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单词 solar wind
释义
solar wind

Physics
  • A continuous outward flow of charged particles, mostly protons and electrons, from the sun’s corona into interplanetary space. The particles are controlled by the sun’s magnetic field and are able to escape from the sun’s gravitational field because of their high thermal energy. The average velocity of the particles in the vicinity of the earth is about 450 km s−1 and their density at this range is about 8×106 protons per cubic metre.


Astronomy
  • The continuous outflow of ionized gas from the Sun’s corona. The solar wind consists of electrons, protons, and (to a lesser extent) the nuclei of elements such as helium. As the gas expands into interplanetary space it carries with it magnetic field lines that are twisted into a spiral pattern by the Sun’s rotation. Three distinct components to the solar wind can be identified: the fast and slow solar wind streams, and the transient wind due to coronal mass ejections (CMEs). The fast wind arises from coronal holes where magnetic field lines in the corona directly open out into space. It has generally very stable properties, with speeds at 1 au of 700–800 km/s. The slow solar wind arises from regions where closed magnetic field structures occur in the Sun’s corona; average speeds at 1 au are 300–400 km/s. It shows more variability in terms of temperature, density, and element composition than the fast solar wind. CMEs can travel outwards from the Sun at velocities up to 3000 km/s, and have enhanced density and magnetic fields over the background solar wind. When fast solar wind streams catch up with slower streams, they produce co-rotating interaction regions (CIRs) where intense magnetic fields can be produced, bounded by forward and reverse shock fronts. When these CIRs encounter the Earth, they produce geomagnetic storms.

    At solar minimum, when the Sun’s global magnetic has its simplest form, the slow solar wind is concentrated in the ecliptic plane around the heliospheric current sheet. If the current sheet is tilted relative to the ecliptic plane, then the fast wind streams can be detected at Earth on a repeating cycle of 27 days as the Sun rotates. At solar maximum the structure is more complex, with fast solar wind streams interspersed among the slow solar wind, which extends over all latitudes. Both the fast and slow solar wind are accelerated to supersonic speeds within a few solar radii of the Sun’s surface. The solar wind interacts with the Earth and other planets that have magnetic fields to produce their magnetospheres. The solar wind extends for over 100 au from the Sun. Its boundary is marked by the heliopause.


Space Exploration
  • A stream of atomic particles, mostly protons and electrons, from the Sun's corona, flowing outwards at speeds of between 300 kps/200 mps and 1 000 kps.

    The fastest streams come from ‘holes’ in the Sun's corona that lie over areas where no surface activity occurs. The solar wind pushes the gas of comets' tails away from the Sun, and ‘gusts’ in the solar wind cause geomagnetic disturbances and aurorae on Earth.


Geology and Earth Sciences
  • General term for the stream of high-energy particles (mainly protons, electrons, and alpha particles) emitted by the Sun. The particles have velocities of hundreds of kilometres per second and ‘wind’ strength is greatest during periods of maximum solar activity. In the neighbourhood of the Earth the solar wind has velocities in the range of 300–500 km/sec and an average density of 107 ions/m3. See also cosmic radiation.


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