Here at the Almanac, we believe that solar science, the study of sunspots and other solar activity, can influence weather here on Earth. In this article, we explain the basics of solar activity, solar cycles, and what's up with the Sun now.
What Is Solar Activity?
The Sun is always active. It has weather. It has storms. And its storms can affect Earth's weather.
- Sunspots are magnetic storms on the surface of the Sun.
- Solar flares are intense blooms of radiation that come from the release of the magnetic energy associated with sunspots. The NOAA ranks solar flares using five categories from weakest to stongest: A, B, C, M, and X. Each category is 10 times stronger than the one before it. Within each category, a flare is ranked from 1 to 9, according to strength, although X-class flares can go higher than 9. According to NASA, the most powerful solar flare recorded was an X28 (in 2003).
- Coronal mass ejections (CMEs) are bursts of solar material (clouds of plasma and magnetic fields) that shoot off the sun's surface. Other solar events include solar wind streams that come from the coronal holes on the Sun and solar energetic particles that are primarily released by CMEs.
Solar Flare. Credit: jpl.nasa.gov
What is a Solar Cycle?
The number of sunspots increase and decrease over time in a regular, approximately 11-year cycle, called the solar or sunspot cycle. The exact length of the cycle can vary. More sunspots mean increased solar activity—flares and CMEs. The highest number of sun spots in any given cycle is designated "solar maximum," while the lowest number is designated "solar minimum."
Eleven years in the life of the Sun, spanning most of solar cycle 23, as it progressed from solar minimum (upper left) to maximum conditions and back to minimum (upper right) again, seen as a collage of ten full-disk images of the lower corona. Credit: NASA
How Does Solar Activity Affect Weather and Earth?
Solar activity affects the Earth in many ways, some which we are still coming to understand.
Damage to 21st-century satellites and other high-tech systems in space can be caused by an active Sun which generates geomagnetic storms.
Even in inactive solar cycles, the Sun emits large solar flares—which could cause billions of dollars in damage to the world's high-tech infrastructure—from GPS navigation to power grids to air travel to financial services.
- Radiation hazards for astronauts and satellites can be caused by a quiet Sun. Weak solar winds allow more galactic cosmic rays into the inner solar system.
- Weather on Earth can also be affected. According to Bob Berman , astronomer for The Old Farmer's Almanac: Recently, NOAA scientists concluded that four factors determined global temperatures: carbon dioxide levels, volcanic eruptions, Pacific El Niño pattern, and the Sun's activity.
- Global climate change including long-term periods of global cold, rainfall, drought, and other weather shifts may also be influenced by solar cycle activity, based on historical evidence:
Times of depressed solar activity seem to correspond with times of global cold. For example, during the 70-year period from 1645 to 1715, few, if any, sunspots were seen, even during expected sunspot maximums. Western Europe entered a climate period known as the "Maunder Minimum" or "Little Ice Age." Temperatures dropped by 1.8 to 2.7 degrees Fahrenheit.
Conversely, times of increased solar activity have corresponded with global warning. During the 12th and 13th centuries, the Sun was active, and the European climate was quite mild.
Yearly-averaged sunspot numbers from 1610 to 2008. Researchers believe upcoming Solar Cycle 24 will be similar to the cycle that peaked in 1928, marked by a red arrow. Credit: NASA/MSFC
Solar Cycle 24
As of January 15, 2015, we are over six years into Cycle 24.
The solar minimum occured in 2008 and 2009; during those two years, there were almost NO sunspots, a very unusual situation that had not happened for almost a century. Due to the weak solar activity, galactic cosmic rays were at record levels.
Solar Maximum: The Sun's record-breaking sleep ended in 2010. In 2011, sunspot counts jumped up. In February of 2012, the sunpot numbers reached a peak of 66.9.
In late 2013, NASA reported, "The sun's global magnetic field is about to reverse polarity." The sunspot number climbed into the 70s. This is still very low. By February of 2014, sunspots averaged 102.8 spots a day, which is the first time the cycle broke 100.
In April, 2014, the sunspot number peaked a second time, reaching 81.9. This is likely the solar maximum. Many cycles are double peaked, however, this is the first time the second peak was larger than the first peak (in February, 2012).
Cycle 24 has been a weak solar cycle—the smallest since Cycle 14 (which had a maximum of 64.2 in February of 1906). What will happen next? Stay tuned!
What does all this mean?
- Quiet-to-average cycles mean a cooling pattern over the next few decades. Temperatures have been colder than it would have been otherwise. Sunspots are similar to a bathtub of lukewarm water; if you trickle in cold or hot water, it may take a while to notice the difference. If this cooling phase on Earth, however, is offset by any warming caused by increasing greenhouse gases, they also raise the question of whether an eventual warming cycle could lead to more rapid warming on Earth than expected.