News

March 29, 2022:

Winner of GEM Outstanding Student Poster Award:

EPSS Space Physics graduate student Colin Wilkins won an award for best Inner Magnetosphere Section Poster at the 2022 Geospace Environment Modeling (GEM) Summer Workshop last week. Colin's posted was titled "Statistical Characterization of the Electron Isotropy Boundary from ELFIN Observations."

The GEM meeting is the premiere topical conference in Magnetospheric Physics; this year it attracted about 320 people, including more than 100 of them students from around the world. Colin’s was one of a handful selections, in the most competitive section. Congratulations!

March 29, 2022:

THEMIS-ELFIN observations of whistler wave electron precipitation :

UCLA scientists have discovered a new source of super-fast, energetic electrons raining down on Earth’s atmosphere, a phenomenon that contributes to the colorful aurora borealis but also poses hazards to satellites, spacecraft and astronauts.

The researchers observed unexpected, rapid “electron precipitation” from low-Earth orbit using the ELFIN mission, a pair of tiny satellites built and operated on the UCLA campus by undergraduate and graduate students guided by a small team of staff mentors.

By combining the ELFIN data with more distant observations from NASA’s THEMIS spacecraft, the scientists determined that the sudden downpour was caused by whistler waves, a type of electromagnetic wave that ripples through plasma in space and affects electrons in the Earth’s magnetosphere, causing them to “spill over” into the atmosphere.

The THEMIS and ELFIN satellites (orbits shown in cyan and green, respectively) worked together to help understand the mystery of electron rain. When whistler waves (purple) interact with the electrons, they can give them extra energy (red spiral), which causes them to fall into the atmosphere.

Their findings, published March 25 in the journal Nature Communications, demonstrate that whistler waves are responsible for far more electron rain than current theories and space weather models predict.

“ELFIN is the first satellite to measure these super-fast electrons,” said Xiaojia Zhang, lead author and a researcher in UCLA’s department of Earth, planetary and space sciences. “The mission is yielding new insights due to its unique vantage point in the chain of events that produces them.”

Central to that chain of events is the near-Earth space environment, which is filled with charged particles orbiting in giant rings around the planet, called Van Allen radiation belts. Electrons in these belts travel in Slinky-like spirals that literally bounce between the Earth’s north and south poles. Under certain conditions, whistler waves are generated within the radiation belts, energizing and speeding up the electrons. This effectively stretches out the electrons’ travel path so much that they fall out of the belts and precipitate into the atmosphere, creating the electron rain.

One can imagine the Van Allen belts as a large reservoir filled with water — or, in this case, electrons. As the reservoir fills, water periodically spirals down into a relief drain to keep the basin from overflowing. But when large waves occur in the reservoir, the sloshing water spills over the edge, faster and in greater volume than the relief drainage. ELFIN, which is downstream of both flows, is able to properly measure the contributions from each flow.

The low-altitude electron rain measurements by ELFIN, combined with the THEMIS observations of whistler waves in space and sophisticated computer modeling, allowed the team to understand in detail the process by which the waves cause rapid torrents of electrons to flow into the atmosphere.

The findings are particularly important because current theories and space weather models, while accounting for other sources of electrons entering the atmosphere, do not predict this extra whistler wave–induced electron flow, which can affect Earth’s atmospheric chemistry, pose risks to spacecraft and damage low-orbiting satellites.

The researchers further showed that this type of radiation belt electron loss to the atmosphere can increase significantly during geomagnetic storms, disturbances caused by enhanced solar activity that can affect near-Earth space and Earth’s magnetic environment.

Although space is commonly thought to be separate from our upper atmosphere, the two are inextricably linked. Understanding how they’re linked can benefit satellites and astronauts passing through the region, which are increasingly important for commerce, telecommunications and space tourism.

Since its inception in 2013, more than 300 UCLA students have worked on ELFIN (Electron Losses and Fields investigation), which is funded by NASA and the National Science Foundation. The two microsatellites, each about the size of a loaf of bread and weighing roughly 8 pounds, were launched into orbit in 2018, and since then have been observing the activity of energetic electrons and helping scientists to better understand the effect of magnetic storms in near-Earth space. The satellites are operated from the UCLA Mission Operations Center on campus.

“It’s so rewarding to have increased our knowledge of space science using data from the hardware we built ourselves,” said Colin Wilkins, a co-author of the current research who is the instrument lead on ELFIN and a space physics doctoral student in the department of Earth, planetary and space sciences.

October 6, 2021:

Researchers Find Standing Waves at Edge of Earth's Magnetic Bubble:

Congrats to Martin Archer et al. for their recent publication in Nature Communications. Using a combination of theory, THEMIS observations and global simulations, they discovered magnetopause standing waves propagating against the flow of the solar wind.

Earth sails the solar system in a ship of its own making: the magnetosphere, the magnetic field that envelops and protects our planet. The celestial sea we find ourselves in is filled with charged particles flowing from the Sun, known as the solar wind. Just as ocean waves follow the wind, scientists expected that waves traveling along the magnetosphere should ripple in the direction of the solar wind. But a new study reveals some waves do just the opposite.

An animated illustration of magnetospheric waves, in light blue. At the front of the magnetosphere, these waves appear to be still. Credits: M. Archer/E. Masongsong/NASA

Studying these magnetospheric waves, which transport energy, helps scientists understand the complicated ways that solar activity plays out in the space around Earth. Changing conditions in space driven by the Sun are known as space weather. That weather can impact our technology from communications satellites in orbit to power lines on the ground. “Understanding the boundaries of any system is a key problem,” said Martin Archer, a space physicist at Imperial College London who led the new study, published today in Nature Communications. “That’s how stuff gets in: energy, momentum, matter.”

Archer focuses on surface waves, meaning waves that require a boundary — in this case, the edge of the magnetosphere — to travel along. Previously, he and his colleagues established this boundary vibrates like a drum. When a strong burst of solar wind beats against the magnetosphere, waves race towards Earth’s magnetic poles and get reflected back.

The latest work considers the waves that form across the entire surface of the magnetosphere, using a combination of models and observations from NASA’s THEMIS mission, Time History of Events and Macroscale Interactions during Substorms.

The researchers found when solar wind pulses strike, the waves that form not only race back and forth between Earth’s magnetic poles and the front of the magnetosphere, but also travel against the solar wind. Archer likened these two kinds of movement to crossing a river: A boat can go from one riverbank to the other (traveling towards the poles) and upstream (against the solar wind). At the front of the magnetosphere, these waves appear to stand still.

The THEMIS satellites’ observations from within the magnetosphere first hinted some waves might be traveling against the solar wind. The researchers used models to illustrate how the energy of the wind coming from the Sun and that of the waves going against it could cancel each other out. It’s similar to what happens if you try walking up a downwards escalator. “It’s going to look like you’re not moving at all, even though you’re putting in loads of effort,” Archer said.

These standing waves can persist longer than those that travel with the solar wind. That means they’re around longer to accelerate particles in near-Earth space, leading to potential impacts in the radiation belts, aurora, or ionosphere. Archer expects standing waves may occur elsewhere in the universe, from the magnetospheres of other planets to the peripheries of black holes. Studying the waves close to home can help scientists understand such distant boundaries.

By translating the wave models and data into the audible range, we can listen to the sound of these curious waves.

September 24, 2021:

Earth can make auroras without solar activity:

Congrats to Xu Zhang et al. for their feature on Spaceweather.com! Using THEMIS observations and statistical analyses, they revealed an atmospheric electron beam source for ECH waves, which in turn can power the diffuse aurora.

Diffuse auroras and the Big Dipper, photographed by Emmanuel V. Masongsong in Fairbanks, AK

No solar storms? No problem. Earth has learned to make its own auroras. New results from NASA’s THEMIS-ARTEMIS spacecraft show that a type of Northern Lights called "diffuse auroras" comes from our own planet–no solar storms required.

Diffuse auroras look a bit like pea soup. They spread across the sky in a dim green haze, sometimes rippling as if stirred by a spoon. They’re not as flamboyant as auroras caused by solar storms. Nevertheless, they are important because they represent a whopping 75% of the energy input into Earth’s upper atmosphere at night. Researchers have been struggling to understand them for decades.

“We believe we have found the source of these auroras,” says UCLA space physicist Xu Zhang, lead author of papers reporting the results in the Journal of Geophysical Research: Space Physics and Physics of Plasmas.

It is Earth itself.

Earth performs this trick using electron beams. High above our planet’s poles, beams of negatively-charged particles shoot upward into space, accelerated by electric fields in Earth’s magnetosphere. Sounding rockets and satellites discovered the beams decades ago. It turns out, they can power the diffuse auroras.

The video, below, shows how it works. The beams travel in great arcs through the space near Earth. As they go, they excite ripples in the magnetosphere called Electron Cyclotron Harmonic (ECH) waves. Turn up the volume and listen to the waves recorded by THEMIS-ARTEMIS:

ECH waves, in turn, knock other electrons out of their orbits, forcing them to fall back down onto the atmosphere. This rain of secondary electrons powers the diffuse auroras.

"This is exciting," says UCLA professor Vassilis Angelopoulos, a co-author of the papers and lead of the THEMIS-ARTEMIS mission. "We have found a totally new way that particle energy can be transferred from Earth’s own atmosphere out to the magnetosphere and back again, creating a giant feedback loop in space."

According to Angelopoulos, Earth’s polar electron beams1 sometimes weaken but they never completely go away, not even during periods of low solar activity. This means Earth can make auroras without solar storms.

The sun is currently experiencing periods of quiet as young Solar Cycle 25 sputters to life. Pea soup, anyone?

May 11, 2020:

SpaceNews.com interviews ELFIN about remotely operating CubeSats during Covid-19 Lockdown:

Students operating the twin Electron Losses and Fields Investigation (ELFIN) cubesats were heading into finals at the University of California, Los Angeles, when they realized they needed to quickly transition to remote operations. "As soon as all of us were done taking three-hour tests, we had three-hour meetings to figure out what we needed the satellites to do and how to make it as easy as possible from a software and technical perspective," said Sharvani Jha, ELFIN software development lead.

UCLA students began establishing remote access soon after ELFIN launched in 2018 alongside NASA’s Ice, Cloud and land Elevation Satellite-2. "We have winter break and summer break where we would not be in Los Angeles physically," said Rebecca Yap, ELFIN mission operations manager. "Being able to set up a flexible operations workflow was important."
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