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

November 3, 2006November 3, 2006

NLC galleryNLC gallery

NLC viewing geometryNLC viewing geometry

ISS, Courtesy NASA

Radar, Lidar observationsRadar, Lidar observations

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

RAM

Sun

RAMRAMSUN SU

N

Particle Trap (PAT) instrumentParticle Trap (PAT) instrument

PMS

ENLC

nn

m

o

z

x

y

Sun-illumination ModelSun-illumination Model

Spin averaged PAT upleg profiles Spin averaged PAT upleg profiles

Surface Electron

Generation (SEG)

Additive negative

dust

PAT 1 Graphite

PAT2 Gold

Positively Charged Aerosols??

Dusty Plasma Lab,Dusty Plasma Lab, Abbas et. al. 2006 Abbas et. al. 2006

Still waiting on funding to do the ice grain experiment for space dusts, but until then we are using non-volatile non-cryogenic dust.

PhotoCurrents to Rocket PhotoCurrents to Rocket SheathSheath

Holzworth, 2001 GRL

Calculated Work FunctionsCalculated Work Functions

Particle Trap (PAT) instrumentParticle Trap (PAT) instrument

PMS

ENLC

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

180˚ 90˚ 0˚

Ionospheric Ionospheric Chapman layerChapman layer

Ice charging ModelIce charging Model

Ice grains are in Ice grains are in equilibrium with UV and equilibrium with UV and Ne. <q> ~ -1Ne. <q> ~ -1

Chapman layer e- Chapman layer e- are ~10eV <q> > -are ~10eV <q> > -11

Abbas--proposalAbbas--proposal

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