Solar winds: New research deepens understanding of Earth’s interaction with the solar wind

Before we dive into the story in full, lets understand what a solar wind is, its causes and effects.

What is a solar wind

The solar wind is a stream of energized, charged particles, primarily electrons and protons, flowing outward from the Sun, through the solar system at speeds as high as 900 km/s and at a temperature of 1 million degrees (Celsius). It is made of plasma.

What is the solar wind made of

The solar wind is a collection of streams of energetic particles that originate on the Sun. You can think of the particles of the solar wind as nothing less than the solar corona itself. This is because the distant corona expands outwards due to not enough restraining force from gravity, or from the pressure of the interstellar gas, to confine the distant corona.

The solar wind escapes through the coronal holes at supersonic speeds. As the outer corona disperses, it must be replaced by gases welling up from below (lower corona).

The composition of the solar wind is a mixture of materials found in the solar plasma, composed of ionized hydrogen (electrons and protons) with an 8% component of helium (alpha particles) and trace amounts of heavy ions and atomic nuclei: C, N, O, Ne, Mg, Si, S, and Fe ripped apart by heating of the Sun’s outer atmosphere, that is, the corona.

SOHO also identified traces of some elements for the first time such as P, Ti, Cr and Ni and an assortment of solar wind isotopes identified for the first time: Fe 54 and 56; Ni 58,60,62.

Note that although the solar wind is electrically balanced, the solar wind consists almost exclusively of charged particles (stripped away nuclei from atoms) and is an excellent electrical conductor. These electrically conducting particles is technically known as a plasma, so it may be misleading to think of the solar wind as like Earth “winds”.

What causes the solar wind

The solar wind is caused by the hot solar corona, which is the outermost layer of the solar atmosphere, expanding into space. The corona is the “rim” of the Sun that is visible to the naked eye during a solar eclipse.

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The solar wind is what blows the tails of comets back away from the bodies of comets as they go through the solar system.

What then are the effects of a solar wind

According to NASA

The solar wind impacting Earth’s magnetosphere is responsible for triggering those majestic auroras typically seen at locations close to our north and south poles. In some cases it can also set off space weather storms that disrupt everything from our satellites in space, to ship communications on our oceans, to power grids on land.

Full story

As the Earth orbits the sun, it plows through a stream of fast-moving particles that can interfere with satellites and global positioning systems.

Now, a team of scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and Princeton University has reproduced a process that occurs in space to deepen understanding of what happens when the Earth encounters this solar wind.

The team used computer simulations to model the movement of a jet of plasma, the charged state of matter composed of electrons and atomic nuclei that makes up all the stars in the sky, including our sun. Many cosmic events can produce plasma jets, from relatively small star burps to gigantic stellar explosions known as supernovae.

When fast-moving plasma jets pass through the slower plasma that exists in the void of space, it creates what is known as a collision-less shock wave.

These shocks also occur as Earth moves through the solar wind and can influence how the wind swirls into and around Earth’s magnetosphere, the protective magnetic shield that extends into space.

Understanding plasma shock waves could help scientists to forecast the space weather that develops when the solar wind swirls into the magnetosphere and enable the researchers to protect satellites that allow people to communicate across the globe.

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The simulations revealed several telltale signs indicating when a shock is forming, including the shock’s features, the three stages of the shock’s formation, and phenomena that could be mistaken for a shock.

“By being able to distinguish a shock from other phenomena, scientists can feel confident that what they are seeing in an experiment is what they want to study in space,”

said Derek Schaeffer, an associate research scholar in the Princeton University Department of Astrophysics who led the PPPL research team. The findings were reported in a paper(link is external) published in Physics of Plasmas that followed up on previous research reported here and here.

The plasma shocks that occur in space, like those created by Earth traveling against the solar wind, resemble the shock waves created in Earth’s atmosphere by supersonic jet aircraft. In both occurrences, fast-moving material encounters slow or stationary material and must swiftly change its speed, creating an area of swirls and eddies and turbulence.

But in space, the interactions between fast and slow plasma particles occur without the particles touching one another. “Something else must be driving this shock formation, like the plasma particles electrically attracting or repelling each other,” Schaeffer said. “In any case, the mechanism is not fully understood.”

To increase their understanding, physicists conduct plasma experiments in laboratories to monitor conditions closely and measure them precisely. In contrast, measurements taken by spacecraft cannot be easily repeated and sample only a small region of plasma. Computer simulations then help the physicists interpret their laboratory data.

Today, most laboratory plasma shocks are formed using a mechanism known as a plasma piston. To create the piston, scientists shine a laser on a small target. The laser causes small amounts of the target’s surface to heat up, become a plasma, and move outward through a surrounding, slower-moving plasma.

Schaeffer and colleagues produced their simulation by modeling this process. “Think of a boulder in the middle of fast-moving stream,” Schaeffer said. “The water will come right up to the front of the boulder, but not quite reach it. The transition area between quick motion and zero [standing] motion is the shock.”

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The simulated results will help physicists distinguish an astrophysical plasma shock wave from other conditions that arise in laboratory experiments. “During laser plasma experiments, you might observe lots of heating and compression and think they are signs of a shock,” Schaeffer said. “But we don’t know enough about the beginning stages of a shock to know from theory alone. For these kinds of laser experiments, we have to figure out how to tell the difference between a shock and just the expansion of the laser-driven plasma.”

In the future, the researchers aim to make the simulations more realistic by adding more detail and making the plasma density and temperature less uniform.

They would also like to run experiments to determine whether the phenomena predicted by the simulations can in fact occur in a physical apparatus. “We’d like to put the ideas we talk about in the paper to the test,” says Schaeffer.

Support for this research came from the DOE Office of Science and the National Atmospheric and Space Administration. Simulations were performed on the Titan supercomputer at the Oak Ridge Leadership Computing Facility, a user facility at the DOE’s Oak Ridge National Laboratory.

PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas ultra-hot, charged gases and to developing practical solutions for the creation of fusion energy.

The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science

Sources

Stanford solar centre

Qualitative Reasoning Group Northwestern University

NASA

DOE/Princeton Plasma Physics Laboratory

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