The intensity of the Sun and heat on Earth

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Discussion Overview

The discussion centers on the reasons for temperature variations on Earth, particularly why it is hotter at the equator compared to other regions. Participants explore concepts related to solar intensity, the angle of sunlight, atmospheric effects, and scattering of light, with a focus on both theoretical and conceptual aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the intensity of the Sun's rays is greater at the equator due to a higher density of solar beams per area, as the curvature of the Earth affects scattering.
  • Another viewpoint suggests that the Poynting vector has a component normal to the Earth's surface at the equator, contributing to greater intensity.
  • One participant discusses the role of absorption and scattering, noting that when the Sun is directly overhead, the light travels through less atmosphere, resulting in less attenuation.
  • A question is raised about the direction of scattered light, specifically whether light absorbed directly above the equator is scattered towards the equator or in other directions.
  • Another participant mentions the Earth's axial tilt and its impact on solar intensity during different seasons, indicating that sunlight must traverse more atmosphere in winter at higher latitudes, leading to reduced intensity.
  • There is a reference to Rayleigh scattering as a complex subject related to the scattering of light, with a suggestion that scattering events can be treated as new sources of light propagation.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the factors influencing temperature differences across latitudes, and the discussion remains unresolved with no consensus reached.

Contextual Notes

Limitations include assumptions about the behavior of light in the atmosphere, the dependence on definitions of intensity and scattering, and the complexity of atmospheric interactions that are not fully explored.

Who May Find This Useful

This discussion may be of interest to those studying atmospheric science, physics, or environmental science, particularly in relation to solar energy and climate variations.

Niles
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Hi all.

Is the explanation for the fact that it is hotter at equator than other places at the Earth that the intensity of the Suns waves are greater at equator, since the number of beams per area is larger (since they are not scattered that much because of the lack of curvature)?

I hope yoou can enlighten me. Thanks in advance.

- Niles.
 
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Is it perhaps even more correct to say that Poyntings vector only has a component normal to the surface of the Earth at equator, and this the intensity is greatest here?
 
Look at it in terms of absorption and scatter. If the Sun is directly overhead, the light has less atmosphere to traverse, and arrives at the Earth's surface with the least amount of attenuation. Where can the Sun be directly overhead at local noon? The latitude changes with the seasons and can range from the Tropic of Cancer to the tropic of Capricorn and any latitude in between.
 
How do we know that a beam of light that is absorbed by an atom straight above the equator will also be scattered towards the equator, and not in some other direction?

And also (this is regarding to seasons), when it is summer in the Northern Hemisphere, it says here (http://ksnn.larc.nasa.gov/k2/s_seasons.html ) that the light of the Sun hits the Northern Hemisphere more "directly". Do they mean the Poynting vector here or what?
 
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As turbo-1 mentioned, it's basically do to the fact that in winter due to the Earth's tilt off the earth-sun orbiting axis (I'm sure that has a less retarded name but I don't feel like looking it up). This tilt means that far from the equator in winter the sun's rays have to traverse more atmosphere to reach the surface and thus lose intensity due to scattering.

Now, scattering of light is a rather complicated subject but as for your question of direction you might find a discussion of Rayleigh Scattering illuminating (just wiki it) but the short answer is that classically we often treat a light scattering event as a new 'source' if you will and the superposition of all these randomly distributed (random because air molecules are randomly spaced) 'sources' results in a net forward propagation.
 
Thank you for your explanation. It is very good.
 

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