Wednesday, September 19, 2007

solar wind

The solar wind is a stream of charged particles which are expelled from the upper atmosphere of the sun. It consists mostly of high-energy electrons and protons that are able to get away the sun's gravity in part because of the high temperature of the corona and the high kinetic energy particles gain through a process that is not well understood at this time.

They are directly related to the solar wind, together with geomagnetic storms that can knock out power grids on Earth, auroras and the plasma tail of a comet always pointing away from the sun. While early models of the solar wind used primarily thermal energy to accelerate the material, by the 1960s it was clear that thermal hurrying alone cannot account for the high speed solar wind. Some additional acceleration mechanism is required, but is not presently known, but most likely relates to magnetic fields in the solar atmosphere. The solar wind is answerable for the overall shape of Earth's magnetosphere, and fluctuations in its speed, density, direction, and entrained magnetic field powerfully affect Earth's local space environment.

Tuesday, September 04, 2007

Tsunami

A tsunami is a series of waves shaped when a body of water, such as an ocean, is rapidly displaced. Earthquakes, group movements above or below water, volcanic eruptions and other underwater explosions, landslides, large meteorite impacts and testing with nuclear weapons at sea all have the potential to produce a tsunami. The effects of a tsunami can range from imperceptible to devastating. The word tsunami comes from the Japanese words meaning harbor and wave. For the plural, one can either follow usual English practice and add an s, or use an invariable plural as in Japanese. The term was created by fishermen who returned to port to find the area neighboring their harbor devastated, although they had not been conscious of any wave in the open water. Tsunamis are general throughout Japanese history; approximately 195 events in Japan have been recorded.
A tsunami has a much smaller amplitude (wave height) offshore, and a very long wavelength, which is why they generally pass unobserved at sea, forming only a passing bulge in the ocean. Tsunami have been historically referred to as tidal waves because as they approach land, they take on the characteristics of a vicious onrushing tide rather than the sort of cresting waves that are formed by wind action upon the ocean. Since they are not really related to tides the term is considered misleading and its treatment is discouraged by oceanographers.