|
12 February 2019
from
QueenMaryUniversityLondon Website
Artist rendition of a plasma jet impact (yellow)
generating
standing waves at the magnetopause boundary (blue)
and in
the magnetosphere (green).
The
outer group of four THEMIS probes
witnessed the flapping of the magnetopause
over
each satellite in succession, confirming
the
expected behavior/frequency of the theorized
magnetopause eigen-mode wave.
(Credit: E. Masongsong/UCLA, M. Archer/QMUL, H. Hietala/UTU)
The Earth's
magnetic shield
booms like a
drum when it is hit
by strong
impulses, according to
new research
from
Queen Mary
University of London.
As an impulse strikes the outer boundary of the shield, known as the
magnetopause, ripples travel along
its surface which then get reflected back when they approach the
magnetic poles.
The interference of the original and reflected waves leads to a
standing wave pattern, in which specific points appear to be
standing still while others vibrate back and forth.
A drum resonates
like this when struck in exactly the same way.
This study (Direct
Observations of a Surface Eigen-mode of the Dayside Magnetopause),
published in Nature Communications, describes the first time
this effect has been observed after it was theoretically proposed 45
years ago.
Movements of the magnetopause are important in controlling the flow
of energy within our space environment with wide-ranging effects on
space weather, which is how phenomena from space can potentially
damage technology like,
The discovery that the boundary moves in this way sheds light on
potential global consequences that previously had not been
considered.
Hard to detect
Dr Martin Archer, space physicist at Queen Mary University
of London, and lead author of the paper, said:
"There had been
speculation that these drum-like vibrations might not occur at
all, given the lack of evidence over the 45 years since they
were proposed.
Another possibility
was that they are just very hard to definitively detect.
"Earth's magnetic
shield is continuously buffeted with turbulence so we thought
that clear evidence for the proposed booming vibrations might
require a single sharp hit from an impulse.
You would also need
lots of satellites in just the right places during this event so
that other known sounds or resonances could be ruled out.
The event in the
paper ticked all those quite strict boxes and at last we've
shown the boundary's natural response."
The researchers used
observations from five
NASA THEMIS satellites when they
were ideally located as a strong isolated plasma jet slammed into
the magnetopause.
The probes were able to
detect the boundary's oscillations and the resulting sounds within
the Earth's magnetic shield, which agreed with the theory and gave
the researchers the ability to rule out all other possible
explanations.
Solar wind
impact
Many impulses which can impact our magnetic shield originate from
the
solar wind, charged particles in the form of plasma that
continually blow off the Sun, or are a result of the complicated
interaction of the solar wind with
Earth's magnetic field, as was
technically the case for this event.
The interplay of Earth's magnetic field with the solar wind forms a
magnetic shield around the planet, bounded by the magnetopause,
which protects us from much of the radiation present in space.
Other planets like Mercury, Jupiter and Saturn also have similar
magnetic shields and so the same drum-like vibrations may be
possible elsewhere.
Further research is needed to understand how often the vibrations
occur at Earth and whether they exist at other planets as well.
Their consequences also
need further study using satellite and ground-based observations.
More information
| 