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Dim ENA Emissions from 1-30 keV

Dim ENA Emissions from 1-30 keV. D.J. McComas, P. Valek, J.L. Burch, and C.J. Pollock Southwest Research Institute San Antonio, TX H.O. Funsten, R.M. Skoug, M.F. Thomsen Los Alamos National Laboratory Los Alamos, NM Yosemite Meeting – 8 February 2002. Introduction/Outline.

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Dim ENA Emissions from 1-30 keV

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  1. Dim ENA Emissions from 1-30 keV D.J. McComas, P. Valek, J.L. Burch, and C.J. Pollock Southwest Research Institute San Antonio, TX H.O. Funsten, R.M. Skoug, M.F. Thomsen Los Alamos National Laboratory Los Alamos, NM Yosemite Meeting – 8 February 2002

  2. Introduction/Outline • Looking for dim ENA emissions requires careful attention to all MENA backgrounds • Search for extended plasma sheet emissions • Find extended emissions associated w/ SDPSs • Find a remarkable background association w/ EPs • Examine low background emissions for annual and directional asymmetries • Discuss possible implications for heliospheric ENAs

  3. MENA Sensor Head Design

  4. Sources of Background Counts • Coincident events • Energetic ions passing/scattering through collimator • Some penetrating radiation • Non-coincident events • Solar and geocoronal UV (Ly-a & shorter) • MCP dark counts (typically ~1 cm-2) • Most penetrating radiation • Electronic noise • Electronic crosstalk

  5. Culling MENA Backgrounds • Only possible with complete information (“statistics data” or direct events) • Remove unphysical events • Too short and negative times-of-flight • Too small pulse heights • Illegal locations (stops in starts, gutters, etc.) • Correct high fluxes for under sampling • Not required for dim events examined here

  6. Raw Culled Head 1 MENA/Imm Stats: June 10, 2000; 11:01:37-11:21:38 (10 spins)

  7. Raw Culled Heads 1-3 MENA/Imm Stats: June 10, 2000; 11:01:37-11:21:38 (10 spins)

  8. Studying Dim ENA emissions • Achievable under locally quiet conditions • Not generally possible during storms • IMAGE at high altitude in Lobe • Culling required to remove spurious points • Must view away from bright emissions • Solar UV • Terrestrial scattered UV • Near-Earth ENA emissions

  9. 40-min Averaged MENA Images Typical Extended PS

  10. The Near-Earth Plasma Sheet 5 10 15 20 25 0 r [R ] E Borovsky et al., JGR, 103, 1998

  11. “Superdense” Plasma Sheet Borovsky et al., JGR, 103, 1998

  12. Superdense Plasma Sheet Intervals • Identified in MPA data in Geosync • 31 days over 8 months (Oct-May 2001) • 13 intervals suitable for comparison • Low enough backgrounds • Descent viewing (seasonal and orbital) • 11 of 13 show extended ENA emissions • Several strong examples • Very low background and excellent viewing • Extended PS ENA emissions clearly associated with superdense intervals • SDPSs extend well beyond Geosync

  13. GOES-8 Background Data • GOES-8 --- NOAA Geosync satellite • Energetic Particle Sensor (EPS) data* • Differential proton flux channel • 700 keV – 4 MeV (penetrates collimator) • May be tail of lower energy distribution • May scatter in collimators and/or gratings • Enter MENA through aperture • Create correlated start/stop (“real”) events * Thanks to Terry Onsager and NOAA/SEC

  14. April 2001

  15. May 2001

  16. MENA vs GOES

  17. Annual Variation of ENAs away from Earth Black = 2000 Red = 2001 Counts per Spin Day of year

  18. Spatial Variation of ENAs away from Earth Uncorrected • - GCI latitude vs longitude • - 366 apogee spins (of 530) • GOES < 5 / cm2 s sr MeV • Holes at IMAGE Z-axis • Bright near solar apex • (~271 ra, 30 dec) Coverage Corrected

  19. The Heliospheric interaction with the LISM Taken from Gruntman et al., JGR, 106, 2001

  20. Penetration of ENAs into Inner HSp Gruntman et al., JGR, 106, 2001 McComas et al., GRL, 26, 1999

  21. Models of HSp Interaction ENAs near 1 AU Gruntman et al., JGR, 106, 2001

  22. ACR generated ENAs Czechowski et al., ICRC 2001, 2001

  23. Model Energy Distributions of ACR-ENAs Czechowski et al., ICRC 2001, 2001

  24. Summary • Able to examine dim ENA emissions by careful attention to various MENA backgrounds • Found a remarkable background associated w/ GOES energetic protons • Discovered quite distant plasma sheet emissions associated w/ “superdense plasma sheet” intervals • SDPSs extend well beyond Geosync • Discovered annual and directional asymmetries in dim ENA emissions from ~1-30 kev that may be from heliospheric ENAs

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