What are solar cycles—and what causes them? How do solar cycles affect our weather? Here’s our quick solar cycle beginner’s guide to help you understand the basics of how our Sun’s 11-year solar cycle works.
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 weather (the weather we feel at the surface) are influenced by the small changes the Sun undergoes during its solar cycle.
What is the Solar Cycle?
The simpliest solar cycle definition is: “The solar cycle is the cycle that the Sun’s magnetic field goes through approximately every 11 years.”
Let’s explain: Remember that the Sun is a hot ball of glowing, electrically-charged gases. 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.
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 a sunstorm and a lot of activity beneath the surface. More sunspots means more solar activity.
There does seem to be an ebb and flow or “cycle” to this magnetic flow and movement. 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 high and then high to low. The peak of sunspot activity is known as solar maximum and the low is known as solar minimum.
Note: 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
Sunstorms, Flare-Ups, and Eruptions!
Our burning star may seem like it’s a constant, unchanging ball, always looking the same. However, just like planet Earth, the Sun has weather. It has giant storms! It flares up! It ejects huge bubbles of gas from the surface toward space and our planet. Here are some definitions:
- Sunspots indicate active magnetic fields. 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?”
- Solar flares appear as flashes of light on the Sun, and are associated with sunspots. 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) are massive clouds of particles that spread into space! Large pieces of magnetic energy are hurled from the Sun into interplanetary space 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
Why Does the Solar Cycle Happen?
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. According to Bob Berman, astronomer for The Old Farmer’s Almanac, NOAA scientists have now concluded that four factors determine 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.
Painting by Abraham Hondius, “The Frozen Thames, looking Eastwards towards Old London Bridge,” 1677. Image credit: Museum of London.
The Maunder Minimum or “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” or “Little Ice Age”—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 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.
What Solar Cycle Are We In Now?
Record-keeping of solar cycles began in 1755 with Solar Cycle 1. We are now nearing the end of Solar Cycle 24, approaching the solar minimum and the start of Solar Cycle 25.
- By solar minimum, we mean the lowest number of sunspots. After some years of high activity, the Sun will ramp down with fewer sunspots or almost no sunspots. The temperature cools.
- Conversely, solar maximum is the highest number of sunspots in any given cycle. A new cycle starts with a “solar maximum” littered with solar storms and sunspots. The temperature warms.
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.