Its recent turmoil is particularly newsworthy because the Sun was very quiet for an unusually long time. Astronomers had a tough time explaining the extended solar minimum. New computer simulations imply that the Sun's long quiet spell resulted from changing flows of hot plasma within it.
"The Sun contains huge rivers of plasma similar to Earth's ocean currents," says Andres Munoz-Jaramillo, a visiting research fellow at the Harvard-Smithsonian Center for Astrophysics (CfA). "Those plasma rivers affect solar activity in ways we're just beginning to understand."
The Sun is made of a fourth state of matter - plasma, in which negative electrons and positive ions flow freely. Flowing plasma creates magnetic fields, which lie at the core of solar activity like flares, eruptions, and sunspots.
Astronomers have known for decades that the Sun's activity rises and falls in a cycle that lasts 11 years on average. At its most active, called solar maximum, dark sunspots dot the Sun's surface and frequent eruptions send billions of tons of hot plasma into space. If the plasma hits Earth, it can disrupt communications and electrical grids and short out satellites.
During solar minimum, the Sun calms down and both sunspots and eruptions are rare. The effects on Earth, while less dramatic, are still significant. For example, Earth's outer atmosphere shrinks closer to the surface, meaning there is less drag on orbiting space junk. Also, the solar wind that blows through the solar system (and its associated magnetic field) weakens, allowing more cosmic rays to reach us from interstellar space.
The most recent solar minimum had an unusually long number of spotless days: 780 days during 2008-2010. In a typical solar minimum, the Sun goes spot-free for about 300 days, making the last minimum the longest since 1913.
"The last solar minimum had two key characteristics: a long period of no sunspots and a weak polar magnetic field," explains Munoz-Jaramillo. (A polar magnetic field is the magnetic field at the Sun's north and south poles.) "We have to explain both factors if we want to understand the solar minimum."
To study the problem, Munoz-Jaramillo used computer simulations to model the Sun's behavior over 210 activity cycles spanning some 2,000 years. He specifically looked at the role of the plasma rivers that circulate from the Sun's equator to higher latitudes. These currents flow much like Earth's ocean currents: rising at the equator, streaming toward the poles, then sinking and flowing back to the equator. At a typical speed of 40 miles per hour, it takes about 11 years to make one loop.
Munoz-Jaramillo and his colleagues discovered that the Sun's plasma rivers speed up and slow down like a malfunctioning conveyor belt. They find that a faster flow during the first half of the solar cycle, followed by a slower flow in the second half of the cycle, can lead to an extended solar minimum. The cause of the speed-up and slowdown likely involves a complicated feedback between the plasma flow and solar magnetic fields.
"It's like a production line - a slowdown puts 'distance' between the end of the last solar cycle and the start of the new one," says Munoz-Jaramillo.
The ultimate goal of studies like this is to predict upcoming solar maxima and minima - both their strength and timing. The team focused on simulating solar minima, and say that they can't forecast the next solar minimum (which is expected to occur in 2019) just yet.
"We can't predict how the flow of these plasma rivers will change," explains lead author Dibyendu Nandy (Indian Institute of Science Education and Research, Kolkata). "Instead, once we see how the flow is changing, we can predict the consequences."
Christine Pulliam | EurekAlert!
A quantum walk of photons
24.05.2017 | Julius-Maximilians-Universität Würzburg
Scientists propose synestia, a new type of planetary object
23.05.2017 | University of California - Davis
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.
In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...
23.05.2017 | Event News
22.05.2017 | Event News
17.05.2017 | Event News
24.05.2017 | Earth Sciences
24.05.2017 | Life Sciences
24.05.2017 | Life Sciences