We’ve been hearing a lot recently about how the lack of sunspots and a slow subsurface current herald a time of silent solar activity. However, with a new big juicy sunspot coming into view within the next twenty-four hours and new research on other aspects of solar activity, perhaps a re-evaluation is required.
Sarah Gibson of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, USA is the lead author of a paper that looks at the solar wind. In particular, the fast solar wind, which was previously believed to switch off during solar minima. The results showed that in this solar minimum, with the lowest number of sunspots in 75 years, the fast solar wind is three times stronger than during the last solar minimum in 1996.
The two streams – fast and slow – of the solar wind are related to areas on the Solar surface that produce x-rays. When the Sun is photographed in x-rays, dark areas where none are being produced called coronal holes are sometimes seen. The fast wind comes from those, with the slow wind from the rest of the surface. Coronal holes are normally seen at the poles, but during this minimum, they have lingered at the equator for longer than expected. The result is for more than half the time during 2008, the Earth was caught in the fast stream. The magnetospheric response to the turbulent stream is the generation of aurorae, which leads to upper atmospheric heating, ionisation and electrical currents. This could mean the conventional wisdom of measuring solar activity by sunspot numbers is wrong.
It does look like things are changing however, as the fast solar wind appears to be abating, two years later than expected.