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During the Leonid meteor shower on 18 November 1999, the five spectrographic imagers onboard the Midcourse Space Experiment (MSX) satellite recorded the first complete meteor spectra from 110 to 860 nm. The observation occurred at 00:23:36.2 UT, at which time satellite was pointed at a tangent altitude of 100 km over 37.2°N and 78.2°E. The spectrograph slits were oriented approximately parallel to the horizon, and the meteor passed approximately perpendicular through the slits’ fields of view. All five spectrographic images serendipitously observed the passage of the object and each recorded 1–2 frames of data. Common meteor emissions from iron, sodium, and oxygen were observed in the visible, but the ultraviolet spectrum displayed a wealth of new features. The most intense features appeared in the middle ultraviolet (250–300 nm) from neutral and singly ionized iron and singly ionized magnesium. Far ultraviolet (110–130 nm) features included oxygen and nitrogen, a bright hydrogen Lyman α emission, and ionized iron and magnesium emissions. Also seen in the far ultraviolet were weak but recognizable emissions from neutral carbon. The ultraviolet emissions were much stronger than those in the visible and near-infrared. The meteor had a visual magnitude of −2.8 at 100 km, but the energy of emissions in the ultraviolet (110–337 nm) exceeded the energy of the visible (337–560 nm) by a factor of at least 5. The new Lyman α and carbon emissions in the far UV as well as the overall intensity of the ultraviolet spectrum suggest important applications for ultraviolet observations of meteors.

The Ultraviolet and Visible Imaging and Spectrographic Imaging (UVISI) instrument on the Midcourse Space Experiment (MSX) satellite obtained unique ultraviolet (200–350 nm) images and spectrographic images of polar mesospheric clouds over both the northern and southern poles during the summers of 1997–1999. Imager observations revealed that PMCs have essentially the same altitudes in the north and south (82.7 ± 1.3 km) and that cloud altitudes remain essentially constant with latitude. Imagery from below the horizon showed PMC structures with scales ranging from 100 to over 500 km. Integrated from 235 nm to 265 mn, PMC limb intensities were essentially the same in both hemispheres, averaging 12 mega-Rayleighs at peak altitude. Intensities increased with latitude toward the poles. Spectrographic observations reveal the clouds have a solar-like spectrum from 200 nm to 600 nm, but that short of 315 nm the spectrum is contaminated with ground albedo effects. Between 200 nm and 315 nm, the scattering ratio (PMC spectral intensity to solar irradiance) is less steep than that expected from pure Rayleigh scattering. When the scattering ratio is least-squares fit to a log-normal distribution of Mie scatterers, the distribution has a mode radius of 65 nm and a dispersion of 1.2 with no dependence on latitude or time from solstice. The slope of the scattering ratio changes as a function of altitude relative to the altitude peak of the PMC intensity, suggesting that particles 3 km above this peak are smaller than particles at the peak and 3 km below.

Observations of the spatial structure and distribution of Polar mesospheric clouds (PMCs) in the northern and southern polar regions were made during the arctic summers of 1998–1999 and austral summer of 1997–1998 by a middle ultraviolet imager (235–263 nm). The imager look-point made multiple transpolar passes over the Arctic and Antarctic and obtained thousands of images of PMCs at latitudes poleward of 55°. The unprecedented accuracy and stability of the satellite platform (∼10 μrad) allowed investigation of both the large-scale (100 km) and small scale (∼1 km) spatial structures of PMCs. The UV imager readily observed PMCs distinct from the atmospheric backgrounds. The clouds existed in discrete, filamentary structures throughout the polar region above latitudes of ∼55°. Vertically, PMCs generally lie between altitudes of 82.0 and 83.0 km, but within this range, cloud altitudes are essentially random on transpolar scales of ∼1000 km. In some instances, the clouds cluster at common altitudes for distances of ∼100 km. The PMC altitudes do not appear correlated with latitude or local time. A diffuse signal above the clouds, possibly related to Polar Mesospheric Summer Echoes, was observed in some cases. Horizontally, PMCs exhibit structure on scales of ∼50 km to ∼1000 km that is probably related to gravity wave activity in the polar region. The horizontal periodicities of the PMCs can remain stable for at least 24 hours.

Long-lived upstream energetic ion events at Jupiter appear to be very similar in nearly all respects to upstream ion events at earth. A notable difference between the two planetary systems is the enhanced heavy ion compositional signature reported for the Jovian events. This compositional feature has suggested that ions escaping from the Jovian magnetosphere play an important role in forming upstream ion populations at Jupiter. In contrast, models of energetic upstream ions at earth emphasize in situ acceleration of reflected solar wind ions within the upstream region itself. Using Voyager 1 and 2 energetic ion measurements near the magnetopause, in the magnetosheath, and immediately upstream of the bow shock, the compositional patterns are examined together with typical energy spectra in each of these regions. Characteristic spectral changes are found late in ion events observed upstream of the bow shock at the same time that heavy ion fluxes are enhanced and energetic electrons are present. A model involving upstream Fermi acceleration early in events and emphasizing energetic particle escape in the prenoon part of the Jovian magnetospehre late in events is presented to explain many of the features in the upstream region of Jupiter.