overview of lightning research at university of new hampshire
TRANSCRIPT
Overview of Lightning Research at University of New Hampshire
Ningyu Liu and Joseph DwyerDepartment of Physics &
Space Science Center (EOS)University of New Hampshire
Northeast Radio Observatory Corporation (NEROC) Symposium: Radio Science And Related TopicsMIT Haystack Observatory, 4 November 2016
Outline
• Optical Observations of Lightning and Transient Luminous Events
• Modeling Ionospheric Impact of Thunderstorms and Lightning
• Energetic Radiation from Thunderstorms and Lightning
Outline
• Optical Observations of Lightning and Transient Luminous Events
• Modeling Ionospheric Impact of Thunderstorms and Lightning
• Energetic Radiation from Thunderstorms and Lightning
Lightning and Transient Luminous EventsA
ltitu
de (km
)
100
50
0
Ionosphere
StratosphereBlue jet
Elve
Halo
Sprite
Cloud-to-ground lightning
002001
Gigantic jet
Distance (km)
Pasko (2003), Electric jets, Nature, 423, 927–929.
Lightning Propagation: Complex Dynamics and Spatial Structures
Two lightning flashes observed on May 20th, 2016
Fractal Modeling and Detailed Lightning Channel Structure
10
y (km)
Lightning discharge after 971 step(s)
5010
5
x (km)
0
10
0
9
8
7
6
5
4
3
2
1
z (k
m)
ln(R)5 6 7 8
ln(N
)
-2
-1
0
1
2
3
4
5
6Fractal dimension D = 2.6119
Fractal modeling results obtained by Prof. Jeremy Riousset at ERAU High-resolution Image of lightning channel [Bazelyan and Raizer, 2000].
Simulating Streamer Initiation and Propagation to Study Lightning Initiation
HydrometeorElectron Density
Charge Density
Electric Field
Longitudinal Current Density
Radial Current Density
• The current carried by the streamer exponentially increases with a timescale of a few nanoseconds, which can lead to strong HF/VHF radiation [Shi et al., 2016].
• Recent RF measurements suggest that the most powerful VHF source in nature, known as Narrow Bipolar Events or Compact Intracloud Discharges, consists of many streamers [Rison et al., 2016].
Videos of Jets and Gigantic Jets (Standard Rate)
Field 180(km)
70
60
50
40
30
20 17.1 km
Field 6 Field 12 Field 18 Field 19 Field 21 Field 24 Field 2580
(km)
70
60
50
40
30
20
Field 1
70(km)
60
50
40
30
20 19.9 km
Field 6 Field 7 Field 15 Field 26 Field 27 Field 34 Field 53
70(km)
60
50
40
30
20
Event 180
(km)
70
60
50
4042 km
30
20
Event 2
70
(km)
60
50
40
30
20
Event 380
(km)
70
60
50
40
30
20
Event 480
(km)
70
60
50
40
30
20
Event 580
(km)
70
60
50
40
30
20
Event 680
(km)
70
60
50
40
30
20
Event 7
70
(km)
60
50
40
30
20
39 km47 km
48 km
Liu et al. (2015a), Upward electrical discharges observed above Tropical Depression Dorian, Nat. Commun., 6, 5995, doi:10.1038/ncomms6995.
High-Speed Imaging of Jets and Gigantic Jets
• Neither high-speed images nor spatially-resolved spectra have been reported.
• For gigantic jets, does the upward discharge propagate all the way up to the ionosphere? Or are electrical discharges triggered in the lower ionosphere, which then propagate downward?
• Are they as hot as lightning channels?
Field 1
70
(km)
60
50
40
30
20
Field 6 Field 7
50mm or 85mm focal lens
VS4-1845HS-Gen III Intensifier
VPH grism with 0.2-0.3 nm resolution
Light from jet
GPS receiver
Phantom V411 CMOS Camera
Outline
• Optical Observations of Lightning and Transient Luminous Events
• Modeling Ionospheric Impact of Thunderstorms and Lightning
• Energetic Radiation from Thunderstorms and Lightning
Steady State Lower Ionosphere Conductivity Model
Electron Density
Electric Field
JTotal = σEz︸︷︷︸
Conduction
+ ε0∂Ez/∂t︸ ︷︷ ︸
Displacement
JTotal = JCharging − JLightningJTotal ∼ 10
−8A/m2
[Riousset et al., 2010]
Maxwellian relaxtion time ~ 10s ms
at ~70 km altitude [Liu et al., 2015]
ε0∂Ez/∂t ∼ 0, JTotal ∼ σEz
80 km
40 km
70 km
60 km
50 km
90 km
JTotal
JTotal
JTotal
• Thunderstorms can establish an electrostatic field and steady current in the upper atmosphere.
• The electric field is sufficient to modify electron mobility and electron attachment coefficient [Salem et al., 2015, 2016].
E =J
�,
dni
dt= 0 = Si � Li,
X
i
n+i =
X
i
n�i ,
� =X
i
eniµi
Salem, M. A., N. Liu, and H. K. Rassoul (2015), Geophys. Res. Lett., 42, doi:10.1002/2015GL063268.Salem, M. A., N. Liu, and H. K. Rassoul (2016), Geophys. Res. Lett., 43, doi:10.1002/2015GL066933.
Hourly Variation of Ionospheric Density Above Thunderstorms
• The hourly variation of the lower ionospheric density correlates with underlying lightning activity [e.g., Shao et al., Nat. Geosci., 2013].
• Modeling investigation of the effects of thunderstorms [Salem et al.., Geophys. Res. Lett., 2015, 2016].
Shao et al. (2013), Reduction of electron density in the night-time lower ionosphere in response to a thunderstorm, Nat. Geosci., 6, 29–33, doi:10.1038/ngeo1668.
UT (h)
Altit
ude
(km
)
Ionospheric Impact of Lightning: Halos and Sprites
• A plasma fluid discharge model is typically used — Poisson’s equation and transport equations of electrons and ions.
• The model accounts for ionization, attachment, detachment, electron drift, electron diffusion, etc.
Liu, N. Y. (2012), Multiple ion species fluid modeling of sprite halos and the role of electron detachment of O− in their dynamics, J. Geophys. Res., 117, A03308, doi:10.1029/2011JA017062.
Electron Density
Electric Field
Significant Ionospheric Impact of Impulsive Lightning
A fast propagating streamer head
~107 m/s
• Conducted for an impulsive lightning stroke detected in Florida in 2014.
• Electron density is increased in a significant volume of the lower ionosphere.
• Peak electron density reaches 3x109 m-3, more than 4 orders of magnitude higher than the ambient.
Electron Density
Electric Field
104105
106107
108
109
104105
106107
108
109
104105
106107
108
109
104105
106107
108
109
104105
106107
108
109
104105
106107
108
109
Electron Density
t = 1.17 ms
(km)-60 -40 -20 0 20 40 60
(km
)
40
50
60
70
80
90
1041051061071081091010
(m-3)
Electron Density (m-3)103 105 107 109
h (k
m)
40
50
60
70
1.2 ms1.0 ms
80
90
0.6 ms
0-0.4 ms
0.8 ms
E/Ek
0 0.5 1 1.5 2h
(km
)40
50
60
70
80
90
1.2 ms1.0 ms
0.4 ms
0.8 ms
0.6 ms
Liu, N., L. D. Boggs, and S. A. Cummer (2016), Observation-constrained modeling of the ionospheric impact of negative sprites, Geophys. Res. Lett., 43, doi:10.1002/2016GL068256.
Streamer Initiation from Mesospheric Structures
105
107
109
1011t = 23.4 ms
104
106
108
1PN2 (R)
(km
)
t = 23 ms
71
72
73
74
(km)
(km
)
−5 0 571
72
73
74
Electron Density (m-3)10 km Scale Structure
(km)
(km
)
t = 50 ms
−6 −4 −2 0 2 4 6
72
7414 km Scale Structure: Electron Density (m-3)
1051071091011
Liu et al. (2015b), Sprite streamer initiation from natural mesospheric structures, Nat. Commun., 6, 7540, doi:10.1038/ncomms8540.
Outline
• Optical Observations of Lightning and Transient Luminous Events
• Modeling Ionospheric Impact of Thunderstorms and Lightning
• Energetic Radiation from Thunderstorms and Lightning
Energetic Radiation Produced by Thunderstorms
http://www.nasa.gov/mission_pages/GLAST/news/fermi-thunderstorms.html
Physical Mechanism of Terrestrial Gamma Ray Flashes
5 10 15 20 25 30 35 40t (ms)
0
20
40
60
coun
ts
BATSE TGF 3925
5 10 15 20 25 30 35 40t (ms)
0
20
40
60
coun
ts
BATSE TGF 2185
5 10 15 20 25 30 35 40t (ms)
0
20
40
60
80
coun
ts
BATSE TGF 3813
5 10 15 20 25 30 35 40t (ms)
0
20
40
60
coun
ts
BATSE TGF 6185
5 10 15 20 25 30 35 40t (ms)
0
20
40
60
coun
ts
BATSE TGF 8006
5 10 15 20 25 30 35 400
0.5
1
1.5
2 x 1019
t (ms)
Phot
ons/
s
(b)
(km)
(km
)
t = 21 ms
−2 0 28
9
10
11
12
13
14
15
16(V/m)
0
4x105
8x105
12x105
(km)
t = 21 ms
−2 0 2
(m−3)
104
105
106
107
(km)
t = 21 ms
−2 0 2
(m−3)
1
10
102
103
E/n Runaway Electron Density Runaway Positron Density
Liu, N. Y., and J. R. Dwyer (2013), Modeling terrestrial gamma ray flashes produced by relativistic feedback discharges, J. Geophys. Res., doi:10.1002/jgra.50232.
Summary
• The UNH lightning team works on nearly all aspects of lightning-related research. We conduct observational, modeling, and theoretical research to understand various forms of electrical discharges in earth’s atmosphere and their impact.
• We welcome collaborative projects.
Contact info:
Ningyu Liu ([email protected])
Joseph Dwyer ([email protected])