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Solar Radiation: Earth’s Shape, Slanting Rays, and Energy Exchange
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- Insolation: The earth’s surface primarily receives energy in short wavelengths, which is termed as “incoming solar radiation” or “insolation.”
- Geoid Shape: The Earth resembles a geoid shape (sphere-like shape).
- Angle of Solar Rays: The sun’s rays fall slantwise at the top of the atmosphere.
- Interception of Solar Energy: Out of this, the Earth intercepts a small portion of the sun’s energy.
- Solar Constant: On average, the earth receives 1.94 calories per sq. cm per minute at the top of the atmosphere.
The Passage of Solar Radiation through the Atmosphere
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Distribution of Solar Radiation: Earth’s Orbital Tango, Tilt, and Latitude Influence
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- Changing Earth-Sun Distance: The changing distance between the Earth and the Sun varies the solar output throughout the year.
- The annual insolation on 3rd January is slightly more than on 4th July is due to perihelion.
- Axial Tilt: The Earth’s axis is angled at 66½° with its orbital plane.
- This angle significantly influences insolation received at different latitudes.
- Latitude: The amount of insolation is also determined by the angle of the sun’s rays which depends on the latitude of a place.
- The higher the latitude the less is the angle they make with the surface of the earth resulting in slant sun rays which cover more area and energy get distributed and the net energy received per unit area decreases.
- Atmospheric Effects: Moreover, slant rays pass through a greater depth of the atmosphere, leading to more absorption, scattering, and diffusion.
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Atmospheric Influence on Insolation: Solar Radiation Alchemy
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- Atmospheric Transparency to Solar Radiation: The atmosphere is mostly transparent to short-wave solar radiation.
- As solar radiation passes through the atmosphere, gases like water vapour and ozone absorb much of the near-infrared radiation.
- Scattering of Visible Light: Small particles in the troposphere scatter the visible spectrum of the light.
- This scattering results in the blue colour of the sky and the red colour of the rising and setting sun.
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Spatial Distribution of Insolation on Earth’s Surface: Solar Radiation Tapestry
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- Subtropical deserts: It receives the highest insolation due to minimal cloudiness.
- The equator: It receives less insolation compared to the tropics.
- Continents vs. Oceans: At the same latitude, continents generally receive more insolation than oceans.
- Seasonal Variations: During winter, middle and higher latitudes receive less radiation compared to summer.
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