Winter 2009 Issue

VHF PROPAGATION

Old and New Science

By Tomas Hood, NW7US

Figure 1. Earth’s magnetic field gets stretched out into a comet-like shape with a tail of magnetism that stretches millions of miles behind Earth, opposite from the Sun. The Sun has a wind of gas that pushes Earth’s field from the left to the right in this drawing. (Credit: NASA)

During solar Cycle 23’s approximately eleven years, scientists have worked with increased passion and resources to discover everything possible about the Sun, space weather, and geophysical and ionospheric phenomena. They’ve been busy launching many new satellites and other research spacecraft, building new models to better fit the resulting data, and discovering many new and revealing facts in the mix of all of the rich and new data.

One amazing discovery involves the magnetic connection between our Sun and Earth. The reigning model described a process whereby solar material (charged solar matter) may enter into our atmosphere, triggering aurora and creating geomagnetic disturbances. Conventional understanding of the process required the magnetic orientation of the magnetic field lines of the solar wind to be oriented “southward” in relationship to Earth’s magnetosphere before solar material could effectively enter through a “hole” in the resulting reconnection of the two magnetic-field structures. As the two fields became aligned in this way, it is called “reconnection.” When a reconnection occurs, it allows material on the solar wind to “ride” the field lines down toward Earth’s northern and southern magnetic poles. If the orientation is “northward,” then this reconnection between the Sun’s and Earth’s magnetic fields would not occur, and solar material would be deflected around the Earth by the magnetosphere. As a result, the magnetosphere is stretched far out into space away from the sun (see figure 1). The new discovery radically alters this model.

During February 2007 NASA launched five spacecraft for the primary goal of exploring macroscale interactions during ionospheric and geomagnetic substorms. This project is called THEMIS, the acronym for Time History of Events and Macroscale Interactions during Substorms, and it is the fifth medium-class mission under NASA’s Explorer Program. The University of California, Berkeley’s Space Sciences Laboratory managed the project development and is currently operating the THEMIS mission. Swales Aerospace, Beltsville, Maryland, built the THEMIS satellites.

Scientists, using THEMIS, discovered a breach in Earth’s magnetic field ten times larger than anything previously thought to exist. However, the breach itself is not the biggest surprise. Researchers are even more amazed at the strange and unexpected way it forms, overturning long-held ideas of space physics.
“At first I didn’t believe it,” says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. “This finding fundamentally alters our understanding of the solar-wind–magnetosphere interaction.”

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