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


Features

More Features »

Announcements

More Announcements »

Subject Areas

Astrophysics

Previous Synopsis

Biological Physics

Protein Shells Take a Strength Test

Read More »

Next Synopsis

Related Articles

Viewpoint: Neutron Star Merger Seen and Heard
Cosmology

Viewpoint: Neutron Star Merger Seen and Heard

For the first time, researchers have detected both light and gravitational waves from the same event in space. Read More »

Synopsis: Self-Interacting Dark Matter Scores Again
Cosmology

Synopsis: Self-Interacting Dark Matter Scores Again

Dark matter that interacts with itself provides a better description of the speeds of stars in galaxies than dark matter that doesn’t self-interact. Read More »

Synopsis: Searching for Neutron Star Gravitational Waves
Astrophysics

Synopsis: Searching for Neutron Star Gravitational Waves

The first run of LIGO and Virgo’s gravitational-wave search shows no evidence of spinning asymmetric neutron stars, but recent upgrades could make the detection possible. Read More »

More Articles