Synopsis: Solar Down Time

A theoretical model of sunspots shows that their occasional disappearance may be due to a combination of fluctuations in the Sun’s polar magnetic field and outer layer flows.
Synopsis figure
NASA/Solar Dynamics Laboratory

Our Sun takes a break every half-millennium or so from its usual cycle of sunspot activity. These so-called “grand minima” may influence the Earth’s climate, as evidenced by a cold spell during the Maunder minimum (1645-1715). Scientists would therefore like to know more about the physics underlying these sunspot variations. A new theoretical analysis assumes that grand minima originate from fluctuations of the Sun’s magnetic field and circulation in its outer layers. The model, reported in Physical Review Letters, correctly matches the estimated occurrence of minima in the past.

A sunspot is a temporary dark region on the Sun’s surface, which results from a concentration of magnetic flux. Astronomical observations show that a drop in sunspot numbers comes with a decrease in solar brightness and solar flare counts. Typically, the number of sunspots falls and rises in an 11-year cycle, but sometimes sunspots disappear for several decades at a time. Studies of atmospheric isotopes estimate that our Sun experienced 27 grand minima in the last 11,000 years.

Previous work suggested that a grand minimum may be triggered by weakening in the Sun’s magnetic field and circulation. To study this further, Arnab Choudhuri and Bidya Karak of the Indian Institute of Science in Bangalore, India, started with a solar dynamo model that reproduces much of sunspot behavior. They then introduced observationally-inspired random fluctuations in both the amplitude of the polar magnetic field and the speed of meridional flows in the Sun’s outer layers. The model was consistent with data, predicting 24 to 30 grand minima over 11,000 years. – Michael Schirber


Announcements

More Announcements »

Subject Areas

Astrophysics

Previous Synopsis

Biological Physics

Protein Shells Take a Strength Test

Read More »

Next Synopsis

Related Articles

Synopsis: Did Black Hole “Mimickers” Produce LIGO Signal?
Astrophysics

Synopsis: Did Black Hole “Mimickers” Produce LIGO Signal?

Recently detected gravitational waves might not be a signature of black holes but of other massive objects that lack an event horizon. Read More »

Synopsis: Blazar Tally
Astrophysics

Synopsis: Blazar Tally

Researchers estimate that blazars produce 86% of the extragalactic gamma-ray background. Read More »

Synopsis: Supernova Footprint on the Moon
Astrophysics

Synopsis: Supernova Footprint on the Moon

Lunar soil samples reveal an unusually high level of radioactive iron, which suggests a supernova in our vicinity within the last few million years. Read More »

More Articles