A sixth region in the magnetosphere?
As you probably know, Earth's magnetosphere, 'the invisible bubble of magnetic fields and electrically charged particles that surrounds and protects the planet from the periodically lethal radiation of the solar wind,' was discovered in 1958. Until now, it was composed of five regions, including the ionosphere or the Van Allen radiation belts. Now, a U.S. research team has discovered a sixth region, called the warm plasma cloak. But read more...
You can see above an illustration showing the different regions of the magnetosphere. "The white arrows show the path that individual ions take as they are carried into the magnetosphere by the polar wind and then move from region to region in the magnetosphere." (Credit: Rick Chappell, Vanderbilt University). Here is a link to a slightly larger version of this picture.
The research team was led by Rick Chappell, research professor of physics and director of the Dyer Observatory at Vanderbilt University. The other members of the research team are Mathew M. Huddleston from Trevecca University, Tom Moore and Barbara Giles from the National Aeronautics and Space Administration (NASA), and Dominique Delcourt from the Centre d'Etude des Environments Terrestre et Planétaires, Observatoire de Saint-Maur in France.
As the Vanderbilt University news release mentioned above is short on details, let's look at a multimedia version of this story available on Exploration, Vanderbilt's online research magazine (David F. Salisbury, December 12, 2008, Adobe Flash format).
Let's start with some comments from Rick Chappell. "Although it is invisible, the magnetosphere has an impact on our everyday lives. For example, solar storms agitate the magnetosphere in ways that can induce power surges in the electrical grid trigger blackouts, interfere with radio transmissions and mess up GPS signals. Charged particles in the magnetosphere can also damage the electronics in satellites and affect the weather by impinging on the upper layers of the atmosphere. These are some practical reasons why it is important to understand the magnetosphere's structure and behavior."
But do you have an idea of the size of the magnetosphere? "It is huge: five to six Earth diameters on the side facing the Sun, 10 to 12 diameters around and with a tail that streams more than a million miles away from the Sun. This dynamic magnetic structure shields Earth's surface from the solar wind, the stream of charged particles that continuously boils off the Sun’s surface. As the strength of the solar wind varies, the magnetosphere expands and contracts. The different regions in the magnetosphere are distinguished by the energy and behavior of the charged particles that they contain. The ions’ energy level is measured in electron volts (eV). The typical ion floating around in the air at sea level has an energy level of about one-fortieth of an eV. The energy of ions in the magnetosphere range from a few eV to millions of eV."
As five regions of the magnetosphere have been known for some time, how did these researchers find a new one? "Chappell and his colleagues pieced together a natural cycle that can accelerate the low-energy ions that originate from the ionosphere, a part of the upper atmosphere that is ionized by solar radiation, up to the higher energies characteristic of those that populate different regions in the magnetosphere. This brought the existence of the new region, the warm plasma cloak, into focus. The warm plasma cloak is a tenuous region that starts on the night side of the planet and wraps around the dayside but then gradually fades away on the afternoon side. As a result, it only reaches about three-quarters of the way around the planet. It consists of warm ions with energies in the 10 eV to 3 thousand electron volts (keV) range."
Just to refresh your memory, here are the five regions of the magnetosphere that were previously known: the ionosphere, the plasmasphere, the Van Allen radiation belts, the ring current and the magnetotail streams out from the polar regions.
So how does the research team find a sixth region? Partially because of a piece software written by Dominique Delcourt which "can predict how ions move in the earth’s magnetic field. 'These motions are very complicated. Ions spiral around in the magnetic field. They bounce and drift. A lot of things can happen, but Dominic developed a mathematical code that can predict where they go,' says Chappell. When the researchers applied this computer code to the satellite observations, some patterns became clear for the first time. One was the prediction of how ions could move upward from the ionosphere to form the warm plasma cloak."
This research work has been published online on September 4, 2008 by the Journal of Geophysical Research in its Space Physics section under the name "Observations of the warm plasma cloak and an explanation of its formation in the magnetosphere."
Here is an excerpt of the abstract. "Measurements from the ATS, ISEE, SCATHA, DE, and POLAR satellites establish the characteristics of this 'warm plasma cloak' of particles that is draped over the nightside region of the plasmasphere and is blown into the morning and early afternoon dayside sector by the sunward convective wind in the magnetosphere. The satellite observations combined with the predictions of an ion trajectory model are used to describe the formation and dynamics of the warm plasma cloak."
Sources: Vanderbilt University news release, December 12, 2008; and various websites
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