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MEA Chapter 2 notes

MEA Chapter 2 notes - Chapter 2 Heating Earth's Surface and...

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Chapter 2: Heating Earth’s Surface and Atmosphere Earth-Sun Relationships - Solar radiation accounts for more than 99.9% of the energy that heats the earth and its atmosphere - This energy is not distributed evenly, however, as it varies by: - - It is this uneven distribution of energy that creates most of what we consider to be weather. Earth’s Motions - Rotation: - Revolution: The Seasons - Regulated by the amount of solar radiation received by the surface of the Earth; which is dictated by: 1) angle at which the radiation strikes the surface, - radiation striking the earth perpendicularly is: - -
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2) length of the “day” (# of daylight hours) - longer days allow for more radiation to be absorbed by the earth’s surface (Table 2.2) Earth’s Orientation - These changes are due to the Earth being tilted by 23.5 o from the plane of its elliptical orbit around the sun (Fig 2.5) The Earth’s axis (center of rotation) points in the same direction into space all year long; as a result: The NH:
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Solar Elevation Angle (Noontime) Figure 2.6 and Box 2.2 (The Analemma) provide ways to calculate the solar elevation angle ( 5 ) at local noon for any latitude and time of year. This angle can also be calculated using the following equation: ( 29 + × × - Φ - = 365 ) 10 ( 360 cos 5 . 23 90 N o o β where: Once we know the solar elevation angle ( 5 ), we can then calculate the: Solar Radiation (Noontime ) β sin 1367 2 × = meter Watts J which provides an instantaneous measure of the intensity of the solar radiation (Watts) per square meter (ignoring effects of atmosphere).
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Solstices and Equinoxes (Northern Hemisphere) Summer Solstice “Astronomical start of summer” ( ~June 21 : Julian Day 173) Sun is at its highest position in the sky, as a result, radiation shines down on the surface: - - - each latitude (in NH) will have: - the farther north you go, the greater the # of daylight hours (Table 2.2) - from Arctic Circle (66.5 o N) north, 24 hours of sunlight - The noon sun is directly overhead at 23.5 o N, the: Fig. 2.7a
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Exercise : Calculate the noon solar elevation angle for Raleigh (35 o N) at the summer solstice (Day 173). + × × - - = 365 ) 10 173 ( 360 cos 5 . 23 35 90 o o o β = β Modified (for Raleigh) Fig. 2.2a Exercise: Calculate the noon solar radiation for Raleigh 5 . 78 sin 1367 2 × = meter Watts J = J - - From Table 2.2 we can see that Raleigh will have 14.4 hours of daylight at the summer solstice -
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Winter Solstice Astronomical start of winter”
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