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Radiation Belt Precipitation due to Manmade VLF Transmissions: Satellite Observations

Radiation Belt Precipitation due to Manmade VLF Transmissions: Satellite Observations. Rory J Gamble 1 , Craig J Rodger 1 , Mark A Clilverd 2 , Neil R Thomson 1 , Simon L Stewart 1 , Robert J McCormick 1 , Michel Parrot 3 , Jean-André Sauvaud 4 , Jean-Jacques Berthelier 5.

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Radiation Belt Precipitation due to Manmade VLF Transmissions: Satellite Observations

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  1. Radiation Belt Precipitation due to Manmade VLF Transmissions: Satellite Observations Rory J Gamble1, Craig J Rodger1, Mark A Clilverd2, Neil R Thomson1, Simon L Stewart1, Robert J McCormick1, Michel Parrot3, Jean-André Sauvaud4, Jean-Jacques Berthelier5. 1 - Department of Physics, University of Otago, Dunedin, New Zealand 2 - Physical Sciences Division, British Antarctic Survey (NERC), Cambridge, United Kingdom 3 - Laboratoire de Physique et Chimie de l'Environnement, Orleans, France 4 - Centre d'Étude Spatiale des Rayonnements, Toulouse, France 5 - Centre d'Études des Environnements Terrestre et Planétaires, Saint Maur des Fosses, France

  2. Introduction/Motivation - We know that inner belt losses are dominated by waves, but don't know relative importance of different types. - Manmade VLF transmissions may dominate losses in the inner radiation belts [Abel and Thorne, 1998] - Particle enhancements not well-tied to VLF wave observations. - Occurrence frequency of drift-loss cone enhancements above transmitters is unknown. - DEMETER satellite can be used to study trapped electron population characteristics. - Ground-based Radiation Belt Remediation.

  3. History • Imhof et al. (1973): • - VLF transmitter interactions first observed as narrow peaks in satellite electron spectrometer data. • - Energy of peak flux followed first-order resonance relationship for a single VLF transmitter.

  4. Imhof, W. L. et al. (1973), Dynamic Variations in Intensity and Energy Spectra of Electrons in the Inner Radiation Belt. J. Geophys Res. 78 (22).

  5. History • Datlowe and Imhof (1990): • - Determined that resonances observed by the S81-1 satellite are probably dueto NWC and NAA. • - Quantitatively showed that interaction is by first order cyclotron resonance.

  6. History Figure 1. Datlowe, D. (2006), Differences between transmitter precipitation peaks and storm injection peaks in low altitude energetic electron spectra, J. Geophys Res., 111, A12202, doi:10.1029/2006JA011957

  7. DEMETER Satellite • Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions • - Developed by CNES (France)‏ • - Instruments including: • ICE (Electric field detector)‏ • IDP (Energetic particle detector)‏ • - Data for invariant latitudes below ~65°, L~1-7 • - Low Earth orbit: 710km altitude • - Sun-synchronous polar orbit (see next slide)‏ http://smsc.cnes.fr/DEMETER/index.htm

  8. DEMETER Orbit Configuration

  9. DEMETER - ICE -Records one component of E field vector -We use VLF power spectrum data (type '1132')‏ - 1024 channel FFT - 19.5Hz– 20kHz (19.5Hz /channel)‏ - Averaged spectrum given every 4s

  10. DEMETER – Nighttime ICE World map ice, showing nwc, at night time.

  11. DEMETER – Daytime ICE Received power ~1200 times lower over transmitter during local daytime.

  12. DEMETER - IDP - Records energetic electron fluxes spectra - Very good quality: - 17.8 keV channel resolution - 73keV – 2.35MeV (128 channels)‏ - Complete spectrum every 4s - Looks perpendicularly to the orbital plane of satellite (never illuminated by the sun)‏ - Measures particle fluxes inside (or just outside) the drift loss cone.

  13. DEMETER – Daytime IDP

  14. DEMETER – Nighttime IDP

  15. NWC VLF Transmitter • - US Naval VLF transmitter (Northwest Cape, Australia)‏ • - Well located to influence inner belt energetic particles: • - higher latitude transmitters interact with energies lower than IDP instrument can detect. • - immediately east of the SAMA • - L=1.45, inner radiation belt - One of the world’s most powerful: 1000kW radiated power - Frequency: 19.8kHz, within DEMETER’s 20kHz resolution - Signal strength is recorded by OmniPAL reciever in Dunedin (AARDDVARK network).

  16. NWC Dunedin

  17. NWC VLF Transmitter

  18. NWC VLF Transmitter

  19. Single Half-Orbit: West of NWC

  20. Single Half-Orbit: West of NWC Pcolors of ICE and IDP as a function of time

  21. Single Half-Orbit: East of NWC

  22. Single Half-Orbit: East of NWC Pcolors of ICE and IDP as a function of time, including wisp

  23. Wisp Characteristics

  24. Wisp Characteristics

  25. Wisp Characteristics

  26. Day Night East 46 (0)‏ 43 (40)‏ West 46 (0)‏ 45 (3)‏ Wisp Occurence - Data from 12 August – 26 September 2005 period - Half orbits which pass within +/- 25º longitude of the Tx are selected for closer inspection. - These half orbits are visually inspected for the presence of wisps (blind inspection)‏ - Half orbits are sorted into day/night and east/west orbits Over 95% of night, eastern orbits showed wisps!

  27. NWC Dependence - Apart from short periods of weekly daytime routine maintenance, NWC is rarely down - Continuous recordings of NWC signal strength show that NWC was offline for 15 days (13 – 28 June 2005)…

  28. NWC Dependence - Apart from short periods of weekly routine maintenance, NWC is rarely down - Continuous recordings of NWC signal strength show that NWC was offline for 15 days (13 – 28 June 2005). - All suitable orbital passes from this period were examined. Result: No wisps seen while NWC was offline.

  29. Lower L Middle L Upper L Lower E (keV)‏ Middle E (keV)‏ Upper E (keV)‏ Peak Flux Enhancement Mean 1.62 1.71 1.84 105 181 280 410 x bg Median 1.61 1.71 1.85 94 169 281 111 x bg Wisp Characteristics The L range, energy range and maximum flux enhancement (w.r.t. a reference background spectrum) was recorded for each wisp. Lower energy bound limited by instrument Upper energy can be as large as 453 keV Peak flux can be as large as 3600 times background levels

  30. Variation with L of the first-order equatorial cyclotron resonant energy with a 19.8 kHz wave (black), and the plasmaspheric electron number density used in this calculation (dashed gray). Compiled by C. J. Rodger using Chang and Inan [1983], Carpenter and Anderson [1992], Mahaian and Brace [1969]

  31. NPM Hawaii

  32. NPM Hawaii - L=1.17, inner radiation belt - Also potentially well positioned for study: - more equatorial than NWC - further east of NWC - Less powerful: 500kW radiated power - Expect higher interaction energy No evidence of wisps was found due to NPM

  33. Conclusions - DEMETER is used to study enhancements in DLC electron population due to NWC - NWC operation directly associated with DLC enhancements: - Interaction relies on night time ionosphere - Very common: ~95% of suitable orbits showed clear interaction. - Also using DEMETER to characterise stormtime processes

  34. January 2005 Storm Period

  35. January 2005 Storm Period

  36. Storm Period Movie

  37. Acknowledgements Craig Rodger Neil Thomson Mark Clilverd Simon Stewart & Robert McCormick Polar Environments Research Theme CNES/DEMETER

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