Charge exchange between heavy, high charge state solar wind ions and exospheric neutral atoms creates soft X-ray emission throughout the terrestrial magnetosheath. This led Robertson et al. to ask the question: "What would IMAGE see if it had a soft X-ray instrument on board."

To answer that question, they simulated X-ray emission from the terrestrial magnetosheath as it would be observed by IMAGE (see diagram above). They conclude that the X-ray emission from the important cusp region, through which solar wind plasma can have direct access to the upper atmosphere, is dominant. They further discuss how X-ray and low energy neutral atom imaging observations (see thumbnail at right) of the magnetosheath serve as highly complementary techniques for determining global magnetosheath and cusp properties. This work has been published in the Journal of Geophysical Research, Space Physics (click here for pdf version of the manuscript by Robertson et al.)

In-situ spacecraft observations have shown that reconnection is operative poleward of the cusp for northward IMF. However, it has been uncertain how stable this region is. Taguchi et al. in a paper recently accepted in Advances in Polar Upper Atmosphere Research show that remote sensing with the LENA imager can be applied to determine the stability of the reconnection site. By using LENA neutral atom and SuperDARN radar data during a 24 minute period of high dynamic pressure and northward interplanetary magnetic field on March 27, 2001, Taguchi et al. show that reconnection and significant neutral atom emission occurred in the direction of the very high latitude magnetopause (see thumbnail 1 on the left). By monitoring the neutral atom emission, they show that the reconnection spot can shift considerably in a time period as short as ten minutes (see thumbnail 2 on the right). (click here for a PDF version of the Taguchi et al. article)

The ionosphere serves as an important source of plasma to the plasma sheet and magnetosphere in general. To determine how the ionospheric contribution changes in individual substorms, Nose et al. examined three geomagnetic storm intervals when IMAGE was near apogee and Geotail was in the nightside plasmasheet and both spacecraft observed ionospheric ions. As reported in their paper from the Eight International Conference on Substorms held in late March (http:/www.ics8.ca), they found that the neutral atom flux enhancements at storm-time substorms indicate that theses substorms can cause rapid (10-20 minutes) increases of the low energy ion flux over the ionosphere by up to an order of magnitude (see thumbnail). They report that the O+/H+ energy density ratio in the plasma sheet also increases rapidly. Coordinated multi-spacecraft studies such as the Nose et al. work eventually will reveal the full properties of geomagnetic storms and will allow us to mitigate the threats they pose. (click here for a PDF version of the Nose et al. article)

Neutral atom imaging provides an excellent global perspective, especially when viewing the Earth's auroral zone (the oval shaped regions around the north and south magnetic poles where the aurora is typically observed). This global perspective is supplemented and enhanced when there are other in situ (a Latin term that means in place or in position) observations available. In a recent paper in Geophysical Research Letters (click here for a PDF version), Fuselier et al. report on an event where the LENA imager was imaging neutrals created by charge exchange of ion outflow from the auroral zone and the Fast Auroral SnapshoT (FAST) spacecraft was making simultaneous in situ measurements of the ion outflow. The images show that the outflow occurs over nearly the entire dayside auroral oval at high latitudes, including the cusp. Although the FAST spacecraft observed the outflow only as it passed over the auroral zone and only at a specific position on the auroral oval, the LENA imager provided a global perspective of this outflow that was uninterrupted for nearly 2.5 hours! The combination of the two types of measurements leads to a better understanding of the global imaging and shows that ion outflow is a global and very steady process.

With activity ramping up on the Magnetospheric Multiscale Mission
( "SwRI" and "FPI" ), a mission to unlock the mysteries of magnetic reconnection, a ubiquitous process that converts magnetic field energy to particle energy, results on magnetic reconnection are particularly timely. In a recently accepted paper in Geophysical Research Letters (click here for pdf version), Taguchi et al. present simultaneous observations from IMAGE/LENA and the SuperDARN radar on March 27, 2001 showing LENA high latitude emission coincident with the enhancement of the sunward flow of the reverse convection in the ionosphere (Image to the right). By mapping field lines from the magnetosphere to the ionosphere, the authors infer that the source ions for the neutral atom emission are in the sunward flow region. They conclude that LENA can monitor ion entry caused by cusp magnetic reconnection, illustrating that neutral atom imaging complements in-situ observations of magnetic reconnection.