On December 10-11, 2019, Iceland received one of the largest snow storms in its history. The so-called "10-year storm," brought winds of 100 miles per hour (161 km/h), with one weather station reporting gusts of up to 149 mph (240 km/h).
Sustained winds reached 90 mph (145 km/h) in the Northeast part of the country, and 10 feet (3 m) of snow fell in the North. The storm was so severe that the Icelandic Meteorological Office issued an unprecedented "red alert."
The snow cyclone caused atmospheric pressure to drop to 944 millibars (mbar) on land, while the average pressure at sea level is usually over 1,000 millibars. Compare that to the 946 millibars that Hurricane Sandy brought with it when it made landfall in New Jersey in 2012.
Iceland's, Europe's and North America's weather has historically been tied to the sunspot activity of the Sun. According to NASA, in 2020, the Sun, which is currently in solar cycle #25, will reach its lowerst activity in over 200 years.
What is the solar cycle?
The solar cycle is a periodic 11-year fluctuation in the Sun's magnetic field, during which its North and South poles trade places. This has an enormous effect on the number and size of sunspots, the level of solar radiation, and the ejection of solar material comprised of flares and coronal loops.
The solar cycle was first noted in 1775 by Danish astronomer Christian Horrebow who observed that the number and size of sunspots repeated itself.
In 1843, the German astronomer Samuel Heinrich Schwabe also noted this fluctuation in the number of sunspots, and Swiss astronomer Rudolf Wolf reconstructed the cycle all the way back to observations of the Sun made by Galileo.
Wolf created a sunspot counting scheme known as the Wolf Index, and a numbering scheme whereby the 1755 - 1766 cycle was designated Cycle #1.
At the beginning of a sunspot cycle, sunspots appear at the Sun's mid-latitudes, both north and south. They then move toward the equator until a solar minimum is reached. Eventually, sunspots decay and release magnetic flux onto the Sun's surface or photosphere.
The solar cycle's effect on weather
The period between 1645 and 1715 was marked by a prolonged sunspot minimum, and this corresponded to a downturn in temperatures in Europe and North America. Named after astronomers Edward Maunder and his wife Annie Russell Maunder, this period became known as The Maunder Minimum. It is also known as "The Little Ice Age."
In Great Britain and the Netherlands, canals and rivers froze deeply enough for people to ice skate on them, and festivals took place on the rivers themselves. On England's frozen Thames River, the first "frost fair" took place in 1608, and the last took place in 1814.
A 2010 study looked at temperature records going all the way back to 1659, which are contained within the Central England Temperature record. The scientists found that "Average solar activity has declined rapidly since 1985 and cosmogenic isotopes suggest an 8% chance of a return to Maunder minimum conditions within the next 50 years."
A surprising conclusion of a 2002 study was that the Sun's surface rotation slowed during the deepest part of the Maunder Minimum, which was the winter of 1683-1684. This is the coldest winter on record according to the Central England Temperature record.
The Sun's radiance also varies with the solar cycle. The solar luminosity is 0.07% higher during the solar maximum than it is during the solar minimum. The ratio of ultraviolet to visible light varies.
Predictions for solar cycle #25 made by the National Oceanic and Atmospheric Administration's (NOAA) Space Weather Prediction Center (SWPC), NASA and the International Solar Energy Society (ISES) anticipate a deep minimum, and a maximum that will occur between the years 2023 and 2026. During that maximum, they predict the Sun will have between 95 and 130 sunspots.
A bad space weather day
The Sun's magnetic field gives structure to its corona. This is the outermost part of the Sun's atmosphere which can only be seen during solar eclipses.
When there are disruptions in the Sun's magnetic field, coronal mass ejections (CMEs) can occur. These send ultraviolet and X-ray radiation and energetic particles towards Earth where they can have a serious impact on Earth's upper atmosphere. Today, this is called "space weather".
The high energy particles can be dangerous for astronauts who are outside of Earth's protective magnetic field. NASA designs for future Mars missions include a radiation "storm shelter" where astronauts can ride out a space weather storm.
CMEs are 50 times more frequent during solar maxima than they are during solar minima. An exception to this rule occured during December 2006, which was near to the solar minimum, when one of the brightest CMEs on record occured on December 5, 2006.
The new solar cycle, #25, officially starts in 2020, and will reach its maximum sometime in 2025.