In a recently accepted paper in the Journal of Geophysical Research, Wilson and Moore analyze LENA perigee data from the Summer of 2000 and find a strong correlation between the Ap index, which measures the general level of geomagnetic activity over the globe due to currents flowing in the Earth's ionosphere and magnetosphere, and the low energy neutral atom flux soon after perigee [see the figure to the right].

They conclude that many of the emitted ENA come from the auroral zone and are produced by energized ionospheric ions rather than through precipitation. Among the data they analyzed was one of the most spectacular events seen in the LENA data: The Bastille Day Storm [the figure to the right]. At the time of the LENA data, Polar UVI auroral images show an unusually intense oval centered at about 60 degrees magnetic latitude (see inset). Wilson and Moore conclude that for this event, the neutral atoms observed by LENA originate primarily in the auroral oval.

Wurz et al. argue in a paper recently accepted for publication in the AIP Conference Proceedings that the secondary stream comprises primarily hydrogen atoms with energy of about 1 keV and that the shape of the distribution most likely represents the spatial distribution in longitude of the secondary stream source. Based on the LENA data, Wurz et al. deduce a secondary stream density of 4x10^-2 cm^-3 and a temperature of about 3x10⁴ K. They believe the source to be the region upstream of the termination shock and point out that the Mars Express/ASPERA-3 instrument may be able to observe the secondary stream.

Click here for a PDF file of the Wurz et al. paper.

In a recent paper accepted in Advances in Polar Upper Atmosphere Research, Taguchi et al. show that during an event on April 11, 2001 the motion of the emission observed by LENA at high altitudes and the latitudinal motion of the backscattered signal detected by the SuperDARN radar in the dayside ionosphere have similar behavior which appears controlled by the interplanetary magnetic field north-south component. The variations observed imply that the cusp moves equatorward during the event while undergoing brief poleward shifts

Click here for a PDF file of the Taguchi et al. paper.