Sunny with Some Spots
When observing the Sun, the most obvious visible features are usually its sunspots, which are well defined surface areas that appear darker than their surroundings because of lower temperatures. Sunspots are regions of intense magnetic activity where convection is inhibited by strong magnetic fields, reducing energy transport from the hot interior to the surface. The magnetic field causes strong heating in the corona, forming active regions that are the source of intense solar flares and coronal mass ejections. the number of such spots varies over time generally in a 11 year cycle. Right now the spots are mostly gone for about 2 years which is highly unusual and may portend dramatic solar events to come which will affect the whole earth.
The solar sunspot cycle has a great influence on space weather, and is a significant influence on the Earth's climate due to its effect on overall luminosity. Sunspot minima tend to be correlated with colder temperatures, and longer than average solar cycles tend to be correlated with hotter temperatures. In the 17th century, the solar cycle appears to have stopped entirely for several decades; very few sunspots were observed during this period. During this era, which is known as the Maunder minimum or Little Ice Age, Europe experienced very cold temperatures.
This is not the only known sunspot/climate low temperature minimum observed. The Dalton one happened between 1790 and 1830 while the Sporer happened around 1500.
The sun entered a normal low sunspot time in 2007 so that 2008 was expected to have few spots. Computer models predicted that when the spots did return, they would do so in force. This would have meant more solar storms than normal with resulting interference with satellite reception and transmissions.
The first sign that the prediction was wrong came when 2008 turned out to be even calmer than expected. That year, the sun was spot free 73 per cent of the time. Only the minimum of 1913 was more recently pronounced, with 85 per cent of that year clear.
It was not unto December 2009 that there was swarm of spots on the sun announcing the start of the next cycle. Even with the solar cycle finally under way again, the number of sunspots has so far been well below expectations. Something appears to have changed inside the sun, something the models did not predict.
Observations from space and ground based telescopes suggests that the answer lies in the behavior of two vast conveyor belts of gas that endlessly cycle material and magnetism through the sun's interior and out across the surface. On average it takes 40 years for the conveyor belts to complete a circuit.
When this was further studied it was noticed that the conveyor belt flows of gas across the sun's surface have been speeding up since 2004.
The circulation deep within the sun tells a different story. Rachel Howe and Frank Hill of the National Solar Observatory in Tucson, Arizona, have used observations of surface disturbances, caused by the solar equivalent of seismic waves, to infer what conditions are like within the sun. Analyzing data from 2009, they found that while the surface flows had sped up, the internal ones had slowed to a crawl.
The sun is the major source of energy on earth and it certainly drives the climate and perhaps the overall climate change such as global warming. Though not a variable star its luminosity does vary and a small change in that can have dramatic effects on how warm or cold the world is.
The lower solar activity during the Maunder Minimum also affected the amount of cosmic radiation reaching the Earth. The scale of changes resulting in the production of carbon-14 in one cycle is small (about 1 percent of medium abundance) and can be taken into account when radiocarbon dating is used to determine the age of archaeological artifacts.
Although sunspots are making a belated comeback after the protracted solar minimum, the signs are that all is not well. For decades, William Livingston at the National Solar Observatory in Tucson, Arizona, has been measuring the strength of the magnetic fields which puncture the sun's surface and cause the spots to develop. Last year, he and colleague Matt Penn pointed out that the average strength of sunspot magnetic fields has been sliding dramatically since 1995.
If the trend continues, in just five years the field will have slipped below the threshold magnetic field needed for sunspots to form.
How likely is this to happen? Mike Lockwood at the University of Reading, UK, has scoured historical data to look for similar periods of solar inactivity, which show up as increases in the occurrence of certain isotopes in ice cores and tree rings. He found 24 such instances in the last few thousand years. On two of those occasions, sunspots all but disappeared for decades. Lockwood puts the chance of this happening now at just 8 per cent.
If sunspots cease for a time, that phenomena is related to decreased global temperatures. In time we will find out what it all means.
For further information: http://www.newscientist.com/article /mg20627640.800-whats-wrong-with-the-sun.html?full=true or http://en.wikipedia.org/wiki/Sun