The sun may be heading for a rest period as the sunspot cycle seems to be fading and entering towards its maximum, and there are indications of weakening magnetic activity near the poles.
A missing jet stream, fading spots, and slower activity near the poles say that our Sun is heading for a rest period even as it is acting up for the first time in years, according to scientists at the National Solar Observatory (NSO) and the Air Force Research Laboratory (AFRL).
As the current sunspot cycle, Cycle 24, begins to ramp up toward maximum, independent studies of the solar interior, visible surface, and the corona indicate that the next 11-year solar sunspot cycle, Cycle 25, will be greatly reduced or may not happen at all.
The results were announced at the annual meeting of the Solar Physics Division of the American Astronomical Society, which is being held this week at New Mexico State University in Las Cruces.
This is highly unusual and unexpected, Dr. Frank Hill, associate director of the NSO's Solar Synoptic Network, said of the results. But the fact that three completely different views of the Sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation.
Spot numbers and other solar activity rise and fall about every 11 years, which is half of the Sun's 22-year magnetic interval since the Sun's magnetic poles reverse with each cycle. An immediate question is whether this slowdown presages a second Maunder Minimum, a 70-year period with virtually no sunspots -- during 1645-1715.
We expected to see the start of the zonal flow for Cycle 25 by now, Hill explained, but we see no sign of it. This indicates that the start of Cycle 25 may be delayed to 2021 or 2022, or may not happen at all.
This decline in sunspots coincided with below-normal temperatures, in a climate period known as the Little Ice Age that struck Europe and North America, where temperatures dropped by 1.8 to 2.7 degrees Fahrenheit (1-1.5 degrees Celsius).
But scientists warn that the temperature change due to a decline in sunspot activity would likely be minimal and not enough to compensate for global warming.
We are NOT predicting a mini-ice age. We are predicting the behavior of the solar cycle. In my opinion, it is a huge leap from that to an abrupt global cooling, since the connections between solar activity and climate are still very poorly understood. My understanding is that current calculations suggest only a 0.3 degree C decrease from a Maunder-like minimum, too small for an ice age. It is unfortunate that the global warming/cooling studies have become so politically polarizing, Hill said in a statement.
Scientists also see a long-term weakening trend in the strength of sunspots, and predict that by Cycle 25 magnetic fields erupting on the Sun will be so weak that few, if any, sunspots will be formed. Spots are formed when intense magnetic flux tubes erupt from the interior and keep cooled gas from circulating back to the interior. For typical sunspots this magnetism has a strength of 2,500 to 3,500 gauss (Earth's magnetic field is less than 1 gauss at the surface); the field must reach at least 1,500 gauss to form a dark spot.
Scientists observed that the average field strength declined about 50 gauss per year during Cycle 23 and now in Cycle 24. They also observed that spot temperatures have risen exactly as expected for such changes in the magnetic field. If the trend continues, the field strength will drop below the 1,500 gauss threshold and spots will largely disappear as the magnetic field is no longer strong enough to overcome convective forces on the solar surface.
Moving outward, Richard Altrock, manager of the Air Force's coronal research program at NSO's Sunspot, NM, facilities has observed a slowing of the rush to the poles, the rapid poleward march of magnetic activity observed in the Sun's faint corona. Altrock used four decades of observations with NSO's 40-cm (16-inch) coronagraphic telescope at Sunspot.
A key thing to understand is that those wonderful, delicate coronal features are actually powerful, robust magnetic structures rooted in the interior of the Sun, Altrock explained. Changes we see in the corona reflect changes deep inside the Sun.
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature.
If the sunspots were isolated from the surrounding photosphere it would be brighter than an electric arc. Sunspots expand and contract as they move across the surface of the Sun and can be as large as 80,000 kilometers (50,000 miles) in diameter, making the larger ones visible from Earth without the aid of a telescope.
Sunspots were first observed by Chinese astronomers in 800 B.C., systematic observations of sunspots through the telescope started around 1600. In 1843, a German astronomer Samuel Schawbe first discovered that the number of sunspots wax and wane in a cyclic fashion with an 11-year periodicity. This is called the sunspot cycle or the solar cycle.
So astronomers will be watching the sun carefully over the next couple of years to find out if the activity on the Sun contributes to climate change on Earth.
Some scientists say current findings mean that we are at the beginning of a Maunder Minimum, a 70-year period that began around 1645 when hardly any sunspots were observed.
In cycles 21 through 23, solar maximum occurred when this rush appeared at average latitude of 76 degrees, Altrock said. Cycle 24 started out late and slow and may not be strong enough to create a rush to the poles, indicating we'll see a very weak solar maximum in 2013, if at all. If the rush to the poles fails to complete, this creates a tremendous dilemma for the theorists, as it would mean that Cycle 23's magnetic field will not completely disappear from the polar regions (the rush to the poles accomplishes this feat). No one knows what the Sun will do in that case.
All three of these lines of research point to the familiar sunspot cycle shutting down for a while.
If we are right, Hill concluded, this could be the last solar maximum we'll see for a few decades. That would affect everything from space exploration to Earth's climate.