What is the amount of solar energy at the outer atmosphere of the earth and incoming solar radiation reach Earth's surface so easily?
Averaged over the entire planet, the amount of sunlight arriving at the top of Earth’s atmosphere is only one-fourth of the total solar irradiance, or approximately 340 watts per square meter.
Respected Sir,
The solar constant is the amount of solar radiation received per unit area at the outer atmosphere of Earth when the Sun is at its mean distance. The average value of the solar constant is approximately 1361 watts per square meter (W/m²). This represents the total solar irradiance (energy per unit time and unit area) at the top of the Earth's atmosphere.
However, not all of this energy reaches the Earth's surface. Several factors contribute to the reduction of solar radiation as it travels through the Earth's atmosphere:
Absorption by the Atmosphere:
Some solar radiation is absorbed by gases in the Earth's atmosphere, particularly in the ultraviolet and shorter wavelengths. Ozone in the stratosphere is particularly effective at absorbing UV radiation.
Scattering:
Particles and gases in the atmosphere scatter shorter wavelengths of sunlight (blue and violet light) more effectively than longer wavelengths (red and yellow light). This scattering is responsible for the blue color of the sky during the day.
Reflection by Clouds and Atmospheric Particles:
Clouds, aerosols, and other atmospheric particles reflect a portion of incoming solar radiation back into space.
Path Length Through the Atmosphere:
The angle of sunlight and the path length through the atmosphere can affect the amount of solar radiation reaching the Earth's surface.
Despite these losses, a significant amount of solar radiation does reach the Earth's surface. On a clear day, about 70% to 90% of the incoming solar radiation can penetrate the atmosphere and reach the surface. This sunlight is crucial for driving various Earth processes, including photosynthesis, the water cycle, and the generation of wind and ocean currents.
The solar radiation outside the earth's atmosphere is calculated using the radiant power density (Hsun) at the sun's surface (5.961 x 107 W/m2), the radius of the sun (Rsun), and the distance between the earth and the sun. The calculated solar irradiance at the Earth's atmosphere is about 1.36 kW/m2. About 23 percent of incoming solar energy is absorbed in the atmosphere by water vapor, dust, and ozone, and 48 percent passes through the atmosphere and is absorbed by the surface. Thus, about 71 percent of the total incoming solar energy is absorbed by the Earth system. The solar energy reaching on unit area at outer edge of the earth's atmosphere exposed perpendicularly to the rays of the Sun at the average distance between the Sun and earth as solar constant. About 30 percent of incoming solar radiation is reflected out into space and plays no role in Earth's climate system. Of the remaining 70 percent, 23 percent of incoming solar radiation is absorbed in the atmosphere, either by water vapor, atmospheric particles, dust and ozone. Of the 340 watts per square meter of solar energy that falls on the Earth, 29% is reflected back into space, primarily by clouds, but also by other bright surfaces and the atmosphere itself. About 23% of incoming energy is absorbed in the atmosphere by atmospheric gases, dust, and other particles. Solar energy warms Earth, causes wind and weather, and sustains plant and animal life. The energy, heat, and light from the sun flow away in the form of electromagnetic radiation (EMR). The electromagnetic spectrum exists as waves of different frequencies and wavelengths. The solar radiation that reaches the Earth's surface without being diffused is called direct beam solar radiation. The sum of the diffuse and direct solar radiation is called global solar radiation. Atmospheric conditions can reduce direct beam radiation by 10% on clear, dry days and by 100% during thick, cloudy days. Atmospheric gas molecules and aerosols deflect solar radiation from its original path, scattering (reflecting) some radiation back into deep space and some toward Earth's surface. Clouds reflect much more incoming solar radiation than they absorb. At Earth's average distance from the Sun (about 150 million kilometers), the average intensity of solar energy reaching the top of the atmosphere directly facing the Sun is about 1,360 watts per square meter. Even if we use 5% of this energy, it is more than 50 times our requirement. The total solar radiation absorbed by the earth and its atmosphere is 3.8 X 1024 Joules/year.
The amount of solar energy at the outer atmosphere of the Earth is approximately 1,361 watts per square meter (W/m²), which is known as the solar constant. However, only about 49% of this incoming solar radiation reaches Earth's surface. The remaining energy is absorbed or reflected back into space by the Earth's atmosphere.
Here's a breakdown of how the incoming solar radiation is distributed:
- Reflected by clouds and atmosphere: 30%
- Absorbed by atmosphere: 19%
- Reaches Earth's surface: 49%
The amount of solar radiation that reaches Earth's surface varies depending on several factors, including the time of day, the season, the latitude, and the amount of cloud cover. At the equator, the average daily solar radiation is about 5.5 kWh/m², while at the poles, it is only about 2.5 kWh/m².
Despite the reduction in solar radiation due to the atmosphere, Earth still receives a significant amount of energy from the Sun. This energy is essential for life on Earth, driving photosynthesis in plants and providing warmth.
The solar radiation outside the earth's atmosphere is calculated using the radiant power density (Hsun) at the sun's surface (5.961 x 107 W/m2), the radius of the sun (Rsun), and the distance between the earth and the sun. The calculated solar irradiance at the Earth's atmosphere is about 1.36 kW/m2. The solar energy reaching on unit area at outer edge of the earth's atmosphere exposed perpendicularly to the rays of the Sun at the average distance between the Sun and earth is known as solar constant. About 23 percent of incoming solar energy is absorbed in the atmosphere by water vapor, dust, and ozone, and 48 percent passes through the atmosphere and is absorbed by the surface. Thus, about 71 percent of the total incoming solar energy is absorbed by the Earth system. Of the 340 watts per square meter of solar energy that falls on the Earth, 29% is reflected back into space, primarily by clouds, but also by other bright surfaces and the atmosphere itself. About 23% of incoming energy is absorbed in the atmosphere by atmospheric gases, dust, and other particles. Solar radiation that is not absorbed or reflected by the atmosphere reaches the surface of the Earth. The Earth absorbs most of the energy reaching its surface, a small fraction is reflected. Atmospheric gas molecules and aerosols deflect solar radiation from its original path, scattering (reflecting) some radiation back into deep space and some toward Earth's surface. Clouds reflect much more incoming solar radiation than they absorb. At Earth's average distance from the Sun (about 150 million kilometers), the average intensity of solar energy reaching the top of the atmosphere directly facing the Sun is about 1,360 watts per square meter. About 23 percent of incoming solar energy is absorbed in the atmosphere by water vapor, dust, and ozone, and 48 percent passes through the atmosphere and is absorbed by the surface. Thus, about 71 percent of the total incoming solar energy is absorbed by the Earth system. The amount of solar energy reaching the Earth is 70 percent. The surface of the Earth absorbs 51 percent of the insolation. Water vapor and dust account for 16 percent of the energy absorbed.