Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cluster spacecraft catch crashing waves in Earth’s magnetic bubble

12.08.2004


A bevy of satellites buzzing around in the Earth’s magnetosphere has found at least part of the answer to a long-standing puzzle about the source of the charged particles that feed the aurora.


Three-dimensional computer simulation of the space waves or vortices that inject the solar wind plasma into the Earth’s magnetic field. Green-blue areas represent the solar wind plasma, and red-orange areas represent plasma trapped in Earth’s magnetic field. Earth’s magnetosphere develops ripples and folds like a flag in the wind as the solar wind blows past. This turbulence creates rolling waves on the edges of the magnetosphere that engulf the solar wind into the magnetosphere (see orange wavelike structure in the cut-away portion of the image). The blue, green and orange swirl behind the wave is the vortex that mixes the solar wind into the magnetosphere. The vortices are huge structures, measuring more than 20,000 miles across. (Kentaro Tanaka of Tokyo Institute of Technology)



The charged particles come from explosions on the sun and smash into the Earth’s magnetic field, which repels the bulk of them. But many slip through, often via a physical process called magnetic reconnection, where the magnetic field traveling with the particles breaks and reconnects with the Earth’s field, opening a window for the particles to surge through. Once inside, these excited particles can spiral down toward the poles and create brilliant auroras when they hit the atmosphere.

But magnetic reconnection happens only when the solar wind’s magnetic field direction is 180 degrees opposite from that of the magnetic field of the Earth. When the two fields are aligned, there is no obvious physical process allowing entry of charged particles, at least at the leading edge of the Earth’s magnetosphere.


Three years ago, however, the four satellites of the Cluster mission, operated by the European Space Agency (ESA), passed through the tail of the Earth’s magnetic field, which stretches hundreds of thousands of miles in the shadow of the Earth, and observed a new process that could allow entry of the solar wind particles.

The satellite data revealed eddies and vortices in Earth’s magnetosphere. These waves are kicked up by the solar wind as it blows past the magnetosphere. If these vortices, called non-linear Kelvin-Helmholtz waves, detach and spin off into Earth’s magnetosphere, they could carry charged particles from the solar wind inside - enough to explain the hot, magnetically charged gas, or plasma, stored inside the tail of Earth’s field.

"The Kelvin-Helmholtz instability has often been ignored as an important solar wind entry process," said Tai Phan, a space physicist at the University of California, Berkeley’s Space Sciences Laboratory and a co-author of the paper. "Thanks to its multi-spacecraft measurements, Cluster has now proven the existence of these large-scale vortices that could lead to substantial entry of solar wind to populate the Earth’s magnetosphere."

Phan, lead-author Hiroshi Hasegawa of Dartmouth College, New Hampshire, and their colleagues in Japan and Europe report their conclusions in the Aug. 12 issue of Nature.

A solar wind of charged particles blows incessantly past the Earth, compressing its magnetic field and pulling it into a teardrop shape pointing away from the sun. Periodic solar storms pump up the wind and send more particles toward Earth, which create atmospheric disturbances - auroras, magnetic storms, and radiation belt storms - that can affect satellites as well as radio communications. The goal of the Cluster mission and numerous other Earth satellites is to understand how space weather affects the Earth environment.

One big question is how these charged particles penetrate the protective magnetic field and fill up the magnetic bubble around Earth, and what triggers these particles to suddenly flame down onto the poles, creating colorful auroras. Magnetic reconnection explains the entry of charged particles when the solar wind magnetic field is anti-parallel to the Earth’s field, but when the fields are parallel, they should present an impenetrable barrier to this flow. Spacecraft measurements dating to 1987 clearly show, however, that the magnetosphere is three to five times fuller when the fields are aligned than when they are not. So how is the solar wind getting in?

Part of the answer came on Nov. 20, 2001, when the Cluster flotilla was heading around from behind the Earth and had just arrived at the dusk side of the planet, where the solar wind slides past the Earth’s magnetosphere. There it began to encounter gigantic vortices of gas at the magnetopause, the outer edge of the magnetosphere.

"People have seen waves on the surface of the magnetosphere, but they couldn’t tell if they were small ripples or crashing, rolling waves," Phan said. "You have to have big vortices to get the solar wind inside."

"These vortices were really huge structures, about six Earth radii across," said Hasegawa. The team’s results place the size of the vortices at almost 40,000 kilometers each.

These vortices are products of non-linear Kelvin-Helmholtz instability, which occur when two adjacent flows travel past each other at different speeds and the friction between them kicks up eddies and vortices. Examples of such instabilities are the waves whipped up by the wind slipping across the surface of the ocean. When a KHI-wave rolls up into a vortex, it becomes known as a "Kelvin Cat’s eye." The data collected by Cluster have shown density variations of the electrified gas at the magnetopause precisely like those expected when traveling through a Kelvin Cat’s eye.

Scientists had postulated that, if these structures were to form at the magnetopause, they might be able to pull large quantities of the solar wind inside the magnetosphere as they collapse. Once the solar wind particles are carried into the inner part of the magnetosphere, they can be excited strongly, allowing them to smash into the Earth’s atmosphere and give rise to the auroras.

Cluster’s discovery strengthens this scenario but does not show the precise mechanism by which the gas is transported into the Earth’s magnetic bubble. Thus, scientists still do not know whether this is the only process to fill up the magnetosphere when the magnetic fields are aligned. For those measurements, Hasegawa said, scientists will have to wait for a future generation of magnetospheric satellites.

Phan, in fact, suspects there are other mechanisms that allow entry of solar wind particles when the solar wind and Earth’s field’s are parallel. Detection last year by UC Berkeley scientists of a proton aurora over the Earth’s poles may indicate that magnetic reconnection around the Earth’s polar regions, instead of at the bow of the magnetosphere, can allow particles in.

The Cluster satellites, built by ESA with significant participation from the National Aeronautics and Space Administration, were launched in summer 2000. The Cluster mission investigates three-dimensional structures throughout the Earth’s magnetosphere and solar wind. NASA supports U.S.-based researchers associated with the mission.

"These multi-point, high time-resolution observations open a new window into understanding the connection of the solar wind to the Earth’s magnetosphere," said William Peterson, NASA’s geospace program scientist.

Coauthors, in addition to Hasegawa and Phan, are Masaki Fujimoto, Henri Rème, Andre Balogh, Malcolm W. Dunlop and graduate students C. Hashimoto and R. TanDokoro.

Robert Sanders | EurekAlert!
Further information:
http://www.berkeley.edu
http://www.esa.int

More articles from Physics and Astronomy:

nachricht New NASA study improves search for habitable worlds
20.10.2017 | NASA/Goddard Space Flight Center

nachricht Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>