Sunspots, indicative of solar magnetic activity, follow an approximately 11-year cycle but can also experience extended periods of low activity called grand minima. The Maunder Minimum, from 1645 to 1715, is an iconic example of such an anomaly.
To better understand the solar dynamo during this period, researchers like Limei Yan examined Korean historical texts, which offer data on equatorial aurorae and add to the knowledge of the sun's behavior during the Maunder Minimum.
What Is the Maunder Minimum?
The Maunder Minimum, sometimes called the Grand Solar Minimum, denotes a span from 1645 to 1715 during which solar activity significantly dwindled, marked by a notable absence of sunspots. This period of diminished solar output corresponded with a global cooling, commonly termed a "mini ice age."
Nevertheless, NASA points out that this cooling effect might have also been influenced by heightened volcanic activity at the time. While records of sunspots provide some understanding of the Maunder Minimum, numerous aspects of this peculiar period continue to elude scientific comprehension.
Korean Chronicles Reveal Solar Cycles Were Once Shorter Than Normal
The sun typically follows an approximately 11-year solar cycle, transitioning from a minimum phase to a maximum phase and back. Scientists monitor this cycle by tracking the number of sunspots on the sun's surface, which become more frequent leading up to and during the solar maximum.
In a recent study published in AGU Advances, researchers examined historical auroral records from Korea and made an intriguing discovery. They found that during the Maunder Minimum, the solar cycles were notably shorter, averaging around eight years, which is three years shorter than contemporary solar cycles.
These auroral records were derived from three separate chronicles documenting various aspects of Korean history, including royal affairs, state matters, weather observations, and astronomical phenomena spanning from 918 to 1910.
The researchers identified descriptions of "red vapors" or "vapors like firelight" in the astronomical sections of these chronicles. They believe these descriptions referred to the West Pacific Anomaly (WPA), an area above Korea known for producing red auroras even though it's distant from the magnetic poles.
These unique red auroras persisted despite reduced solar activity due to the thinner Earth's magnetic field in this region, making them a valuable proxy for tracking solar cycle progression.
The dates of these red auroras revealed an eight-year solar cycle during the Maunder Minimum. The reasons behind long-term solar cycle variations like the Maunder Minimum remain a mystery, and experts are uncertain about the factors that caused the shortened cycles during that period.
However, these new findings offer crucial insights into understanding this enigmatic epoch more comprehensively, shedding light on long-term solar activity trends. Although recent solar cycles have displayed a slight decrease in activity and variations in cycle length, the current solar cycle's notable activity and rapid approach to solar maximum suggest that a new era of reduced solar activity may not be imminent.
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