Sunlight

The solar radiation or solar radiation is emitted by the sun radiation. The electromagnetic spectrum of the sun is the greatest intensity in the range of visible light ( sunlight). Depends on the wavelength of the solar radiation is more or less strongly absorbed by the atmosphere. The incident at the earth's surface intensity also strongly depends on the weather and the sun's position.

Is usually not expected to the sun radiation, the addition of the electromagnetic radiation emitted by the sun is also prone particle mass. This consists of the charged particles of the solar wind and the neutrinos, resulting from the nuclear fusion inside the sun.

• 2.1 attenuation through the atmosphere

Solar spectrum

The electromagnetic radiation from the sun is at its maximum at 500 nm wavelength (blue- green light), but ranges from hard X-rays with less than 0.1 nm to long radio waves. The range is from about 140 nm ( UVC) to about 10 cm (microwave ) is approximately that of a blackbody at a temperature of around 6000 K, the temperature of the photosphere.

In the range of near infrared radiation (NIR) to the UV spectrum includes a plurality of absorption lines, the so-called Fraunhofer lines. They are caused by absorption of radiation in the chromosphere of the Sun.

Solar flares, their frequency depend on the solar activity, increase the radiation in the X-ray range in the short term by orders of magnitude, but contribute little to the total radiation. Often they are accompanied by long-wave radio emission (english radio bursts ), which is categorized depending on the intensity curve as type I to type V.

Radio emission

The quiet sun shines throughout the radio window. There, their spectrum is no longer that of a black body, but the effective temperature increases from 6000 K at 1 cm wavelength to 1,000,000 K at 10 m at. Also with the wavelength increasing the apparent diameter of the sun, the radiation is increasingly dominated by the external atmosphere. Is synchrotron faster electrons spiral about the magnetic field lines. The main radiation components of a disturbed sun are:

• Slow change in radiation proportional to the sunspot number, which shall include Solar radio flux index.
• Noise storms (english Noise storms ) above 100 MHz, duration of several days.
• Ray bursts (english radio bursts ) in conjunction with flares and CME, duration seconds to days. They are divided into categories I to V.

Solar constant

The total power of the electromagnetic radiation of the sun will be dominated by the thermal radiation of the photo- sphere, which varies by less than 0.1%. The falling to earth performance varies due to the eccentricity of Earth's orbit during the year by almost 7 %. The average power per unit area is called the solar constant. It is considered outside the Earth's atmosphere and is

That are produced during nuclear fusion inside the solar neutrinos carry 2% of the fusion power continues.

Attenuation due to the atmosphere

The intensity of solar radiation on the ground is lower than outside the atmosphere, the absorption and scattering is strongly wavelength dependent: the almost half of the solar radiation making up visual proportion reached on a clear day and the sun is high for most of the earth's surface. The non-visible radiation is predominantly near-infrared (NIR) radiation is absorbed by about a quarter in the atmosphere, mostly by water molecules. Of the ultraviolet radiation that makes up less than 10 % of the radiation, UVA penetrates largely, mainly weakened by Rayleigh scattering, which is also responsible for ensuring that the sky is blue and one is brown in partial shade. UVB is strongly absorbed by the ozone layer, UVC of atmospheric oxygen.

The exact calculation of the radiation flux as a function of sun position and height above sea level is difficult. Approximation, we consider only the layer thickness to be permeated the atmosphere in air mass units ( air mass ) and the duration of sunshine. Clouds reduce the direct radiation, fume increases the diffuse radiation. Diffuse radiation and direct radiation in one place together form the global radiation.

Irradiance

If the solar radiation, oblique, it is distributed over a larger surface, the irradiance decreases. This effect occurs with the sine of the elevation angle. The influence of the seasons in the tropics is hardly noticeable because of the sun at noon, there is always steep. The difference between summer and winter looks towards the poles getting stronger.

In Central Europe the summer midday sun is high in 60 ° to 65 ° and exudes with ideal weather conditions with an irradiance of about 700 watts / square meter. In the winter there are only 13 ° to 18 ° and even at lunch only about 247 watts / square meter.

The heating of the surface depends on the length of the bright day. The end of June, the duration in Central Europe about 16 hours, in December eight hours. The ratio of the total incident solar energy is between these months about 5:1 to 10:1, but is softened by heat storage mainly through the seas ( sea).

Measurement

The measurement of solar radiation via pyranometer, pyrheliometer or shine autographs. The latter are used to determine the duration of sunshine, especially. The solar constant is, however, measured by radiometer.

Radiation balance

The temperature of the earth's surface is determined by the global radiation balance, the radiation budget, so that the combination of absorption and reflection and re-emission and scattering is detected.