Observing ion cyclotron waves

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Observing ion cyclotron waves
NSF Workshop on Small Satellite Missions for
Space Weather and Atmospheric Research George
Mason University, Arlington Campus, VA
M. R. Lessard, M. Widholm, P. Riley, H. Kim M.
J. Engebretson
University of New Hampshire Augsburg College
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Pressure pulses, EMIC waves and the ring current
1. Electromagnetic Ion Cyclotron (EMIC) waves
first observed in the vicinity of the
plasmapause, associated with anisotropic proton
distributions (10s of keV) and increased levels
of cold plasma. 2. Likely plays a role in
thermalizing ring current protons immediately
following magnetic storms Cornwall et al., 1970
Lyons and Thorne, 1972 Cornwall et al., 1970
Lyons and Thorne, 1972. 3? Satellite studies
confirm an increase occurrence of EMIC waves
during storms Bräysy et al.,1998 and Erlandson
and Ukhorsky, 2001. Can contribute significantly
to ring current losses during recovery phase. 4?
Several studies show ground observations of EMIC
waves associated with pressure pulses Olson and
Lee, 1983 Kangas et al., 1986 Arnoldy et al.,
1988 Arnoldy et al., 1996. Recent work shows
ground/satellite observations of these waves with
precipitation of protons with several keV energy
Arnoldy et al., 2005.
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Pressure pulses, EMIC waves and the ring current
Energetic particle Precipitation region
lt-propagation
EMIC wave generation region
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EMIC wave propagation and radiation belt electrons

• Ground observations (Engebretson et al,
  manuscript under review) show
• Narrowband Pc 1-2 waves are rarely if ever
  observed on the ground during the main and early
  recovery phases of magnetic storms.
• As storm recovery progresses, occurrence of Pc
  1-2 waves increases, at first during the daytime
  and afternoon sectors, but at all local times
  typically by days 3 or 4.
• Why waves are seen in space during onset and main
  phase and consistently not seen on the ground is
  not understood - likely implication is that some
  reflection and/or absorption of these waves takes
  place away from the equator. Or, perhaps the
  satellite-based observations are, in fact,
  atypical.

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EMIC wave propagation and radiation belt electrons
May cause precipitation of 10-50 MeV electrons.
Have also been identified as major contributors
to parasitic electron loss into the atmosphere
at MeV energies e.g., Lyons and Thorne, 1972
Summers and Thorne, 2003, Summers et al.,
2004. SAMPEX measures energetic particles at
520 to 670 km, but has no information regarding
waves and, especially, has no information about
waves near the equator!! In order to understand
the relationship between storms, EMIC waves and
the radiation belts, observations of
precipitating particles need to made in
conjunction with wave activity near the equator.
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Example EMIC waves recorded at Halley Station in
Antarctica
L4.2, MLT UT - 3h http//dabs.nerc-bas.ac.uk/q
look/Qlook_Catalog.html
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Measurement objectives

• Fundamental space weather objectives are
  contained in the relationship between
• Ring current particles..
• EMIC wave
  generation/propagation..
• 
  Radiation belt electrons
• Needed measurement
• Explore the region near and away from the equator
  to observe the generation and propagation of EMIC
  waves.
• Simultaneously, observe regions lower in altitude
  in order to measure precipitating energetic
  electrons.
• Possible satellite configurations include string
  of pearls, identical orbits at different MLT, or
  a combination of both. Others???

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Measurement techniques 1
Fluxgate magnetometer

• Issues
• Dynamic range versus resolution are usually
  traded off such that resolution suffers. Eg.,
  Cluster magnetometer has a noise floor of 5 pT
  vHz, but resolves only 125 pT in near-Earth
  regions (to measure /- 1024 nT).
• This resolution is typical of existing and
  previous satellite missions (including ST-5), but
  falls far short of the pT resolution in
  ground-based instruments.
• 2. Ultimate noise floor (5 pT vHz for Cluster,
  8 pT vHz for MMS) may not be optimal for EMIC
  waves.

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Measurement techniques 1
Fluxgate magnetometer - possible solution
Subtract a baseline from the raw signal. Note
that the subtraction must be accurate to within
1 part in 106. Digitize the residual signal
separately from the DC signal. Signals the order
of a gt5 pT vHz may be detectable.
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Measurement techniques 2
Induction coil magnetometer for ground-based
applications. Uses 16 spools, with 10,000 turns
on each spool to achieve 1 pT minimum
discernable signal (or better). Core is
high-permeability.
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Measurement techniques 2

• Improving perfomance - how to shrink an existing
  design (objective is to detect 1 pT or less)
• Update preamp, reduce noise x4. This would reduce
  the number of turns required by x4. If we are
  willing to accept a resolution that is worse by
  x2, can use 20,000 turns in existing design.
  Total mass of this sensor would be 0.8 kg.
• Use higher performance mumetal, reduce core mass
  by 20. The mumetal in existing design was not
  intended for space flight and better materials
  exist. Some concern about saturation (solution is
  to apply a DC bias to the core). Expected mass
  would be .4 kg.