stereo observations of langmuir waves and ion events in ... · (filbert and kellogg 1979 and many...
TRANSCRIPT
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STEREO Observations of Langmuir Waves and IonEvents in the Terrestrial Foreshock
M. Pulupa, S.D. Bale, R.P. Lin, J. Luhmann, D.E. Larson,R. Ergun, K. Goetz, M. Kaiser, M. Maksimovic
STEREO Science Working Group Meeting20-22 April 2008
Meudon, France
Outline
Introduction
Early STEREO Orbit
Electron Foreshock
Ion Foreshock
Conclusions andFuture Work
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Introduction
Early STEREO Orbit
Electron Foreshock
Ion Foreshock
Conclusions and Future Work
The Foreshock
Introduction
The Foreshock
Instruments
Early STEREO Orbit
Electron Foreshock
Ion Foreshock
Conclusions andFuture Work
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• The foreshock is the regionupstream of Earth’s bowshock that is magneticallyconnected to the shock.
• Particles in the interplan-etary medium travel alongfield lines and can be mir-rored by the bow shock.
• The reflected beams causebump-on-tail velocity distri-butions and generate Lang-muir wave emission.
(Filbert and Kellogg 1979 andmany others)
Instruments
Introduction
The Foreshock
Instruments
Early STEREO Orbit
Electron Foreshock
Ion Foreshock
Conclusions andFuture Work
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STE:
• 2-100keV• Solid state detector• Electrons, ions, neutrals• 4 look directions, down-
stream and upstream (STE-U is not working)
XGSE
YGSE
D0
D1
D2
D3Sun
Nominal Parker spiral
SWEA:
• 8-2000 eV• Electrostatic detector• Nearly 4π angular resolution
Late 2006: Petal Orbit
Introduction
Early STEREO Orbit
Late 2006: PetalOrbitEarly 2007:STEREO/Ahead inthe Foreshock
Electron Foreshock
Ion Foreshock
Conclusions andFuture Work
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Early 2007: STEREO/Ahead in the Foreshock
Introduction
Early STEREO Orbit
Late 2006: PetalOrbitEarly 2007:STEREO/Ahead inthe Foreshock
Electron Foreshock
Ion Foreshock
Conclusions andFuture Work
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Electron Foreshock
Introduction
Early STEREO Orbit
Electron Foreshock
Electron Event
Electron spectra
Distribution ofelectron events
Ion Foreshock
Conclusions andFuture Work
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Electron Foreshock Event
Intense Langmuir waves at fp accom-panied by STE and SWEA electronsindicate foreshock electron beam.
SWEA PADs
STE PADs
Energy spectra for each STE lookdirection. Electron beam is visible inSTE D0 and D3.
Electron spectra
Introduction
Early STEREO Orbit
Electron Foreshock
Electron Event
Electron spectra
Distribution ofelectron events
Ion Foreshock
Conclusions andFuture Work
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• Blue = Parallel, Red = Perpendicular.• Electron beam present in both SWEA and STE.• Pitch angle coverage limited by fixed look directions of STE.
Distribution of electron events
Introduction
Early STEREO Orbit
Electron Foreshock
Electron Event
Electron spectra
Distribution ofelectron events
Ion Foreshock
Conclusions andFuture Work
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Hundreds of events, no imme-diately obvious organization byspacecraft position.
Electrons continue to be ob-served months into 2007. (Theblank space is due to incompletecataloguing, not a data gap ora dearth of events.)
Ion Foreshock
Introduction
Early STEREO Orbit
Electron Foreshock
Ion Foreshock
Ion Foreshock
Ion spectra
Foreshock eventwith fine structureDistribution of ionevents
Conclusions andFuture Work
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Ions in the ULF Foreshock
Strong ULF fluctuations
Only intermittent Langmuirwave activity
Monoenergetic, mostlyisotropic beam from around10-80 keV suggests diffuseions rather than electrons.Note anticorrelation be-tween peak flux and peakwave activity.
Field aligned ion beam orelectrons near beginning ofevent?
(Mazelle 2002 and others)
Ion spectra
Introduction
Early STEREO Orbit
Electron Foreshock
Ion Foreshock
Ion Foreshock
Ion spectra
Foreshock eventwith fine structureDistribution of ionevents
Conclusions andFuture Work
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• Blue = Parallel, Red = Perpendicular.
Ion Foreshock Event with FineStructure
Evolution of lower and upper energycutoffs, at times upper limit of ener-gies reaches ≥ 100 keV
Same general structure seen in allSTE look directions, but there issome difference in intensity.
No plasma wave activity
Magnetic field mostly dominatedby Bx with By and Bz fluctuatingaround 0.
No evidence of electrons
Distribution of ion events
Introduction
Early STEREO Orbit
Electron Foreshock
Ion Foreshock
Ion Foreshock
Ion spectra
Foreshock eventwith fine structureDistribution of ionevents
Conclusions andFuture Work
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Light blue dot is an ion event,dark blue dot is an ion eventwith associated ULF activity.
Ion events continue, but ULFevents die out. Issue of distanceversus depth.
Conclusions and Future Work
Introduction
Early STEREO Orbit
Electron Foreshock
Ion Foreshock
Conclusions andFuture WorkConclusions andFuture Work
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• STE and SWEA see many examples of electrons and ionsupstream of the foreshock. STEREO/A continues to observeupstream particles well into 2007.
• STE can measure the energy spectrum of foreshock electronbeams with good sensitivity and energy resolution. However, itis limited by incomplete pitch angle coverage.
• STE also sees ion events, including ULF events. The strengthand frequency of ULF events decreases as STEREO/A movesfarther from the bow shock, but it is unclear whether this isdue to distance or depth in the foreshock.
• Put observations in magnetic coordinates (organized by θBN
and depth in foreshock) rather than GSE coordinates. A betterbow shock model is necessary.
• Resolve ambiguous events and use current SWEA data.
Introduction
Early STEREO Orbit
Electron Foreshock
Ion Foreshock
Conclusions andFuture WorkConclusions andFuture Work
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Thank you!