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Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre (W/m 2) in SI units.
The solar constant (GSC) measures the amount of energy received by a given area one astronomical unit away from the Sun. More specifically, it is a flux density measuring mean solar electromagnetic radiation (total solar irradiance) per unit area. It is measured on a surface perpendicular to the rays, one astronomical unit (au) from the Sun ...
If the extraterrestrial solar radiation is 1,367 watts per square meter (the value when the Earth–Sun distance is 1 astronomical unit), then the direct sunlight at Earth's surface when the Sun is at the zenith is about 1,050 W/m 2, but the total amount (direct and indirect from the atmosphere) hitting the ground is around 1,120 W/m 2. [6]
Of the ~340 W/m 2 of solar radiation received by the Earth, an average of ~77 W/m 2 is reflected back to space by clouds and the atmosphere and ~23 W/m 2 is reflected by the surface albedo, leaving ~240 W/m 2 of solar energy input to the Earth's energy budget. This amount is called the absorbed solar radiation (ASR).
Solar activity and climate. Solar irradiance (yellow) plotted with temperature (red) since 1880. Patterns of solar irradiance and solar variation have been a main driver of climate change over the millions to billions of years of the geologic time scale. Evidence that this is the case comes from analysis on many timescales and from many sources ...
Solar radiation is absorbed by the Earth's land surface, oceans – which cover about 71% of the globe – and atmosphere. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection .
Surface albedo is defined as the ratio of radiosity Je to the irradiance Ee (flux per unit area) received by a surface. [2] The proportion reflected is not only determined by properties of the surface itself, but also by the spectral and angular distribution of solar radiation reaching the Earth's surface. [3]
Proposed methods of reflecting more sunlight to reduce Earth's temperature. Solar radiation modification (SRM), also known as solar radiation management, or solar geoengineering, refers to a range of approaches to limit global warming by increasing the amount of sunlight (solar radiation) that the atmosphere reflects back to space or by reducing the trapping of outgoing thermal radiation.