On the use of Specific Entropy for Onboard Plasma Regime Characterization

Spring 2000, AGU Poster SM31A-12

J. Bonnell, S. Boardsen, M. Rilee, M. Bhat, and S. Curtis

Abstract

The locations of the magnetopause and other structures in the
Sun-Earth environment are fundamental inputs to the development of
Space Weather tools and operational models.  In this work, we present
an analysis of Hawkeye (1974-1978) data using the ion entropy as a
tool to distinguish between different regions of the magnetosphere and
as a magnetopause transition indicator.  The specific entropy of the
ions of an isotropic plasma is $S=p/n^{5/3}$.  Previous work with
ISEE-2 data has shown that $S$ is an indicator of magnetosheath and
plasma sheet plasmas, and that other boundary layer populations may
favor particular values of $S$.  Thus the single parameter $S$,
calculated from plasma moments, can provide much information about the
plasma environment in the vicinity of the spacecraft and its place
relative to the global structure.  The information provided by $S$
would be useful for onboard science management, real time information
for Space Weather, and multi spacecraft operations.  However, if the
determination of $S$ is to have any impact on the real time capability
of the spacecraft science instrumentation, then $S$ must be computed
onboard.


The Solar Terrestrial Probe Line Science Application Team of NASA's
Remote Exploration and Experimentation Project (REE/STP) has been
developing applications that take advantage of advanced computer
architectures that may dramatically improve the computing resources
available on board spacecraft.  The REE/STP Plasma Moment Application
(PMA) has been developed for REE's prototype flight processor to
examine issues associated with the development of onboard analyses of
plasma instrument data.  To test the PMA in a relevent, simulated
environment on real data, we are applying the PMA to Hawkeye plasma
instrument data to produce the fluid moments that are used to produce
$S$.  Details of the PMA as applied Hawkeye are the subject of another
presentation at this conference.