Physics – Geophysics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm31d..03m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM31D-03
Physics
Geophysics
[2704] Magnetospheric Physics / Auroral Phenomena, [2712] Magnetospheric Physics / Electric Fields, [2753] Magnetospheric Physics / Numerical Modeling, [4455] Nonlinear Geophysics / Nonlinear Waves, Shock Waves, Solitons
Scientific paper
Observations from the Fast Auroral SnapshoT (FAST) spacecraft indicate that a strong localized electric field often exists at the boundary between the ionosphere and auroral cavity in the upward current region. The observed electric field structures are found to have widths that are on the order of tens of electron Debye lengths and have components both parallel and perpendicular to Earth’s magnetic field and are therefore said to be an “oblique” electric field. These oblique electric fields have previously been modeled by static BGK double layer solutions. Dynamic Vlasov simulations have shown that a non-oblique double layer models the parallel component of the observed electric field structures well, is quasi-stable and persists long enough to account for the often observed ion phase space holes in the auroral cavity. However, to date, it has not been clear how an oblique double layer can form and remain quasi-stable. Using an open boundary 1D3V particle-in-cell simulation, we present a parameter study of over 20 simulations in which we vary cold electron density and temperature and show the necessary conditions for maintaining both oblique and non-oblique double layers at the lower boundary of the upward current region. The simulation includes an assumed density cavity, hot auroral cavity electrons, cold ionospheric electrons, a hot H+ component and anti-earthward traveling H+ and O+ ion beams. We do not assume that any localized potential drop initially exists. Rather, if a DL forms, it does so self-consistently at the interface of the dense ionosphere and tenuous auroral cavity. Based on the PIC results, we find that the oblique double layer requires a cold (< 5 eV) ionospheric electron population to remain quasi-stable. We also compare the shape of the simulated double layer with observed double layers and show that the observed asymmetric shape can also be explained by the temperature and density of the cold ionospheric electrons. We will also present results of simulated double layers from a 2D3V PIC simulation. We will examine the evolution of both the oblique and non-oblique double layers in two spatial dimensions and again show that the oblique 2D double layer is quasi-stable and retains its planar geometry, justifying the 1D3V simulations of oblique double layers. Furthermore, we will examine the plasma waves which form in the vicinity of the 2D double layer and make comparisons with observations.
Ergun Robert E.
Main D. S.
Newman Dara
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