Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm52b..02t&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM52B-02
Physics
[2700] Magnetospheric Physics, [2728] Magnetospheric Physics / Magnetosheath, [2740] Magnetospheric Physics / Magnetospheric Configuration And Dynamics, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions
Scientific paper
Here, we present unprecedented, multipoint observations of a recently predicted astrophysical plasma phenomenon, foreshock bubbles, which have not been identified previously in situ. First modeled and described in Omidi et al. [JGR, 2010], foreshock bubbles are kinetic phenomena that develop when plasma in Earth's quasi-parallel shock region, known as the foreshock, interacts with a discontinuity in the IMF. Foreshock bubbles develop a central, core region, which is characterized by low density and magnetic field strength, hot plasma temperatures, and highly deflected, sometimes even sunward, plasma flows. The expanding core region is surrounded by a compression layer of enhanced density and field strength that culminates in a fast magnetosonic shock on the upstream edge of the bubble, since it acts as a barrier to the upstream solar wind. The entire bubble structure scales with the foreshock region (order of 10 RE), grows in time, and is convected with the solar wind, such that if a foreshock bubble forms upstream of the bow shock on Earth's dayside, it will impact the magnetosheath and magnetosphere resulting in rapid expansion and compression of the entire system. Additionally, since foreshock bubbles consist of two, converging shocks, they should be particularly efficient at accelerating particles. For the observations, NASA's THEMIS spacecraft are used in conjunction with NOAA-GOES and the THEMIS ground magnetometer network to observe this new phenomenon and its effects on the magnetosphere. Using two spacecraft in the foreshock region, we clearly show that the events in question are fully consistent with the predictions of Omidi et al. [JGR, 2010], and the events exhibit several key inconsistencies with another, similar, and well-established foreshock phenomenon, hot flow anomalies. We discuss the events' global effects on the magnetosphere using two spacecraft along the dayside magnetopause, GOES at geosynchronous orbit, and ground magnetometers across North America, all of which clearly observe the global disturbance resulting from the foreshock bubble's impact. We finish with details on the observations of the energetic ions and electrons accelerated in the foreshock bubble, potentially by a combination of first and second order Fermi and shock drift acceleration processes. Solar wind ions are clearly isotropized and accelerated by the event, while solar wind electrons are also isotropized and accelerated up to ~10 keV, producing a suprathermal flux enhancement of up to two orders of magnitude. We conclude on a most interesting note, namely that this new phenomena is common and should play a role in energetic particle acceleration at collisionless, quasi-parallel shocks throughout the Universe.
Angelopoulos Vassilis
Omidi Nojan
Sibeck David G.
Turner Lincoln D.
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