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More than 20 years ago, scientists theorized that a consistent flow of charged particles blew away from a portion of Earth’s magnetosphere in what was termed a “plume.” The wind driving this plume, it was surmised, carried a steady flow of material out of the plasmasphere—an area of the inner magnetosphere made up of cool, charged plasma composed of electrons and positive ions. However, direct observation of the wind eluded researchers until a recent study that utilized data taken from the European Space Agency’s Cluster spacecraft.

Iannis Dandouras of the University of Toulouse (France) studied the properties of the ions found in the plasmasphere and, after creating a filtering technique that eliminated other sources of noise, detected plasma motion along Earth’s radial magnetic field lines. He discovered a wind that continuously propelled plasmasphere material outward into the magnetosphere, even when the Earth’s magnetic field was undisturbed by energized solar particles. The wind, it turns out, blows out the plasma at speeds of more than 5,000 km per hour. 

“After long scrutiny of the data, there it was: a slow but steady wind, releasing about 1 kilogram of plasma every second into the outer magnetosphere—this corresponds to almost 90 tons every day,” Dandouras says. “It was definitely one of the nicest surprises I’ve ever had!”

The plasmasphere wind is generated by an imbalance between gravitational, centrifugal, and gradient forces within the magnetosphere. It plays a significant part in the mass budget of the plasmasphere while also influencing Earth’s radiation belt activity. Crossing the belts can cause radiation hazards for satellites and astronauts. Material from the plasmasphere can also cause delays in the propagation of GPS signals traveling through it.

“Understanding the various source and loss mechanisms of plasmaspheric material, and their dependence on the geomagnetic activity conditions, is thus essential for understanding the dynamics of the magnetosphere, and also for understanding the underlying physical mechanisms of some space weather phenomena,” explains Dandouras.

The study was published in a recent issue of Annales Geophysicae. (Source: European Geosciences Union)