7:15 AM | *The solar minimum and an increase in volcanic activity*

Taal Volcano, near Manila, erupted on January 12, 2020 and sent an ash plume an estimated 6-9 miles high disrupting hundreds of flights in Manila. Image Credit: Kenji Cheow / Facebook from Anilao, Batangas

Overview

Over the long term, the sun is the main driver of weather and climate on Earth and it is also connected to such phenomenon as the aurora borealis also known as the northern lights, upper atmospheric high-latitude blocking, and the influx of cosmic rays into Earth’s atmosphere.  The aurora borealis tends to occur more often during times of increased solar activity though they can actually take place at any time of a solar cycle.  On the other hand, there is a tendency for more frequent high-latitude blocking events in the atmosphere during periods of low solar activity and these episodes can play an important role in winter weather conditions across the central and eastern US. The influx of cosmic rays into the Earth’s atmosphere from outer space tends to increase dramatically during solar minimums which we are experiencing at the current time.  Interestingly, there is evidence that solar activity plays a role in volcanic activity on our planet.  In fact, in times of low solar activity such as during the current solar minimum, volcanic activity tends to rise. Indeed, there has been a significant amount of volcanic activity in recent weeks including the latest eruption in the Philippines.  

In this time-series animation captured by Japan's Himawari-8 satellite, the volcanic plume from the Taal eruption can be seen spreading on Jan. 12 and Jan. 13, 2020. (Image credit: NASA Earth Observatory)

Consequences of a solar minimum

Solar minimum is a normal part of the 11-year sunspot cycle, but the last one and the current one have been far deeper than most. In fact, the number of spotless days in 2019 reached 281 days (77% of the time) and this was the quietest year in terms of sunspots since 1913.  The just ended solar cycle 24 turned out to be one of the weakest in more than a century – continuing a weakening trend that began in the 1980’s – and, if the latest forecasts are correct, the next solar cycle will be the weakest in more than 200 years.

One of the consequences of a solar minimum is a tendency for increased “high-latitude blocking” events in the atmosphere during the wintertime with higher pressure compared to normal over such places as Greenland, Iceland and northern Canada.  This type of atmospheric pattern often results in more numerous and longer-lasting cold air outbreaks for the central and eastern US in the winter season. (see Perspecta Weather Winter Outlook) and can increase the chances for significant snow. 

This graph shows the annual count of sunspots from 1610 to 2000. Sunspot cycles average 11 years in length and there were extended periods of low solar activity during the Maunder and Dalton minima. Courtesy of Tom Ford.Data courtesy of David Hathaway (NASA/MSFC).

Another consequence of a solar minimum is a weakening of the ambient solar wind and its magnetic field which, in turn, allows more and more cosmic rays to penetrate the solar system. Galactic cosmic rays are high-energy particles originating from outside the solar system that can impact the Earth’s atmosphere. Our first line of defense from cosmic rays comes from the sun as its magnetic field and the solar wind combine to create a 'shield' that fends off cosmic rays attempting to enter the solar system. The shielding action of the sun is strongest during solar maximum and weakest during solar minimum with the weakening magnetic field and solar wind. The intensity of cosmic rays varies globally by about 15% over a solar cycle because of changes in the strength of the solar wind, which carries a weak magnetic field into the heliosphere, partially shielding Earth from low-energy galactic charged particles.

Sakurajima (Kyushu, Japan): MODIS satellite imagery shows a volcanic ash plume over Japan on 1/10/20 that rose up to estimated 8000 feet. Image Credit: NASA

In addition to the impact on the phenomena cited above, studies (e.g., paper 1) have shown a correlation between solar activity and volcanic activity here on Earth. Volcanic activity in the past has been compared to annual sunspot numbers and it has been found that there is a reduction during periods of prolonged maxima of solar activity and an increase in times of solar minimum. The exact relationship between solar activity and volcanic activity is still not clear and there are numerous theories. 

From his Monticello home in Virginia, Thomas Jefferson recorded the severe weather of 1816 in his weather diary. Jefferson was just one of many observers who recorded unusually cold weather during the summer of 1816. The unusual weather was not confined to eastern North America as there was strange weather recorded all over the world. The cold and rainy summer in Switzerland even inspired Mary Wollstonecraft Shelley to begin the novel “Frankenstein”. Courtesy of the Jefferson papers, Manuscript Division, Library of Congress, Gerard W. Gawalt. Source: “Year without a Summer”

One publication connects the Tambora volcanic eruption in Indonesia during April 1815 to the unusually long period of low solar activity known as the Dalton Minimum (c. 1795-1823). The following year of 1816 was unusually cold throughout much of the world and it is now referred to as the “year without a summer”. Another study suggests that the increase in cosmic rays during times of low solar activity actually causes and increase in volcanic activity.  Another theory suggests that solar flares may cause changes in atmospheric circulation patterns that abruptly alter the Earth's spin. The resulting jolt probably triggers small earthquakes which may temporarily relieve some of the stress in volcanic magma chambers, thereby weakening, postponing, or even aborting imminent large eruptions.

Dukono, North Maluku, Indonesia: MODIS satellite imagery shows a volcanic ash plume over Indonesia on 12/29/19 that rose up to estimated 7000 feet. Image Credit: NASA

Volcanic activity is critical with respect to climate as eruptions can bring a large amount of dust and gas into the atmosphere – especially at high levels – and this can impact solar irradiance levels on Earth for many months. In fact, after large volcanic eruptions, a decrease of the average surface temperature has followed usually lasting 1-3 years.  

Recent volcanic activity

Forty-three years after its last eruption, the Taal volcano in the Philippines roared back to life on January 12th, 2020 and sent steam, ash and pebbles 9 miles high. Lava gushed from the volcano and forced villagers to flee and resulted in a shut-down of Manila’s international airport. Clouds of ash blew more than 60 miles to the north reaching the capital of Manila. Taal underwent frequent eruptions in the mid-1960’s and then again in 1977 (both solar minimum time periods). In 2006, 2008, 2010 and 2011, the volcano periodically trembled with earthquakes and occasionally showed increased hydrothermal activity (superhot liquids seeping to the surface), all reminders that Taal remained an active volcano.

The capital of the Philippines, Manila, is some 60 miles to the north of the Taal volcano. Source: Google Maps

Elsewhere, Puerto Rico has experienced more than 1000 earthquakes just since the beginning of 2020 with the most recent being registered as a 5.9 quake on the island’s southern coast.  Meanwhile, in South America, the Sabancaya volcano in Peru has erupted and sent an ash plume several miles up into the atmosphere. And in Mexico, the Popcatepetl volcano burst to life on Thursday, January 9th in a spectacular gush of lava and clouds of ash that hurled incandescent rock about 20,000 feet into the sky.  This active stratovolcano in Mexico is about 40 miles to the southeast of Mexico City.

Stay tuned…the current solar minimum likely has many more months to go before solar activity begins to pick up on a consistent basis and we’ll continue to monitor potential volcanic activity around the world.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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