Ion Outflow in the Dayside Cusp Ionosphere and its Dependence on Soft Electron Energy Flux

Details Ion Outflow in the Dayside Cusp Ionosphere and its Dependence on Soft Electron Energy Flux Ion Outflow in the Dayside Cusp Ionosphere and its Dependence on Soft Electron Energy Flux

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm31c..07b&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SM31C-07

Physics

[2400] Ionosphere, [2437] Ionosphere / Ionospheric Dynamics, [2455] Ionosphere / Particle Precipitation, [2706] Magnetospheric Physics / Cusp

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) O+ upflows within the cusp at altitudes between 640 km and 768 km. We report a significant association between ion upflow and precipitating magnetosheath electron energy flux in this altitude range, but no causal links between upflow and either wave power or the magnitude of the dc electric field. The correspondence between upflow and logarithm of the electron energy flux suggests a mechanism whereby ions are accelerated locally by ambipolar electric fields that are driven by the soft electrons. Significant ion upflows are not observed for electron energy fluxes below ˜1010 eV cm-2s-1, which suggests that any ambipolar fields present above 640 km must be in equilibrium with gravity and pressure gradients under this condition. The lack of correspondence between │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 observe narrow regions of large downflow that imply either a re-balancing of the ionosphere toward a low-Te equilibrium during which gravity dominates the pressure gradients, or convection of the upflowing ions away from the precipitation region, outside of which the ions must fall back into equilibrium at lower altitudes.

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