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Archive for June 2009

Another weak SC24 spot

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Another weak SC24 sunspot appears in the southern hemisphere

Would spots this weak have been seen by 19th Century observers?

Written by John A

June 22, 2009 at 1:19 pm

Posted in Solar Cycle 24

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NASA: The mystery of the missing sunspots solved?

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Hot off the press.

NASA announces yet another explanation for the late arrival of Solar Cycle 24 (nearly two years after it was supposed to have started).

June 17, 2009: The sun is in the pits of a century-class solar minimum, and sunspots have been puzzlingly scarce for more than two years. Now, for the first time, solar physicists might understand why.

At an American Astronomical Society press conference today in Boulder, Colorado, researchers announced that a jet stream deep inside the sun is migrating slower than usual through the star’s interior, giving rise to the current lack of sunspots.

Rachel Howe and Frank Hill of the National Solar Observatory (NSO) in Tucson, Arizona, used a technique called helioseismology to detect and track the jet stream down to depths of 7,000 km below the surface of the sun. The sun generates new jet streams near its poles every 11 years, they explained to a room full of reporters and fellow scientists. The streams migrate slowly from the poles to the equator and when a jet stream reaches the critical latitude of 22 degrees, new-cycle sunspots begin to appear.

Original Caption:
Above: A helioseismic map of the solar interior. Tilted red-yellow bands trace solar jet streams. Black contours denote sunspot activity. When the jet streams reach a critical latitude around 22 degrees, sunspot activity intensifies.

Howe and Hill found that the stream associated with the next solar cycle has moved sluggishly, taking three years to cover a 10 degree range in latitude compared to only two years for the previous solar cycle.

The jet stream is now, finally, reaching the critical latitude, heralding a return of solar activity in the months and years ahead.

“It is exciting to see”, says Hill, “that just as this sluggish stream reaches the usual active latitude of 22 degrees, a year late, we finally begin to see new groups of sunspots emerging.”

The current solar minimum has been so long and deep, it prompted some scientists to speculate that the sun might enter a long period with no sunspot activity at all, akin to the Maunder Minimum of the 17th century. This new result dispells those concerns. The sun’s internal magnetic dynamo is still operating, and the sunspot cycle is not “broken.”

So we should be seeing SC24 sunspots appearing now that the jet stream has reached the critical latitude of 22° ?

Let’s check out of the window:

The spotless disk of the Sun

The spotless disk of the Sun

Magnetogram shows little magnetic behaviour

Magnetogram shows little magnetic behaviour

OK, maybe it was just an off day on the Sun. What about the trend?

Sunspot trends to May 2009

So far, indistinguishable from zero.

Here’s the 3D view of what the solar scientists are tracking/modelling (click to see the movie):

This movie reveals motions of the Sun’s interior as measured with helioseismology on data from GONG and SOHO/MDI. East to west motion is color coded: blue is slow, red is fast. A red band in the outer third of the Sun moves slowly down from near each pole toward the equator; that band is the jet stream that is associated with sunpot emergence and the solar cycle. As of early 2009 the Cycle 24 jet streams have just reached N/S 22 degrees latitude, and new sunspots are beginning to emerge.

Now I hate to be a killjoy, but all of this effort has failed to convince me that a deep down “jetstream” of charged plasma reaching a “critical” latitude can explain why the Sun remains so very quiet.

On, they’ve got yet another sun speck recorded yesterday, that by today had disappeared. Exactly the same behaviour we’ve been having for 12 months with no end in sight.

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Written by John A

June 17, 2009 at 11:36 am