Flashcards in 8.7 The Energy Balance Of The Earth Deck (7):
What is the average intensity?
The solar constant is S=1400Wm-2. The radiation that reaches the Earth can be thought of as passing through a disc of radius equal to the Earths radius R. The power indent on this disc is therefore P = SpiR^2. This power is thought to be distributed over the entire surface of the Earth and so the average intensity incident on Earth is
I = (SpiR^2)/(4piR^2) = S/4 = 350 Wm-2
About 30% is reflected which means that the Earths surface received an average radiation of 350 x 0.70 = 250Wm-2
What is the greenhouse effect?
With an stomps here some of the radiation emitted by the Earth's surface gets absorbed by gases in the atmosphere and then re radiated in all directions including back down to Earth warming the Earth.
What is the mechanism of photon absorption by greenhouse effect?
Like atoms molecules exist in discrete energy states. The difference between molecular energy levels correspond to infrared photon energies. The radiation emitted by the Earth's surface is in the infrared region. Hence some of this radiation is absorbed by these gases exciting their molecule to a higher energy state. This radiation is realised when the molecules makes a transition back down to its original state.
What are the natural sources of water vapour?
Evaporation of water from oceans, rivers and lakes.
What are the natural and human related sources of carbon dioxide?
Forest fires, volcanic eruption, evaporation of waters from oceans and burning of fossil fuels in power plants and cars, and burning of forests.
What are the natural and human related sources of methane?
Wetlands, oceans, lakes and rivers, flooded rice fields, farm animals, termites, processing coal, natural gas and oil and burning of biomass.