Solar wind cosmic rays and radioactive decay

Solar radiation is the principal source of energy driving the atmospheric processes that produce the global climate, but it is not the only one. Earth is also exposed to the solar wind. This is a stream of particles that constantly move outward from the outermost region of the Sun's atmosphere, called the corona, traveling at 155-500 miles per second (250-800 km s-1). The particles comprising the solar wind are charged and consist mainly of protons (+) and electrons (-). The wind is directed by the Sun's magnetic field and its intensity varies with the number of sunspots (see "Edmund Walter Maunder and the unreliable Sun" on pages 70-78). Solar-wind particles are captured by the Earth's magnetic field and travel along field lines. These descend over the North and South Pole, and that is where the particles also descend, encountering atoms and molecules of atmospheric gases as they do so. Those encounters release the photons of light that are visible as the auroras. The solar wind does not affect climate directly, but it does interact with cosmic radiation.

Solar wind, cosmic rays, and radioactive decay

The solar spectrum

Light, radiant heat, gamma rays, X rays, microwaves, and radio waves are all forms of electromagnetic radiation. This radiation travels as waves or particles called photons moving at the speed of light. The various forms differ in their wavelengths, which is the distance between one wave crest and the next. The shorter the wavelength, the more energy the radiation has. A range of wavelengths is called a spectrum. The Sun emits electromagnetic radiation at all wavelengths, so its spectrum is wide. The diagram shows the electromagnetic spectrum.

Gamma rays are the most energetic form of radiation, with wavelengths between I0-10 ,um and

10 14 ,um (a micron, ,um, is one-millionth of a meter, or about 0.00004 inch; I0-10 is 0.00000000001). Next come X rays, with wavelengths of l0-5-l0-3 ,um. The Sun emits gamma and X radiation, but all of it is absorbed high in the Earth's atmosphere and none reaches the surface. Ultraviolet (UV) radiation is at wavelengths of 0.004-4 ,um; the shorter wavelengths, below 0.2 ,um, are absorbed in the atmosphere but longer wavelengths reach the surface.

Visible light has wavelengths of 0.4-0.7 ,um, infrared radiation 0.8 ,um-l mm, and microwaves 1 mm-30 cm. Then come radio waves with wavelengths up to 100 km (62.5 miles).

The electromagnetic spectrum

Cosmic radiation comprises the nuclei of the most abundant elements. Protons—hydrogen nuclei—are the most plentiful. In addition to nuclei there are electrons, positrons, neutrinos, and gamma-ray photons. All of these have very high energies. Unlike solar-wind particles, they pass through the Earth's magnetic field and enter the atmosphere, where they collide with the nuclei of nitrogen and oxygen atoms. These collisions

Nitrogen And Oxygen Atoms Colliding

Solar and terrestrial produce secondary cosmic rays, comprising altered atomic nuclei, particles radiation resulting from the fragmentation (spallation) of nuclei, and a range of elementary particles including gamma-ray photons. These particles trigger cloud formation and so cosmic radiation does affect the climate.

Earth also generates energy by the radioactive decay of elements, principally uranium, thorium, and potassium, below the surface. The interior of the Earth may still retain some heat from the time of its formation and may generate heat through the continuing accumulation of metals in the core, but radioactive decay is the principal source of terrestrial heat.

The internal heat of the Earth drives the movement of tectonic plates and the raising of mountain ranges, slowly but steadily altering the surface geography and topography, and it causes volcanic eruptions. The distribution of the continents and the size and orientation of mountain ranges affect the formation and movement of air masses, so there is a sense in which internal heat influences climates over long timescales. Volcanic eruptions have a more immediate effect, by injecting gases and particles into the atmosphere.

Energy to move air masses, evaporate water, and generate all the features of the world's climates is supplied by the radiation we receive from the Sun. This energy is then reradiated from the Earth's surface and so returns to space. In addition to solar and terrestrial radiation, the global climate is also affected by cosmic radiation, the intensity of which is influenced by the intensity of the solar wind. Finally, radioactive decay releases the energy that causes continents to move, oceans to grow wider and narrower, mountain chains to rise, and volcanoes to erupt, all of which have climate effects.

The radiation balance

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    Where are radio waves absorbed in atmosphere?
    7 years ago
  • julia
    What processes produce and distribute solar wind particles?
    4 years ago

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