The South Atlantic Anomaly (or SAA) is the region where Earth Earth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density. It is also referred to as the World, the Blue Planet,[note 3] and Terra.[note 4]'s inner Van Allen radiation belt The Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. This field is not uniformly distributed around the Earth. On the sunward side, it is compressed because of the solar wind, while on the other side it is elongated to around three earth radii. This creates a cavity makes its closest approach to the planet's surface. For a given altitude, the radiation intensity is greater within this region than elsewhere. The Van Allen radiation belts are symmetric with the Earth's magnetic axis, which is tilted with respect to the Earth's rotational axis by an angle of ~11 degrees. Because of this tilt, the inner Van Allen belt is closest to the Earth's surface over the south Atlantic ocean, and farthest from the Earth's surface over the north Pacific ocean.[2]
The South Atlantic Anomaly is of great significance to astronomical satellites In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon and other spacecraft A spacecraft is a craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters space then returns to the Earth. For an orbital spaceflight, a spacecraft enters a closed orbit around the planetary body. Spacecraft used for human spaceflight carry people on board as crew or passengers. Spacecraft used for robotic that orbit In physics, an orbit is the gravitationally curved path of one object around a point or another body, for example the gravitational orbit of a planet around a star the Earth at several hundred kilometers altitude; these orbits take satellites through the anomaly periodically, exposing them to several minutes of strong radiation each time. The International Space Station The International Space Station is an internationally developed research facility currently being assembled in Low Earth Orbit. On-orbit construction of the station began in 1998 and is scheduled to be completed by 2011, with operations continuing until at least 2015. The station can be seen from the Earth with the naked eye, and, as of 2009[, orbiting with an inclination Inclination in general is the angle between a reference plane and another plane or axis of direction of 51.6°, requires extra shielding to deal with this problem. The Hubble Space Telescope The Hubble Space Telescope is a space telescope that was carried into orbit by the space shuttle in April 1990. It is named after the American astronomer Edwin Hubble. Although not the first space telescope, the Hubble is one of the largest and most versatile, and is well-known as both a vital research tool and a public relations boon for does not take observations while passing through the SAA.[3]
The shape of the SAA changes over time. Since its initial discovery in the late 1950s, the southern limits of the SAA have remained roughly constant while a long-term expansion has been measured to the northwest, the north, the northeast, and the east. Additionally, the shape and particle density of the SAA varies on a diurnal A day is a unit of time equivalent to approximately 24 hours. It is not an SI unit but it is accepted for use with SI. The SI unit of time is the second basis, with greatest particle density corresponding roughly to local noon. At an altitude of approximately 500 km, the SAA spans from -50° to 0° geographic latitude and from -90° to +40° longitude.[4] The highest intensity portion of the SAA drifts to the west at a speed of about 0.3 degrees per year, and is noticeable in the references listed below. The drift rate of the SAA is very close to the rotation differential between the Earth's core The interior structure of the Earth, similar to the other terrestrial planets, is layered. These layers can be defined by either their chemical or their rheological properties. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific and its surface, estimated to be between 0.3 and 0.5 degrees per year.[citation needed]
Current literature suggests that a slow weakening of the geomagnetic field is one of several causes for the changes in the borders of the SAA since its discovery. As the geomagnetic field continues to weaken, the inner Van Allen belt gets closer to the Earth, with a commensurate enlargement of the SAA at given altitudes.[citation needed] Some scientists, including Dr. Pieter Kotze, head of the geomagnetism group at the Hermanus Magnetic Observatory in the southern Cape, believe that the anomaly is a side effect of geomagnetic reversal A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged. These events often involve an extended decline in field strength followed by a rapid recovery after the new orientation has been established. These events occur on a scale of thousands of.[citation needed]
See also
- Geomagnetic reversal A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged. These events often involve an extended decline in field strength followed by a rapid recovery after the new orientation has been established. These events occur on a scale of thousands of
- Geomagnetic storm A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in space weather. Associated with solar coronal mass ejections , coronal holes, or solar flares, a geomagnetic storm is caused by a solar wind shock wave which typically strikes the Earth's magnetic field 24 to 36 hours after the event. This only
- Space weather Space weather is the concept of changing environmental conditions in near-Earth space. It is distinct from the concept of weather within a planetary atmosphere, and deals with phenomena involving ambient plasma, magnetic fields, radiation and other matter in space. "Space weather" often implicitly means the conditions in near-Earth space
- Van Allen Belts The Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. This field is not uniformly distributed around the Earth. On the sunward side, it is compressed because of the solar wind, while on the other side it is elongated to around three earth radii. This creates a cavity
- Operation Argus
References
- ^ "ROSAT SAA" (HTML). http://heasarc.gsfc.nasa.gov/docs/rosat/gallery/misc_saad.html. Retrieved 2007-10-16.
- ^ Stassinopoulos, E.G.; Staffer, C.A. (2007), Forty-Year Drift and Change of the SAA, NASA Goddard Spaceflight Center
- ^ "Hubble Achieves Milestone: 100,000th Exposure". STScI. 1996-07-18. http://hubblesite.org/newscenter/archive/releases/1996/25/text/. Retrieved 2009-01-25.
- ^ "The South Atlantic Anomaly" (HTML). Ask an Astrophysicist. http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961004.html. Retrieved 2007-10-16.
Categories: Earth Categories: Places | Planets of the Solar System | Nature | Atlantic Ocean | Geomagnetism
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Figure 12 15 Results showing artificial electron flux decay in the magnetic anomaly over the South Atlantic Back to the text
