Physics
Scientific paper
Jun 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992spie.1744...19r&link_type=abstract
Proc. SPIE Vol. 1744, p. 19-30, Instrumentation for Magnetospheric Imagery, Supriya Chakrabarti; Ed.
Physics
1
Scientific paper
Trapped in the magnetosphere are two distinct ion populations: the cold (approximately 1000 degree(s)K) H(superscript +) and He(superscript +) in the plasmasphere and the hot (20 - 200 keV) H(superscript +) and O(superscript +) in the ring current. Both populations respond strongly to geomagnetic storm disturbances in the global electric and magnetic fields, so images of them would provide powerful diagnostics of magnetosphere processes. Fortunately, 'proof-of- concept' spacecraft measurements have demonstrated that plasmaspheric He(superscript +) can be imaged in the re-radiation of the solar He(304 angstroms) line, in the extreme ultraviolet (EUV), and that the ring current H(superscript +) and O(superscript +) can be imaged using the energetic neutral atoms (ENA) produced when singly-charged hot ions charge exchange with the Earth's tenuous H-atom exosphere (hydrogen geocorona). Because both He(304 angstroms) and ENA emission are 'optically thin', images of the complex 3-dimensional structure of the plasmasphere He(superscript +) or ring current H(superscript +) and O(superscript +) populations exhibit considerable variation in intensity and configuration, depending upon the point of view of the image. Consequently, the design of practicable magnetospheric EUV and ENA imagers has required the computer simulation of these emissions. The models for the plasmasphere and ring current incorporates decades of in situ spacecraft particle measurements and ground-based observations into the framework of the theory of magnetospheric processes. Examples of simulated He(304 angstroms) and ENA images are presented, along with the derived instrumental requirements. Finally, there is the important question of the accuracy with which physically significant parameters can be extracted from actual images using computerized algorithms. An example is given of an ENA image analyzed by means of the Powell minimization algorithm.
Mauk Barry H.
Meier Robert R.
Roelof Edmond C.
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