Mini-flares observed on sun’s surface in a relatively quiet solar cycle


COLUMBUS (WCMH) — The recent high–resolution images of miniature solar flares taken by a European Space Agency and NASA spacecraft, Solar Orbiter, captured the tiny eruptions for the first time.

“This is an exciting result,” said Robert Harmon, Chair of the Deptartment of Physics and Astronomy at Ohio Wesleyan University, who was not involved in this research. “The energy released by these miniature flares may help to solve the mystery of how the Sun’s outer atmosphere, the corona, is heated to millions of degrees.”

Solar Orbiter captures ‘campfires’ on the surface of the sun (white arrows).
Credits: Solar Orbiter/EUI Team (ESA & NASA); CSL, IAS, MPS, PMOD/WRC, ROB, UCL/MSSL

Solar Orbiter launched Feb. 9 took images of the mini-flares when it was a little more than 48 million miles from the solar surface, a little more than half the distance from Earth. During the next year and half, the spacecraft will pass by Venus and Earth to use their gravity to alter its orbit, in order to get an even closer view, and ultimately pass within 26.1 million miles of the Sun, Harmon said.

The sun has been in a quieter phase during the past decade, if you count the number of sunspots. Don Stevens, director of Perkins Observatory at Ohio Wesleyan University, said the number of spotless days on the sun this year (74 percent as of July 22) is not especially significant.

“It takes a couple of years for the cycle to ramp up from minimum. I suspect later this year we’ll see sunspot activity increase. From what I have seen from models, we should still get an average maximum in the coming cycle,” Stevens said.

Sunspot cycles average 11 years from a minimum to maximum and back to a minimum. Currently we are near the minimum between Solar Cycles 24 and 25. Cycle 24 had the weakest solar maximum (2013) in a century. Sunspots are dark, cool patches on the sun estimated to be about 3,300 degrees Fahrenheit cooler than the sun’s outer surface, or photosphere, where the temperature is near 10,000 degrees.

During a solar minimum, the sun’s brightness dims slightly, based on 140 years of observations. The virtual disappearance of sunspots viewed through early telescopes between 1645 and 1715, known as the Maunder Minimum, coincided with the Little Ice Age in northern Europe and parts of North America.

The relationship between sunspots and the total solar output have intrigued scientists for centuries. Even though more sunspots would suggest a cooler solar surface, faculae, or bright hot spots, begin to appear around the edge (limb) of the solar disk. Numerous sunspots are associated with solar flares that unleash high-speed bursts of X-rays and charged particles into space.

Sunspots develop when lines of magnetic field become twisted and poke through the surface. Harmon, whose research involves studying “starspots” on other stars, noted that observations bear this out. “Stars similar to the Sun but younger tend to have much larger spots on them than our Sun does, because they have much stronger magnetic fields.”

One of the benefits of a geomagnetic storm is viewing stunning auroras mostly confined to higher latitudes–the northern and southern lights–following a coronal mass ejection (CME), which disturbs Earth’s magnetic field about 24 to 36 hours after the eruption. CMEs contain a substantial emission of plasma from the solar corona carried through space by the solar wind at speeds of about 1 million mph.

A large CME can damage the electronics blow out transformers causing widespread power outages. “In 2012, there was a very large CME that if it had hit Earth would have caused trillions of dollars in damage, and it would have taken months to years to pick up the pieces, Harmon said. “A better understanding of the Sun’s magnetic activity is crucial to helping us prepare for future events.”

Solar maxima bring high levels of ultraviolet radiation, warming the top of Earth’s atmosphere and exerting a drag on the International Space Station and satellites. Greater heating of the stratosphere is linked to the development of large waves that propagate through Earth’s atmosphere, which has an impact on storm tracks (high-altitude jet stream winds) and weather patterns.

During a solar minimum, increased galactic cosmic rays bombard the solar system, which raises the risk of cancer for astronauts. A decrease in solar ultraviolet radiation causes Earth’s upper atmosphere to cool and contract. Model data suggest the Sun’s magnetic activity was far greater 500 million or more years ago.

Total solar irradiance (TSI), which measures the solar energy output over all wavelengths striking Earth’s upper atmosphere, has been observed to dip 0.1 to 0.2 percent during a sunspot minimum. However, the decrease in ultraviolet radiation is more substantial.

2020 total: 153 days (74%)
2019 total: 281 days (77%)
2018 total: 221 days (61%)
2017 total: 104 days (28%)
2016 total: 32 days (9%)
2015 total: 0 days (0%)
2014 total: 1 day (<1%)
2013 total: 0 days (0%)
2012 total: 0 days (0%)
2011 total: 2 days (<1%)
2010 total: 51 days (14%)
2009 total: 260 days (71%)
2008 total: 268 days (73%)
2007 total: 152 days (42%)
2006 total: 70 days (19%)

Spotless Days (annual percent)

Updated 22 July 2020

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