Speedy Solar Tsunami Races Across Sun's Surface

How do you measure the Sun's magnetic field? Measure a solar tsunami, of course. Scientists have used the event that was observed by NASA's Solar Dynamics Observatory and the Japanese Hinode spacecraft to make the first accurate estimates of the Sun's field.

Solar tsunamis are produced by enormous explosions in the Sun's atmosphere, called coronal mass ejections (CMEs). Often associated with solar flares, CMEs are flung from the sun into space, driving solar tsunamis on the surface of the sun. These tsunamis can race at speeds of up to 1,000 kilometers per second. Yet like the tsunamis on earth, these solar tsunamis are shaped by their environment; the sun's magnetic field determines exactly how fast the tsunami can travel.

Usually, it's difficult to measure the Sun's magnetic field. Visible as loops and structures in the star's atmosphere, the magnetic field has to be estimated using computer simulations. Yet the speed variation in a solar tsunami makes it perfect for measuring this field.

The researchers first examined the density of the solar atmosphere through which the tsunami travelled. Then, the scientists used a combination of imaging and spectral observations in order to examine the magnetic field. The instruments on Hinode acted as a microscope to track how the field around sunspots in generated, shapes itself and then fades away.

"We've demonstrated that the Sun's atmosphere has a magnetic field about ten times weaker than a normal fridge magnet," said David Long of the UCL Mullard Space Science Laboratory, in a news release. "These are rare observations of a spectacular event that reveal some really interesting details about our nearest star."

The findings are crucial for understanding CMEs a bit better. An Earth-directed CME, for example, can affect satellites and technological infrastructure. This can have serious impacts for communications across our planet.

"As our dependency on technology increases, understanding how these eruptions occur and travel will greatly assist in protecting against solar activity," said Long.

The findings are published in the journal Solar Physics.