The Earth鈥檚 protective magnetosphere often develops two large holes that let in the largest leaks of solar wind, scientists say. Surprisingly, the holes are rended open in an interaction with the Sun鈥檚 magnetic field that was previously thought to shield the Earth from solar particles.
Understanding how these holes form will help them better predict the electrical storms that cause power grid blackouts and auroras, activity that will peak in 2011 or 2012 as sunspots hit their maximum level.
Scientists at the meeting in San Francisco this week said they had been entirely wrong about how solar particles that cause the storms were entering the Earth鈥檚 magnetosphere, a bubble of magnetism that surrounds Earth and protects us from charged particles from the Sun.
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Scientists once believed that the particles entered when the Sun鈥檚 magnetic field was aligned opposite to that of the Earth鈥檚. But the team鈥檚 findings show that 20 times more solar particles enter the Earth鈥檚 magnetic field when it is aligned in the same direction as the Sun鈥檚 magnetic field than when the two are opposed.
In June 2007, NASA鈥檚 five probes flew through one of the tears just as it was opening. Sensors recorded a torrent of solar wind particles streaming into the magnetosphere, said team member of the University of New Hampshire.
Levee breach
鈥淭he opening was huge 鈥� four times wider than Earth itself,鈥� said Raeder. 鈥淭his kind of influx is an order of magnitude greater than what we thought was possible.鈥�
In separate research, Wenhui Li, also of the University of New Hampshire, and colleagues offer an explanation. As charged particles flow out from the Sun, they carry solar magnetic fields past Earth.
The team鈥檚 computer simulations show that even though the Earth鈥檚 and the Sun鈥檚 magnetic fields point in the same direction at equatorial latitudes, they point in opposite directions at high latitudes. When the opposite fields are pressed together, they connect and tear holes in Earth鈥檚 magnetic field over the poles.
Energised particles
However, when solar and terrestrial magnetic fields point in opposite directions and reconnect in a different way, the Sun鈥檚 charged particles get energised and cause magnetic storms that can overload power lines with excess current, causing widespread blackouts.
鈥淚f the solar field has been aligned with the Earth鈥檚 for a while, we now know Earth鈥檚 field is heavily loaded with solar particles and primed for a strong storm,鈥� said Raeder in a statement. 鈥淭his discovery gives us a basic predictive capability for the severity of solar storms, similar to a hurricane forecaster鈥檚 realisation that warmer oceans set the stage for more intense hurricanes.鈥�
鈥淚n fact, we expect stronger storms in the upcoming solar cycle,鈥� he continued. 鈥淭he Sun鈥檚 magnetic field changes direction every cycle, and due to its new orientation in the upcoming cycle, we expect the clouds of particles ejected from the Sun will have a field which is at first aligned with Earth, then becomes opposite as the cloud passes by.鈥�
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