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First observations of a foreshock bubble: Implications for global magnetospheric dynamics and particle acceleration . Drew L. Turner, Nick Omidi , David G. Sibeck , and Vassilis Angelopoulos. Earth’s Foreshock Region. Quasi-parallel shock region - PowerPoint PPT Presentation
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THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
114 September 2011
First observations of a foreshock bubble:
Implications for global magnetospheric dynamics and particle acceleration Drew L. Turner, Nick Omidi,
David G. Sibeck, and Vassilis Angelopoulos
THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
214 September 2011
Earth’s Foreshock Region• Quasi-parallel shock region
• Characterized by suprathermal ions back-streaming from the bow shock
• Significant plasma instability and waves in this region
• Magnetopause disturbances can result from: – Hot flow anomalies (HFAs)– Foreshock cavities– Foreshock bubbles
IMF
Ion Foreshock
Magnetosheath
MagnetosphereSolar Wind
Omidi et al. [JGR 2005]
THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
314 September 2011
• Recent finding by Omidi et al. [JGR 2010] using 2.5-D hybrid simulations– Ions treated kinetically via
PIC; electrons as massless fluid
– 2-D in space; 3-D for currents and fields
• Demonstrated that foreshock “bubbles” can form after a discontinuity in the IMF
• These can then penetrate the sheath and disturb the magnetopause
• Foreshock bubbles have not yet been identified in-situ
Omidi et al. [JGR 2010]
Foreshock Bubbles
THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
414 September 2011
Bastille Day 2008• THEMIS-B and TH-C were in
the ion foreshock for much of the last half of the day
• TH-E and -D were near the magnetopause
• Several GOES were also available at GEO
• Several interesting foreshock events were observed, incl. one in particular just before 22:00 UT
THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
514 September 2011
Bastille Day 2008• Multiple foreshock phenomena observed in a
few hours…
THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
614 September 2011
Foreshock Bubbles• Features are consistent with foreshock bubble
simulations and are clearly moving with the solar wind
• Enhanced fluxes of energetic electrons and ions are consistent with additional particle acceleration
Omidi et al. [JGR 2010]Hybrid sim. predictions
THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
714 September 2011
FBs or HFAs?• HFAs shouldn’t be observed at TH-B; they are only
within ~2 RE of the bow shock• HFAs have compression regions on both sides• HFAs do not convect with the solar wind
THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
814 September 2011
Particle Acceleration• FBs involve two
converging shocks; they are ideal for significant particle acceleration by a combination of 1st and 2nd order Fermi and shock-drift acceleration!
THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
914 September 2011
Magnetosphere Effects3 compressions, consistent with 3 FBs
THEMIS/ARTEMIS SWG MeetingAnnapolis, MD
ARTEMIS
THEMIS
1014 September 2011
Conclusions
• Foreshock bubbles should occur regularly
• Like HFAs, foreshock bubbles can have drastic effects on the magnetosphere
• Foreshock bubbles are efficient particle accelerators via 1st and 2nd order Fermi and shock drift processes
• We plan on conducting further studies to identify more FBs and to compare and contrast HFAs and FBs
• These are first observations identified as a foreshock bubble, confirming the predictions made by Omidi et al. [2010] based on hybrid simulations
• Care must be taken using multi-point observations to distinguish between HFAs and foreshock bubbles
VY
Z
Omidi and Sibeck [JGR 2007]