Ion Outflow in the Auroral Downward-Current Region: Moving Double Layers (DLs) vs. the Static Extended Potential Drop, and Parametric Studies for the DL-associated ion outflow

Details Ion Outflow in the Auroral Downward-Current Region: Moving Double Layers (DLs) vs. the Static Extended Potential Drop, and Parametric Studies for the DL-associated ion outflow Ion Outflow in the Auroral Downward-Current Region: Moving Double Layers (DLs) vs. the Static Extended Potential Drop, and Parametric Studies for the DL-associated ion outflow

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm31b0452h&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SM31B-0452

Physics

2704 Auroral Phenomena (2407), 2712 Electric Fields (2411), 2720 Energetic Particles: Trapped, 2736 Magnetosphere/Ionosphere Interactions (2431), 2753 Numerical Modeling

Scientific paper

Test particle simulations of ion outflow in the auroral downward-current region are performed to compare the effect of a series of localized, moving double layers (DLs) and a static, altitudinally extended parallel electric field ( Eallel). The profiles of DL potential, extended Eallel, and heating rates are based on in- situ observations and dynamic simulations. Moving DLs give rise to intermittent ion out-fluxes along the flux tube with time, supporting the observations that physical processes of the ion outflow might be intermittent. DL evacuates the downward-current-region flux tube via ion outflow effectively compared to the time scale of a convecting flux tube. The out-flowing ions in the DL run do not necessarily have to pass through the retarding potential of the DL, and appear to be "plowed" in front of the DL. The pressure-cooker ions that flow anti- earthward above the extended Eallel have to overcome the upper boundary of the extended Eallel which acts as a high-energy "filter" for ions appoaching from below. Ion density profile and distribution functions of the DL run dynamically change as a function of the relative distance to the DL and time, while those in the extended Eallel run are maintained stationary throughout the run. Parametric studies of the DL-associated heating profile, DL velocity, and DL starting alitude indicate that both H+ and O+ ions are observed to respond more efficiently for an intense, localized heating profile, rather than a moderate, wider heating along the flux tube. A faster DL greatly reduces number fluxes of both outflowing ions, and a slower DL retards H+ outflow a bit due to a limited source population in the lower ionosphere, but promotes O+ outflows by increasing the exposure time of ion heating.

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