Overview of Lightning Research at University of New Hampshire

Transcription

1 Overview of Lightning Research at University of New Hampshire Ningyu Liu and Joseph Dwyer Department of Physics & Space Science Center (EOS) University of New Hampshire Northeast Radio Observatory Corporation (NEROC) Symposium: Radio Science And Related Topics MIT Haystack Observatory, 4 November 16

2 Outline Optical Observations of Lightning and Transient Luminous Events Modeling Ionospheric Impact of Thunderstorms and Lightning Energetic Radiation from Thunderstorms and Lightning

3 Outline Optical Observations of Lightning and Transient Luminous Events Modeling Ionospheric Impact of Thunderstorms and Lightning Energetic Radiation from Thunderstorms and Lightning

4 Lightning and Transient Luminous Events 100 Elve Ionosphere Halo Altitude Gigantic jet Sprite Stratosphere Blue jet 0 Cloud-to-ground lightning Distance Pasko (03), Electric jets, Nature, 423,

5 Lightning Propagation: Complex Dynamics and Spatial Structures Two lightning flashes observed on May th, 16

6 Fractal Modeling and Detailed Lightning Channel Structure 6 Fractal dimension D = Lightning discharge after 971 step(s) z ln(n) x y ln(r) Fractal modeling results obtained by Prof. Jeremy Riousset at ERAU High-resolution Image of lightning channel [Bazelyan and Raizer, 00].

7 Simulating Streamer Initiation and Propagation to Study Lightning Initiation Electron Density Hydrometeor 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., 16]. 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., 16].

8 Videos of Jets and Gigantic Jets (Standard Rate)

9 Event 1 80 Event 2 39 km Field 1 80 Event 3 42 km Field 6 Field Event 4 80 Event 5 80 Event 6 80 Event 7 47 km 48 km Field 18 Field 19 Field 21 Field 24 Field km Field 1 Field 6 Field 7 Field 15 Field 26 Field 27 Field 34 Field km Liu et al. (15a), Upward electrical discharges observed above Tropical Depression Dorian, Nat. Commun., 6, 5995, doi: / ncomms6995.

10 High-Speed Imaging of Jets and Gigantic Jets Field 1 Field 6 Field 7 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? GPS receiver VS4-1845HS-Gen III Intensifier mm or 85mm focal lens VPH grism with nm resolution Are they as hot as lightning channels? Phantom V411 CMOS Camera Light from jet

11 Outline Optical Observations of Lightning and Transient Luminous Events Modeling Ionospheric Impact of Thunderstorms and Lightning Energetic Radiation from Thunderstorms and Lightning

12 Steady State Lower Ionosphere Conductivity Model 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., 15, 16]. E = J, dn i dt =0=S i L i, X n + i = X n i, i i = X i en i µ i 90 km 80 km km km km km Maxwellian relaxtion time ~ 10s ms at ~ km altitude [Liu et al., 15] ε 0 E z / t 0, J Total σe z Electron Density J Total = σe }{{} z Conduction Electric Field J Total + ε 0 E z / t }{{} Displacement J Total Salem, M. A., N. Liu, and H. K. Rassoul (15), Geophys. Res. Lett., 42, doi: /15gl Salem, M. A., N. Liu, and H. K. Rassoul (16), Geophys. Res. Lett., 43, doi: /15gl J Total = J Charging J Lightning J Total 10 8 A/m 2 [Riousset et al., 10] J Total

13 Altitude 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., 13]. Modeling investigation of the effects of thunderstorms [Salem et al.., Geophys. Res. Lett., 15, 16]. UT (h) Shao et al. (13), Reduction of electron density in the night-time lower ionosphere in response to a thunderstorm, Nat. Geosci., 6, 29 33, doi: /ngeo1668.

14 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. Electron Density The model accounts for ionization, attachment, detachment, electron drift, electron diffusion, etc. Electric Field Liu, N. Y. (12), Multiple ion species fluid modeling of sprite halos and the role of electron detachment of O in their dynamics, J. Geophys. Res., 117, A038, doi: /11ja0162.

15 Significant Ionospheric Impact of Impulsive Lightning Conducted for an impulsive lightning stroke detected in Florida in 14. Electron density is increased in a significant volume of the lower ionosphere. Peak electron density reaches 3x10 9 m -3, more than 4 orders of magnitude higher than the ambient. h Electron Density t = 1.17 ms Electron Density ms ms 0.6 ms 0.8 ms 1.2 ms 1.0 ms h ~10 7 m/s (m -3 ) ms 0.8 ms 1.0 ms 1.2 ms Electric Field A fast propagating streamer head Electron Density (m -3 ) E/E k Liu, N., L. D. Boggs, and S. A. Cummer (16), Observation-constrained modeling of the ionospheric impact of negative sprites, Geophys. Res. Lett., 43, doi: /16gl

16 Streamer Initiation from Mesospheric Structures 10 km Scale Structure t = 23 ms Electron Density (m -3 ) t = 23.4 ms PN 2 (R) km Scale Structure: Electron Density (m -3 ) t = ms Liu et al. (15b), Sprite streamer initiation from natural mesospheric structures, Nat. Commun., 6, 75, doi: /ncomms85.

17 Outline Optical Observations of Lightning and Transient Luminous Events Modeling Ionospheric Impact of Thunderstorms and Lightning Energetic Radiation from Thunderstorms and Lightning

18 Energetic Radiation Produced by Thunderstorms

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20 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 (Ningyu.Liu@unh.edu) Joseph Dwyer (Joseph.Dwyer@unh.edu)