Where on Earth is the Sun's radiation the weakest and why do tropical regions receive a greater input of solar radiation than the poles?
The Sun's radiation is the weakest at the poles because the Earth is tilted at an angle of 23.5 degrees relative to its orbit around the Sun. This means that the Sun's rays are more concentrated at the equator than at the poles, and the longer the path of sunlight through the atmosphere, the more the sunlight is scattered and absorbed. As a result, the poles receive less energy from the Sun than the equator.
This is why tropical regions receive a greater input of solar radiation than the poles. The Sun's rays are almost perpendicular to the surface at the equator at solar noon, and so the sunlight is not spread over a large area. This means that the sunlight is concentrated and can heat the Earth's surface more effectively. At the poles, the Sun's rays are spread over a larger area because they are angled more obliquely to the surface. This means that the sunlight is not as concentrated and cannot heat the Earth's surface as effectively.
In addition, the atmosphere at the equator is thicker than the atmosphere at the poles. This means that there is more air to absorb and scatter the sunlight at the equator. As a result, the sunlight that reaches the Earth's surface at the equator is less intense than the sunlight that reaches the Earth's surface at the poles.
The combination of these factors means that the tropical regions of the Earth receive a greater input of solar radiation than the poles. This is why the tropical regions are generally warmer than the polar regions.
Incoming solar radiation is strongest at the Equator and weakest at the Poles. If air did not move around the atmosphere, the Equator would get hotter and hotter, and the Poles would get even colder! However, air moves from warm to cold regions and redistributes all of the incoming solar energy. The Earth's atmosphere and magnetic shield protect us from cosmic radiation. Earth's magnetic shield protects us from the cosmic radiation and is strongest at the equator and weakest near the poles. The magnetic shield diverts most of the radiation around the earth. Note that the sunlight strikes the planet perpendicular to the surface near the equator, but it strikes at an oblique angle near the poles, such that L2>L1. This means that the insolation is more concentrated near the equator and weaker near the poles. So, at polar latitudes, incoming solar radiation is spread over an even larger surface area, and is even less intense than at mid latitudes. In addition, the sun's rays become scattered and diffuse as they travel through the Earth's atmosphere, and this effect increases with latitude. Latitude affects UV radiation, which is strongest at the equator and declines toward the poles. The equator receives more incoming solar radiation than the poles because Earth is spherical. At the equator, the sun's rays are almost perpendicular to the surface at solar noon. At the lower sun angles characteristic of high latitudes, the sun's rays are spread over a larger surface area. At the poles, the ice, snow and cloud cover create a much higher albedo, and the poles reflect more and absorb less solar energy than the lower latitudes. Through all of these mechanisms, the poles absorb much less solar radiation than equatorial regions, which is why the poles are cold and the tropics are very warm. The Sun's rays strike Earth's surface most directly at the Equator. Near the poles, the Sun's rays strike the surface at a slant. This spreads the rays over a wide area. The more focused the rays are, the more energy an area receives. The Equator, at 0° latitude, receives a maximum intensity of the sun's rays all year. As a result, areas near Earth's Equator experience relatively constant sunlight and little solstice variation. This causes the Sun's rays to strike the Earth's surface at different angles, creating variances in temperatures on Earth. The more slanted the sun's rays are, the longer they travel through the atmosphere, becoming more scattered and diffuse. Because the Earth is round, the frigid polar regions never get a high sun, and because of the tilted axis of rotation, these areas receive no sun at all during part of the year.
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