The South Atlantic magnetic anomaly (SAMA) and signals of the Earth´s magnetic poles reversal

Important variations in the magnetic field, observed by satellites in certain areas of the globe, could herald an inversion of the poles. This phenomenon has already come about several times in the history of the planet. Is the Earth losing its compass? This is what a study by the Department of Geomagnetism and Paleomagnetism of the Paris Geophysical Institute (l’Institut de physique du globe de Paris [IPG]) would have us believe.
We are all contained by the Earth’s magnetic field without really noticing it. We become aware of it only when we use a compass to find our way. This is the most obvious manifestation of the Earth’s magnetism, which has existed for 3 billion years and is generated 3,000 kilo-meters under our feet by the stirring of our planet’s liquid iron core. This liquid iron core causes the Earth to act like a giant magnet; the magnetic lines are organized on a bipolar basis, more or less in alignment with the Earth’s rotational axis.
This bipolar configuration, however, is not permanent. It varies with the movement of the Earth’s liquid core, and in the past, the positions of the magnetic poles have been known to switch entirely. These phenomena were verified by paleomagnetic studies on ancient volcanic basalts. The latter contain magnetic grains that kept both the orientation and strength of the Earth’s magnetic field when they became solid.
The Earth’s magnetosphere is a close- to-spherical magnetic field that surrounds our planet. As a matter of fact, this magnetosphere shields us from the constant bombardment that our globe suffers as a consequence of t its exposition to the Sun. It is estimated that the Sun is blowing several radiation particles, in many directions, around 1 billion kilograms of electrons, protons and other forms of dense matter per second.
There is a spot in this magnetic shielding that actually plays as a hole letting the incoming solar wind to penetrate close to our ground and release a larger radiation dose comparatively to other areas where the magnetosphere shows a more uniform profile. That dip is said to be caused by the eccentric displacement of the center of the
magnetic field from the geographical center of the Earth as well as the displacement between the magnetic and geographic poles. This dip is dubbed the South Atlantic magnetic anomaly (SAMA). It is occupying the area between Southeast Brazil and South Africa.
The minimum value, of the total geomagnetic field F of about 22,850 nT is found around 26° South and 54° West, which agrees well with the International Geomagnetic Reference Field (IGRF) model for the year 2000. The F field strength within the radius of about 1000 km around the F minimum point is less than 23,000 nT. It can be noted that the anomaly is dynamic, the center of the anomaly, that is the area of F minimum, has traveled in the last century from near Rio de Janeiro (23°.0 S, 43°.0 W) to Rio Grande do Sul (29°.0 S, 54°.0 W). These locations are determined from a combination of the magnetic maps prepared by the Brazilian National Observatory, Ministry of Science and Technology, Rio de Janeiro and the IGRF models Marins (2002). The center of F minimum and location of magnetic equator both have undergone a large secular variation unseen elsewhere. It is thought that this westward drift of the center of the anomaly and magnetic equator may be related to the westward drift of the geomagnetic axis of the Earth. The present value of F at São Martinho da Serra (SMS) (29°.43 S, 53°.80 W) is 22,883 nT and it is decreasing at the rate of 28 nT/year.
If the South Atlantic magnetic anomaly (SAMA) is taken as signal of an imminent reversal of our planet´s magnetic poles, how imminent is the reversal occurrence?

The thermosphere

The thermosphere is the biggest of all the layers of the earth's atmosphere directly above the mesosphere and directly below the exosphere. Within this layer, ultraviolet radiation causes ionization. The International Space Station has a stable orbit within the middle of the thermosphere, between 320 and 380 kilometers (200 and 240 mi). Auroras also occur in the thermosphere.
Named from the Greek θερμός (thermos) for heat, the thermosphere begins about 80 kilometers (50 mi) above the earth. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation by the small amount of residual oxygen still present. Temperatures are highly dependent on solar activity, and can rise to 1,500 °C (2,730 °F). Radiation causes the atmosphere particles in this layer to become electrically charged, enabling radio waves to bounce off and be received beyond the horizon. At the exosphere, beginning at 500 to 1,000 kilometers (310 to 620 mi) above the Earth's surface, the atmosphere turns into space.
The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, because it is so near vacuum that there is not enough contact with the few atoms of gas to transfer much heat. A normal thermometer would read significantly below 0 °C (32 °F), due to the energy lost by thermal radiation overtaking the energy acquired from the atmospheric gas by direct contact.
The dynamics of the lower thermosphere (below approximately 120 kilometers (75 mi)) are dominated by atmospheric tide, which is driven, in part, by the very significant diurnal heating. The atmospheric tide dissipates above this level since molecular concentrations do not support the coherent motion needed for fluid flow.

The day the solar wind disappeared

From May 10-12, 1999, the solar wind that blows constantly from the Sun virtually disappeared in the most drastic and longest-lasting decrease ever observed. Dropping to a fraction of its normal density and to half its normal speed, the solar wind died down enough to allow physicists to observe particles flowing directly from the Sun's corona to Earth. This severe change in the solar wind also drastically changed the shape of Earth's magnetic field and produced a rare auroral display at the North Pole.
Starting late on May 10 and continuing through the early hours of May 12, the density of the solar wind dropped by more than 98%. Because of the drop-off of the wind, energetic electrons from the Sun arrived at the Earth in narrow beams, known as the strahl. Under normal conditions, electrons from the Sun are diluted, mixed, and redirected in interplanetary space and by Earth's magnetic field (the magnetosphere). But in May 1999, several satellites detected electrons arriving at Earth with properties similar to those of electrons in the Sun's corona, suggesting that they were a direct sample of particles from the Sun.
"This event provides a window to see the Sun's corona directly," said Dr. Keith Ogilvie, project scientist for NASA's Wind spacecraft and a space physicist at Goddard Space Flight Center. "The beams from the corona do not get broken up or scattered as they do under normal circumstances, and the temperature of the electrons is very similar to their original state on the Sun."
"Normally, our view of the corona from Earth is like seeing the Sun on an overcast, cloudy day," said Dr. Jack Scudder, space physicist from the University of Iowa and principal investigator for the Hot Plasma Analyzer (HYDRA) on NASA's Polar spacecraft. "On May 11, the clouds broke and we could see clearly."
Scudder, Ogilvie, and other scientists affiliated with the International Solar-Terrestrial Physics program (ISTP) presented their findings at the Fall Meeting of the American Geophysical Union in San Francisco's Moscone Center. Researchers working with more than a dozen spacecraft observed various facets of this event…...

Mike Carlowicz, ISTP Science Writer, 301-286-6353
mcarlowi@pop600.gsfc.nasa.gov
Bill Steigerwald, NASA GSFC Public Affairs, 301-286-5015,
wsteiger@pop100.gsfc.nasa.gov

The Gregorian Calendar

The Gregorian calendar is the calendar that is used nearly everywhere in the world. A modification of the Julian calendar, it was first proposed by the Calabrian doctor Aloysius Lilius, and was decreed by Pope Gregory XIII, for whom it was named, on 24 February 1582 via the papal bull Inter gravissimas. Its years are numbered per the perceived birth year of Jesus Christ, which is labeled the "anno Domini" era. This era was created in the 6th century by Roman monk Dionysius Exiguus.
The number of days in a Gregorian year is the average number of days per year in the time interval of 400 years of the Gregorian calendar. The Gregorian calendar was established in 1582 by the Pope Gregorio XIII and replaced the Julian calendar established by the roman emperor Julius Caesar in the year 46 B.C.
The Gregorian calendar contains regular years (with 365 days each) and leap years (with 366 days each). The rule used to decide if a year is a regular year or a leap year is quite simple. The year is a leap year if it is a multiple of 4, the centennial years excluded. A centennial year will be a leap year if it is a multiple of 400. So the most recent leap years we had are 2000, 2004 and 2008. Note that 2000 is a leap year only because it is a multiple of 400. The year 1900 was not a leap year. The same can be said of the year 2100 (despite the fact they are multiples of 4). The next leap year will happen in 2012

The South Atlantic Magnetic Anomaly - SAMA

The South Atlantic Magnetic Anomaly (SAMA) refers to the area where the Earth's inner Van Allen radiation belt comes closest to the Earth's surface. This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher than usual levels of radiation. The effect is caused by the non-concentricity of the Earth and its magnetic dipole. The SAMA is the near-Earth region where the Earth´s magnetic field is weakest.
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. The intersection between the magnetic and rotation axis of the Earth is located ~500 kilometers (300miles) more to the North, above the centre of the Earth. Because of this tilt and translation, 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
The illustration shows a cross-sectional view of the Van Allen radiation belts, noting the point where the South Atlantic Anomaly occurs
The South Atlantic Magnetic Anomaly is of great significance to astronomical satellites and other spacecraft that orbit the Earth at several hundred kilometers altitude; these orbits take satellites through the anomaly periodically, exposing them to several minutes of strong radiation, caused by the trapped protons in the inner Van Allen belt, each time. The International Space Station, orbiting with an inclination of 51.6°, requires extra shielding to deal with this problem. The Hubble Telescope does not take observations while passing through the SAMA. Astronauts are also affected by this region which is said to be the cause of peculiar 'shooting stars' seen in the visual field of astronauts.
The shape of the SAMA changes over time. Since its initial discovery in 1958, the southern limits of the SAMA 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 SAMA varies on a diurnal basis, with greatest particle density corresponding roughly to local noon. At an altitude of approximately 500 km (300 mi), the SAMA spans from -50° to 0° geographic latitude and from -90° to +40° longitude. The highest intensity portion of the SAMA drifts to the west at a speed of about 0.3 degrees per year. The drift rate of the SAA is very close to the rotation differential between the Earth´s core and its surface, estimated to be between 0.3 and 0.5 degrees per year.

The Earth´s Magnetosphere

The magnetosphere of Earth is a region in space whose shape is determined by the extent of Earth's internal magnetic field, the solar wind plasma, and the interplanetary magnetic field (IMF). In the magnetosphere, a mix of free ions and electrons from both the solar wind and the Earth's ionosphere is confined by electromagnetic forces that are much stronger than gravity and collisions.
In spite of its name, the magnetosphere is distinctly non-spherical. All known planetary magnetospheres in the solar system possess more of an oval tear-drop shape due to the effects of the solar wind.
On the side facing the Sun, the distance to its boundary (which varies with solar wind intensity) is about 70,000 km (10-12 Earth radii or RE, where 1 RE=6371 km; unless otherwise noted, all distances here are from the Earth's center). The boundary of the magnetosphere ("magnetopause") is roughly bullet shaped, about 15 RE abreast of Earth and on the night side (in the "magnetotail" or "geotail") approaching a cylinder with a radius 20-25 RE. The tail region stretches well past 200 RE, and the way it ends is not well-known.