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Taming the Solar Wind

Over a decade ago, a research team at Augsburg College and the University of New Hampshire observed unexpected ~1 hertz waves in the Earth's magnetic field. Their data came from very high-latitude, ground-based observatories in Antarctica and Arctic Canada. The origin of these waves was not obvious and puzzled scientists for a long time.

Now, the same researchers have identified the source of these waves in an unlikely region: The magnetospheric plasma mantle. In this region, the mixed solar wind and magnetospheric plasma meet near the boundary of Earth's magnetotail--the long, comet tail-like extension of Earth's magnetic field into space.

Although researchers have known for many decades that activity in Earth's space environment is ultimately driven by disturbances on the sun, carried outward to Earth via the invisible solar wind, the paths by which mass, energy and momentum from these disturbances reach Earth continue to reveal their subtleties. Many earlier satellite and ground-based studies observed wave activity in a narrow, high-latitude region called the magnetospheric cusp, which provides entry for solar wind plasma into near-Earth space. For over two decades, many high-latitude waves were assumed to have originated in this cusp, and many computer simulations of space weather continue to be based on that assumption.

This study shows that some plasma waves that reach Earth at very high latitudes come instead from locations downstream or tailward of Earth, rather than sunward. A more complete understanding of the origins of these and other waves may help space scientists to better characterize and predict space weather--including the impacts of magnetic storms that can damage spacecraft, interrupt high-latitude communications and even threaten long-distance electrical power lines.

After the research team compared observations of these waves in space and on the ground, they used the full complement of instruments on the European Space Agency's high-altitude cluster satellites to identify their source: Solar wind protons injected into the outer part of Earth's magnetosphere. As these protons flow tailward or downstream, they become unstable and generate waves that direct energy back upstream toward Earth.Thus, although these protons themselves do not reach Earth, they generate magnetospheric ~1 hertz waves that do.

Image

  • artist's concept of the heliosphere
Artist's concept of the heliosphere.
NASA/Goddard Space Flight Center Conceptual Image Lab

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