Formation of Double Layer-Like Structures in Ionospheric Alfven Resonator

Details Formation of Double Layer-Like Structures in Ionospheric Alfven Resonator Formation of Double Layer-Like Structures in Ionospheric Alfven Resonator

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm21a1665s&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM21A-1665

Computer Science

Sound

7815 Electrostatic Structures, 7836 Mhd Waves And Instabilities (2149, 2752, 6050), 7839 Nonlinear Phenomena (4400, 6944), 7852 Solitons And Solitary Waves (4455)

Scientific paper

A two-dimensional numerical multi-fluid MHD model describing excitation of ionospheric Alfvén resonator (IAR) by a shear Alfvén wave is developed. In the model, the plasma consists of hydrogen and oxygen ions and electrons with finite temperatures. The nonlinear Lorentz force of the Alfvén wave, gravity force, and thermal pressure are included. The simulated area extends from the top-side ionosphere up to altitudes of a few Earth radii. The model uses density and temperature profiles typical for high-latitude auroral regions. For cold plasmas, Sydorenko, Rankin, and Kabin (2008) have found that the nonlinear force of standing IAR oscillations can produce deep density cavities in less than one minute that are similar to the ones observed in low-altitude magnetosphere. Here it is shown that at later stages (more than about one minute after the beginning of simulation), thermal pressure effects play an important role: perturbation of the initial equilibrium state by electron and ion flows that are created by the nonlinear Lorentz force amplifies the electric field directed along the geomagnetic field in proportion to the density gradient. Light hydrogen ions are accelerated by this electric field much stronger than the heavy oxygen ions. Eventually, at some locations the hydrogen ion flow speed may approach and even exceed the local sound speed. In this case, simulation reveals double layer-like structures with strong (about 0.1 mV/m) localized electric field directed upward. Evolution of such structures depends on the density and temperature profiles, as well as on the amplitude and frequency of the excited IAR eigenmode. The present study qualitatively supports available satellite measurements of intense parallel electrostatic fields in plasma cavities in the low-altitude magnetosphere [e.g., Chaston et al., 2007]. Chaston, C. C. et al., (2007), J. Geophys. Res., 112, A05215, doi:10.1029/2006JA012007. Sydorenko D., R. Rankin, and K. Kabin (2008), J. Geophys. Res., doi:10.1029/2008JA013579, in press.

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