Noctilucent Clouds, Polar Mesospheric Summer Echoes, and Dusty Plasmas

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Noctilucent Clouds, Polar Mesospheric Summer
Echoes, and Dusty Plasmas

• R. B. Sheldon (1), H. D. Voss (2), P. A. Webb
  (3), W. D. Pesnell (3),R. A. Goldberg (3), J.
  Gumbel (4), M. P. Assis (2)
• 1) NSSTC, 2) Taylor University 3) NASA/GSFC, 4)
  Stockholm University
• November 3, 2006

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NLC gallery
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NLC viewing geometry
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ISS, Courtesy NASA
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Radar, Lidar observations
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Observations Open Questions

• NLC are gt20nm ice grains forming at the mesopause
  140K. Reported since 1885. Peak occurrence after
  summer solstices. Explained by mesosphere weather
• PMSE first observed in 1979 at Poker Flat, are
  related to lt10nm charged ice grains usually in a
  layer 2 km above NLC, that reflect radar
  (50MHz-2GHz or 2'-100' wavelengths). Strongest
  at midnight, weakest at dusk.
• PMSE How do they reflect? Why do they form? What
  relation to NLC?

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How can aerosols reflect radar?

• Charged aerosols? large plasma density?
• If they are positive, then electron density rises
• Draine Sutin 87 argued for nm dust to become
  positive (because of large E-fields)
• Havnes flies retarding grids, Gumbel flies
  alternating plates, Rapp, Horanyi, et al fly
  magnets to exclude electrons and trap positive
  ions/aerosols
• PMSEs have negative dust, NLCs maybe positive?
• Charged aerosols? large plasma gradients?
• Langmuir probes see bite-outs
• Havnes argues for dust vortices to make holes
• Multiple Langmuir probes never agree on
  bite-outs
• Reflections are coherent Bragg, not incoherent
  turbulence

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DROPPS Rocket Concept
Rocket in ram, 1 km/s Particle Impact, PID
Particle Trap, PAT Particle Spect., SSD
Probes and Plasma Optical sensors, e-
precip. Wake effects Sublimation Rocket
Interactions Goldberg et al. GRL 2001
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PID Charge/Mass Telescopes and PAT
Sun
RAM
RAM
SUN
SUN
RAM
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Particle Trap (PAT) instrument
PMSE
NLC
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Sun-illumination Model
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Positively Charged Aerosols??
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Calculated Work Functions
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Particle Trap (PAT) instrument
PMSE
NLC
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Water Cluster Ion Charging
Vostrikov 87, Andersson 97
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Water Work Function

• Assuming the rocket work function 5.04V
• Gold 5.3 ?wet 4.92 eV
• Carbon 4.9?wet 4.87 eV

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Electron Density Bite-outs??
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DEMETERLangmuir Probes
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DROPPSLangmuir Probes
Bite-outs are sharp decrease Nelt 1/10
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Upleg and Downleg for Charge Telescope grids 1, 2
3
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Big Bite-out, where's the PMSE?
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Langmuir Probe Theory
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PID Upleg profile
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PID Downleg profile
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PID TelescopesShockLangmuir Plasma ProbeX10
DensityCushioned Deceleration HeatingSublimatio
nClean Time (200ms )
Gumbel and Smiley Simulations
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Chamber Clean Out Time

•  t x2 / D  where x 8cm length of telescope
  (or back plate to CGRID2)              and D
  diffusion constant. D 1/3 ltvgt L  where ltvgt is
  average thermal speed and L is mean free path L
  1 / (n s)  where the density (from Smiley) is
  4e21/m3                and s cross section for
  water molecules or clusters. Guessing for s
  pi (r), where r (cube root of density) 0.3
  nm           (and of course, water cluster ions
  might be bigger)   s 3e-19 m2Giving   L
  8e-4 mThen ltvgt sqrt(3kT/m) where m 30 AMU,
  T 500K (from Smiley)        giving 642
  m/sFinally, D 0.18and the diffusion time
  x2/D 0.082/0.18 36ms

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Mitchell et al (2001) analysis
Upleg vs downleg PMSE observed with blunt probes
and Aft probe. Note blunt temporally PRECEDES
aft biteout. -blunt nearly simultaneous. UV
Spin modulation strong on upleg, and contributes
to biteout signature, less so on downleg.
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Charged Dust Collection
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PID and PAT compared
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Ionospheric Chapman layer
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Ice charging Model

• Ice grains are in equilibrium with UV and Ne.
  ltqgt -1

• Chapman layer e- are 10eV ltqgt gt -1
• Abbas--proposal

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Range and Secondary e- in Ice
Minima!
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PIXIE Xray vs Kp,Dst(1996-98)
Petrinec, GRL 1999
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Precipitating Electron effects

• The dusk side is depleted in electrons
• The energy of the electrons changes the
  Chapman-layer altitude. Double peaked energy
  spetra would produce double layers in atmosphere.
• Electron energy is a function of MLT
  magnetosphere activity.

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Dust Acoustic Waves
Thomas, 2002
U Iowa, Physics Today, 2004
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Conclusions

• There is no evidence for positive charged
  aerosols. Water work function explains current.
• Electron density bite-outs are likely
  instrumental
• PMSE's are subvisible lt10nm ice that has a high
  charge state. The charge state may be a direct
  result of gt10 keV electron precipitation
• Dust Acoustic Waves may be responsible for the
  Bragg-reflected radar returns