On this date, the solar noon radiation values at the top of the atmospheree and at the surface at this place are 1317 WM-2 and 920 WM-2. Why is the surface value lower than the value at the top of the atmosphere?
The surface radiation value is lower than the radiation value at the top of the atmosphere due to various factors that influence the amount of radiation reaching the surface.
1. Atmospheric Absorption: As sunlight travels through the atmosphere, it encounters molecules and particles that absorb and scatter some of the radiation. This absorption reduces the amount of radiation reaching the surface.
2. Reflection and Scattering: Some of the incoming radiation is reflected back into space by the atmosphere, clouds, aerosols, or surface features such as snow, ice, or water bodies. This reflected radiation does not reach the surface, resulting in a lower surface radiation value.
3. Path Length: The path length traveled by sunlight is longer when it passes through the atmosphere compared to when it reaches the surface directly from the top of the atmosphere. This elongated path allows for greater opportunities for absorption and scattering, further reducing the surface radiation value.
4. Atmospheric Composition: The composition of the atmosphere affects the absorption and scattering of radiation. For example, greenhouse gases like carbon dioxide and water vapor absorb certain wavelengths of radiation, contributing to the difference in radiation values between the top of the atmosphere and the surface.
These factors combined result in a decrease in radiation from the top of the atmosphere to the surface.
The surface value of solar radiation is lower than the value at the top of the atmosphere primarily due to a process called atmospheric attenuation. Atmospheric attenuation refers to the reduction in the intensity of solar radiation as it passes through and interacts with the Earth's atmosphere.
There are several factors that contribute to this attenuation:
1. Scattering: When sunlight interacts with gas molecules and particulate matter in the atmosphere, it can be redirected in various directions. This scattering phenomenon reduces the amount of direct solar radiation reaching the surface.
2. Absorption: The atmosphere contains gases, such as water vapor, carbon dioxide, and ozone, which have specific absorption characteristics. These gases can absorb certain wavelengths of solar radiation, particularly in the infrared and ultraviolet regions of the electromagnetic spectrum. As a result, some of the solar radiation is absorbed and converted into heat energy within the atmosphere.
3. Reflection: The Earth's surface reflects a portion of the incoming solar radiation back into space. This reflected radiation, known as albedo, reduces the amount of solar radiation that reaches the surface.
4. Cloud cover: Clouds can significantly reduce the amount of solar radiation reaching the surface by reflecting, scattering, and absorbing the incoming sunlight. The presence of clouds acts as a barrier between the Sun and the Earth's surface, leading to a lower surface radiation value.
5. Elevation and distance: The angle at which solar rays encounter the Earth's surface varies with latitude, time of day, and season. Therefore, locations at higher latitudes or higher elevations may receive lower solar radiation values due to the oblique angle of the Sun's rays.
It's important to note that the values you provided (1317 WM-2 and 920 WM-2) represent average measurements of solar radiation and can vary depending on various atmospheric conditions, geographical location, and time of year.