Radiation Belt Precipitation due to Manmade VLF Transmissions

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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
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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.
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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.
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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).
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History
Datlowe and Imhof (1990) - Determined that
resonances observed by the S81-1 satellite are
probably due to NWC and NAA. - Quantitatively
showed that interaction is by first order
cyclotron resonance.
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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,
doi10.1029/2006JA011957
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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, L1-7 - Low Earth orbit
710km altitude - Sun-synchronous polar orbit (see
next slide)?
http//smsc.cnes.fr/DEMETER/index.htm
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DEMETER Orbit Configuration
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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
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DEMETER Nighttime ICE
World map ice, showing nwc, at night time.
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DEMETER Daytime ICE
Received power 1200 times lower over transmitter
during local daytime.
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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.
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DEMETER Daytime IDP
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DEMETER Nighttime IDP
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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
• - L1.45, inner radiation belt
• - One of the worlds most powerful 1000kW
  radiated power
• - Frequency 19.8kHz, within DEMETERs 20kHz
  resolution
• - Signal strength is recorded by OmniPAL reciever
  in Dunedin (AARDDVARK network).

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NWC
Dunedin
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NWC VLF Transmitter
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NWC VLF Transmitter
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Single Half-Orbit West of NWC
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Single Half-Orbit West of NWC
Pcolors of ICE and IDP as a function of time
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Single Half-Orbit East of NWC
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Single Half-Orbit East of NWC
Pcolors of ICE and IDP as a function of time,
including wisp
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Wisp Characteristics
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Wisp Characteristics
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Wisp Characteristics
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Wisp Characteristics
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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!
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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)
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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.
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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
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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
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NPM Hawaii
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NPM Hawaii
- L1.17, 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
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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
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January 2005 Storm Period
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January 2005 Storm Period
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Storm Period Movie
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Acknowledgements
Craig Rodger Neil Thomson Mark Clilverd Simon
Stewart Robert McCormick Polar Environments
Research Theme CNES/DEMETER