Date:  Wednesday, February 8, 1995
Time:  4:15 PM   Refreshments at 4:00
Location:  ERL 126


Imaging and Spectroscopy of Atmospheric X-rays:
Experimental Methods and Recent Results

David Chenette
Space Sciences Laboratory
Lockheed Palo Alto Research Labs



Abstract


Energetic electrons from earth's magnetosphere are often precipitated into
the upper atmosphere as a result of geomagnetic disturbances. These
electrons can be a major source of ionization and can significantly modify
the chemistry and dynamics of the upper atmosphere. Monitoring these
precipitating electrons is therefore essential to understanding an
important component of the coupling between the magnetosphere, ionosphere,
and upper atmosphere. Direct measurements of the intensities and energy
spectra of the precipitating electrons provide detailed information, but
only at a single location. By measuring bremsstrahlung x-rays emitted from
the top of atmosphere the precipitating electron intensities and fluxes can
be sensed remotely, and large areas can be covered from a single platform.
Lockheed has flown a series of x-ray spectrometers for this purpose, each
with its own unique design features and scientific objectives. One
instrument, AXIS, is currently operating aboard NASA's Upper Atmosphere
Research Satellite, and another, PIXIE, is being prepared for launch late
this year on NASA's POLAR satellite. We will describe these two
instruments, which use very different measurement techniques. We also will
discuss the interactions of precipitating electrons with the upper
atmsophere and how we extract electron spectra from the x-ray measurements.
Recent results from the AXIS/UARS instrument will be presented and compared
with results anticipated from PIXIE.