Solar Cycles

The sun has a magnetic field that flips approximately every 11 years.  Sunspots and solar flares are caused by the magnetic activity of the sun. The sunspots and solar flares can affect the earth by changing the amount of incoming sunlight and interacting with the earth's magnetic field. The disruption of our electromagnetic field interferes with our all of our electronics, radios and satellites and can cause the aurora borealis in the Northern Hemisphere.

Why do I care? The solar cycles affect not just Earth’s energy balance, but its electromagnetic field. If you get irritated when your TV and phone is on the blink, you should learn more about solar cycles and when they might affect you. Changes in sunspots can also herald changes in incoming sunlight that could affect the local climate.

I should already be familiar with: Earth's Energy Balance


The sun is the major source of energy that drives our weather and climate. The energy that the sun gives off changes a little bit every day. In the long term, larger changes in the solar output come in roughly 11 year cycles called sunspot cycles. Sunspots are cooler areas on the sun’s surface that give off less energy than the surrounding areas, causing them to appear darker. Figure A is from the solar minimum with lots of sunspots from July 19, 2000 and Figure B is from the solar maximum with no sunspots from March 18, 2009.

Sunspots are actually a side effect of the sun’s magnetic field. They are also associated with high energy disturbances like solar flares and coronal mass ejections, which can affect the amount of solar energy and particles reaching Earth, disrupting the earth's magnetic field. Streams of solar particles ejected from the sun during solar flares can get caught in the earth's magnetic field, leading to colorful displays of Northern Lights in polar regions. Sunspots have been observed for thousands of years, starting with the ancient Chinese, but have been monitored more carefully since the development of the telescope during the Renaissance. 

The Left image from July of 2000 shows a lot of sunspots. The image on the right from March of 2009 shows a blank sun.
Figure A (left) from July of 2000 shows a lot of sunspots. Figure B (right) from March of 2009 shows a blank sun. (Images from NASA).

While solar cycles statistically have not been proven to have a direct effect on weather, there is some indication that solar cycles have an effect on climate. From 1645 to 1715 there were almost no sunspots. This period is called the Maunder minimum, named for the British astronomer who discovered it. The Maunder minimum actually coincides with the peak of the Little Ice Age, a cool period affecting Europe from the 1300s to the 1800s. The Dalton minimum, a 25 year span at the beginning of the 1800s when sunspots were half as numerous as normal, corresponds to the end of the Little Ice Age. Some people claim there is a connection between the 22 year solar cycle and the roughly 20 year drought cycle in the Great Plains. The Old Farmer’s Almanac actually use solar cycles in their long term forecasts. One interesting bit of information is the ozone layer tends to reach a maximum at the same time as the solar maximum, allowing the ozone layer to absorb the excess radiation. This is thought to affect the tropical Hadley cell circulation and the tracks of mid-latitude cyclones. Scientists are still looking for a scientific explanation that would clarify the relationship between sunspots and weather and climate.

Below is a video from the National Academies of Science that explains how the energy output of the sun changes year to year and how these changes affect and influence the changing climate.