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Solar Cycle 24: Ho Hum or Gee Whiz?


by Bill Chameides | February 1st, 2010
posted by Erica Rowell (Editor)

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This Class C solar flare from January 17, 2010 was followed by several more, culminating in two more powerful Class M flares on January 19, 2010. Was this a wake-up call or a hiccup? (NASA)

This post has been updated.

The Sun may be waking up.

Everyone, they say, has ups and down; the Sun does too. Every 11 years or so, the Sun goes from a maximum in activity to a minimum and back to a maximum. There are a lot of unknowns pertaining to the solar cycle, but it is believed that disruptions in the Sun’s magnetic field (caused by different rates of rotation in the star’s polar and equatorial regions) trigger the cycle’s ebb and flow.

During times of maximum activity there are lots of sunspots and solar flares as well as a small uptick in the total solar irradiance emitted to by the Sun (referred to by scientists as TSI), and of course vice versa for solar minimum. (More on sunspots here. More on solar flares here.)

Variations in solar activity are more than a scientific curiosity. Solar flares, for example, can disrupt or even wipe out radio communications. Variations in TSI can affect global temperatures. In fact it is believed that periods of extreme solar quiescence such as the so-called Maunder Minimum (named after the English scientist Edward W. Maunder, who identified it) may have led to a mini ice age that hit regions of North America and Europe in the late 1600s.

Sun’s Recent Activity of Keen Interest to Scientists

For these reasons scientists have been puzzling over the Sun’s recent behavior.

The last solar maximum, during Cycle 23, peaked in 2000, and probably provided a little oomph to 1998’s record-making warmth.

In 2008 the Sun reached Cycle 23’s solar minimum and sort of stayed there. It stayed there so long in fact that some began to wonder if the Sun would ever wake up, and the cries of an impending ice age echoed in the blogosphere (another example here). Finally in December 2008 the Sun awoke and began Cycle 24.

But by most indications, Cycle 24 will be a very weak cycle. While Cycle 23 peaked out in 2000 with an average sunspot number of 120, the current consensus prediction for Cycle 24 is for a maximum sunspot number of only about 90, to peak around May 2013. (Note: This prediction is a bit different from a year ago when the panel issued two conflicting predictions. See my related post from last year.)

With an average daily sunspot number of about 11, December 2009’s sunspot activity aligned well with the current prediction of about 13. (The month’s maximum sunspot number was 30 on December 20.) And the month of January was much the same with an average sunspot number of 13.

But there was one surprising aspect of the Sun’s behavior in January — a number of large solar flares. On January 17 and 18, the Soviet TESIS Satellite observed moderate Class C flares, and then on the 19th observed a series of increasingly intense flares, culminating in two Class M flares. (Flares are categorized according to the power they emit: A, B, C, M, and X.) These were the first large flares seen on the Sun since the summer of 2007.

Is this uptick in solar flares an anomaly or a sign that we are headed for a more dynamic and energetic sunspot cycle than what has been predicted? We’ll have to wait and see.

In the meantime, you may be interested to know there are a host of amateur scientists our there following the Sun’s every change. They are a great source of up-to-the-minute information. Check them out: here and here.

Correction 2/22/2010.
We corrected usage of the term sunspot number.

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2 Comments

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  1. L5
    Feb 10, 2010

    “Sunspot number” and “number of sunspots” do NOT mean the same thing. The “sunspot number” is calculated using a formula developed by a Swiss astronomer named Wolf. The sunspot number today is 55 and the there certainly are not 55 sunspots today.

    • Bill Chameides
      Feb 22, 2010

      Rick: I hope not, but apologies for being fast and loose with the terminology and thanks for pointing it out to us. To be correct, we should have used “sunspot number” instead of “number of sunspots.” To clarify for the rest of our readers: Sunspots are the physical manifestation of changes in magnetic field. The sunspot number is a calculated value that measures activity incorporating both number of spots and clusters. For more see http://www.ngdc.noaa.gov/stp/SOLAR/SSN/ssn.html We have updated the post accordingly.

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