Posts Tagged ‘solar wind’

A New View Of The Solar System: Astrophysical Jets Driven By The Sun

February 19, 2015 Leave a comment

As the sun skims through the galaxy, it flings out charged particles in a stream of plasma called the solar wind, and the solar wind creates a bubble extending far outside the solar system known as the heliosphere. For decades, scientists have visualized the heliosphere as shaped like a comet, with a very long tail extending thousands of times as far as the distance from the Earth to the sun.

New research suggests that the sun’s magnetic field controls the large-scale shape of the heliosphere “much more than had been previously thought,” says Merav Opher, associate professor of astronomy and director of the Center for Space Physics at Boston University (BU). In the new model, the magnetic field squeezes the solar wind along the sun’s North and South axes, producing two jets that are then dragged downstream by the flow of the interstellar medium through which the heliosphere moves.

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Origin Of High-Latitude Auroras Revealed

December 18, 2014 Leave a comment

Auroras are the most visible manifestation of the Sun’s effect on Earth, but many aspects of these spectacular displays are still poorly understood. Thanks to ESA’s Cluster and NASA’s Image satellites working together, a particular type of very high-latitude aurora has now been explained.

Although separated by some 150 million kilometres, the Sun and Earth are connected by the solar wind. This stream of plasma – electrically charged atomic particles – is launched by the Sun and travels across the Solar System, carrying its own magnetic field with it.

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NASA Deciphering The Mysterious Math Of The Solar Wind

February 28, 2013 Leave a comment

Many areas of scientific research — Earth’s weather, ocean currents, the outpouring of magnetic energy from the sun — require mapping out the large scale features of a complex system and its intricate details simultaneously.

Describing such systems accurately, relies on numerous kinds of input, beginning with observations of the system, incorporating mathematical equations to approximate those observations, running computer simulations to attempt to replicate observations, and cycling back through all the steps to refine and improve the models until they jibe with what’s seen. Ultimately, the models successfully help scientists describe, and even predict, how the system works.

Understanding the sun and how the material and energy it sends out affects the solar system is crucial, since it creates a dynamic space weather system that can disrupt human technology in space such as communications and global positioning system (GPS) satellites.

However, the sun and its prodigious stream of solar particles, called the solar wind, can be particularly tricky to model since as the material streams to the outer reaches of the solar system it carries along its own magnetic fields. The magnetic forces add an extra set of laws to incorporate when trying to determine what’s governing the movement. Indeed, until now, equations for certain aspects of the solar wind have never been successfully devised to correlate to the observations seen by instruments in space. Now, for the first time, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., has created a set of the necessary equations, published in Physical Review Letters on Dec. 4, 2012.

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Cassini Sheds Light On Cosmic Particle Accelerators

February 21, 2013 Leave a comment

During a chance encounter with an unusually strong blast of solar wind arriving at Saturn, the international Cassini spacecraft detected particles being accelerated to ultra-high energies, similar to the acceleration that takes place around supernova explosions.

Shock waves are commonplace in the Universe, for example in the aftermath of a stellar explosion as debris accelerates outwards in a supernova remnant, or when the flow of particles from the Sun – the solar wind – impinges on the magnetic field of a planet to form a bow shock.

Under certain magnetic field orientations and depending on the strength of the shock, particles can be accelerated to close to the speed of light at these boundaries. Indeed, very strong shocks at young supernova remnants are known to boost electrons to ultra-relativistic energies, and may be the dominant source of cosmic rays, high-energy particles that pervade our Galaxy.

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When A Planet Behaves Like A Comet

February 6, 2013 Leave a comment

A comparison of the ionosphere of Venus under different solar wind conditions. Credit: ESA/Wei et al. (2012)

A comparison of the ionosphere of Venus under different solar wind conditions. Credit: ESA/Wei et al. (2012)

ESA’s Venus Express has made unique observations of Venus during a period of reduced solar wind pressure, discovering that the planet’s ionosphere balloons out like a comet’s tail on its nightside. The ionosphere is a region of weakly electrically charged gas high above the main body of a planet’s atmosphere. Its shape and density are partly controlled by the internal magnetic field of the planet.

For Earth, which has a strong magnetic field, the ionosphere is relatively stable under a range of solar wind conditions. By comparison, Venus does not have its own internal magnetic field and relies instead on interactions with the solar wind to shape its ionosphere. The extent to which this shaping depends on the strength of the solar wind has been controversial, but new results from Venus Express reveal for the first time the effect of a very low solar wind pressure on the ionosphere of an unmagnetised planet.

As this significantly reduced solar wind hit Venus, Venus Express saw the planet’s ionosphere balloon outwards on the planet’s ‘downwind’ nightside, much like the shape of the ion tail seen streaming from a comet under similar conditions.

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The Solar Wind Is Swirly

December 22, 2012 Leave a comment

Using ESA’s Cluster quartet of satellites as a space plasma microscope, scientists have zoomed in on the solar wind to reveal the finest detail yet, finding tiny turbulent swirls that could play a big role in heating it. Turbulence is highly complex and all around us, evident in water flowing from a tap, around an aircraft wing, in experimental fusion reactors on Earth, and also in space.

In the stream of charged particles emitted by the Sun – the solar wind – turbulence is thought to play a key part in maintaining its heat as it streams away and races across the Solar System. As the solar wind expands, it cools down, but to a much smaller extent than would be expected if the flow were smooth.

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Solor Storms Can Destabilize Power Grids At Midlatitudes

August 31, 2012 Leave a comment

The Sun is capable of disrupting electrical systems on Earth in a variety of ways, from solar flares and coronal mass ejections to proton storms. Typically, it is only objects far above the Earth’s surface, or systems at high altitudes at polar latitudes, that are considered at risk except during the most powerful storms. Notable recent examples include solar activity during March 1989 and October 2003 (the “Halloween Storms”), which knocked out power in Quebec, Canada, and Sweden, respectively. Research by Marshall et al., however, finds that even a moderate event can have destructive effects far from the typical regions of concern.

At 1:20 UT on 6 November 2001, a high-density pocket of solar wind, 18 nanoPascals above the background pressure, sped past the Solar and Heliospheric Observatory (SOHO) satellite, which was orbiting 197 Earth radii above the Earth toward the Sun. In half an hour, this high-pressure wave traveled more than a million kilometers (620,000 miles) to the Earth’s magnetopause. The high-pressure pulse induced currents both in the magnetopause and in power lines across New Zealand, causing alarms to be tripped and a transformer to fail catastrophically. Extending from 35 degrees South to 46 degrees South, New Zealand is typically considered outside the region susceptible to such solar activity. A Northern Hemisphere equivalent would be a zone extending from Maine to North Carolina. The authors find currents of up to 27.4 amperes in transformer earth lines that were supposed to be neutral. For comparison, the Halloween Storms 2 years later caused peak currents of 23.4 amperes and no serious damage, though the authors suggest that this may have been due to damage prevention measures implemented following the 2001 event.

Source: Space Weather

Magnetic Turbulence Trumps Collisions To Heat Solar Wind

August 17, 2012 Leave a comment

New research led by University of Warwick physicist Dr Kareem Osman has provided significant insight into how the solar wind heats up when it should not. The solar wind rushes outwards from the raging inferno that is our Sun, but from then on the wind should only get cooler as it expands beyond our solar system since there are no particle collisions to dissipate energy. However, the solar wind is surprisingly hotter than it should be, which has puzzled scientists for decades. Two new research papers led by Dr Osman may have solved that puzzle.

The new research led by Dr. Kareem Osman at the University of Warwick’s Centre for Fusion, Space and Astrophysics has revealed how turbulence heats the solar wind. He says:

“Turbulence stretches and bends magnetic field lines, and often two oppositely directed field lines can come together to form a current sheet. These current sheets, which are distributed randomly in space, could be sites where the magnetic field snaps and reconnects transferring energy to particle heating. There are also many more ways that current sheets can heat and accelerate the plasma.”

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Shear Layers In Solar Winds Affect Earth’s Magnetosphere

Human society is increasingly reliant on technology that can be disrupted by space weather. For instance, geomagnetic storms can cause high-latitude air flights to be rerouted, costing as much as $100,000 per flight; induce errors of up to 46 meters (151 feet) in GPS systems; and affect satellites and the International Space Station. Space weather is determined by how the solar wind, a stream of hot plasma from the Sun, interacts with Earth’s magnetic field. In studying space weather, scientists have largely neglected the fact that the solar wind contains layers of very strong velocity shear. Scientists understand very little about how these wind shears affect space weather.

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Electric Moon Jolts The Solar Wind

With the moon as the most prominent object in the night sky and a major source of an invisible pull that creates ocean tides, many ancient cultures thought it could also affect our health or state of mind – the word “lunacy” has its origin in this belief. Now, a powerful combination of spacecraft and computer simulations is revealing that the moon does indeed have a far-reaching, invisible influence – not on us, but on the Sun, or more specifically, the solar wind.

Unlike Earth, the moon is not surrounded by a global magnetic field. “It was thought that the solar wind crashes into the lunar surface without any warning or ‘push back’ on the solar wind,” says Dr. Andrew Poppe of the University of California, Berkeley. Recently, however, an international fleet of lunar-orbiting spacecraft has detected signs of the moon’s presence “upstream” in the solar wind. “We’ve seen electron beams and ion fountains over the moon’s day side,” says Dr. Jasper Halekas, also of the University of California, Berkeley.

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