Cluster Observations of Non-linear Waves in the Foreshock Region

Details Cluster Observations of Non-linear Waves in the Foreshock Region Cluster Observations of Non-linear Waves in the Foreshock Region

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh53b2037l&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SH53B-2037

Physics

Plasma Physics

[2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions, [4455] Nonlinear Geophysics / Nonlinear Waves, Shock Waves, Solitons, [7839] Space Plasma Physics / Nonlinear Phenomena, [7867] Space Plasma Physics / Wave/Particle Interactions

Scientific paper

In Earth's foreshock regions upstream moving particles interact with the solar wind and generate ULF waves when resonant condition is matched. These waves are convected downstream and may enter the magnetosheath, and serve as an important contributor to the transfer of solar wind energy into the magnetosphere. There is a group of nonlinear fluctuations and transient structures in the foreshock regions (e.g. density holes, SLAMS), whose physical mechanism has not been fully understood. It is likely that these transient structures are nonlinearly steepened ULF waves, which are related to back streaming ions or to the plasma temperature anisotropy. We have studied these waves using Cluster observations, which allow us to determine comprehensive wave properties (the propagation direction, phase velocity in the plasma frame, polarization etc.). The observations show that for both linear and nonlinear fluctuations there exist Alfven type (left hand polarized in the plasma rest frame) and fast mode type (right hand polarized in the plasma frame) waves. Corresponding ion distributions show that the ion often consists of the solar wind beam and hotter ion components of back streaming ions with Tpara > Tperp. When the wave amplitude grows, the energetic component became more diffuse (Tpara ~ Tperp ) and the peak disappears. The changes indicate that the energetic ion component serves as the energy source of the waves. High frequency waves are excited at edges and within the transient structures, which include whistler mode waves and electrostatic waves at higher harmonics of electron cyclotron frequencies. These high frequency waves may play important roles in plasma heating within the structures.

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