Nightside barrier gently brakes 'bursty' plasma bubbles

December 20, 2019

HOUSTON - (Dec. 20, 2019) - The solar wind that pummels the Earth's dayside magnetosphere causes turbulence, like air over a wing. Physicists at Rice University have developed new methods to characterize how that influences space weather on the nightside.

It's rarely quiet up there. The solar wind streams around the Earth and cruises off into the night, but closer to the planet, parcels of plasma get caught in the turbulence and sink back toward Earth. That turbulence causes big ripples in the plasma.

With the help of several spacecraft and computational tools developed over the past decade, Rice scientists led by space plasma physicist Frank Toffoletto can now assess the ripples, called buoyancy waves, caused by the turbulence.

These waves, or oscillations, have been observed in the thin layer of magnetic flux along the base of the plasma sheet that tails away from the planet's nightside. The Rice theory is the first to quantify their motion.

The theory adds another element to the Rice Convection Model, an established, decades-in-the-making algorithm that helps scientists calculate how the inner and middle magnetosphere will react to events like solar storms that threaten satellites, communications and power grids on Earth.

The new paper in JGR Space Physics by Toffoletto, emeritus professor Richard Wolf and former graduate student Aaron Schutza starts by describing the bubbles -- "bursty bulk flows" predicted by Wolf and Rice alumnus Duane Pontius in 1990 -- that fall back toward Earth through the plasma tail.

Functionally, they're the reverse of buoyant air bubbles that bob up and down in the atmosphere because of gravity, but the plasma bubbles respond to magnetic fields instead. The plasma bubbles lose most of their momentum by the time they touch down at the theoretical, filamentlike boundary between the inner plasma sheet and the protective plasmasphere.

That sets the braking boundary into a gentle oscillation, which lasts mere minutes before stabilizing again. Toffoletto compared the motion to a plucked guitar string that quickly returns to equilibrium.

"The fancy name for this is the eigenmode," he said. "We're trying to figure out the low-frequency eigenmodes of the magnetosphere. They haven't been studied very much, though they appear to be associated with dynamic disruptions to the magnetosphere."

Toffoletto said the Rice team has in recent years discovered through simulations that the magnetosphere doesn't always respond in a linear fashion to the steady driving force of the solar wind.

"You get all kinds of wave modes in the system," he said, explaining that bursty bulk flows are one such mode. "Every time one of these things come flying in, when they hit the inner region, they basically reach their equilibrium point and oscillate with a certain frequency. Finding that frequency is what this paper is all about."

As measured by the THEMIS spacecraft, the periods of these waves are a few minutes and the amplitudes are often bigger than the Earth.

"Understanding the natural frequency of the system and how it behaves can tell us a lot about the physical properties of plasma on the nightside, its transport and how it might be related to the aurora," he said. "A lot of these phenomena show up in the ionosphere as auroral structures, and we don't understand where these structures come from."

Toffoletto said the models suggest buoyant waves may play a role in the formation of the ring current that consists of charged particles that flow around Earth as well as magnetospheric substorms, all of which are connected to the aurora.

He said that no more than a decade ago, many magnetosphere simulations "would look very uniform, kind of boring." The Rice group is collaborating with the Applied Physics Laboratory to include the Rice Convection Model in a newly developed global magnetosphere code called "Gamera," named after the fictional Japanese monster.

"Now, with such higher-resolution models and much better numerical methods, these structures are starting to show up in the simulations," Toffoletto said. "This paper is one little piece of the puzzle we're putting together of how the system behaves. All this plays a big role in understanding how space weather works and how that in turn impacts technology, satellites and ground-based systems."

The Rice Convection Model itself was refreshed this month in a paper led by recent Rice alumnus Jian Yang, now an associate professor of Earth and space sciences at the Southern University of Science and Technology, Shenzhen, China.
-end-
The new study was supported by a NASA Heliophysics Supporting Research grant.

Read the abstract at https://doi.org/10.1029/2019JA027516.

This news release can be found online at https://news.rice.edu/2019/12/20/nightside-barrier-gently-brakes-bursty-plasma-bubbles/

Follow Rice News and Media Relations via Twitter @RiceUNews.

Video:

https://civspace.jhuapl.edu/Science/tools/gamera/videos/Hex3D.mp4
A magnetohydrodynamic simulation by the Gamera project at the Johns Hopkins Applied Physics Laboratory shows bursty bulk flows (in red and brown) in the plasma sheet approaching Earth on the nightside. Rice University space plasma physicists have developed algorithms to measure the buoyancy waves that appear in thin filaments of magnetic flux on the nightside. (Credit: Gamera/APL)

https://youtu.be/8oIF7f-ZQSE
A simulation by Rice University space plasma physicist Frank Toffoletto shows buoyancy wave oscillations in a magnetic field, due to bursty bulk flows drawn toward Earth on the nightside. (Credit: Frank Toffoletto/Rice University)

Image for download:

https://news-network.rice.edu/news/files/2019/12/0113_BUOYANCY-1-WEB.jpg
An image from a magnetohydrodynamic simulation by the Gamera project at the Johns Hopkins Applied Physics Laboratory shows bursty flows (in red and brown) in the plasma sheet. Rice University space plasma physicists developed algorithms to measure the buoyancy waves that appear in thin filaments of magnetic flux on Earth's nightside. (Credit: K. Sorathia/JHUAPL)

Related materials:

Video lecture: The Effects of Plasma Sheet Bubbles on the Inner Magnetosphere

The Inertialized Rice Convection Model: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JA026811

Buoyancy Waves in Earth's Magnetosphere: Calculations for a 2D Wedge Magnetosphere: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2017JA025006

Theory of thin-filament motion in Earth's magnetotail and its application to bursty bulk flows: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/1999JA900005

Space Plasma Physics at Rice: https://physics.rice.edu/space-plasma-physics

Grid Agnostic MHD for Extended Research Applications (Gamera): http://civspace.jhuapl.edu/gamera

Wiess School of Natural Sciences: https://naturalsciences.rice.edu

Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,962 undergraduates and 3,027 graduate students, Rice's undergraduate student-to-faculty ratio is just under 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for lots of race/class interaction and No. 4 for quality of life by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finan

Jeff Falk
713-348-6775
jfalk@rice.edu

Mike Williams
713-348-6728
mikewilliams@rice.edu

Rice University

Related Solar Wind Articles from Brightsurf:

Wind beneath their wings: Albatrosses fine-tuned to wind conditions
A new study of albatrosses has found that wind plays a bigger role in their decision to take flight than previously thought, and due to their differences in body size, males and females differ in their response to wind.

New research deepens understanding of Earth's interaction with the solar wind
A team of scientists at PPPL and Princeton University has reproduced a process that occurs in space to deepen understanding of what happens when the Earth encounters the solar wind.

Hydropower plants to support solar and wind energy in West Africa
Study maps smart electricity mix composed of solar, wind and hydropower for West Africa -- regional cooperation can provide up to 60% reliable and clean electricity

Solar and wind energy sites mapped globally for the first time
Researchers at the University of Southampton have mapped the global locations of major renewable energy sites, providing a valuable resource to help assess their potential environmental impact.

New research helps explain why the solar wind is hotter than expected
When the sun expels plasma, the solar wind cools as it expands through space -- but not as much as the laws of physics would predict.

Solar wind samples suggest new physics of massive solar ejections
A new study led by the University of Hawai'i (UH) at Mānoa has helped refine understanding of the amount of hydrogen, helium and other elements present in violent outbursts from the Sun, and other types of solar 'wind,' a stream of ionized atoms ejected from the Sun.

Supporting structures of wind turbines contribute to wind farm blockage effect
Much about the aerodynamic effects of larger wind farms remains poorly understood.

Parker Solar Probe traces solar wind to its source on sun's surface: coronal holes
New data from the Parker Solar Probe, which got closer to the sun than any other spacecraft, allowed physicists to map the source of a major component of the solar wind that continually peppers Earth.

Closest-ever approach to the sun gives new insights into the solar wind
The Parker Solar Probe spacecraft, which has flown closer to the sun than any mission before, has found new evidence of the origins of the solar wind.

SwRI-built instrument confirms solar wind slows farther away from the Sun
Measurements taken by the Solar Wind Around Pluto (SWAP) instrument aboard NASA's New Horizons spacecraft are providing important new insights from some of the farthest reaches of space ever explored.

Read More: Solar Wind News and Solar Wind Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.