Earth’s magnetic field: Observing the Birkeland currents

Plots of AMPERE magnetic perturbations and radial current density from the northern hemisphere for 24 February 2014 with start times from 1530 UT through 1700 UT.

When the supersonic solar wind hits the Earth’s magnetic field, a powerful electrical connection occurs with Earth’s field, generating millions of amperes of current that drive the dazzling auroras.

These so-called Birkeland currents connect the ionosphere to the magnetosphere and channel solar wind energy to Earth’s uppermost atmosphere.

Solar storms release torrential blasts of solar wind that cause much stronger currents and can overload power grids and disrupt communications and navigation.

Now for the first time, scientists are making continuous, global measurements of the Birkeland currents, opening a new window on our understanding of our home planet’s response to solar storms.

Using the Active Magnetosphere and Planetary Electrodynamics Response Experiment, based on the 66 Iridium satellites orbiting the Earth, authors of a Geophysical Research Letters study have discovered that Earth’s response to onsets in forcing from the solar wind occurs in two distinct stages.

Currents first appear near noon in the polar regions and remain steady for about half an hour.

Then the second stage begins, when strong currents appear near midnight and eventually join the initial currents near noon.

Most of the solar wind energy is deposited in the polar atmosphere by processes initiated in the second stage.

The authors note that scientists are working to understand how the delay between the first and second stages could give near-term warning of impending space weather disruptions.

Full Citation: Anderson, B. J., H. Korth, C. L. Waters, D. L. Green, V. G. Merkin, R. J. Barnes, and L. P. Dyrud(2014), "Development of large-scale Birkeland currents determined from the Active Magnetosphere and Planetary Electrodynamics Response Experiment" - Geophys. Res. Lett., 41, 3017–3025, doi:10.1002/2014GL059941.

Plasma Plume protects the Earth against solar storms

The Earth's magnetic field, or magnetosphere, stretches from the planet's core out into space, where it meets the solar wind, a stream of charged particles emitted by the sun. 

For the most part, the magnetosphere acts as a shield to protect the Earth from this high-energy solar activity.

But when this field comes into contact with the sun's magnetic field, a process called "magnetic reconnection," powerful electrical currents from the sun can stream into Earth's atmosphere, whipping up geomagnetic storms and space weather phenomena that can affect high-altitude aircraft, as well as astronauts on the International Space Station.

Now scientists at MIT and NASA have identified a process in the Earth's magnetosphere that reinforces its shielding effect, keeping incoming solar energy at bay.

By combining observations from the ground and in space, the team observed a plume of low-energy plasma particles that essentially hitches a ride along magnetic field lines, streaming from Earth's lower atmosphere up to the point, tens of thousands of kilometers above the surface, where the planet's magnetic field connects with that of the sun.

In this region, which the scientists call the "merging point," the presence of cold, dense plasma slows magnetic reconnection, blunting the sun's effects on Earth.

John Foster

"The Earth's magnetic field protects life on the surface from the full impact of these solar outbursts," says John Foster, associate director of MIT's Haystack Observatory.

"Reconnection strips away some of our magnetic shield and lets energy leak in, giving us large, violent storms."

"These plasmas get pulled into space and slow down the reconnection process, so the impact of the sun on the Earth is less violent."

Foster and his colleagues publish their results in this week's issue of Science.

Philip Erickson

The team includes Philip Erickson, principal research scientist at Haystack Observatory, as well as Brian Walsh and David Sibeck at NASA's Goddard Space Flight Center.

Mapping Earth's magnetic shield
For more than a decade, scientists at Haystack Observatory have studied plasma plume phenomena using a ground-based technique called GPS-TEC, in which scientists analyze radio signals transmitted from GPS satellites to more than 1,000 receivers on the ground.

Large space-weather events, such as geomagnetic storms, can alter the incoming radio waves—a distortion that scientists can use to determine the concentration of plasma particles in the upper atmosphere.

Using this data, they can produce two-dimensional global maps of atmospheric phenomena, such as plasma plumes.

These ground-based observations have helped shed light on key characteristics of these plumes, such as how often they occur, and what makes some plumes stronger than others but as Foster notes; "this two-dimensional mapping technique gives an estimate only of what space weather might look like in the low-altitude regions of the magnetosphere."

To get a more precise, three-dimensional picture of the entire magnetosphere would require observations directly from space.

Toward this end, Foster approached Walsh with data showing a plasma plume emanating from the Earth's surface, and extending up into the lower layers of the magnetosphere, during a moderate solar storm in January 2013.

Walsh checked the date against the orbital trajectories of three spacecraft that have been circling the Earth to study auroras in the atmosphere.

As it turns out, all three spacecraft crossed the point in the magnetosphere at which Foster had detected a plasma plume from the ground.

The team analyzed data from each spacecraft, and found that the same cold, dense plasma plume stretched all the way up to where the solar storm made contact with Earth's magnetic field.

More information: "Simultaneous Ground- and Space-Based Observations of the Plasmaspheric Plume and Reconnection" Science, 2014.

NASA WIND Spacecraft captures image of Magnetosphere

A complex system of charged particles from the Sun and magnetic structures piles up in front of the Earth. 

Scientists now hope to better understand this area in front of the Bow shock, known as the foreshock, as it can help explain how energy from the rest of space makes its way into the magnetosphere.

Earth is seen as a tiny speck surrounded by an enormous magnetic 'bubble' surging through space in this image released by Nasa.

Far from the usual view of a blue and green globe spinning peacefully in the solar system, the dramatic picture illustrates the speed and energy of the magnetosphere that surrounds Earth as it moves around the sun.

Scientists studying data collected by Nasa's WIND spacecraft have used it to create a more detailed snapshot of the way solar particles streaming in from the sun bounce off the bubble.

Nasa researchers have been examining data from WIND - which travelled through the region at the boundary of the magnetosphere 17 times between 1998 and 2002 - to find out more about the 'dramatic' changing conditions within the complex, turbulent system called the foreshock.

As the magnetosphere ploughs through space, it sets up a standing bow wave or bow shock - much like that in front of a moving ship. The foreshock lies just in front of this bow wave.

Conditions in the foreshock change in response to solar particles streaming in from the sun, moving magnetic fields and a host of waves sweeping through the region, according to Nasa.

Lynn Wilson, deputy project scientist for Wind at Nasa's Goddard Space Flight Center in Greenbelt, Maryland, explained how 'cool squiggles' she stumbled upon in the data 'turned out to be a special kind of magnetic pulsations called short large amplitude magnetic structures, which we call SLAMS for short'.

Studying the region around these 'rogue waves' and how they propagate may help to establish what accelerates narrow jets of charged particles back out into space and away from Earth.

David Sibeck

David Sibeck, a space scientist at Goddard who is co-author of the paper, explained how space weather events that seem small can have 'profound effects downstream', from affecting GPS satellites to prompting solar storms.

'The front of the magnetosphere is right in the line between sun and Earth, so it's a crucial place to understand which small things can lead to big results,' he said.

'What happens to Earth's magnetic field depends on what's happening here at the front of the bow shock and what's happening there is dramatic.

'It's going to affect how much energy moves into the magnetosphere. Once inside the magnetosphere, it can create powerful solar storms and impact communications and GPS satellites that we depend on daily.'

According to Nasa: 'The more we know about what happens in the frothy, turbulent area in front of Earth, the more we know about how the solar wind and other material bursting off the sun may be able to penetrate into near Earth-space.'

Nasa Solar Wind Mission encounters 'SLAMS' waves

Earth is surrounded by a giant magnetic bubble called the magnetosphere. 

As it travels through space, a complex system of charged particles from the sun and magnetic structures piles up in front of it. 

Scientists wish to better understand this area in front of the bow shock, known as the foreshock, as it can help explain how energy from the rest of space makes its way past this boundary into the magnetosphere. Nasa Solar Wind Mission.

Credit: NASA/GSFC 

As Earth moves around the sun, it travels surrounded by a giant bubble created by its own magnetic fields, called the magnetosphere.

As the magnetosphere plows through space, it sets up a standing bow wave or bow shock, much like that in front of a moving ship.

Just in front of this bow wave lies a complex, turbulent system called the foreshock. Conditions in the foreshock change in response to solar particles streaming in from the sun, moving magnetic fields and a host of waves, some fast, some slow, sweeping through the region.

To tease out what happens at that boundary of the magnetosphere and to better understand how radiation and energy from the sun can cross it and move closer to Earth, NASA launches spacecraft into this region to observe the changing conditions.

From 1998 to 2002, NASA's Wind spacecraft traveled through this foreshock region in front of Earth 17 times, providing new information about the physics there.

"I stumbled on some cool squiggles in the data," says Lynn Wilson, who is deputy project scientist for Wind at NASA's Goddard Space Flight Center in Greenbelt, Md.

"They turned out to be a special kind of magnetic pulsations called short large amplitude magnetic structures, (SLAMS)."

SLAMS are waves with a single, large peak, a little like giant rogue waves that can develop in the deep ocean.

By studying the region around the SLAMS and how they propagate, the Wind data showed SLAMS may provide an improved explanation for what accelerates narrow jets of charged particles back out into space, away from Earth.

Tracking how any phenomenon catalyzes the movement of other particles is one of the crucial needs for modeling this region.

In this case, understanding just how a wave can help initiate a fast-moving beam might also help explain what causes incredibly powerful rays that travel from other solar systems across interstellar space toward Earth.

Wilson and his colleagues published a paper on these results in the Journal of Geophysical Research online on March 6, 2013.

The material pervading this area of space – indeed all outer space – is known as plasma. Plasma is much like a gas, but each particle is electrically charged so movement is governed as much by the laws of electromagnetics as it is by the fundamental laws of gravity and motion we more regularly experience on Earth.

"One of the unique things about space weather is how little things can have big effects," says David Sibeck, a space scientist at Goddard who is a co-author on the paper.

"An event might seem small and just generate local turbulence, but it can have profound effects downstream.

The front of the magnetosphere is right in the line between sun and Earth, so it's a crucial place to understand which small things can lead to big results."

Since the 1970s, researchers have known that particles seem to be reflecting off the magnetosphere, creating intense particle jets called field aligned ion beams, but it's not been clear how.

Now, the Wind data helps provide a more detailed snapshot of how they form, as it travels through a slew of SLAMS and the ion beams.

The scientists' job was to map where these events happen in space and time and to try to determine which events initiate which.

Wilson says that the solar wind constantly moves toward Earth's bow shock and then reflects off it.

"What happens to Earth's magnetic field depends on what's happening here at the front of the bow shock," says Sibeck.

"And what's happening there is dramatic. It's going to affect how much energy moves into the magnetosphere. Once inside the magnetosphere, it can create powerful solar storms and impact communications and GPS satellites that we depend on daily."

RBSP Mission: Energetic particles in the magnetosphere emit radio waves - Video

Energetic particles in the magnetosphere emit radio waves that are audible to humans. The NASA Radiation Belt Storm Probes mission's (RBSP) instrumentation captured an instance of the event. The 'chorus' phenomenon is well known by scientists. Credit: NASA / SPACE.com

NASA SDO Image: long filament of solar material - HD Video

A long filament erupted on the sun on August 31, 2012, shown here in a movie captured by NASA's Solar Dynamics Observatory (SDO) from noon EDT to 1:45 a.m. the next morning.

The filament lies in the lower left corner of the sun.

The movie shows light at 304 Angstroms and 171 Angstroms, both of which help scientists observe the sun's atmosphere, or corona.

A long filament of solar material that had been hovering in the sun's atmosphere, the corona, erupts out into space.

The coronal mass ejection, or CME, travelled at over 900 miles per second. 

The CME did not travel directly toward Earth, but did connect with Earth's magnetic environment, or magnetosphere, causing auroras to appear on the night of Monday, September 3.

Picture: NASA/GSFC/SDO / Rex Features