Solar Cycle Prediction

(Updated 2009/12/08)

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Predicting the behavior of a sunspot cycle is fairly reliable once the cycle is well underway (about 3 years after the minimum in sunspot number occurs [see Hathaway, Wilson, and Reichmann Solar Physics; 151, 177 (1994)]). Prior to that time the predictions are less reliable but nonetheless equally as important. Planning for satellite orbits and space missions often require knowledge of solar activity levels years in advance.

A number of techniques are used to predict the amplitude of a cycle during the time near and before sunspot minimum. Relationships have been found between the size of the next cycle maximum and the length of the previous cycle, the level of activity at sunspot minimum, and the size of the previous cycle. Among the most reliable techniques are those that use the measurements of changes in the Earth's magnetic field at, and before, sunspot minimum. These changes in the Earth's magnetic field are known to be caused by solar storms but the precise connections between them and future solar activity levels is still uncertain. Of these "geomagnetic precursor" techniques three stand out. The earliest is from Ohl and Ohl [Solar-Terrestrial Predictions Proceedings, Vol. II. 258 (1979)] They found that the value of the geomagnetic aa index at its minimum was related to the sunspot number during the ensuing maximum. The primary disadvantage of this technique is that the minimum in the geomagnetic aa index often occurs slightly after sunspot minimum so the prediction isn't available until the sunspot cycle has started. An alternative method is due to a process suggested by Joan Feynman. She separates the geomagnetic aa index into two components: one in phase with and proportional to the sunspot number, the other component is then the remaining signal. This remaining signal faithfully represents the sunspot numbers several years in advance. The maximum in this signal occurs near sunspot minimum and is proportional to the sunspot number during the following maximum. This method does allow for a prediction of the next sunspot maximum at the time of sunspot minimum. A third method is due to Richard Thompson [Solar Physics 148, 383 (1993)]. He found a relationship between the number of days during a sunspot cycle in which the geomagnetic field was "disturbed" and the amplitude of the next sunspot maximum. His method has the advantage of giving a prediction for the size of the next sunspot maximum well before sunspot minimum. We have employed these methods along with several others to determine the size of the next sunspot cycle using a technique that weights the different predictions by their reliability. [See Hathaway, Wilson, and Reichmann J. Geophys. Res. 104, 22,375 (1999)] Our current analysis indicates a maximum sunspot number of about 78 ± 18 for cycle 24. We then use the shape of the sunspot cycle as described by Hathaway, Wilson, and Reichmann [Solar Physics 151, 177 (1994)] and determine a starting time for the cycle by fitting the data to produce a prediction of the monthly sunspot numbers through the next cycle. We find a starting time of March 2008 with minimum occurring in November or December 2008 and maximum in April or May 2013. The predicted numbers are available in a text file, as a GIF image, and as a pdf-file. As the cycle progresses, the prediction process switches over to giving more weight to the fitting of the monthly values to the cycle shape function. At this phase of cycle 24 we now give little weight to the curve-fitting technique of Hathaway, Wilson, and Reichmann Solar Physics 151, 177 (1994). That technique currently gives highly uncertain (but small) values. Note: These predictions are for "smoothed" International Sunspot Numbers. The smoothing is usually over time periods of about a year or more so both the daily and the monthly values for the International Sunspot Number should fluctuate about our predicted numbers. The dotted lines on the prediction plots indicate the expected range of the monthly sunspot numbers. Also note that the "Boulder" numbers reported daily at www.spaceweather.com are typically about 35% higher than the International sunspot number. Another indicator of the level of solar activity is the flux of radio emission from the Sun at a wavelength of 10.7 cm (2.8 GHz frequency). This flux has been measured daily since 1947. It is an important indicator of solar activity because it tends to follow the changes in the solar ultraviolet that influence the Earth's upper atmosphere and ionosphere. Many models of the upper atmosphere use the 10.7 cm flux (F10.7) as input to determine atmospheric densities and satellite drag. F10.7 has been shown to follow the sunspot number quite closely and similar prediction techniques can be used. Our predictions for F10.7 are available in a text file, as a GIF image, and as a pdf-file. Current values for F10.7 can be found at: http://www.spaceweather.ca/sx-4-eng.php.

Solar Cycle Predictions Web Links

Solar Influences Data Analysis Center

Royal Greenwich Observatory/USAF/NOAA Sunspot Record 1874-2008

Solar Cycle 23 Panel: Summary of Panel Findings

Solar Cycle 24 Panel: Summary of Panel Findings

What's Wrong with the Sun? (Nothing)

July 11, 2008: Stop the presses! The sun is behaving normally.

So says NASA solar physicist David Hathaway. "There have been some reports lately that Solar Minimum is lasting longer than it should. That's not true. The ongoing lull in sunspot number is well within historic norms for the solar cycle."

This report, that there's nothing to report, is newsworthy because of a growing buzz in lay and academic circles that something is wrong with the sun. Sun Goes Longer Than Normal Without Producing Sunspots declared one recent press release. A careful look at the data, however, suggests otherwise.

But first, a status report: "The sun is now near the low point of its 11-year activity cycle," says Hathaway. "We call this 'Solar Minimum.' It is the period of quiet that separates one Solar Max from another."

Above: The solar cycle, 1995-2015. The "noisy" curve traces measured sunspot numbers; the smoothed curves are predictions. Credit: D. Hathaway/NASA/MSFC. [more]

During Solar Max, huge sunspots and intense solar flares are a daily occurrence. Auroras appear in Florida. Radiation storms knock out satellites. Radio blackouts frustrate hams. The last such episode took place in the years around 2000-2001.

During Solar Minimum, the opposite occurs. Solar flares are almost nonexistent while whole weeks go by without a single, tiny sunspot to break the monotony of the blank sun. This is what we are experiencing now.

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Although minima are a normal aspect of the solar cycle, some observers are questioning the length of the ongoing minimum, now slogging through its 3rd year.

"It does seem like it's taking a long time," allows Hathaway, "but I think we're just forgetting how long a solar minimum can last." In the early 20th century there were periods of quiet lasting almost twice as long as the current spell. (See the end notes for an example.) Most researchers weren't even born then.

Hathaway has studied international sunspot counts stretching all the way back to 1749 and he offers these statistics: "The average period of a solar cycle is 131 months with a standard deviation of 14 months. Decaying solar cycle 23 (the one we are experiencing now) has so far lasted 142 months--well within the first standard deviation and thus not at all abnormal. The last available 13-month smoothed sunspot number was 5.70. This is bigger than 12 of the last 23 solar minimum values."

In summary, "the current minimum is not abnormally low or long."

The longest minimum on record, the Maunder Minimum of 1645-1715, lasted an incredible 70 years. Sunspots were rarely observed and the solar cycle seemed to have broken down completely. The period of quiet coincided with the Little Ice Age, a series of extraordinarily bitter winters in Earth's northern hemisphere. Many researchers are convinced that low solar activity, acting in concert with increased volcanism and possible changes in ocean current patterns, played a role in that 17th century cooling.

For reasons no one understands, the sunspot cycle revived itself in the early 18th century and has carried on since with the familiar 11-year period. Because solar physicists do not understand what triggered the Maunder Minimum or exactly how it influenced Earth's climate, they are always on the look-out for signs that it might be happening again.

The quiet of 2008 is not the second coming of the Maunder Minimum, believes Hathaway. "We have already observed a few sunspots from the next solar cycle," he says. (See Solar Cycle 24 Begins.) "This suggests the solar cycle is progressing normally."

What's next? Hathaway anticipates more spotless days¹, maybe even hundreds, followed by a return to Solar Max conditions in the years around 2012.

SOLAR CYCLE UPDATE

2008 has been a year of few sunspots and mostly blank suns. A solar cycle update just released by NASA solar physicist David Hathaway shows why. We are experiencing the lowest ebb of solar minimum:

In the plot, the noisy curve is the International Sunspot Number measured by a worldwide network of solar observers. The smoothed curves are predictions for the future. We see that sunspot numbers may remain low for many months to come before beginning a rapid ascent in early 2009 toward the next solar maximum. It's something to look forward to. Meanwhile, stay tuned for quiet.

THREE RED SPOTS: How many red spots does Jupiter have? On March 17th, Mike Salway of Australia looked through his 12-inch telescope and counted three:

Red spot #1 is the Great Red Spot you've heard about, hundreds of years old and twice as wide as Earth. Red spot #2 is Oval BA, which formed white in 2000 and turned red in 2006. Red spot #3 is a newcomer, "the Little Red Spot," says Salway, possibly only weeks old.

All these spots are storms--anticyclones big enough to swallow a rocky planet. What makes them red? Curiously, no one knows why the Great Red Spot itself is red. A favorite idea is that the storm dredges "chromophores" (color-changing compounds) from deep inside Jupiter up to the cloudtops where sunlight triggers a chemical reaction with red by-products. But what are the chromosphores and what is the chemical reaction? It's a mystery--now multiplied by three.

Jupiter is emerging from the glare of the sun as a bright morning star, visible in the southeast before sunrise: sky map. "I'm still waiting for some 'excellent' morning to deliver the best resolution and detail," says Salway, "but as Jupiter keeps climbing I'm sure it will come soon."

The aurora oval

The auroral zones represent the places on earth where auroras occur most often and with greatest intensity. It was the Swiss physicist Herman Fritz (1829-1902), in the 1881 book "Das Polarlicht." who first showed that the northern lights have a maximum zone close to 67 degrees north. He called this belt the auroral zone. Thus, the auroral zones encompass the statistical distributions in latitude of all visible, night side auroras. The more detailed location of the auroral zones is based on professor Størmer's extensive auroral observations between 1910 and 1950.

The momentary, instantenous distribution of the auroras as a function of both latitude and local time were mapped by ground, rocket and satellite measurements in the 1960s. The best overview was obtained by satellite photos of the earth. Then it was discovered that the auroras display a continous oval zone around the magnetic pole in both hemispheres. Thus the auroral ovals are the regions on earth where the auroras are seen most often and with the greatest intensity.

The auroral oval is nearly twice as wide and twice as far from the magnetic pole at midnight as at midday, about 23 degrees and 12 degrees, respectively. On the night side the oval is roughly 10 degrees (about 1100 kilometres) closer to the equator than at the day side.

The auroral oval can be regarded as fixed in space with reference to the sun. As the earth revolves underneath, the daily variations in the aurora's position occur. In the Scandinavian sector you find that Andøya Rocket Range is located under the oval at night, while the oval lies across Svalbard during daytime. Halfway between northern Norway and Svalbard, northern lights can be observed in zenith both morning (around 0600) and evening (around 1800).

Modern studies have clearly shown that the shapes and locations of the ovals vary greatly with solar activity. With increasing activity on the sun, the oval widens and spreads, mainly towards the equator.

Current Auroral Oval:

Switch to: Europe, USA, New Zealand, Antarctica
Credit: NOAA/POES
Updated:
What is the auroral oval?

Coronal Holes

Earth is inside a solar wind stream flowing from the indicated coronal hole.

IS A NEW SOLAR CYCLE BEGINNING?

Dec. 14, 2007: The solar physics community is abuzz this week. No, there haven't been any great eruptions or solar storms. The source of the excitement is a modest knot of magnetism that popped over the sun's eastern limb on Dec. 11th, pictured below in a pair of images from the orbiting Solar and Heliospheric Observatory (SOHO).

It may not look like much, but "this patch of magnetism could be a sign of the next solar cycle," says solar physicist David Hathaway of the Marshall Space Flight Center.

Above: From SOHO, a UV-wavelength image of the sun and a map showing positive (white) and negative (black) magnetic polarities. The new high-latitude active region is magnetically reversed, marking it as a harbinger of a new solar cycle.

For more than a year, the sun has been experiencing a lull in activity, marking the end of Solar Cycle 23, which peaked with many furious storms in 2000--2003. "Solar minimum is upon us," he says.

The big question now is, when will the next solar cycle begin?

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It could be starting now.

"New solar cycles always begin with a high-latitude, reversed polarity sunspot," explains Hathaway. "Reversed polarity " means a sunspot with opposite magnetic polarity compared to sunspots from the previous solar cycle. "High-latitude" refers to the sun's grid of latitude and longitude. Old cycle spots congregate near the sun's equator. New cycle spots appear higher, around 25 or 30 degrees latitude.

The region that appeared on Dec. 11th fits both these criteria. It is high latitude (24 degrees N) and magnetically reversed. Just one problem: There is no sunspot. So far the region is just a bright knot of magnetic fields. If, however, these fields coalesce into a dark sunspot, scientists are ready to announce that Solar Cycle 24 has officially begun.

Solar Cycle 23 is coming to an end. What's next? Image credit: NOAA/Space Weather Prediction Center.

Many forecasters believe Solar Cycle 24 will be big and intense. Peaking in 2011 or 2012, the cycle to come could have significant impacts on telecommunications, air traffic, power grids and GPS systems. (And don't forget the Northern Lights!) In this age of satellites and cell phones, the next solar cycle could make itself felt as never before.

The furious storms won't start right away, however. Solar cycles usually take a few years to build to a frenzy and Cycle 24 will be no exception. "We still have some quiet times ahead," says Hathaway.

Meanwhile, all eyes are on a promising little active region. Will it become the first sunspot of a new solar cycle? Stay tuned for updates from Science@NASA.

SUNSPOT 978

Giant sunspot 978 hasn't exploded yet, but it is seething with activity. Witness this video recorded by Gary Palmer of Los Angeles on Dec. 11th:

"There is a magnetic filament that seems to leapfrog over the leading spot," he points out. "Isn't Mother Nature wonderful!"

Sunspot 978 continues to grow: movie. It now covers an expanse of Sun about as wide as the planet Jupiter, making it a fine target for backyard solar telescopes (Palmer used a Coronado SolarMax90). It has also developed a "beta-gamma" magnetic field that harbors energy for M-class solar flares. Will it erupt? Stay tuned!

more images: from John Nassr of Baguio, Philippines; from Malcolm Park of London, UK; from Pete Lawrence of Selsey, West Sussex, UK; from Paul Haese of Blackwoo, South Australia;