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Paul R. Krehbiel†, Jeremy A. Riousset‡, Victor P. Pasko‡, Ronald J. Thomas§, William Rison§, Mark A. Stanley* & Harald E. Edens†
†Physics Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA ([email protected]; [email protected])‡CSSL Laboratory, Department of Electrical Engineering, Pennsylvania State University, PA 16802, USA ([email protected]; [email protected])§Electrical Engineering Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA ([email protected]; [email protected])*114 Mesa Verde Road, Jemez Springs, NM, 87025, USA ([email protected])
Upward electrical discharges from thunderstorms
Acknowledgment: This research was supported by the United States National Science Foundation under grant ATM-0652148 to the Pennsylvania State University.
Thunderstorms produce cloud-to-ground discharges, which most commonly appear in the form of negative cloud-to-ground and bolt-from-the-blue dis-charges [Rison et al., Geophys. Res. Lett., 26(23), pp.3573–3576, 1999; Thomas et al., Geophys. Res. Lett., 28(1), pp. 143–146, 2001]. On some occa-sions, they also produce upward electrical discharges, so-called blue jets [Wescott et al., Geophys. Res. Lett., 22(10), pp. 1209–1212, 1995; Sentman et al., Geophys. Res. Lett., 93(20), pp. 2857–2860, 1995; Boeck et al., J. Geo-phys. Res., 19(99), p. 1992, 1995] and gigantic jets [Pasko et al., Nature, 416, pp. 152–154, 2002; Su et al., Nature, 423, pp. 974–976, 2003]. The present study is based on both observations and numerical simulations using a sto-chastic model [Riousset et al., J. Geophys. Res. 112, D15203, 2007], and indi-cates that the mechanisms by which blue and gigantic jet discharges escape out of clouds are similar to those of downward cloud-to-ground lightning.
I. Abstract
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II. Numerical Models
Figure 2. Algorithm of development of the discharge trees [Riousset et al., 2007] (based on hy-potheses by Kasemir [1960] and Niemeyer et al. [1984]). (a) Model of the thundercloud using re-sults from the Cylindrical Disk Model. (b) Stochastic model of the discharge.
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Cylindrical Disk Model of the Thundercloud
Fractal Model of the Lightning Discharge
Figure 1. Thundercloud model. (a) Lightning-inferred charge structure and estimated charging currents in a normally electrified storm over Langmuir Laboratory on July 31, 1999, including the expected screening charge at the upper cloud boundary (dashed line). (b) Modeling of the same thundercloud using a Cylindrical Disk Model [e.g., Krehbiel et al., 2004; Behnke et al., 2005].
(a) (b)
Start
Load ChargeLayers
Derive φamb
at boundaries
Derive φamb
(SOR)
Derive φ(φ=φ
amb)
Derive E(FDM)
E>Einit
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Cloud Model
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Leader Model
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III. Jet ScenarioLeader escape from the thundercloud
• Discharge propagation is favored in region of intense charge density [e.g., Williams et al., 1985; Coleman et al., 2003; Mansell et al., 2002; Riousset et al., 2007]: ⇒ Dominant occurrence of intracloud discharges.
• Occurrences of cloud-to-ground lightning, blue jets [Wescott et al., 1985; Sentman et al. 1995; Boeck et al.,1995], gigantic jets [Pasko et al., 2002; Su et al., 2003] are well documented: ⇒ Possibility of lightning propagation in clear air.
• Propagation in a positive or negative layer: ⇒ Channel potential dragged toward positive or negative values.
• If positive cloud charge ≈ negative cloud charge: ⇒ Development as intracloud discharge.
• If positive cloud charge >> or << negative cloud charge: ⇒ High channel potential (positive or negative); ⇒ Smaller sensitivity to low density charge regions; ⇒ Development in clear air (as cloud-to-ground lightning or jets).
III. Jet Scenario (cont.)Blue Jet Scenario
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(c) (d)Figure 3. Basic scenario leading to blue jet formation. (a,b) Vertical electric field (Ez) and potential (V ) profiles along the axis of a cylindrical disk model of the July 31 storm, immediately before and after a negative cloud-to-ground (−CG) discharge. (c,d) Predicted occurrence of an upward discharge fol-lowing the −CG [Krehbiel, 2005]. ‘x’ denotes the potential at which each discharge is initiated.
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Figure 4. Simulated blue jet discharge resulting from the pre-dicted charge configuration of Fig. 3c,d. Blue and red numbers indicate the charge content of each charge layer in Coulombs.
• Occurrence of −CG results in: ⇒ Cloud charge imbalance; ⇒ Increase in cloud potential V and electric field Ez at the top of the cloud (Fig. 3a, b); ⇒ Favorable conditions for jet initiation.
• Subsequent charging of the thunderstorm yields: ⇒ Initiation of a discharge in the upper levels of the thundercloud; ⇒ Upward discharge escape allowed by a high channel potential; ⇒ Upward propagation favored by scaling of the leader propagation threshold with neutral density (~7 km) [e.g., Raizer et al., 2006, 2007]. • The ambient potential profiles encountered by upward discharges are analogous to those experienced by a −CG discharge (Fig 3b) [Coleman et al., 2003], except for the polarities being reversed.
• Discharge type (e.g., IC, CG, BJ) is the result of a competition as to where the triggering occurs first (e.g., Fig. 3a,c). ICs usually win this competition; charge imbalances help favor triggering of CGs and BJs.
IV. Case Study: STEPS 2000 JetLightning Mapping Array Data
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Jet simulation
Figure 5. Upward negative jet from an inverted-polarity storm on June 12 UTC during STEPS 2000. (a) Lightning mapping observations of the jet (time vs. source point altitude) and the preceding bilevel intracloud dis-charge. (b,c) Overlay of the jet on the closest vertical and plan position (PPI) radar scans through the storm.
Figure 6. (a) Lightning mapping observations of the jet in the vertical North-South plane and preceding bilevel intracloud discharge of Fig. 5. (b) Numerical simulation of the same jet. Blue and red numbers indicate the charge content of each charge layer in Coulombs.
(a)
(b) (c)
(a)
(b)
• Preceding intracloud lightning discharge and upward jet are two distinctly separate events (Fig. 5a);• Jet extends ~2 km above cloud top, which was essentially con-stant at ~11.5 km altitude over the full extent of the dissipating storm and in the vicinity of the jet (Fig. 5b, Fig. 6a);• Prior IC locally removed positive charge from the lower storm level (Fig. 5b,c); jet occurred 10 s later directly above the unbalanced region (Fig. 5c);• Jet propagated 4 km in 60 ms at a speed of 7x104 m/s and had negative polarity (Fig. 5a,b).
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(a) (b) (c) (d)(f)
Intracloudlightning
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Low-altitudeIC lightning
(low IC)
Blue jet(+BJ)
Bolt-from-the-blue(−BFB)
Gigantic jet (−GJ)Negative cloud-to-ground
lightning(−CG)
(e)Figure 7. Simulated discharges illustrating different lightning types in a normally electrified storm. (a–f) Blue and red contours and numbers indicate nega-tive and positive charge regions and charge amounts (in C), respectively, each assumed to have a Gaussian spatial distribution. A partially analogous set of discharges occurs or would be predicted to occur in storms having inverted electrical structures.
V. Summary: Discharge Types
The principal results and contributions, which follow from the studies presented in this work, can be summarized as follows:• Development of a self-consistent, unified theory of lightning and jet discharges based on the concept of bi-directional, overall neutral and equipotential lightning leaders;• Presentation of a jet discharge observed by Lightning Mapping Array (LMA) in a STEPS 2000 thunderstorm;• Modeling of the STEPS 2000 jet and comparison with LMA data;• Modeling of typical lightning and jet discharges resulting from the above theory using realistic cloud configurations emphasizing charge imbalance as a principal factor allow-ing formation of a leader with high potential that enables it to escape from the thunder-cloud.
VI. Conclusions Behnke, S. A., R. J. Thomas, P. R. Krehbiel, and W. Rison (2005), Initial leader veloci-ties during intracloud lightning: Possible evidence for a runaway breakdown effect, J. Geophys. Res., 110 (D12), D10207, doi:10.1029/2004JD005312. Boeck, W. L., O. H. Vaughan, R. J. Blakeslee, B. Vonnegut, M. Brook, and J. McKune (1995), Observations of lightning in the stratosphere, J. Geophys. Res., 100, 1465. Coleman, L. M., T. C. Marshall, M. Stolzenburg, T. Hamlin, P. R. Krehbiel, W. Rison, and R. J. Thomas (2003), Effects of charge and electrostatic potential on lightning propa-gation, J. Geophys. Res., 108 (D9), 4298, doi:10.1029/2002JD002718. Kasemir, H. W. (1960), A contribution to the electrostatic theory of a lightning discharge, J. Geophys. Res., 65 (7), 1873–1878. Krehbiel, P. (2005), On the initiation of upward lightning discharges above thunder-storms, Eos Trans. AGU, 86 (18), Jt. Assem. Suppl., Abstract AE11A-05. Krehbiel, P., W. Rison, R. Thomas, T. Marshall, M. Stolzenburg, W. Winn, and S. Huny-ady (2004), Thunderstorm charge studies using a simple cylindrical charge model, electric field measurements, and lightning mapping observations, Eos Trans. AGU, 85 (47), Fall Meet. Suppl., Abstract AE23A-0843. Mansell, E. R., D. R. MacGorman, C. L. Ziegler, and J. M. Straka (2002), Simulated three-dimensional branched lightning in a numerical thunderstorm model, J. Geophys. Res., 107 (D9), 4075, doi:10.1029/2000JD000244. Niemeyer, L., L. Pietrono, and H. J. Wiesmann (1984), Fractal dimension of dielectric breakdown, Phys. Rev. Lett., 52 (12), 1033–1036, doi:10.1103/PhysRevLett.52.1033. Pasko, V. P., M. A. Stanley, J. D. Matthews, U. S. Inan, and T. G. Wood (2002), Electrical discharge from a thundercloud top to the lower ionosphere, Nature, 416, 152–154, doi: 10.1038/416152a.
Raizer, Y. P., G. M. Milikh, and M. N. Shneider (2006), On the mechanism of blue jet formation and propagation, Geophys. Res. Lett., 33 (23), L23801, doi: 10.1029/2006GL027697. Raizer, Y. P., G. M. Milikh, and M. N. Shneider (2007), Leader–streamers nature of blue jets, J. Atmos. Solar-Terr. Phys., 69 (8), 925–938, doi:10.1016/j.jastp.2007.02.007. Riousset, J. A., V. P. Pasko, P. R. Krehbiel, R. J. Thomas, and W. Rison (2007), Three-dimensional fractal modeling of intracloud lightning discharge in a New Mexico thunderstorm and comparison with lightning mapping observations, J. Geophys. Res., 112 (D15203), doi:10.1029/2006JD007621. Rison, W., R. J. Thomas, P. R. Krehbiel, T. Hamlin, and J. Harlin (1999), A GPS-based three-dimensional lightning mapping system: Initial observations in central New Mexico, Geophys. Res. Lett., 26 (23), 3573–3576, doi:10.1029/1999GL010856. Sentman, D. D., E. M. Wescott, D. L. Osborne, D. L. Hampton, and M. J. Heavner (1995), Preliminary results from the Sprites94 campaign: Red sprites, Geophys. Res. Lett., 22, 1205–1208. Su, H. T., R. R. Hsu, A. B. Chen, Y. C. Wang, W. S. Hsiao, W. C. Lai, L. C. Lee, M. Sato, and H. Fukunishi (2003), Gigantic jets between a thundercloud and the ionosphere, Nature, 423, 974–976, doi:10.1038/nature01759.Thomas, R. J., P. R. Krehbiel, W. Rison, T. Hamlin, J. Harlin, and D. Shown (2001), Observations of VHF source powers radiated by lightning, Geophys. Res. Lett., 28 (1), 143–146. Wescott, E. M., D. Sentman, D. Osborne, D. Hampton, and M. Heavner (1995), Prelimi-nary results from the Sprites94 aircraft campaign: 2. Blue jets, Geophys. Res. Lett., 22 (10), 1209–1212. Williams, E. R., C. M. Cooke, and K. A. Wright (1985), Electrical discharge propagation in and around space charge clouds, J. Geophys. Res., 90 (D4), 6059–6070.
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