Detection of Charged Aerosol
Particles in the Mesosphere by
Rocket-borne Probes
Scott Robertson & Scott Knappmiller University of Colorado, Boulder
ARR, October 2011
2
Collaborators
• University of Colorado – Zoltan Sternovsky
– Mihaly Horanyi
• University of Washington – Robert Holzworth
– Michael Shimogawa
• Tech. Univ. Graz-Austria – Martin Friedrich
• ARR/ALOMAR-Norway – Michael Gausa
• Stockholm Univ. – Jörg Gumbel
– Misha Khaplanov
– Linda Megner
• FFI/UiOslo – Ulf-Peter Hoppe
• IAP-Germany – Gerd Baumgarten
– Ralph Latteck
– Markus Rapp
3
Outline
1. Noctilucent Clouds
2. Instruments
3. MASS data, 2007
4. CHAMPS payload 2011
5. Summary
1. NOCTILUCENT CLOUDS
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5
Noctilucent Clouds (NLC) “Night Shining
Clouds”
NLC seen from
Space are called
“Polar
Mesospheric
Clouds (PMC).”
6
NLC Environment/Background
D
NLC (140 K)
• NLC are composed of ice
particles.
• Water vapor condenses due to
temperature minimum
(mesopause).
• NLC particles charge in the D-
region of the ionosphere.
• Charging of NLC particles
related to anomalous radar
echoes (Polar Mesospheric
Summer Echoes, PMSE).
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NLC Science Question:
Meteoric smoke particle
formation
Homogeneous nucleation requires lower temperature
Condensation nuclei are required
What are the nuclei?
Meteoric smoke particles
Sulfate particles
Soot particles
Molecular ions
Water cluster ions
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• NLC particles grow to 50 nm in radius, large enough to scatter sufficient light to be visible.
• Mie scattering scales with r6.
NLC detection (1)
ALOMAR lidar Rocket-borne photometer
Stockholm University
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AIM satellite was dedicated to NLC with many instruments
NLC detection (2)
Cloud Imaging Particle
Size Experiment (CIPS)
Solar
Occultation
For Ice
Experiment
(SOFIE)
10
NLC detection (3) In-Situ Particle Detectors
• Blunt cup probe [Havnes et al., 1996]
• Faraday cup [Blix et al., 1990]
• Quadrupole Mass Spectrometer [Viggiano and Hunton, 1999]
• Magnetically Shielded Detectors (Colorado Dust Detectors) [Smiley et al., 2002]
• Gerdien Condenser [Croskey et al., 2001]
• Mesospheric Aerosol Mass Spectrometer (MASS) S. Knappmiller, S. Robertson, Z. Sternovsky, and M. Friedrich: A rocket-borne mass analyzer for charged aerosol particles inthe mesosphere, Rev. Sci. Instrum., 79, 104502-1, 2008.
1. Rocket aerodynamics limit collection of smallest particles
2. Only detect one polarity of charge
3. Limited mass resolution
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Science Questions for MASS
rocket campaign - 2007
Idea: fly a mass spectrometer for heavy particles
• How numerous are the particles?
• How does the number density vary with altitude?
• Do positive and negative particles coexist?
2. MASS INSTRUMENT
MESOSPHERIC AEROSOL SAMPLING SPECTROMETER
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• Have separate detectors for different sizes of particles – (a low-resolution mass spectrometer)
• Have separate detectors for positive and negatively charged particles.
• Avoid aerodynamic drag effects that select particles (air flows through).
Instrument Objectives
The MASS instrument Mesospheric Aerosol Sampling Spectrometer
4 pairs
voltage-
biased
collectors
Air exit
windows
Air sampling
slit ~ 25 cm2
•1ST plate <0.5nm
•2nd plate 0.5-1nm
•3rd plate 1-2nm
•4th plate >3nm
Assuming Ice density
r = 930 kg/m3
Measures each
polarity of charge on
separate collection
plates
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Currents to electrodes are converted to number density:
I = n Zq v A
n = number density Zq = charge on particle
v = rocket velocity, 1050 m/s A = inlet area, 25 cm2
Z = 1 assumed q = electron charge
n = I / (Zq v A)
Resolution: 1 pA = 2.5 cm-3
electrical noise 8pA n = 20 cm-3
Vertical Resolution: 1 meter
MASS data Conversion
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MASS Aerodynamic Design
• Aerodynamic inlet minimizes shock wave above MASS instrument.
• Exit windows mitigates static build-up of pressure within the instrument.
• Verified by DSMC aerodynamic simulations and particle trajectory program.
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Particle Trajectory Simulation
• Input static electric field
• Input number density, temperature, and velocity distribution from DSMC.
• Specify test particle’s initial position, velocity, and mass.
• Calculate a collision frequency.
• Determine if collision has occurred using differential time step.
• Compute collision with air molecule using momentum conservation.
• Calculate collection efficiency for each collection plate.
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101
102
103
104
105
106
0
20
40
60
80
10087.5 km, Pos. Particles, -1 V
Radius [nm]
C
olle
ctio
n E
ffic
iency
[%
]
MASS [amu]
1
2
3
4
NO+
Ions
1 10
B
Calibration Results
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Payload
Forward nosecone is spring-deployed
Aft rocket skin falls away with rocket motor
Two rocket motors: Terrier Mk12 – Improved Orion
Apogee: 133 km
Attitude Control
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Forward Payload Section
MASS Instrument
Faraday Rotation
Antennas
Electric Field Booms
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Aft Payload Section
Electric Field Booms
Photometer
3. MASS DATA
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Conditions at 1st launch
Date of launch: 3 August 2007
Time of launch: 22:51 UTC
Time of AIM overpass: 22:25 UTC
Solar zenith angle: 93.2 degrees
Location: Andøya Rocket Range
ALWIN radar: PMSE observed
ALOMAR lidar: NLC observed earlier
Trondheim webcam: NLC observed
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ALWIN Radar
• Broad PMSE from 81-89 km.
• Two PMSE maxima, 83 km & 88 km.
ALOMAR RMR Lidar
• Cloud peaks at 83 km.
• Resolution 50 m.
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MASS Data Launch I Upleg
Graph A:
Positive
and
Negative
Ions
Graph C:
1-2 nm
Particles
+ & -
Coexist.
Graph B:
0.5-1 nm
Particles,
No
negative
Graph D:
>3 nm
All
negative
particles.
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MASS Data Results
• First time simultaneous measurements of both
positive and negative charge densities
• First mass distribution of NLC particles
– 0.5 - 1nm particles are positive.
– 1 - 2nm equal parts of negative and positive.
– > 3nm all particles are negative.
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Charge Model
• Include photodetachment and photoionization
rates, needed to explain positive particles.
• Model multiple materials:
– Pure NLC ice particles
– Fe2O3 (Hematite) as possible condensation nuclei.
– Spherical Hematite cores coated with monolayers of
ice as large NLC particles.
• High aerosol density case vs. low aerosol
density case relative to electron and ion density
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Kinetic Charge Model
r
en
Z
ZrN ,
Z Charge number
Radius
Number density
Electron density
Ion density
Rate particle charges negatively
Rate particle charges positively
Z
Charge Model used
many times before:
Jensen and Thomas
(1991), Rapp and
Lübken (1999), Rapp,
(2000), Rapp and
Lübken (2001), Draine
and Sutin (1987),
Weingartner and Draine
(2001), and Draine and
Sutin (1987).
1,1,,,,1,1,
,
ZrZrZr
e
ZreZrZr
e
Zre
ZrNNnNn
dt
dN
in
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Charge Model
-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 60.0
0.2
0.4
0.6
0.8
1.0
BPure Ice
Photodetachment
SZA = 93
ne = n
i = 3162 cm
-3
Charg
e P
robability D
istr
ibution P
r,Z
Charge Number Z
Radius
10 nm
20 nm
60 nm
100 nm
4. CHAMPS PAYLOAD
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What are the
NLC condensation nuclei? Meteoric smoke particle
formation
Homogeneous nucleation requires lower temperature than is observed, hence condensation nuclei for heterogeneous nucleation are required.
What are the nuclei?
Meteoric smoke particles
Water cluster ions
Molecular ions
Sulfate particles
Soot particles
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NLC condenstion nuclei
Science Questions:
What can MASS instrument say about condensation nuclei:
1. Meteoric smoke particles are heavier than ions, they will
show up on 0.5 – 1 nm mass channels
2. MASS will find if the charge is positive or negative, or both
3. MASS will find altitude range of detectable particles
4. Day and night launches will reveal whether or not sunlight
changes the charge (photoelectric charging).
But, uncharged particles are not seen.
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Meteoric smoke particle detection
Active photoionization + Faraday cup
ECOMA instrument
[Rapp et al., 2009]
Forward Experimental Section
MASS
Instrumen
t
Pair of
Langmuir
Probes
Pair of
Positive Ion
Probes
Colorado
Dust
Detectors (4)
E-boxes for
MASS and the
Colorado
Dust
Detectors
E-boxes for
Positive Ion Probe
and Langmuir
Probe
Aft Experimental Section
Pirani
Pressure
Gauge
Faraday
Rotation
Antennas E-box for
Faraday
Photo Detectors
(4)
Photo Detectors
E-box
Channeltron
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Thank you!
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NLC Papers • M. Rapp, I. Strelnikova, B. Strelnikova, P. Hoffman, M. Friedrich, J.
Gumbel, L. Megner, U.-P. Hoppe, S. Robertson, S. Knappmiller, M. Wolff, and D. Marsh: Rocket-borne in-situ measurements of meteor smoke: charging properties and implications for seasonal variation, J. Geophys. Res., 115, D00I16, doi:10.1029/2009 JD012725, 2010.
• S. Robertson, M. Horanyi, S. Knappmiller, Z. Sternovsky, R. Holzworth, M. Shimogawa, M. Friedrich, K. Torkar, J. Gumbel, L. Megner, G. Baumgarten, R. Latteck, M. Rapp, U.-P. Hoppe, and M.E. Hervig: Mass analysis of charged aerosol particles in NLC and PMSE during the ECOMA/MASS campaign, Ann. Geophys., 27, 1213-1232, 2009.
• S. Knappmiller, S. Robertson, Z. Sternovsky, and M. Friedrich: A rocket-borne mass analyzer for charged aerosol particles in the mesosphere, Rev. of Sci. Inst., 79, 104502, 2008.
• K. Amyx, Z. Sternovsky, S. Knappmiller, S. Robertson, M. Horanyi, and J. Gumbel: In-situ measurement ofsmoke particles in the wintertime polar mesosphere between 80 and 85 km altitude, J.Atmos. and Solar Terr. Phys., 70, 61-70, 2008.