2005 10 20
By Mitch Battros | ECTV Newsletter
Click here for Part I
Anyone who has used a compass knows that magnetic north and geographic north do not exactly line up. That's because Earth's magnetic dipole is tilted by about 11.5 degrees from its rotational axis and shifted slightly off-center. At the north magnetic pole, the field is stronger, effectively keeping the inner proton belt farther away; at the south magnetic pole, the field is weaker, allowing the proton belt to come closer to the planet's surface. Most of the proton belt is about 1200–1300 kilometers high, but it dips down as low as 200–300 kilometers off the lower coast of Brazil, creating a phenomenon known as the South Atlantic Anomaly. At certain altitudes, the South Atlantic Anomaly is bigger than Brazil itself.
Laboratory simulation of the Earth's magnetic field's. Image source: wikipedia.org
The Earth is the most rapid rotator of the planets of the inner solar system. It rotates once on its axis relative to the stars every 23 hours and 56 minutes (and every 24 hours relative to the Sun). It has a crust and a mantle surrounding a liquid metallic core which in turn encloses a solid metal core. The average radius of the Earth is 6371 km (3,959 miles). Seismic evidence shows that the mantle is about 2886 km (1,793miles) thick and the metallic core about 3485 km (2,165 miles) thick. By volume, 16% of the planet consists of core and 84% of mantle.
The inner solid core is created by the solidification of the outer core as the Earth cools. Thus the inner core is believed to be still growing in size. At present it is about 1221 km (759 miles) in radius and occupies about 4% of the volume of the core. Thus it is still quite small. The energy released by the freezing of the inner core (both latent heat of fusion and gravitational settling) is thought to provide the source of energy for driving the Earth's magnetic dynamo.
The heat released in the interior of the planet by the solidification of the core, by radiative decay and by the general cooling of the Earth, is transmitted to the surface of the planet by a combination of convection and conduction. Convection requires the motion of the material. In a fluid this results in the familiar cells of hot liquid rising, cooling at the top of the cell and sinking back down to the source of the heat, only to be heated and repeat the cycle.
From: Wikipedia Encyclopedia
Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. In the case of the Earth, the magnetic field is believed to be caused by the convection of molten iron and nickel, within the outer planetary core, along with Coriolis effect caused by the overall planetary rotation. When conducting fluid flows across an existing magnetic field, electric currents are induced, creating another magnetic field. When this magnetic field reinforces the original magnetic field, a dynamo is created which sustains itself. Similar magnetic fields are present in many celestial bodies including most stars such as the Sun (which contain conducting plasma) and active galactic nuclei.
Magnetic Field – Dipole Theory
C. T. Russell and J.G. Luhmann Study - UCLA
It has been known at least since W. Gilbert's "De Magnete," written in the reign of Elizabeth I at the end of the 16th century, that the Earth was a giant magnet with a dipolar magnetic field. It was realized not long afterward that the internal magnetic field varied with time. While at present the principal variation is a westward drift, the field undergoes notable other variations including reversals. Today the magnetic pole that is in the northern hemisphere is a south pole. It attracts the north pole of a magnet. In earlier times the pole in the northern hemisphere has been a north pole, and compasses, had they been available at that time, would have pointed in the opposite direction. The frequencies of these reversals are themselves functions of time. For example, 60 million years ago reversals occurred about once every 500,000 years, whereas 10 million years ago reversals occurred 3 times as often, about every 150,000 years [Barton, 1989]! .
South Atlantic Anomaly Presents Dangerous Radiation
Contributions by Gabriel Spera - The Aerospace Corporation - FFRDC
A satellite in a typical low Earth orbit remains safely below the proton belt—except at the South Atlantic Anomaly. Spacecraft passing through this region are bombarded by protons with energies exceeding 10 million electron volts at a typical flux of 3000 particles per square centimeter per second. These particles can be a hazard for space systems and astronauts.
Under European Union Directive 96/29/Euratom: Article 42, which became effective May 13, 2000, airlines belonging to EU Member States are required to assess and limit their aircrews' exposure to cosmic radiation. Compliance with the legislation would be satisfied by the use of a computer program to estimate route doses, which can then be used to plan rosters, taking the individual's likely exposure into account.
As a result of customer concerns and request for support, SEC will implement a new warning and alert for >100 MeV protons exceeding 100 particle flux units (pfu) . The current NOAA Scales warning for high-energy protons is based on 10 MeV, which is not as useful for determining radiation hazards for humans.
Airline Radiation Concerns
United Airlines reported high frequency (HF) communications losses and solar radiation storms which caused planes to be diverted to less dangerous routes. Rerouting and general delays are costly to the airlines. One example of that was a storm that caused a flight to be diverted from a polar route, requiring additional fuel at Tokyo and extending the flight by 5 hrs 30 min.
During another period, 25 flights were flown on less than optimal polar routes due to HF communications problems. Northwest Airlines diverted a Detroit - Beijing flight to a non-polar route due to both HF communications problems (radio blackout) and a solar radiation storm, forcing an unscheduled stop at Fairbanks for fuel. This route change resulted in an approximately 3 hour delay and $100,000 cost to NWA, plus the inconvenience and loss attendants upon disrupting the travel of passengers.
The Director of Flight Operations of Continental Airlines reported that they diverted their daily flight for the second day in succession based on the S3 level of solar radiation storm. The direct impact was 2 hours of extra flight time and additional associated costs.
NASA launched the Terra Earth Observing System spacecraft in 1999 as part of a broad mission to study global climate change. Just one day after launch, the satellite's high-gain antenna spontaneously went into "safe" mode, interrupting communications with the Tracking and Data Relay System satellites. A series of diagnostic tests indicated that an anomalously high current had passed through the motor drive assembly.
Similarly, the Hubble Space Telescope experienced bit errors in communications between subsystems when traveling through the Anomaly. Error detection and correction schemes prevented data loss, but the problem was still annoying to ground controllers. As a result, several high-voltage instruments are powered down before the Hubble enters the South Atlantic Anomaly.
Numerous other missions have been affected as well. ROSAT, the Roentgen Satellite, was an X-ray observatory that flew for much of the 1990s. The unit's position-sensitive proportional counters had to be turned off during passage through the South Atlantic Anomaly to prevent severe damage. ROSAT's high-resolution imager could be left on, but could collect no useful data while in the region. The Topex satellite, which flies at an altitude of about 1000 kilometers, is still prone to random upsets in its altimeter as it passes through the Anomaly, preventing proper data collection.
Perhaps the most serious case was NASA's Modis satellite, which was rendered inoperative in 2001 as it passed through the South Atlantic Anomaly. The failure seemed to be caused by an overvoltage shutdown, probably started when a high-energy ion struck a vulnerable metal-oxide semiconductor field-effect transistor (MOSFET), causing it to fail. It took 16 days to get the satellite back on line.
Random glitches affect humans as well. Since the days of Apollo 11, astronauts in space have reported seeing random flashes of light—with their eyes closed. These flashes are believed to be caused by energetic particles striking sensitive areas of the retina. In a recent experiment, astronauts aboard the Mir wore detector helmets to help researchers correlate the number of reported flashes with the measured particle flux. If the flashes increased when Mir entered the South Atlantic Anomaly, then protons would be revealed as the likely cause; if not, then heavy ions (which appear in equal amounts inside and outside the proton belt) would be indicated. The frequency of the flashes increased in the Anomaly, but only slightly, suggesting that protons alone are not responsible, but neither are heavy ions.
So it seems that the South Atlantic Anomaly may well have a few more surprises in store.
Coming... Part III – Evidence the Magnetic Pole Shift Has Begun
Article from: ECTV Newsletter
Related: Has The Magnetic Pole Reversal Already Begun? South Atlantic Anomaly Could be First Evidence - Part I
The Makings of a Pole Reversal; “Increased Solar Activity” and “Decreased Magnetic Field” - Part III
Earth's Magnetic Field (wikipedia)