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American Geophysical Union/European Space Agency/University of
California, Berkeley Joint Release

20 May 2003                               AGU Contact: Harvey Leifert
AGU Release No. 03-13                                  (202) 777-7507
For Immediate Release                                hleifert{at}agu.org

ESA Contact: Monica Talevi
+31 71 565 3223
Monica.Talevi{at}esa.int

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

Five Spacecraft Join to Solve an Auroral Puzzle

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{at}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 2003, 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{at}ssl.berkeley.edu or +1 (510) 643-5505
    Philippe Escoubet, ESA Cluster Project Scientist:
 Philippe.Escoubet{at}esa.int or +31 71 565 3454

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