Five Spacecraft Join to Solve an Auroral Puzzle

AGU Contact: Harvey Leifert
+1 (202) 777-7507
hleifert@agu.org

ESA Contact: Monica Talevi
+31 71 565 3223
Monica.Talevi@esa.int

UCB Contact: Robert Sanders
+1 (510) 643-6998
rls@pa.urel.berkeley.edu

WASHINGTON – Five spacecraft have made a remarkable set of
observations, leading to a breakthrough in understanding the origin
of a peculiar and puzzling type of aurora. Seen as bright spots in
Earth’s atmosphere and called “dayside proton auroral spots,” they
are now known to occur when fractures appear in the Earth’s
magnetic field, allowing particles emitted from the Sun to pass
through and collide with molecules in our atmosphere.

On March 18, 2002, a jet of energetic solar protons collided with
the Earth’s atmosphere and created a bright “spot” seen by NASA’s
IMAGE spacecraft, just as the European Space Agency’s (ESA)
four Cluster spacecraft passed overhead and straight through the
proton jet. This is the first time that a precise and direct connection
between the proton jet and bright spot has been made, and it results
from the simultaneous observations by Cluster and IMAGE. The
results of the study are published May 21 in Geophysical Research
Letters, a journal of the American Geophysical Union, in a paper
by Tai Phan of the University of California in Berkeley and 24
international colleagues.

Earth’s magnetic field acts as a shield, protecting the planet from
the constant stream of tiny particles ejected by the Sun, known as
the solar wind. The solar wind itself is a stream of hydrogen atoms,
separated into their constituent protons and electrons. When
electrons find routes into our atmosphere, they collide with and
“excite” the atoms in the air. When these excited atoms release
their energy, it is emitted as light, creating the glowing “curtains”
we see as the aurora borealis in the far north and aurora australis in
the far south. Dayside proton auroral spots are caused by protons
“stealing” electrons from the atoms in our atmosphere.

An extensive analysis of the Cluster results has now shown that the
region was experiencing a turbulent event known as “magnetic
reconnection.” Such a phenomenon takes place when the Earth’s
usually impenetrable magnetic field fractures and has to find a new
stable configuration. Until the field mends itself, solar protons leak
through the gap and jet into Earth’s atmosphere, creating the
dayside proton aurora.

Philippe Escoubet, ESA’s Cluster Project Scientist, comments,
“Thanks to Cluster’s observations, scientists can directly and firmly
link for the first time a dayside proton auroral spot and a magnetic
reconnection event.”

Tai Phan, leader of the investigation, now looks forward to a new
way of studying the Earth’s protective shield. He says, “This result
has opened up a new area of research. We can now watch dayside
proton aurorae and use those observations to know where and how
the cracks in the magnetic field are formed and how long the
cracks remain open. That makes it a powerful tool to study the
entry of the solar wind into the Earth’s magnetosphere.”

Proton auroras were globally imaged for the first time by NASA’s
IMAGE (Imager for Magnetopause-to-Aurora Global Exploration)
spacecraft, which revealed the presence of dayside proton auroral
spots. ESA’s Cluster is a collection of four spacecraft, launched on
two Russian rockets during the summer of 2000. They fly in
formation around the Earth, relaying the most detailed information
ever about how the solar wind affects the planet.

The principal investigators for the instruments in the current study
were Henri Reme of CESR/Toulouse, France (Cluster Proton
Detectors), Andre Balogh of Imperial College, London, United
Kingdom (Cluster Magnetic Field Instrument), and Stephen Mende
of University of California, Berkeley (IMAGE/FUV).

The current study was funded by NASA and other organizations.

**********
Notes for journalists:

Journalists (only) may request a pdf copy of the Phan et al. paper
from Emily Crum: ecrum@agu.org

Title: “Simultaneous Cluster and IMAGE Observations of Cusp
Reconnection and Auroral Spot for Northward IMF”

Citation: T. Phan, H. U. Frey, S. Frey, L. Peticolas, S. Fuselier, C.
Carlson, H. Reme, J.-M. Bosqued, A. Balogh, M. Dunlop,
L. Kistler, C. Mouikis, I. Dandouras, J.-A. Sauvaud, S. Mende, J.
McFadden, G. Parks, E. Moebius, B. Klecker, G. Paschmann,
M. Fujimoto, S. Petrinec, M. F. Marcucci, A. Korth, and
R. Lundin, Simultaneous Cluster and IMAGE observations of cusp
reconnection and auroral proton spot for northward IMF, Geophys.
Res. Lett., 30(10), 1509, doi:10.1029/2003GL016885, 2003.

An image illustrating this press release is available at
http://www.agu.org/sci_soc/prrl/phan_image.pdf

Caption for illustration:
“The configuration of spacecraft and the Earth when the
breakthrough was made. On 18 March 2002, NASA’s IMAGE was
closer to the Earth and observing an aurora that contained a dayside
proton auroral spot (bottom left). At the same time, ESA’s Cluster
quartet then passed overhead returning proton data (top left graph),
showing a magnetic reconnection was taking place and that protons
were leaking through Earth’s magnetic shield. These protons were
then being funneled into Earth’s atmosphere along magnetic field
lines to form the spot.”

Image credit: Geophysical Research Letters

Contact information for principal authors:
Tai Phan, Space Sciences Laboratory, University of California,
Berkeley: phan@ssl.berkeley.edu or +1 (510) 643-5505

Harald Frey, Space Sciences Laboratory, University of California,
Berkeley: hfrey@ssl.berkeley.edu or +1 (510) 643-3323

Philippe Escoubet, ESA Cluster Project Scientist:
Philippe.Escoubet@esa.int or +31 71 565 3454