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27 December 2002 - Insights on LENAs Near the Earth
In a recently accepted Journal of Geophysical Research paper, Wilson et al. identify two
different patterns in images of low altitude (<4000 km) low energy (<50 eV) neutral
oxygen in the Earth's environment. Click on thumbnail for example of perigee pass image.
They suggest the different patterns may be due to two main populations: one representing
direct emission from the auroral zone and the other representing a hot but
gravitationally-bound oxygen exosphere that is also created by auroral zone heating processes.
Click here for a pdf file (411 Kb)
of the Wilson et al. paper
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12 November 2002 - Dust in the Wind
More than 200 scientists converged on sunny Pisa, Italy this past June to discuss their latest
results on, what else, the Sun. The Solar Wind 10 meeting featured presentations on coronal
and heliospheric structure and activity, acceleration of the solar wind, waves and turbulence,
future missions and new instrument concepts as well as other topics.
Among the new results was an upper limit deduced by Collier et al. on the amount of dust
between the Sun and the Earth based on LENA neutral solar wind observations. Because the
normally ionized solar wind becomes neutral when it interacts with dust as it travels from
the Sun to the Earth, the neutral solar wind flux measured at the Earth places strict limits
on the amount of dust that can lie inside the Earth's orbit. The measurements, to be published
in the Solar Wind 10 Conference Proceedings, are consistent with determinations based on
zodiacal light, discovered and identified by Cassini in 1683 as resulting from sunlight scattered
off dust particles orbiting the Sun.
Click here for a pdf file (57 Kb)
of the Collier et al. paper
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27 September 2002 - April Showers Bring... Geomagnetic Storms
Some dramatic geomagnetic activity in April of this year presented the opportunity
for space physicists to gather data from a variety of different spacecraft in an attempt
to piece together the chain of events beginning at the Sun and ending in glorious
displays of auroral activity.
Two space physics community meetings -- one this past Spring at the Washington D.C.
American Geophysical Union Meeting, and one over the Summer at the Applied Physics
Laboratory in Laurel, Maryland -- have the LENA team
comparing data with the LANL fleet of geosynchronous spacecraft, the polar orbiting
Polar spacecraft (see figure, click on thumbnail for 8 MByte PDF file), and the quartet
of closely-spaced Cluster spacecraft.
Stay tuned...
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9 May 2002 -
Seeing is Believing: LENA Data Confirm Inferences on Outflow
Space physicists know that the ionosphere routinely loses copious amounts of hydrogen and oxygen
ions to the magnetosphere and interplanetary space from the auroral zone, shown schematically
in the thumbnail at the right.
Establishing a global picture of this ion outflow from the
auroral zone using in situ measurements used to require data accumulation intervals of at least
six months because the spacecraft orbit had to precess through all local times to sample the
outflow at those points.
However, using low energy neutral atom imaging, scientists can now
get global images of ion outflow in times as short as two minutes.
(click
here to see mpg movie of LENA ionospheric outflow -
warning large file 1.4 MByte).
In an article recently accepted in the
Journal of Geophysical Research - Space Physics
, Fuselier et al. show that in the ion outflow event
of June 24, 2000, changes in the solar wind density are associated with episodic bursts
of ion outflow, something suggested by previous observations (click
here for an example), but never imaged
globally --- until now. Fuselier et al. show that the charge exchange altitude or source region
for the low energy neutrals is about one Earth radius (i.e. 2 Earth radii from the center of the
Earth), consistent with a recent correlation analysis done on this event by Khan et al. and that
the ionospheric response to the solar wind signal is extremely rapid.
Click
here for a pdf file of the Fuselier et al. paper
Click
here for a list of outflow events observed
by LENA from May 6, 2000 through Dec 30, 2001
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