What is the Solar Cycle and How Long Does It Last?
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Causes of solar cycles, weather predictions, and other facts
February 14, 2023
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What are solar cycles—and how do they affect weather? Learn the definition of solar cycles, what causes them, how solar cycles are predicted, a little history, and why solar cycles even matter!
Here at The Old Farmer’s Almanac, we believe that all weather on Earth, from the surface of the planet out into space, begins with the Sun. Both space weather and terrestrial (Earth) weather—the weather we feel on our planet’s surface—are influenced by the small changes the Sun undergoes during its solar cycle.
What is the Solar Cycle?
First, remember that our Sun is a glowing, hot ball of electrically-charged gas which is what generates the Sun’s powerful magnetic field. Like Earth’s magnetic field, the Sun’s magnetic field has a north pole and a south pole. The Sun’s high temperatures causes these electrically-charged gases to constantly move around, generating areas of powerful magnetic forces or fields. This motion creates a lot of activity on the Sun’s surface, called solar activity.
The solar cycle is an approximately 11-year cycle experienced by our Sun.During this cycle, the Sun’s solar activity becomes more stormy and builds to a “maximum.” The magnetic fields flip, and the north pole becomes the south pole on the Sun. Then, the Sun’s solar activity settles back down to a “minimum.” And another solar cycle begins.
Note that the exact length of the cycle is not always 11 years; it has been as short as eight years and as long as 14.
Eleven years in the life of the Sun from 1980 (start of solar maximum) to 1986 (near minimum) to 1989 (near maximum again). Credit: NASA
Sunspots, Flare-Ups, and Eruptions!
In areas where the magnetic fields are particularly strong, we may see a black spot—called a sunspot—emerge on the surface of the Sun. This is indicative of stormy weather on the Sun and a lot of active magnetic activity beneath the surface. More sunspots means more solar activity.
The dark spots are cooler than the surrounding areas. Think of them as caps to a magnetic storm that is brewing just below the solar surface. The Sun’s magnetic fields are moving around, getting twisted and concentrated in these regions. Learn more in “What Are Sunspots?”
The total number of sunspots has long been known to vary with an approximately 11-year repetition known as the solar cycle—going from low to a high peak (maximum) and then high to low (minimum).
Associated with sunspots are flashes of light on the Sun, called solar flares. Occasionally, when powerful magnetic fields reconnect, they explode and break through the Sun’s surface! There is a sudden burst light energy and X-rays. Flares are classified according to their strength. The smallest ones are B-class, followed by C, M, and X, the largest. M-class flares can cause brief radio blackouts at the poles and minor radiation storms that might endanger astronauts.
Coronal mass ejections (CMEs)
Massive clouds of particles that spread into space, CMEs are large pieces of magnetic energy are hurled from the Sun at speeds up to several million mph. CMEs can occur when filaments/prominences become unstable and fly away from the Sun. We call this a filament/prominence eruption.
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 flares, CMEs, and other explosions tend to occur near sunspot groups when the Sun is more active. Naturally, all of this solar activity coincide with solar maximum.
Watch solar flares versus CMEs
What Causes the Solar Cycle?
The Sun goes through these cycles due to its magnetic nature. The Sun itself has a north and a south magnetic pole.
Because the Sun’s gases are constantly moving, the magnetic materials constantly gets tangled, stretched, and twisted. Over time, these movements eventually lead to the poles reversing.
The solar cycle happens because of this pole flip! The north becomes south and south becomes north every 11 years or so.
The poles reverse again back to where they started, making the full solar cycle a 22-year phenomenon.
How Does Solar Activity Affect Weather?
The Sun affects both weather and technology (which we’re increasingly dependent on) here on Earth. For example:
GPS, satellites, and other high-tech systems in space can be affected by an active Sun. Some of these systems are not protected by Earth’s atmospheric layers, so large solar flares have the potential to 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 can be caused by a quiet Sun. Weak solar winds allow more galactic cosmic rays into the inner solar system. Even airline pilots and crew can get a higher dose of radiation during solar storms.
Weather on Earth can also be affected. In a 2011 blog by Almanac astronomer Bob Berman, he stated “If the upcoming (solar) maximum is wimpy, as most solar researchers expect, or if the Sun is now entering an extended period of low activity, this is the best thing that it could possibly do for us. Such a scenario would mitigate climate change. Essentially, the Sun has been buying us time.” It turns out that the solar maximum in 2014 was indeed quite weak and “wimpy” compared to the three previous ones. According to the NASAGISTEMPLOTI and HADCRUT4 Global Mean Temperature data sets, the global temperature since that last weak solar maximum in 2014 has not significantly warmed, and one could argue that it is in more of a holding pattern. Is this due to that last wimpy solar maximum? This is hard to say, but there has been a significant slowdown in global warming since it occurred in 2014. Perhaps it may be linked to the rare triple-dip La Niña that we are currently in.
Global climate change, including long-term periods of global cold, rainfall, drought, and other weather shifts, may also be influenced by solar cycle activity.
Painting by Abraham Hondius, “The Frozen Thames, looking Eastwards towards Old London Bridge,” 1677. Image credit: Museum of London.
The Maunder Minimum and the “Little Ice Age”
Times of depressed solar activity seem to correspond with times of global cold in history. The most famous example is the “Little Ice Age.”
Between 1645 and 1715—during what we now call the “Maunder Minimum”—sunspots were exceedingly rare.
Specifically, there were only about 50 sunspots (instead of the usual 40 to 50 thousand) and harsh winters.
For 70 years, temperatures dropped by 1.8 to 2.7 degrees Fahrenheit.
Seven decades of freezing weather, corresponding with the coldest period of the Little Ice Age, led to shorter seasons and ultimately food shortages.
Conversely, times of increased solar activity have corresponded with global warming. During the 12th and 13th centuries, the Sun was active, and the European climate was quite mild.
Experts do not know for certain, however, what caused the Little Ice Age; theories suggest that it was likely due to a combination of events. Some scientists are researching other factors, such as heightened volcanic activity, that corresponded with the time of the Maunder Minimum.
What Solar Cycle Are We In Now?
We are now in Solar Cycle 25. Record-keeping of solar cycles began in 1755 with Solar Cycle 1.
In December, 2019, the sunspot numbers hit the solar minimum and “rock bottom” and the Sun passed from Cycle 24 into Cycle 25. The solar maximum or peak is predicted to happen in July, 2025.
As the cycles can overlap, it can be challenging to predict when a new cycle begins. However, there are some clues. For example, sunspots tend to form nearer the Sun’s equator as the cycle winds down (and at higher latitudes when a new cycle begins). Scientists measure solar cycles by keeping track of the number of sunspots appearing on the Sun’s surface as well as noting the location. A new solar cycle is considered to have begun when sunspots group at higher latitudes with the magnetic polarities of the leading spots opposite that of the previous cycle.