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.