Solar Science

A blog of solar physics

Archive for February 2008

Popular Mechanics on the Solar Minimum

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Joe Pappalardo at Popular Mechanics has a fascinating article on the possible (probable?) result of an extended solar minimum such as that which we are experiencing: global cooling:

Every day, scientists hoping to see an increase in solar activity train their instruments at the sun as it crosses the sky. This is no idle academic pursuit: A lull in solar action could potentially drive the planet’s temperature down, or even prompt a mini Ice Age.

Woah! I wonder if Joe has heard about the overwhelming scientific consensus that denies such a result? Maybe I should sic James Hansen on him…

For millennia, thermonuclear forces inside the star have followed a regular rhythm, causing its magnetic field to peak and ebb, on average, every 11 years. Space weathermen are watching for telltale increases in sunspots, which would signal the start of a new cycle, predicted to have started last March and expected to peak in 2012. “When the sun’s active, it’s a little bit brighter,” explains Ken Tapping, a solar researcher and project director for Canada’s National Research Council.

So far, Tapping reports no change in the magnetic field strength, as measured by radio telescopes. On the more positive side, last month NASA reported a small, earth-sized sunspot with a magnetic field pointing in the opposite direction from those in the previous cycle; qualities that designate the spot as a signal of a new upturn in activity. At the solar maximum, scientists expect to see between 75 and 150 such sunspots per day.

Tapping oversees the operation of a 60-year-old radio telescope that he calls a “stethoscope for the sun.” Recent magnetic field readings are as low as he’s ever seen, he says, and he’s worked with the instrument for more than 25 years. If the sun remains this quiet for another a year or two, it may indicate the star has entered a downturn that, if history is any precedent, could trigger a planetary cold spell that could bring massive snowfall and severe weather to the Northern Hemisphere.

The last such solar funk corresponded with a period of bitter cold that began around 1650 and lasted, with intermittent spikes of warming, until 1715. While there were competing causes for the climatic shift—including the Black Death’s depopulation of tree-cutting Europeans and, more substantially, increased volcanic activity spewing ash into the atmosphere—the sun’s lethargy likely had something to do with it.

Of course, no mention of greenhouse gases.

Just how much influence the sun has on global temperatures has been the subject of sometimes acrimonious debate. While an upswing in solar activity may cause a warming trend, it was discounted in the mid-1990s as the sole driver of current climate change. And for anyone hoping that a solar downswing might bail us out of our current dilemma: Solar influence on climate is slight compared to the impact of man-made greenhouse gases, a National Academy of Sciences report concluded in 1995.

Ah, there it is! So what we have is a contest between global warming due to greenhouse gases, and global cooling due to solar dimming.

Its a dilemma as to what to wish for. Global cooling such as the Little Ice Age would have been a technological challenge to modern 21st Century agriculture, technology and energy resources. What’s there to worry about with global warming? Deserts like the Sahara shrinking is a bad thing to be avoided…like the Plague?

Written by John A

February 7, 2008 at 12:32 pm

Solar Cycle 24: False Starts

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In early January 2008, NASA reported the start of Solar Cycle 24 with the sighting of a tiny reversed polarity spot. It lasted three days and then disappeared.

This was reported by Anthony Watts thus:

Solar physicists have been waiting for the appearance of a reversed-polarity sunspot to signal the start of the next solar cycle. The signal for the start of a new cycle is sighting a particular kind of sunspot. That wait is over.

And the NASA blog said:

“On January 4, 2008, a reversed-polarity sunspot appeared—and this signals the start of Solar Cycle 24,” says David Hathaway of the Marshall Space Flight Center.

Above: Images of the first sunspot of Solar Cycle 24 taken by the NASA/ESA Solar and Heliospheric Observatory (SOHO).

Solar activity waxes and wanes in 11-year cycles. Lately, we’ve been experiencing the low ebb, “very few flares, sunspots, or activity of any kind,” says Hathaway. “Solar minimum is upon us.”

But the first announcement of Solar Cycle 24 wasn’t made by NASA in January 2008 – it was actually made by Ulrich Reith on 31 July 2006, with this post:

Last night it seems to have happend, the first sunspot of solar cycle 24 appeard on the southern hemisphere of the sun.
Very close to NOAA 10902 a tiny spot which should be named 10903 appeared at S12W55.
In the SOHO MDI magnetogramms it clearly shows a reversed polarity if compared to the polarity of cycle 23. (cycle 23: black first towards the western limb and white following black / cycle 24: white in front of black)

And I show the picture with an arrow so you know which spot we’re talking about.
ulrichreith-sc24spot-31072006arrow.GIF

Again, the spot persisted for a few days and disappeared.

So what to believe? The transition between one solar cycle and the next is very difficult to call as during the transition both magnetically polarized spots can be seen. The newer cycle spots are usually high latitude (>20o) North and South of the solar equator. Solar cycle 23 spots still continue to produce and any SC24 spots so far are barely a pixel in size and very rare.

Solar cycle 24 remains difficult to call definitively at this time, in my view.

Written by John A

February 4, 2008 at 4:37 am