This article was written in the midst of an 11-year cycle, when the Earth experienced effects and influences on radio communications, energy, space flights and even weather and forecasting the sun's activity became, therefore, the essence of the matter. Also fitting these days after an unexpected peak of activity and the largest sunspot ever discovered
By: Leslie Mullen on the FIRST SCIENCE website. Translation: Eli Ben David
Most people think of the sun as a featureless and unchanging ball of fire. But the sun actually has seasons, or cycles of relative activity and inactivity. Right now, we are in the midst of the maximum activity state of the current 11-year solar cycle. The sun exhibits many sunspots and flashes on a daily basis. We, on Earth, feel the effects of solar activity - radio communications, electricity distribution, spaceships in orbit and even the weather - are all affected.
Sunspots are relatively cold areas on the sun that appear as dark spots. Scientists count the number of sunspots to measure the size of a solar cycle, and determine how long it lasts. If scientists could predict sunspot activity in advance, not only would we know ahead of time what the sun would do, but it would also be possible to gain a better understanding of how the sun works.
Dr. David Hathaway, along with Robert Wilson and Ed Reichman, examined the many ways scientists predict sunspot activity. They tested each statistical process to see which one worked best, then combined the top two processes to develop their own better prediction method.
"There are many different ways to predict a sunspot cycle," says Hathaway. "But until now there has never been a systematic study to determine if one method works better than another. After testing various methods, we found that some of the techniques that are currently being used are essentially useless."
By testing 15 processes and methods, the scientists found that 8 or 9 were better than average at predicting "Solar Maxima" - when the sun is at its peak. The two best processes, basically used the same information - disturbances in the magnetic fields of the Earth.
"Explosions (eruptions) from the Sun travel through space and hit the Earth, causing the magnetic fields to wiggle and vibrate," Hathaway says.
Joan Feynman of NASA's Jet Propulsion Laboratory developed one of the two methods mentioned. Australian astronomer Richard Thompson developed the second method. Although the two scientists took a different approach to the data, and reported different results, both looked at how the Earth's magnetic fields vibrated during the previous solar cycle to predict the size of the next cycle.
Scientists have no idea why the previous solar activity is related to the activity of the next cycle, or why the earth's response to this activity helps predict the solar cycle. But the relationship allows scientists to estimate what the next solar season will bring us.
The statistical model developed by Hathaway's team uses both Feynman's and Thompson's processes and merges them using a fitting-curve technique. The preliminary methods used by Feynman and Thompson try to determine the total number of sunspots that will appear before the season actually begins.
A graph of sunspot activity observation
The curve-fitting method finds the best curve to match recent solar activity. Based on years of observations, scientists have developed a library of curves that follow the average of a solar cycle. Using their prediction methods, Hathaway's team can select one curve from this library before the solar cycle even begins, then make adjustments as the process progresses. For the current cycle, Hathaway's team predicts a maximum average of 154 sunspots with an uncertainty of plus-minus 20. This forecast has a narrower margin of error than the previous widely accepted forecast, which predicted a maximum of 160- Sun with a margin of error of 30.
"We are in a cycle where the sun is very active," says Hathaway. "Until the middle of 2001, we will see a number of sunspots between 100 and 300 with an average of 154". After that, a gradual decrease in solar activity will begin until the minimum solar level. So far, the sun appears to be following the curve chosen by the scientists. "Monthly calculations are basically jumping all over the place," says Hathaway. "We must remember that the curve is only an average of what is really happening."
In one day, for example, over 300 sunspots were measured - much more than the average of 154. But in the five months leading up to that day, there were only a small number of sunspots than expected. The average number of sunspots meets in the middle to follow the curve chosen by Hathaway's team.
No matter how good the method is, "physical models for predicting sunspot activity, several years in advance, do not yet exist," says Hathaway. "We don't know well enough why the sun does this, to be able to make predictions like the meteorologists do." The meteorologist can calculate information of weather factors, such as temperature and barometric pressure into a computer model to produce a weekly weather forecast. Solar forecasters do not have a physical model since they do not yet know how all the factors of solar activity work together.
A simple model of the sun shows that the surface of the sun is separated into four regions. The energy is produced in the core of the sun (Core), and this energy radiates out through the "radiative zone" in the form of gamma rays and X-rays. In the "convective zone", liquids flow inside a boiling shooter. Movements of these fluids appear as grains or supergrains on the surface of the Sun. A thin layer, where scientists think the Sun's magnetic fields are generated, lies between the heat-conducting region and the radiating region.
Hathaway, along with most solar astronomers, believes that the Sun's magnetic field is the key to understanding the solar cycle. Sunspots are formed when the magnetic field lines, which are just below the Sun's surface, are distorted and pushed through the solar photosphere. The photosphere - or "ball of light" - is the known and visible surface of the sun.
The sun is actually a ball of gas, so it doesn't orbit as strictly as the planets on their moons do. Instead the equatorial regions of the sun circle faster than the polar regions. Because of this "jet stream" near the equator, the magnetic fields embrace and envelop the Sun. "The magnetic field is a lot like a rubber band," says Hathaway. "The fluid flowing inside the sun, called 'Dynamos' stretches, twists and folds the strip, wrapping it around the sun many times over 11 years. When the magnetic field bends it into the heat conduction region, it quickly rises to the surface. As it rises, it warps slightly. This results in a change in the direction of the field, which helps to retract the poles."
The Sun's magnetic poles are retreating in Solar-Maxima. Starting at the equator, with a slow flow on the surface, pulling the magnetic fields with them towards the poles. Conversely, sunspots first appear in mid-latitudes, then, later in the solar cycle, congregate near the equator.
The additional ultraviolet radiation and X-ray radiation created by the magnetic field around the sunspots cause the atmosphere of KDA to heat up and expand. This creates an additional resistance force (drag force) in the area where satellites and space shuttles move in their orbit around the Earth. This force can slowly drag such a spacecraft out of orbit earlier than planned. The ultraviolet activity of sunspots also increases the amount of ozone in the upper atmosphere of the Earth.
Although sunspots are relatively cold areas, the sun is actually warmer when they are present and colder when they are not. Scientists believe that the sun's prolonged inactivity has a direct correlation with colder temperatures on Earth. From 1645 to 1715, astronomers observed very little solar activity. This period of time coincides with the era known as the "Little Ice Age", when rivers and lakes throughout Europe (and perhaps the entire world) froze.
Although there is a good record of solar activity since the invention of the telescope in 1610, scientists need to check other sources to determine if there were even earlier periods of solar activity. Depending on the amounts of carbon-14 and beryllium-10 in the environment, scientists can use ice core samples on Earth to determine levels of solar activity.
"We can travel back in time, before the telescope, by looking at ice-core samples," says Hathaway. "Based on these samples, it turns out that there were other, earlier minima sunspots."
In 1843, amateur astronomer Heinrich Schwabe found that sunspots come and go in a predictable 11-year cycle. Since this announcement, many have tried to attribute all kinds of events on Earth to the solar cycle - some even believed that the sun affects the stock market even though there is no evidence that solar activity affects economic trends.
By predicting what the sun will do in the future we can better prepare for the many other effects that solar activity will have on life on Earth.
