Tuesday, August 6, 2013

Condition of Magnetosphere 11 years ago


I typed into Google search the words "What was Earth's magnetosphere like 11 years ago?" The following is what came up on Google Search. So I decided to share it here in relation to the magnetic poles shifting on the sun right now and within the next 6 months. NASA was saying presently the north magnetic pole is moving significantly on the sun without the south magnetic pole moving also. So, the difference to now might be explained partly by this description below:
begin quote: 
Is it true that the Earth's magnetosphere is expanding?

The shape of the Earth's magnetosphere changes depending on the strength of the solar wind because its outer boundary...called the magnetopause...is in pressure equilibrium with the so-called ram pressure of this wind as it streams by the Earth. Under some conditions, short-term changes lasting a day or so can happen in which the magnetic field of the Earth expands enormously. This happened in a now-famous event in 1999 when an unusually low density pocket in the solar wind passed by. Instead of about 5 atoms per cubic centimeter and a speed of about 300-400 km/sec, the plasma in this cavity had a density of 0.005 atoms/cc. This caused a sharp decrease in the plasma pressure outside the magnetosphere and so, unopposed, the Earth's magnetosphere ballooned outwards almost to the orbit of the Moon. Typically, it is only about 70,000 kilometers in radius, but for a short while, it had expanded to over 300,000 kilometers in radius. (The above illustration is an artist's rendering of the shape of the normal magnetosphere. Courtesy, NASA/ESA SOHO Mission)

According to a NASA/AGU presentation on December 13,1999:
"Starting late on May 10 and continuing through the early hours of May 12, NASA's ACE and Wind spacecraft each observed that the density of the solar wind dropped by more than 98%. Because of the decrease, energetic electrons from the Sun were able to flow to 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 NASA's Goddard Space Flight Center, Greenbelt, MD. "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 on NASA's Polar spacecraft. "On May 11, the clouds broke and we could see clearly."
Fourteen years ago, Scudder and Dr. Don Fairfield of Goddard predicted the details of an event such as occurred on May 11, saying that it would produce an intense "polar rain" of electrons over one of the polar caps of Earth. The polar caps typically do not receive enough energetic electrons to produce visible aurora. But in an intense polar rain event, Scudder and Fairfield theorized, the "strahl" electrons would flow unimpeded along the Sun's magnetic field lines to Earth and precipitate directly into the polar caps, inside the normal auroral oval. Such a polar rain event was observed for the first time in May when Polar detected a steady glow over the North Pole in X-ray images. In parallel with the polar rain event, Earth's magnetosphere swelled to five to six times its normal size. NASA's Wind, IMP-8, and Lunar Prospector spacecraft, the Russian INTERBALL satellite and the Japanese Geotail satellite observed the most distant bow shock ever recorded by satellites. Earth's bow shock is the shock front where the solar wind slams into the sunward edge of the magnetosphere. As the solar wind dissipates on May 11, 1999, the magnetosphere and bow shock around Earth expand to five times their normal size. The aurora, which usually forms ovals around Earth's poles, fills in over the northern polar cap. According to observations from the ACE spacecraft, the density of helium in the solar wind dropped to less than 0.1% of its normal value, and heavier ions, held back by the Sun's gravity, apparently could not escape from the Sun at all. Data from NASA's SAMPEX spacecraft reveal that in the wake of this event, Earth's outer electron radiation belts dissipated and were severely depleted for several months afterward. "The May event provides unique conditions to test ideas about solar-terrestrial interactions," Ogilvie noted. "It also strengthens our belief that we're beginning to understand how the Sun-Earth connection works."
Over the long term, there are as yet no studies to suggest that the magnetosphere is growing in any systematic, constant fashion. However, with the steady decline in the strength of the field, which can be easily measured, in 10,000 years or so we may have to endure a period with little or no magnetic field, or one in a very complex and undifferentiated state. At that time, the global magnetic field may be much smaller than at present, as the ever-present solar wind drives the weakened field closer to the surface of the Earth.

Copyright 1997 Dr. Sten Odenwald
Return to Ask the Astronomer

end quote from:
http://www.astronomycafe.net/qadir/q1686.html

No comments: