Electromagnetic energy conversion at reconnection fronts - PowerPoint Presentation

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Electromagnetic energy conversion at reconnection frontsAngelopoulos et al., Science, Sep. 27, 2013

Supporting Material for Education, Public Outreach and the PressVassilis AngelopoulosDept. of Earth, Planetary and Space Sciences, UCLA

For release: 2pm U.S. E.T. on Thursday, 09/26/13Slide2

Solar activity can cause space weather at Earth. Even steady, slow solar winds can drive the unsteady energy loading and

sudden energy releases at near-Earth space called substorms. Storms and substorms are driven by similar processes that are important to understand. Sun’s corona - the glow visible

during a

solar total eclipse - is a mix of hot, positively charged atoms and electrons that expands outward, towards interstellar space at a million miles an hour. This “solar wind” carries with it Sun’s own magnetic field. During solar maximum the Sun’s surface develops sunspots where the magnetic field is 1000 times more intense than typical. The energy in that magnetic field near the solar surface can heat and accelerate the solar wind above it explosively, occasionally releasing billions of tons of mass into space. (left, from NASA’s SOHO mission). When Earth is in the path of one of these high speed, dense solar wind streams the Sun-Earth interaction is very intense, causing high energy particles near the Earth, inducing currents that damage power distribution lines and powering intense auroras. Such space storms are the most dramatic space weather phenomena. However, even during steady solar wind (right, artist’s concept), space weather is still dynamic.

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Movie courtesy: NASA/SOHO (soho_movie9CME.avi)

Movie courtesy: NASA/SVS (NASA_substorm_a010104_H264_....mp4)

Even steady solar wind can lead to dynamic space weatherSlide3

Solar wind distorts Earth’s magnetic field, creates magnetosphere

The solar wind blowing past Earth distorts Earth’s magnetic field into a long magnetosphere.

As the solar wind buffets magnetized planets it distorts their magnetic fields into windsock-shaped regions, called

magnetospheres (For a movie of that distortion see: BarMagneC.m1v, or click the image above). Earth’s magnetosphere extends more than a million miles behind the Earth, along the Sun-Earth line, on the nightside (to the right of the image). Like the bow wave ahead of a fast moving ship, or a shock wave of a supersonic jet, the bow shock stands ahead of the sunward side of the magnetosphere. Space weather at Earth is powered by the solar wind through a series of energy transformations common to storms and substorms

. The Sun’s rotation winds up energy in its magnetic field, accelerating the solar wind outward. The Earth’s magnetic field captures a fraction of this energy and

re-releases it internal to the magnetosphere to accelerate and heat particles near Earth. It

is this last elusive step, the impulsive energy conversion internal to the magnetosphere, that is the point of our study.3Slide4

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The magnetosphere contains the radiation belts, where most communications and remote sensing satellites orbit

The

radiation belts are filled with high-energy electrons, protons and other charged particles. The charged particles penetrate satellite walls and electronics causing damage through buildup of electrical charge, and also emit radiation (X rays, gamma rays). During magnetic

storms particle fluxes become so intense that sensitive electronics can be disabled and satellites can become inoperable. Astronauts

and future space tourists, immersed in this environment can receive in a short time more than a lifetime’s dose of radiation; storm-time radiation levels can be lethal. Understanding and

predicting Earth’s space weather, is important for our technologies, space exploration and the increasing presence of humans into space.Slide5

Magnetic reconnection allows energy coupling

A cut through a computer model of the magnetosphere under steady, southward solar wind magnetic field.

Sun is on the left (+X). North is to the top (+Z). When the solar wind’s magnetic field (left, red line) is directed nearly opposite to the Earth’s (left, blue line) and the two field lines meet, they snap and re-connect such that solar wind field lines become connected to Earth’s poles. Not much energy is released at first, but dayside reconnection sets the stage for what follows… The fast-moving solar wind sets the magnetosphere into motion. It strips magnetic field lines from the dayside, transports them over the poles and compresses them in the magnetosphere behind the Earth, at the

nightside. This increases the magnetic field (and the energy) in Earth’s long tail, the magnetotail. Eventually, the field lines in the magnetotail reconnect again (right), to initiate the transfer of the magnetic energy back to particle energy. The accelerated particles enter Earth’s radiation belts and also precipitate into the atmosphere causing brilliant auroras. Where and how this nightside energy conversion from magnetic to particle energy occurs has been, so far, unclear.

dayside

nightside

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Image courtesy: N. A.

Tsyganenko

,

SPbUSlide6

Triggered by reconnection, the energy release in Earth’s magnetosphere happens at reconnection fronts.

Past studies had shown that magnetic reconnection initiates the avalanche of energy in substorms. In each substorm cycle, the solar wind motional energy

is stored in the Earth’s stretched

and compressed magnetic field lines on the nightside over tens of minutes to hours. The field lines then snap and reconnect impulsively (in minutes), somewhere near midnight (opposite the Sun), roughly midway between Earth and the moon’s orbit. But where does the stored magnetic energy get converted to particle kinetic energy, once nightside reconnection takes off? The present paper shows that this conversion happens inside thin fronts (boundaries) of intense magnetic flux that are launched on both sides of the reconnection region (see Figure). The converted energy causes particle flows (red arrows), heating (yellow volume), and excites waves. On the earthward side, these energize the radiation belts and cause particle precipitation into the atmosphere that drive brilliant auroras. On the tailward side, giant plasmoids are launched out to interplanetary space. Just as weather fronts come with wind shear, heat waves or rain and drive atmospheric weather, reconnection fronts

cause space particle flow shears, heating and precipitation, driving space weather.

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Reconnection fronts power Earth’s radiation belts and cause brilliant auroras, leading to intense space weather

.

Image courtesy: E. V. Masongsong

, UCLASlide7

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An alignment of ARTEMIS in the tailand six other satellites enabled this study.

The recently

commissioned, dual lunar orbiter mission ARTEMIS provides a unique vantage-point, a lunar perspective of Earth’s space weather phenomena, enabling measurements of the total magnetic flux transported and energy converted in the magnetotail during each substorm. While measuring the global energy responsible for such space weather phenomena, ARTEMIS, together with THEMIS and ancillary Earth-orbiting spacecraft, can also measure the local flux transport and energy conversion on either side of the reconnection site to determine if these match expectations from global transport measurements. During such conjunctions (twice yearly) between ARTEMIS (P1, P2), THEMIS (P3-P5), Geotail (GT), and GOES (G15, G13) it is now possible to observe the reconnection fronts and measure their contribution to magnetic flux transport per unit Y-distance (the electric field), and power conversion rate (like in an ordinary resistor, this power density is current density times the electric field – both measured quantities). This study was based on such a conjunction.

Image courtesy: E. V.

Masongsong

, UCLASlide8

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Local measurements of power conversion agree with global estimate of these quantities by ARTEMIS

The total energy conversion at ARTEMIS matched the integral of the power conversion rate past THEMIS and ARTEMIS, providing the first self-consistent accounting of global energy conversion by local processes in the magnetosphere.

Top panel, red line: global magnetic flux input in the magnetotail determined from upstream solar wind monitors; black line with hash: ARTEMIS’s raw measure of the total flux contained in the

magnetotail; black smooth line: same, but excluding local transients marked "plasmoids” and

“earthward flow bursts”. Tail reconnection is operating when the black smooth line deviates

significantly from the red line, indicating magnetotail flux reduction (green and blue hatched areas). The energy converted from magnetic to particle energy or waves was estimated from this magnetic flux reduction to be ~3x10

15J. Bottom panel: cumulative local power conversion rate at P3 (THEMIS) and at P2 (ARTEMIS). When further integrated by YZ area (3x10

RE2) and duration (1042UT-1112UT, 1800s) it also amounts to energy conversion ~3x1015J, in agreement with the

global

estimate (mostly at reconnection fronts, the vertical lines). Power conversion rate was similar to the total power generating capacity of all power plants on Earth. The total energy converted was approximately equal to the energy released

by

a 7.1 magnitude earthquake.

55GW/R

E

2

x3x10R

E

2

x1800s

-----------

3x10

15

J

0.5GWb



3x10

15

J

P2: 5GW/R

E

2

P3:50GW/R

E

2

0.5GWbSlide9

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Global power conversion occurs at gradients

sharp enough

to perturb electron microscopic motionUnlike atmospheric weather, where kinetic gas processes, such as shocks, have little effect on global dynamics, global space weather is very much controlled by particle dynamics at a microscopic level. Charged particles gyrate around the magnetic field and move with it. If sharp gradients or small-scale waves perturb the particle gyration the particles start to move independently of the magnetic field. Electric fields that arise under such conditions can have a component along the magnetic field, and are then able to accelerate particles to high energies along the magnetic field. This can result in direct electromagnetic energy conversion from fields to particle motion. In the past, such conditions were thought possible only near the reconnection site. However, in the event shown, far from the reconnection site, power conversion occurred at spatial gradients of the order of the electron motion: 20-150km (time is transformed to space using the measured flow, 400-600km/s). Although very thin, multiple reconnection fronts have been observed to move across a large volume of the magnetosphere, and survive over long time-scales (10s of minutes). The reconnection fronts’ longevity, number, propagation length (>200,000km, from reconnection site to radiation belts), and intensity all contribute to their global consequences.

B

z

: Northward magnetic field

E

y: Magnetic flux transportJy: Current densityJyEy: Power conversion densitySlide10

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Space weather prediction is where atmospheric weather prediction was a century ago.

Imagine trying to understand (let alone predict) atmospheric weather with a couple of weather stations in each continent, or with a few stations in the US but no other stations elsewhere in the world… it would be impossible. Just like a century ago, when dozens of weather stations relaying global data via telegraph brought rapid advancements in our understanding of atmospheric weather, space weather’s understanding

to the point of predictability

relies on studies with multiple, highly-capable, well-coordinated observatories, or constellations of small satellites. The next step in that future is coming next year with the launch of NASA’s four-satellite mission MMS to study reconnection phenomena with unprecedented temporal and spatial resolution. THEMIS will be using its

remaining fuel

to further optimize its coordination with MMS and other NASA and international missions during the upcoming

solar maximum.

By simultaneously measuring: electron dynamics with MMS (4); ion dynamics with THEMIS (3); radiation belts responses with Van Allen probes (2); and global dynamics with NASA’s ARTEMIS (2), and other international missions the emerging “System-Observatory” represents the best hope the field has ever had for resolving the vexing problems of space weather. Because processes of reconnection, turbulence and electromagnetic energy conversion occur everywhere in the Universe, including our Sun, other stars, accretion disks and magnetars, studies here at Earth, at our own astrophysical back yard,

can help us understand more distant objects, well beyond reach for our in-situ instruments.

New perspectives on space weather can lead to better understanding of astrophysical objects too

Coordinated NASA

Heliophysics

active missions (2013) are our

best hope for understanding fundamental space processes

Mira

, a mass-shedding red giant, moving thru the interstellar medium, creates a 13-light year long

tail with a bow shock standing against the upstream flow. Its

tail-length to stand-off distance

ratio is comparable

to Earth’s.

Image courtesy of

NASA/GALEXSlide11

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More on ARTEMIS and its lunar captureSlide12

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Critical to the determination of the total energy was ARTEMIS observations of the global energy input.

The Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) mission is a novel NASA approach for efficient

exploration of new, compelling science goals by repurposing capable, versatile assets already in space. A spin-off of NASA’s THEMIS mission, ARTEMIS utilized the remaining on-board fuel on two THEMIS Earth-orbiting satellites to reposition them into lunar orbits. Proposed in 2010 to study the lunar space environment, Earth’s interaction with the solar wind and magnetotail particle acceleration, ARTEMIS was inserted into lunar orbit in the summer of 2011 and has been acquiring high-quality data from there since. ARTEMIS was the first mission to conduct routine operations at the Earth-Moon Lagrange points, the region where Earth’s and Moon’s gravity match each other. During its 9 months there it proved the navigation and operations solutions that will help future lunar exploration from this unique location, while obtaining data critical for the study of

plasmoids, the solar wind and the lunar wake. Early next year it is slated to conduct coordinated exploration of the lunar environment with NASA’s recently launched LADEE mission. ARTEMIS provides a unique and critical node for NASA’s

Heliophysics System Observatory: in addition to its two-point measurements that can resolve spatial from temporal effects, it provides the total energy content of the magnetosphere during storms and

substorms, energy that is principally responsible for space weather activity.http://www.nasa.gov/ARTEMIS ; http://artemis.ssl.berkeley.edu

; http://link.springer.com/journal/11214/165/1/page/1

THEMIS and ARTEMIS are part of NASA’s Explorer program, managed by the Goddard Space Flight Center. The University of California Berkeley’s Space Sciences Laboratory is responsible for mission operations, and built several of the on-board and ground-based instruments. ATK (formerly Swales Aerospace), Beltsville, MD, built the THEMIS probes. ARTEMIS orbit design, navigation and execution was a collaborative effort between JPL, GSFC and UCB. The University of California at Los Angeles built the ground magnetometers and is the PI institution.Slide13

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The sequence of maneuvers that turned THEMIS P1 and P2 into ARTEMIS P1 and P2 took >1year, but was very efficient.

See movie at

: http://www.youtube.com/watch?v=V2vj8nJ83i4&list=PLiuUQ9asub3RLY8-H4kQU5t58UX1nYJPR&index=6Also at: NASA_ARTEMIS_SVS_lunar_orbit_insertion.mp4

Movie credits: NASA/SVS