Observations of thermal plasmas in Jupiter's magnetotail

Details Observations of thermal plasmas in Jupiter's magnetotail Observations of thermal plasmas in Jupiter's magnetotail

Jan 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002jgra..107.1003f&link_type=abstract

Journal of Geophysical Research (Space Physics), Volume 107, Issue A1, pp. SIA 1-1, CiteID 1003, DOI 10.1029/2001JA000077

Physics

12

Planetology: Solar System Objects: Jupiter, Planetology: Fluid Planets: Magnetospheres (2756), Magnetospheric Physics: Planetary Magnetospheres (5443, 5737, 6030), Magnetospheric Physics: Magnetotail

Scientific paper

A survey of thermal plasmas and magnetic fields ispresented for the orbit of the Galileo spacecraft around Jupiter that occurredduring the period May 4 through June 22, 1997. This orbit traversed the magnetotailout to Jovian radial distances of 100.2 RJ in the magnetotail. Perijove was positionedat 9.3 RJ.Three primary ion populations were detected with the plasma analyzer: coolhydrogen ions with temperatures of 10 eV, hot hydrogen ions with temperaturesof ~10 keV, and a third population of heavy ions such as O++,O+, S++, and S+++ withtemperatures in the range of 500 eV. Plasma flows near perijove were in thecorotational direction but with speeds ~60% of those for rigid corotationwith the planet out to radial distances of ~18 RJ. In the radial range of 18-26 RJ therewere significant radial components for the bulk flows, and the flow componentsin the corotational direction reached values expected for rigid corotationwhen the current sheet was crossed. The transient character of the plasmaparameters suggests that strong ion plasma acceleration is occurring in thisregion. The temperatures of the heavy ions increased from 5 × 106K at 9.3 RJto ~108 K at 26 RJ. At distances <20 RJ there is a strong dependence of ion temperatureson System III longitude. The scalar magnetic field outside of the currentsheet in the radial distance range 9.3-20 RJ varied as R-2.78and similar to that for a dipole field, and at distances >50 RJ it varied as R-1.19.The thermal plasma pressure in the current sheet is a factor of ~10 lessthan the magnetic pressure at 9.3 RJ at positions above or below the sheet butbecomes equal to this magnetic pressure at radial distances >30 RJ. The corresponding values of the ratio ofthe plasma to magnetic pressure, β, are in the range of 10-100in the current sheet. The number densities and temperatures of these plasmasare 0.05-0.1 /cm3 and 0.5-1 × 108K, respectively. In the magnetotail the bulk flows of the thermal plasmasexhibit substantial components in the corotational and radially outward directions,but the bulk speeds of 50-200 km s-1 are significantlyless than those for rigid corotation. For this single orbit the average bulkflows were ~50 km s-1 in the premidnight sectorand 200 km s-1 in the early morning sector at radialdistances >~50 RJ.At apojove of 100 RJan antisunward flow of ~200 km s-1 is found thatis supportive of the magnetospheric ``wind'' reported for Voyagermeasurements of energetic charged particles. The 10-hour periodicity of thepairs of current sheet crossings at the position of the Galileo spacecraftincludes a variety of dynamical signatures, which are suggested to be dueto the changes in direction and pressures in the solar wind and due to thetransient acceleration of plasmas in the current sheet.

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