Clouds, Polar Mesospheric Summer Echoes, and Dusty Plasmas R. B. Sheldon (1), H. D. Voss (2), P. R. B. Sheldon (1), H. D. Voss (2), P. A. Webb (3), W. D. Pesnell (3),R. A. Webb (3), W. D. Pesnell (3),R. A. Goldberg (3), J. Gumbel (4), M. A. Goldberg (3), J. Gumbel (4), M. P. Assis (2) P. Assis (2) 1) NSSTC, 2) Taylor University 3) 1) NSSTC, 2) Taylor University 3) NASA/GSFC, 4) Stockholm University NASA/GSFC, 4) Stockholm University November 3, 2006 November 3, 2006
Transcript
Noctilucent Clouds,
Polar Mesospheric
Summer Echoes, and
Dusty PlasmasR. B. Sheldon (1), H. D. Voss (2), P. A. Webb R. B. Sheldon (1), H. D. Voss (2), P. A. Webb
(3), W. D. Pesnell (3),R. A. Goldberg (3), (3), W. D. Pesnell (3),R. A. Goldberg (3), J. Gumbel (4), M. P. Assis (2) J. Gumbel (4), M. P. Assis (2)
1) NSSTC, 2) Taylor University 3) 1) NSSTC, 2) Taylor University 3) NASA/GSFC, 4) Stockholm UniversityNASA/GSFC, 4) Stockholm University
Observations & Open Observations & Open QuestionsQuestions
NLCNLC are >20nm ice grains forming at the are >20nm ice grains forming at the mesopause ~140K. Reported since 1885. Peak mesopause ~140K. Reported since 1885. Peak occurrence after summer solstices. Explained by occurrence after summer solstices. Explained by mesosphere weathermesosphere weather
PMSEPMSE first observed in 1979 at Poker Flat, are first observed in 1979 at Poker Flat, are related to <10nm charged ice grains usually in a related to <10nm charged ice grains usually in a layer 2 km above NLC, that reflect radar layer 2 km above NLC, that reflect radar (50MHz-2GHz or 2'-100' wavelengths). (50MHz-2GHz or 2'-100' wavelengths). Strongest at midnight, weakest at dusk. Strongest at midnight, weakest at dusk.
PMSE: How do they reflect? Why do they form? PMSE: How do they reflect? Why do they form? What relation to NLC?What relation to NLC?
How can aerosols reflect How can aerosols reflect radar?radar?
Charged aerosolsCharged aerosols large plasma density? large plasma density? If they are positive, then electron density risesIf they are positive, then electron density rises
Draine & Sutin 87 argued for nm dust to become positive Draine & Sutin 87 argued for nm dust to become positive (because of large E-fields)(because of large E-fields)
Havnes flies retarding grids, Gumbel flies alternating plates, Havnes flies retarding grids, Gumbel flies alternating plates, Rapp, Horanyi, et al fly magnets to exclude electrons and trap Rapp, Horanyi, et al fly magnets to exclude electrons and trap positive ions/aerosolspositive ions/aerosols
PMSE’s have negative dust, NLC’s maybe positive?PMSE’s have negative dust, NLC’s maybe positive?
Charged aerosolsCharged aerosols large plasma gradients? large plasma gradients? Langmuir probes see “bite-outs” Langmuir probes see “bite-outs”
Havnes argues for dust vortices to make “holes”Havnes argues for dust vortices to make “holes”
Multiple Langmuir probes never agree on “bite-outs”Multiple Langmuir probes never agree on “bite-outs” Reflections are coherent “Bragg”, not incoherent Reflections are coherent “Bragg”, not incoherent
turbulenceturbulence
DROPPS Rocket ConceptRocket in ram, 1 km/s Particle Impact, PID Particle Trap, PAT Particle Spect., SSD Probes and Plasma Optical sensors, …e- precip.Wake effectsSublimationRocket InteractionsGoldberg et al. GRL 2001
PID Charge/Mass Telescopes and PAT PID Charge/Mass Telescopes and PAT
Water Cluster Ion ChargingWater Cluster Ion Charging
Vostrikov 87, Andersson 97
Water Work FunctionWater Work Function Assuming the rocket work function = Assuming the rocket work function =
5.04V5.04V Gold 5.3 Gold 5.3 wet 4.92 eVwet 4.92 eV Carbon 4.9Carbon 4.9wet 4.87 eVwet 4.87 eV
Electron Density Bite-outs??Electron Density Bite-outs??
DEMETERDEMETERLangmuir ProbesLangmuir Probes
DROPPSDROPPSLangmuir Langmuir
ProbesProbes
Bite-outs are sharp decrease Ne< 1/10
Upleg and Downleg for Charge Telescope grids 1, Upleg and Downleg for Charge Telescope grids 1,
2 & 3 2 & 3
Big Bite-out, where's the Big Bite-out, where's the PMSE?PMSE?
Langmuir Probe TheoryLangmuir Probe Theory
PID Upleg profile PID Upleg profile
PID Downleg profile PID Downleg profile
PID TelescopesPID Telescopes
ShockShock
Langmuir Plasma ProbeLangmuir Plasma Probe
X10 DensityX10 Density
Cushioned Deceleration Cushioned Deceleration
HeatingHeating
SublimationSublimation
Clean Time (~200ms ) Clean Time (~200ms )
Gumbel and Smiley Simulations
Chamber Clean Out Time Chamber Clean Out Time t ~ x^2 / D where x= 8cm length of telescope (or back plate to t ~ x^2 / D where x= 8cm length of telescope (or back plate to
CGRID2)CGRID2) and D = diffusion constant. and D = diffusion constant.
D ~ 1/3 <v> L where <v> is average thermal speed and L is D ~ 1/3 <v> L where <v> is average thermal speed and L is mean free pathmean free path
L ~ 1 / (n s) where the density (from Smiley) is 4e21/m^3 L ~ 1 / (n s) where the density (from Smiley) is 4e21/m^3 and s= cross section for water molecules or clusters. and s= cross section for water molecules or clusters.
Guessing for s = pi (r^), where r= (cube root of density) = 0.3 nm Guessing for s = pi (r^), where r= (cube root of density) = 0.3 nm (and of course, water cluster ions might be bigger) (and of course, water cluster ions might be bigger) s = 3e-19 m2 s = 3e-19 m2
GivingGiving L = 8e-4 m L = 8e-4 m
Then <v> = sqrt(3kT/m) where m = 30 AMU, T = 500K (from Then <v> = sqrt(3kT/m) where m = 30 AMU, T = 500K (from Smiley)Smiley) giving 642 m/s giving 642 m/s
Finally, D = 0.18Finally, D = 0.18
and the diffusion time = x^2/D = 0.08^2/0.18 = 36msand the diffusion time = x^2/D = 0.08^2/0.18 = 36ms
Mitchell et al (2001) Mitchell et al (2001) analysisanalysis
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.
Charged Dust CollectionCharged Dust Collection
Dust Trajectories in Charge Telescope Dust Trajectories in Charge Telescope SIMIONSIMION
Particle size range for PAT and PIDParticle size range for PAT and PID
PID and PAT comparedPID and PAT compared
Energetic electron precipitation Energetic electron precipitation (E>40keV)(E>40keV)Pitch Angle scan when
Rocket commanded to point
down
•Quasi Trapped PA Distribution•Scattering of electrons 100km•Pulsation Features (L=6.2)•Major Ionization source•104 electrons cm2/sr/s•Painting PMSE particles
Range and Secondary e- in Range and Secondary e- in IceIce
Minima!
PIXIE Xray vs Kp,Dst(1996-PIXIE Xray vs Kp,Dst(1996-98)98)
Petrinec, GRL 1999
Precipitating Electron effectsPrecipitating Electron effects
The dusk side is depleted in electronsThe dusk side is depleted in electrons The energy of the electrons changes The energy of the electrons changes
the Chapman-layer altitude. Double the Chapman-layer altitude. Double peaked energy spetra would produce peaked energy spetra would produce double layers in atmosphere.double layers in atmosphere.
Electron energy is a function of MLT & Electron energy is a function of MLT & magnetosphere activity. magnetosphere activity.
Dust Acoustic WavesDust Acoustic Waves
Thomas, 2002 U Iowa, Physics Today, 2004
ConclusionsConclusions There is no evidence for positive charged There is no evidence for positive charged
aerosols. Water work function explains aerosols. Water work function explains +current.+current.
Electron density bite-outs are likely Electron density bite-outs are likely instrumentalinstrumental
PMSE's are subvisible <10nm ice that has a PMSE's are subvisible <10nm ice that has a high charge state. The charge state may be high charge state. The charge state may be a direct result of >10 keV electron a direct result of >10 keV electron precipitationprecipitation
Dust Acoustic Waves may be responsible for Dust Acoustic Waves may be responsible for the Bragg-reflected radar returnsthe Bragg-reflected radar returns
