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The weak solar maximum of 2013
An image of the sun's million degree atmosphere taken by NASA's Solar Dynamics Observatory. Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.

The weak solar maximum of 2013

Like every human inquisitive endeavor into the whims of Nature, one looks for patterns in the hope of achieving some predictability. One such pattern is the appearance and disappearance of sunspots on the surface of the Sun. This pattern was first discovered in the mid-nineteenth century by Samuel Heinrich Schwab, who established that an almost eleven-year cycle existed between two successive maxima in the number of sunspots on the solar surface.

These dark blemishes are where strong magnetic fields are concentrated below the visible surface of the Sun, and rise to form myriads of majestic arches filled with several million degree gases. For the most part these remain attached to the Sun, but once in a while, something triggers them to take off in the form of a solar flare (a release of radiation traveling at the speed of light) or a coronal mass ejection (a release of matter traveling at speeds of up to a mere 3,000 km per second). A direct connection between a sunspot group, a sudden flash at the location of the group, and a powerful geomagnetic storm that affected Earth was first recorded by Richard Carrington in 1859.

In the past two decades, solar observers have noted a somewhat unexpected behavior: The peak of the sunspot cycle labeled 23, which occurred in March 2000, was followed by an unusually long minimum that extended into 2008, implying a duration exceeding 12 years. This was also the beginning of sunspot cycle 24, which did not seem to want to pick up. It reached a maximum number of 67 sunspots in November 2013, quite low when compared to previous maxima of over 100 in past cycles. So, why did this alarm people? After all, if the sunspots are directly linked to harmful onslaughts, we should be somewhat relieved that the onslaughts have dwindled.

Historically, during the Maunder Minimum of 1645–1715, the longest minimum on record, hardly any sunspots were observed and the solar cycle seemed to have been disrupted for almost 70 years. This period also coincided with the Little Ice Age of extraordinarily cold winters in the Northern Hemisphere. Could the paucity of sunspots in the current cycle be the precursor of a new ice age? Probably not. Solar cycle 14 had a peak sunspot number of 64 in February 1906, so there is really no good reason to be alarmed at the moment. The only sad part is that at the annual IfA Open House, those sun-gazing through telescopes to see a sunspot might be disappointed.

From a scientific point of view, any disruption of the solar cycle shakes up theories of the emergence of magnetic fields from the solar interior and the formation of sunspots. So for solar physicists, it’s probably time to go back to the drawing board and figure out what’s up with this wicked Sun.

This article by by Shadia Rifai Habbal was originally published in the Na Kilo Hoku, the Institute for Astronomy’s newsletter (Issue No. 49).

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