Physics
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010jgra..11505206b&link_type=abstract
Journal of Geophysical Research, Volume 115, Issue A5, CiteID A05206
Physics
3
Magnetospheric Physics: Cusp, Magnetospheric Physics: Magnetosphere/Ionosphere Interactions (2431), Ionosphere: Ionospheric Dynamics, Ionosphere: Topside Ionosphere, Ionosphere: Particle Acceleration
Scientific paper
We investigate the origin of low-energy (Ek < 10 eV) ion upflows in Earth's low-altitude dayside cusp region. The Cusp-2002 sounding rocket flew from Ny Ålesund, Svalbard, on 14 December 2002, carrying plasma and field instrumentation to an altitude of 768 km. The Suprathermal Ion Imager, a two-dimensional energy/arrival angle spectrograph, observed large (>500 m s-1) ion upflows within the cusp at altitudes between 640 km and 768 km. We report a significant correlation between ion upflow and precipitating magnetosheath electron energy flux in this altitude range. There is only very weak correlation between upflow and wave power in the VLF band. We find a small negative correlation between upflow and the magnitude of the DC electric field for fields less than about 70 mV m-1. The apparent relation between upflow and electron energy flux suggests a mechanism whereby ions are accelerated by parallel electric fields that are established by the soft electrons. Significant ion upflows are not observed for electron energy fluxes less than about 1010 eV cm-2 s-1. The lack of correspondence between ∣$\vec{E∣ and upflow on the one hand, and wave power and upflow on the other, does not rule out these processes but implies that, if operating, they are not local to the measurement region. We also observe narrow regions of large ion downflow that imply either a rebalancing of the ionosphere toward a low-Te equilibrium during which gravity dominates over the pressure gradients or a convection of the upflowing ions away from the precipitation region, outside of which the ions must fall back into equilibrium at lower altitudes.
Burchill J. K.
Clemmons James Hart
Knudsen David J.
Oksavik Kjellmar
Pfaff Robert F.
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