Spring 2009 Issue
More New Space Weather Discoveries
By Tomas Hood, NW7US
Figure 1. Schematic of the Earth’s
magnetosphere. The direction to the Sun is to the left. The IMF
(interplanetary magnetic field), imbedded in the solar wind, impinges
upon the magnetopause. If southward, as here, it connects to the Earth’s
magnetic field at the X-line (shown as circle with X inside), resulting
in a region of field lines connecting from the Earth to deep space.
Plasma from the solar wind enters via the cusp, becomes trapped in the
plasma sheets, and eventually precipitates to Earth or is lost
In the Winter 2009 issue we began to explore
some of the new scientific discoveries and efforts being made in space
weather and radio propagation during solar Cycle 23’s approximately eleven
years. Many new satellites and other research space craft have been
launched and exciting research conducted that is leading to a deeper,
better understanding of our Earth, the Sun, and the interaction between
them. We looked specifically at one of the amazing discoveries made by the
THEMIS (Time History of Events and Macroscale Interactions during
Substorms) mission. This time, let’s continue to look at more of the new
science being pursued by solar scientists.
THEMIS is a mission to investigate what causes
auroras in the Earth’s atmosphere to dramatically change from slowly
shimmering waves of light to wildly shifting streaks of color. Discovering
what causes auroras to change will provide scientists with important
details about how the planet’s magnetosphere works and the important
Sun-Earth connection. During February 2007, NASA launched the five space
craft that make up the THEMIS fleet. The University of California,
Berkeley’s Space Sciences Laboratory managed the project development and
is currently operating the THEMIS mission. Swales Aerospace, of
Beltsville, Maryland, built the THEMIS satellites.
Substorms are atmospheric events visible in the Northern Hemisphere as a sudden brightening of the Northern Lights, or aurora borealis. These substorms are more accurately termed “geomagnetic substorms,” a description of the time-dependent build-up and release of magnetic energy in Earth’s magnetosphere.
We know that space is not a vacuum, at least in our solar system. The Sun’s atmosphere actually extends very far out from the Sun. Space in our system is filled with plasma, a low-density gas in which the individual atoms are charged. The temperature of the Sun’s atmosphere is so high that the Sun’s gravity cannot hold on to it. The plasma streams off the Sun in all directions at speeds of about 400 kilometers per second (about 1-million miles per hour). This is known as the “solar wind.”
The solar wind buffets the Earth’s magnetic field and can produce storms, or more properly substorms, in the Earth’s magnetosphere. Until this explosion was witnessed first-hand by THEMIS, however, scientists did not understand the full mechanisms of how substorms occurred.
The Earth has a magnetic field with a north and a south pole that is enclosed within a region surrounding the Earth called the “magnetosphere.” As the Earth rotates, its hot core generates strong electric currents that produce these magnetic fields, which reach 36,000 miles into space. The solar wind distorts the shape of the magnetosphere by compressing it at the front and causing a long tail to form on the side away from the Sun. This tail is called the magnetotail (figure 1), and on average is a million kilometers long.
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