PPT08 - Radiation Balance

PPT08 - Radiation Balance - Factors controlling the Earths...

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Factors controlling the Earth’s climate – Amount of solar radiation received by Earth: controlled by Intensity of solar radiations Earth’s orbit – Amount of solar radiation absorbed by Earth’s: controlled by Earth’s albedo Atmospheric greenhouse gases – Redistribution of solar radiations on Earth’s surface: controlled by: Atmospheric circulation Ocean circulation First, we have to establish the main factors that control global climate We have a lot of information to integrate and digest to understand the climate during the Mesozoic, throughout Earth’s history, and today. . We must understand the factors that controls: - the amount of incoming solar radiations that reaches and are absorbed by Earth - the redistribution of solar radiations on the Earth’s surface Radiation Balance I Goals for Today 1. COMPARE infrared, ultraviolet , and visible electromagnetic radiation in terms of energy per photon , frequency , and wavelength 2. COMPARE the amount and type of energy emitted by objects at different temperatures 3. PREDICT the effect of varying the factors that determine the amount of solar radiation reaching a planet (or its “solar constant ”) 4. CALCULATE the flux of solar radiation (W/m2) reaching the top of the Earth’s atmosphere What determines how much solar energy Earth gets? The solar constant is the amount of solar radiation or energy (in Joules) reaching Earth per unit time (seconds) and per unit surface area (metres2). Units of the solar constant are Joules/metre2*seconds, which is the same as Watts/m2 (see the extra slide about Key Units). To imagine the solar constant, imagine a piece of cardboard that is one metre square. Imagine the cardboard orbiting Earth at the top of Earth’s atmosphere with its flat side DIRECTLY facing the Sun’s rays. The solar constant is the amount of solar energy hitting the piece of cardboard every second (Watts/m2) A planet’s solar constant depends on a few different factors. An important factor is how much energy is emitted by the star in the planet’s solar system. It turns out that the amount of electromagnetic energy emitted by an object depends on its temperature. The characteristics of that electromagnetic energy (frequency, wavelength, energy per photon) also depend on the object’s temperature . We’ll use two physical “laws” (Stefan-Boltzmann’s and Wein’s) to examine these relationships, and what the consequences are for EARTH.
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Key units for Today’s Goals (International System; SI) • Force (Newton; N) = mass x acceleration A force of 1N accelerates a mass of 1kg at a rate of 1m/sec2 • Energy or work (Joule; J) = Force x distance 1 J is the energy produced (or work done) by a force of 1N moving an object by 1 m • Power (Watt; W) = Energy / time Amount of energy that is emitted, absorbed or reflected per unit time (1J/sec) • Energy flux or intensity (Watt per m2; W/m2) = Power / area Amount of energy that is emitted, absorbed or reflected per unit area per unit time
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PPT08 - Radiation Balance - Factors controlling the Earths...

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