The first data from a formation-flying quartet of satellites has revealed the buffeting that the Earth鈥檚 magnetic field receives from the solar wind in unprecedented detail.
The Cluster satellites, launched by the European Space Agency, flew through the 鈥渂ow shock鈥� 鈥� the front line between the magnetosphere and the solar wind 鈥� a week earlier than expected. The surprise was caused by a particularly severe solar storm that had compressed the magnetosphere.
The mission appears to have arrived in orbit just in time to witness the final crescendo of the Sun鈥檚 11 year cycle of activity. New NASA data, released on Thursday, shows the first clear sign that cycle has just peaked.
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This is good news for Cluster scientists according to Sandra Chapman, at the University of Warwick: 鈥淭his is the ideal time for us to have launched Cluster.鈥�
Bow shock
Cluster is a few months into a minimum two year mission studying how the Earth鈥檚 magnetic field is battered by the solar wind 鈥� a flow of charged sub-atomic particles from the Sun. The solar wind squashes the field on the side facing the Sun, creating a bow shock similar to the bow wave ahead of a ship. Behind Earth, the wind stretches the field into a long magnetic tail.
In January, NASA鈥檚 IMAGE space probe discovered a stream of high-energy electrons trapped in this tail, confirming an earlier theoretical prediction.
Now Cluster has provided valuable data about the bow shock and the solar wind, as Chapman explains: 鈥淲e knew the solar wind was turbulent because the flow is generated by solar flare events, which appear on all scales. Now, Cluster gives us four simultaneous measurements, enabling us to calculate exactly how turbulent.鈥�
Cluster has also shown that the areas above the magnetic poles of the Earth, called 鈥榗usps鈥�, are more variable than anyone suspected.
Knock out storms
It is vital to understand the magnetic field-solar wind interaction because, in the past, particularly violent gusts have disrupted telecommunications, destroyed satellites and knocked out power stations.
鈥淚t also messes up drilling for oil because companies use the Earth鈥檚 magnetic field to determine which way is down. If the magnetic field is flapping around because of space weather and you miss the oil, you lose a lot of money,鈥� says Chapman.
Some theorists even believe that solar wind particles hitting the atmosphere may trigger cloud formation.
Solar flip
The data revealing the peak of the solar maximum was collected by astronomers at the US National Solar Observatory on Kitt Peak, Arizona and analysed by David Hathaway at NASA鈥檚 Marshall Space Flight Center.
For the past eleven years, the Sun鈥檚 north geographic pole has also been home to its north magnetic pole. But a feature of each solar cycle is that the magnetic poles reverse.
And the new NASA data suggests the south magnetic pole has now secured a firm foothold in the Sun鈥檚 northern hemisphere. The Sun鈥檚 activity can now be expected to begin to decline.
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