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Geophysical InstituteUniversity of Alaska
Plasma Chemistry of Sprite Streamers
D.D. Sentman, H.C. Stenbaek-Nielsen (University of Alaska)M.G. McHarg (U.S. Air Force Academy)
J.S. Morrill (Naval Research Laboratory)
Streamers, Sprites, Leaders, Lightning: From Micro- to Macroscales
A Multidisciplinary Workshop on Outstanding Problems in Electrical Discharge Processes
Lorentz CenterLeiden, The Netherlands
8-12 October 2007
Geophysical InstituteUniversity of Alaska
Varieties of Transient Luminous Events in the Upper Atmosphere
GIANTBLUEJET
(Elaboration of figure by Lyons et al. 2000)
PIXIES
TROLL
What chemical residuesare produced in TLEs?
Geophysical InstituteUniversity of Alaska
Outline of Talk
• Optical observations of sprites – a window into lightning induced chemical modifications of the upper atmosphere
• Current state of optical observations
– 1,000 fps observations – first evidence for transient chemical modifications
– 10,000 fps observations – first time-resolved imagery of sprite dynamics
• Simplified model of a sprite streamer
– Based on time and space resolved observations
• Chemical Model– 80+ species, 500+ reactions
– Combines • Electric field-related processes (ionization, excitation) in the head• Chemical reactions in the head and in the trailing region
– Includes reaction chains for positive ions (proton hydrates) and negative ion clusters
Geophysical InstituteUniversity of Alaska
Sprite Gallery – Images From a Variety of SourcesObtained With Different Types of Cameras
(Su – Bare CCD TV)
(Sentman – Color ICCD)
(Wescott – B/W ICCD TV)
(Su – Bare CCD TV)(Sentman – Bare CCD)
(Stanley – Intensified Hi-speed Imager)
(Sentman – ICCD TV)
(Fukunishi – ICCD TV)
(Lyons – ICCD TV)
(Stenbaek-NielsenIntensified High-speed Imager)
Early sprite imagers were intensified CCD TV cameras. Recent research has simultaneously moved in two directions: (1) high speed (10,000 fps) cameras, and (2) inexpensive bare CCD imagers, both TV and integrating systems. Sprites are bright enough (>> 1 MR) that they are now considered "easy" to observe.
Geophysical InstituteUniversity of Alaska
“Reignition” of a SpriteImplies remnant compositional effect
Sequence of 1000 fps images showing a reactivated sprite, taken from Figure 2 of Stenbaek-Nielsen et al. (2000). The top row shows the initial sprite, and the second row shows the reignited event after a 44 ms break.
Study Region
Geophysical InstituteUniversity of Alaska
Sprite Reignition – 1000 fps
(clip)
Sprite at 10,000 fps
• Streamer heads clearly resolved• Dark space behind head implies E ~ 0• Trailing afterglow region chemiluminescence?
Geophysical InstituteUniversity of Alaska
Similarity of Laboratory and Sprite Streamer Structures
Laboratory streamers at various exposure times. Dendritic structures (left) are due to smearing over long (>>1 ns) exposure times. Time resolved structures at right show bright streamer heads only, with no apparent trailing columns.
Sprite streamers at 70 km, with exposure times of 50 s. Equivalent exposure timeat STP is 1 ns.
Streamer heads are similar
[After Ebert et al., The multiscale nature of streamers,Plasma Sources Sci. Technol., 15, S118-S129, 2006.]
Geophysical InstituteUniversity of Alaska
Simplified Streamer Model for 70 km Altitude
Input: E0 = 5 Ek, t = 6 s, M = 14, vs=107 m/s ~ 12 vte(7.5 eV)Output: densities vs time of ne, ion and active species.
5
25 m
Geophysical InstituteUniversity of Alaska
Electric Field Driven Processes
Plasma Chemical Model of Sprite Streamers
Chemical Reactions
+ …
Geophysical InstituteUniversity of Alaska
Electron Energy Distribution Function - Nonthermal
Solution of Time-Stationary Kinetic (Boltzmann) Equation (2-Term SH approximation)
{ } {3/ 2
1/ 2Inelastic
MomentumTransfer
2 2
2( ) 0
2where is energy, ( ), , is electric field, and ( )
3
m
m mm
n n mA n Q n
t M
eEn n A E
m
e ene ee
e e n n en
¶ ¶ ¶= + + =
¶ ¶ ¶
= = =
144424443
At low electric fields n() in air has of a Druyvesteyn-like form [n/1/2 ~ exp(-2/a0
2)]. At reduced fields of /p > 10 V/cm/torr a high energy tail begins to form above the ~ 4 eV barrier in the N2 vibrationalcross section.
The form of this distribution function is characteristic of nitrogen. Other gases possess different equilibrium distributions.
Geophysical InstituteUniversity of Alaska
exp/i
i
BA
p E pa æ ö÷ç ÷= -ç ÷ç ÷çè ø
2
exp/a
a
E BA
p p E ph
- æ öæ ö ÷÷ çç ÷= -÷ çç ÷÷ ç÷ç ÷çè ø è ø
e m
Ep A
p
b
m-æ ö÷ç= ÷ç ÷÷çè ø
( )( / )
( )( / )i d e
a d e
v p E p
v p E p
Ionization coefficientProcess: e* + N2 N2
+ + 2eModeled by:
Attachment coefficientProcess: e + O2 O- + OModeled by
Electron mobilityDefined through drift speeed vd = eEModeled by
Ionization and attachment frequenciesVibrational excitations play a significant role in determiningthe form of the EEDF. In general the excitation frequenciesof the vibrational modes of both ground and excited statesare much larger than the ionization/attachment frequenciesat all undervoltage (E < Ek) and modest (E > Ek) overvoltage fields.
Ionization, Dissociative Attachment, and Vibrational Excitation Frequencies
(Ek=123 Td=32 kV/cm at STP)
Geophysical InstituteUniversity of Alaska
Species followed in the simulation. Bath species N2, O2, H2O, CO2, CO and HCl.
Neutral (36 + 6 bath) Negative (12) Positive (27)
N2(X, v=1-4), N2(A), N2(B), N2(a’),
N2(C), N2(W3, B’, a, w1, E, a’’), N(4S),
N(2D), N(2P), O2(a), O2(b), O2(A), O(3P),
O(1D), O(1S), O3, NO, NO2, NO3, N2O,
N2O5, H, OH, OH*, HO2, H2O2, HNO3,
HO2, NO2, Cl, ClO
e, O-, O2-, O3,
O4-, NO2
-, NO3,
CO3-, CO4
-, OH,
HCO3-, Cl-
N2+, O2
+, N+, O+, N3+, N4
+, O4+, NO+, NO2
+, N2O+,
N2O2+, N2NO+, O2NO+, (H2O)O2
+, (H2O)H+,
(H2O)2H+, (H2O)3H
+, (H2O)4H+, (H2O)OHH+,
(H2O)NO+, (H2O)2NO+, (H2O)3NO+, CO2NO+,
(H2O)2CO2NO+, (H2O)2N2NO+, (HO)N2NO+,
(H2O)2N2NO+
Coupled Chemical Scheme
Solve the coupled set of 68 ODEs
dni = Si – Li
dt
for the species listed below. Si is the source term and Li is loss term for species ni, each summed over RHS and LHS, resp., of all reactions in which ni appears. The numerical integration was performed using a variable step stiff ODE solver.
80+ species, 800+ reactions
Geophysical InstituteUniversity of Alaska
Kinetic Scheme
Reaction set includes
• 30 electric-field driven electron impact processes• 10 electron-ion recombination processes• 25 attachment-detachment processes• 23 ground state chemistry reactions• 75 active species reactions• 27 ion conversion processes• 23 odd-hydrogen and odd-nitrogen processes
(includes hydroxyl chemistry)• 30 positive ion chemistry (hydrates) reactions• 35 negative ion and chlorine reactions• 565 ion-ion recombination (2- and 3-body) reactions• Total: 836• Focus is on basic chemical reactions – no chemistry
derived from vibrational kinetics is included at this stage.
Geophysical InstituteUniversity of Alaska
N2 1P and 2P Emissions
Geophysical InstituteUniversity of Alaska
R5: e* + N2 → e + e + N2+
impact ionizationR6: e* + O2 → e + e + O2
+ impact ionization
R19: e* + O2 → O + O- dissociative attachment
R21: e* + N2 → e + e + N+ + N dissociative ionization
R22: e* + O2 → e + e + O+ + Odissociative ionization
R26: e + N2+ → N + N
dissociative recombination R27: e + N2
+ → N + N(2D)dissociative recombination
R34: e + O2 + O2 → O2- + O2
3-body attachmentR38: e + O3 → O2
- + O dissociative attachment
R232: e + N2O2+ → N2 + O2
dissociative recombination
Electron Sources and Sinks
Principal Source: N2 ionizationPrincipal Sinks: N2O2
+, O3
Lifetime: ~1s
Princip
al S
ourc
ePrincipal
Sinks
Geophysical InstituteUniversity of Alaska
Metastable N2(A3u+) Sources and Sinks
R8: e* + N2 → e + N2(A) impact excitation
R82: N2(A) + O2 → N2 + O2 collisional deactivation
R84: N2(A) + O2 → N2 + O + Odissociative deactivation
R89: N2(A) + O2 → N2 + O2(b) energy transfer
R96: N2(B) + N2 → N2(A) + N2 collisional quenching
R97: N2(B) → N2(A) + h(1PN2) radiative cascade
Principal Source: Radiative cascade from N2(B)Principal Sinks: collisional, dissociative deactivationLifetime: ~1 ms
PrincipalSource
PrincipalSink
Geophysical InstituteUniversity of Alaska
Metastable O2(a1g) Sources and Sinks
R12: e* + O2 → e + O2(a) impact excitation
R88: N2(A) + O2 → N2 + O2(a) energy transfer
R90: N2(A) + O2(a) → N2(B) + O2 energy pooling
R111: O2(a) + O2 → O2 + O2 collisional deactivation
R117: O2(b) + N2 → O2(a) + N2 collisional deactivation
Principal Sources: O2(b), N2(A), O2
Principal Sink: collisional deactivationLifetime: > 1000 s
PrincipalSource
PrincipalSink
Geophysical InstituteUniversity of Alaska
Atomic Oxygen O(3P) Sources and Sinks
R16: e* + O2 → e + O + O impact dissociation
R17: e* + O2 → e + O + O(1D)impact dissociation
R61: N + NO → N2 + O atom transfer
R79: O + O2 + N2 → O3 + N2 3-body association
R84: N2(A) + O2 → N2 + O + O dissociative quenching
R99: N2(B) + O2 → N2 + O + Odissociative quenching
R101: N2(a) + O2 → N2 + O + Odissociative quenching
R124: N(2D) + O2 → NO + O atom transfer
R134: O(1D) + N2 → O + N2
collisional deactivationR135: O(1D) + O2 → O + O2(b)
energy transfer
Numerous processes contributeto creation of atomic oxygen in roughlyequal (ROM) amounts.
PrincipalSource
PrincipalSink
Geophysical InstituteUniversity of Alaska
Geophysical InstituteUniversity of Alaska
(Auroral green line)(~700-900 nm)
(~1.2 m)
(~0.8-1.2 m)
Geophysical InstituteUniversity of Alaska
Nitrogen Oxide
R59: N + O2 → NO + O
R61: N + NO → N2 + O
R124: N(2D) + O2 → NO + O
R125: N(2D) + O2 → NO + O(1D)
R177: N+ + O2 → O+ + NO
Dominant source: N(2D)Dominant sink: N(4S)Lifetime: > 1000 s
Total Production:For diameter = 25 m length = 10 kmN ~ 5 x 1019 molecules/streamer
Geophysical InstituteUniversity of Alaska
Total chemical impact of a very large sprite is likely to be much larger than for a single streamer.
It is unknown at this point what the total chemical impact of sprite-induced perturbations on the larger atmospheric chemical system is.
Further observations and modeling are warranted.
Our calculation was for a single one of these streamers … but what’s the total impact of the entire event?What’s the impact of a thunderstorm? The totality of thunderstorms over the earth?
Volume> 103 km3