absorbed by Earth       =  (Solar constant) x (Shadow Area)       =  S x p R2Earth

Solar Energy Absorbed by Earth

What Happens After the Earth Absorbs Solar Energy?  The Earth warms up and has to emit radiative  energy back to the space to reach a equilibrium condition.  The radiation emitted by the Earth is called “terrestrial radiation” which is assumed to be like blackbody radiation.

Blackbody Radiation  Blackbody     A blackbody is something that emits (or absorbs) electromagnetic radiation with 100% efficiency at all wavelength.  Blackbody Radiation      The amount of the radiation emitted by a blackbody depends on the absolute temperature of the blackbody.

Energy Emitted from Earth

Planetary Energy Balance

Greenhouse Effect

Different Wavelengths of Solar and Earth’s Radiation

Greenhouse Gases

Earth, Mars, and Venus

Three Factors To Determine  Planet Temperature  Distance from the Sun  Albedo  Greenhouse effect

Global Temperature

Greenhouse Effects  On Venus è 510°K (very large!!)  On Earth   è 33°K  On Mars   è 6°K (very small)

Why Large Greenhouse Effect On Venus?  Venus is too close to the Sun  Venus temperature is very high  Very difficult for Venus’s atmosphere to get saturated in water vapor  Evaporation keep on bringing water vapor into Venus’s atmosphere  Greenhouse effect is very large  A “run away” greenhouse happened on Venus  Water vapor is dissociated into hydrogen and oxygen  Hydrogen then escaped to space and oxygen reacted with carbon to form carbon dioxide  No water left on Venus (and no more chemical weathering)

Why Small Greenhouse Effect on Mars?  Mars is too small in size Mars had no large internal heat Mars lost all the internal heat quickly No tectonic activity on Mars Carbon can not be injected back to the atmosphere Little greenhouse effect A very cold Mars!!

Where Does the Solar Energy Go?

Where Is Earth’s Radiation Emitted From?

Important Roles of Clouds In Global Climate

Polarward Energy Transport

How Do Atmosphere and Ocean Transport Heat?