Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm23a2031r&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM23A-2031
Physics
[2154] Interplanetary Physics / Planetary Bow Shocks, [2164] Interplanetary Physics / Solar Wind Plasma, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions
Scientific paper
The terrestrial foreshock is a highly dynamic region. Inside the foreshock particles and waves occupy well defined regions which are delimited by transition regions or boundaries such as the ion foreshock boundary or the ULF wave foreshock boundary. The foreshock compressional boundary (FCB) is a new structure recently reported in global hybrid simulations by Omidi et al. (2009). This structure represents a transition region that separates the highly disturbed foreshock plasma from the solar wind plasma. The FCB is associated with a strong compression of magnetic field and density. Besides the enhancements in the field and density, the FCB also shows a region where these two quantities decrease below the ambient solar wind values. Hybrid simulations have shown that the formation and strength of the FCBs depend on the generation and nonlinear evolution of ultra low frequency waves generated by the interaction of backstreaming ions with the solar wind. In this work, we use Cluster magnetic field and plasma data to show that the foreshock compressional boundary exists and is frequently observed. We find that the compressional boundary is sometimes a transition region between the pristine solar wind plasma and the foreshock plasma. Other times, it separates a region with large amplitude waves from regions with high frequency (f˜0.25 Hz) small amplitude waves. We also study duration, amplitude and orientation of FCBs during 36 crossings for different solar wind conditions (speed, cone angle). Our results reveal that the FCB is a highly nonlinear structure with δB/Bo and δn/no amplitudes around 50% of the ambient values and extensions of a few Earth radii. The FCBs exist for different IMF geometries and Cluster data shows that the solar wind flow is decelerated and deviated around 10% through the FCB.
Blanco-Cano Xochitl
Kajdic Primoz
Omidi Nojan
Rojas-Castillo D.
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