Lightning charge analyses in small Convection and Precipitation Electrification (CaPE) experiment storms (original) (raw)
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Observed electric fields associated with lightning initiation
Geophysical Research Letters, 2005
1] In situ electric field (E) measurements and inferred lightning initiation locations of three cloud-to-ground flashes are used to identify a thunderstorm region in which the preflash E exceeded the threshold for runaway breakdown. The maximum measured E in the region was 186 kV m À1 at 5.77 km altitude, which for runaway electrons is equivalent to 370 kV m À1 at sea level; this E value is $130% of the estimated threshold for an avalanche of runaway electrons. In addition, the volume where E exceeded the runaway threshold was estimated to be 1 -4 km 3 , with a vertical depth of about 1000 m. At least within part of this volume the characteristic scale height for exponential growth of runaway electrons was 100 m or less. Thus for these three flashes the electric field conditions necessary for runaway breakdown existed, and runaway breakdown could have initiated the flashes. Citation: Marshall, T. C., M. Stolzenburg, C. R. Maggio, L. M. Coleman, P. R. Krehbiel, T. Hamlin, R.
The 29 June 2000 supercell observed during STEPS. Part II: Lightning and charge structure
2010
This second part of a two-part study examines the lightning and charge structure evolution of the 29 June 2000 tornadic supercell observed during the Severe Thunderstorm Electrification and Precipitation Study (STEPS). Data from the National Lightning Detection Network and the New Mexico Tech Lightning Mapping Array (LMA) are used to quantify the total and cloud-to-ground (CG) flash rates. Additionally, the LMA data are used to infer gross charge structure and to determine the origin locations and charge regions involved in the CG flashes. The total flash rate reached nearly 300 min Ϫ1 and was well correlated with radar-inferred updraft and graupel echo volumes. Intracloud flashes accounted for 95%-100% of the total lightning activity during any given minute. Nearly 90% of the CG flashes delivered a positive charge to ground (ϩCGs). The charge structure during the first 20 min of this storm consisted of a midlevel negative charge overlying lower positive charge with no evidence of an upper positive charge. The charge structure in the later (severe) phase was more complex but maintained what could be roughly described as an inverted tripole, dominated by a deep midlevel (5-9 km MSL) region of positive charge. The storm produced only two CG flashes (both positive) in the first 2 h of lightning activity, both of which occurred during a brief surge in updraft and hail production. Frequent ϩCG flashes began nearly coincident with dramatic increases in storm updraft, hail production, total flash rate, and the formation of an F1 tornado. The ϩCG flashes tended to cluster in or just downwind of the heaviest precipitation, which usually contained hail. The ϩCG flashes all originated between 5 and 9 km MSL, centered at 6.8 km (Ϫ10°C), and tapped LMA-inferred positive charge both in the precipitation core and (more often) in weaker reflectivity extending downwind. All but one of the ϪCG flashes originated from Ͼ9 km MSL and tended to strike near the precipitation core.
Journal of Geophysical Research-Atmospheres, 2014
1 ground lightning flashes 2 3 4 A. Key points 21 -Inception of subsequent strokes of natural bipolar cloud-to-ground flashes 22 -First report of inception mechanism of negative phase of bipolar CG flashes 23 -High-speed camera and multiple LLS study of bipolar CG flashes 24 25 Abstract: 26 High-speed video records of two bipolar cloud-to-ground flashes were analyzed in 27 detail. They both began with a single positive return stroke that was followed by more 28 than one subsequent weak negative stroke. Due to the elevated cloud-base height of its 29 parent thunderstorm, the preparatory processes of each subsequent negative stroke were 30 documented optically below cloud base. In the first event (Case 1) it was observed that 31 all four subsequent negative strokes were initiated by recoil leaders that retraced one 32 horizontal channel segment previously ionized by the positive leader. Those recoil 33 leaders connected to the original vertical channel segment and propagated towards 34 ground, producing four subsequent strokes that had the same ground contact point as the 35 original positive discharge. The second event (Case 2), in contrast, presented fifteen 36 subsequent strokes that were initiated by recoil leaders that did not reach the original 37 channel of the positive stroke. They diverged vertically towards ground, making contact 38 approximately 11 kilometers away from the original positive strike point. These results 39 constitute the first optical evidence that both single-and multiple-channel bipolar 40 flashes occur as a consequence of recoil leader activity in the branches of the initial 41 positive return stroke. For both events their total channel length increased continuously 42 at a rate of the order of 10 4 m s -1 , comparable to speeds reported for typical positive 43 leaders. 44 Index terms 45 3304 -Meteorology and Atmospheric Dynamics: Atmospheric electricity 46 3324 -Meteorology and Atmospheric Dynamics: Lightning 47 48
Observations within two regions of charge during initial thunderstorm electrification
Quarterly Journal of the Royal Meteorological Society, 1988
Airborne electric field measurements in two small thunderstorms in New Mexico show the existence of a narrow region of charge in each storm during the early stage of electrification. In one case a net negative region of charge was observed at about 7 km (-12°C) about 1.5 km below the radar cloud top, when the electric field was only 600Vm-', and could be accounted for by total charge of-0.01 C with a maximum net space charge density of-0-15 nCm-3, assuming spherical symmetry. This region of charge was about 500 m across and appears to have been associated with an updraught-downdraught transition zone. In the other cloud, a region of net positive charge, also about 500111 across, was detected at 7.7 km (-20°C) about 500m below the radar cloud top, when the electric field was about 2000Vm-'. In both regions of charge, supercooled liquid water and ice particles including graupel were present, and ice particle concentrations, sizes, and collision rates were at a relative maximum, suggesting that the charge generation occurred via a precipitation-based mechanism.
Estimation of charge neutralized by negative cloud-to-ground flashes in Catalonia thunderstorms
Journal of Electrostatics, 2009
Charges neutralized by lightning flashes have been usually located and inferred from the quasi-static changes in the vertical component of electric field (DE) obtained from multiple synchronized measurement stations. In this paper, the charges neutralized by negative cloud-to-ground (ÀCG) lightning flashes are located and inferred using single station electric field measurements in combination with total lightning (cloud-to-ground and intra-cloud) data from lightning detection networks in the north-eastern region of Spain. The altitude of the negative charge region in 8 thunderstorms examined here was in the range of 5.8-7.2 km as inferred from temperature soundings. Charge locations are assumed to be in the region where the VHF (Very High Frequency) sources associated with the discharge are located. The quantity of charge neutralized is calculated using a point charge model and the measured vertical component of electric field (DE) associated with each flash. The results are compared with those previously obtained from measurements carried out in the NASA Kennedy Space Center (KSC) in Florida. The analysis of 260 ÀCG flashes from eight thunderstorms reveals a median charge value of À9.7 C with 95% of the values ranging between À4.5 C and À45 C.
Despite the ubiquity of thunderstorms, lightning, and related electrical phenomena, many important electromagnetic processes in our atmosphere are poorly understood; the key questions about the thundercloud electrification and lightning initiation remain unanswered. The bulk information on particle fluxes correlated with thunderstorm can be used to better understand the electrical structure of thunderclouds. Only very specific electric configuration of the lower part of the cloud can support the sustainable acceleration of the electrons. Our analysis is based on the thunderstorm data from the Aragats Mountain in Armenia, 3200 m above sea level Varieties of particle detectors located at Aragats Space Environmental Center are registering neutral and charged particle fluxes correlated with thunderstorms, so-called Thunderstorm Ground Enhancements (TGEs). Simultaneously the electrical mills and lightning detectors are monitoring the near-surface electric field and type of lightning occurrences; weather stations are measuring plenty of meteorological parameters. In the present paper we relate particle fluxes to the electrical structure of thunderclouds, namely, to the origination of the Lower Positive Charged Region (LPCR) below the main negative charged layer in the middle of the thundercloud, and to lightning occurrences. Only after creation of the lower dipole in the thundercloud can the electrons be accelerated and particle flux be directed downward. Maturity of the LPCR is correlated with increasing particle fluxes. Thus, the temporal evolution of TGE gives direct evidence of the maturity of LPCR, its initiation, and its decaying.
Observation of thunderstorms by multilevel electric field measurement system and radar
Journal of Geophysical Research, 1995
During the summer of 1992, an experiment was conducted in southwestern France, close to the Pyrenees, at the Centre de Recherches Atmosph•riques (CRA) in order to study the evolution of the electric field measured at several levels below thunderclouds. We used a field mill flush to the ground and four field sensors, suspended from an insulated cable and distributed between 0 and 48 m. These altitude sensors separately measure the ambient electric field and the field created by the sensor itself. The Rabelais millimetric radar provides reflectivities and Doppler velocities of cloud and rain systems. Meteorological data like wind velocity, humidity, temperature, and rainfall rate are recorded at the site. Two storm intervals are studied, one on July 30 and one on August 6. Both examples give an idea on how the electric field signature during the development or advection of a convective cloud can be different at the ground and at altitudes of a few tens of meters. The maxima in the electrostatic activity are visible only on the altitude electric field evolution. The maximum value of the electric field between lightning flashes, close to 30 kV m-•, is detected at 48 rn above ground. A vertical gradient of the electric field is observed in this 48-m-thick layer, especially when the field is high. The upward progressive development of this gradient is interpreted in terms of a local charge generated by corona at the ground and rising by conduction. The average charge density in the whole layer reaches around 5 nC m-3 between lightning flashes when the field keeps large values of the same polarity. This density is weaker when the electric field has taken large values of both polarities. Long periods of different electrical activity are observed during both storms (those with large electrostatic fields without any lightning flash and those with lightning activity). The former are associated with a thick stratiform cloud structure, possibly with strong radar echoes above the melting level but without rain reaching the ground; the latter are associated with rain reaching the ground close to the measurement area. These observations suggest that the water liquid phase could play an important role in lightning initiation. while it can reach more close to 20 kV m '• a few meters above [Standler and Winn, 1979; Chauzy and Soula, 1987]. These observations show the effect of a charge layer that develops from the ground due to the generation of corona ions. This layer modifies the electric field produced by the cloud, and therefore the vertical field distribution is changed across the whole layer. A multilevel electric field system was designed by Chauzy et al. [1991] in order to study the vertical distribution of the electric field and the evolution of the corona ions up to altitudes of several hundred meters. The system was suspended from a tethered balloon in Florida at the Kennedy Space Center during the surmners 1989 and 1991, and an interesting event was recorded during the first experiment [Soula
Remote Measurements of Currents in Cloud Lightning Discharges
IEEE Transactions on Electromagnetic Compatibility, 2000
Using measured wideband electric field waveforms and the Hertzian dipole (HD) approximation, we estimated peak currents for 48 located compact intracloud lightning discharges (CIDs) in Florida. The HD approximation was used because 1) CID channel lengths are expected to range from about 100 to 1000 m, and in many cases can be considered electrically short and 2) it allows one to considerably simplify the inverse source problem. Horizontal distances to the sources were reported by the U.S. National Lightning Detection Network (NLDN), and source heights were estimated from the horizontal distance and the ratio of electric and magnetic fields. The resultant CID peak currents ranged from 33 to 259 kA with a geometric mean of 74 kA. The majority of NLDN-reported peak currents for the same 48 CIDs are considerably smaller than those predicted by the HD approximation. The discrepancy is primarily because NLDN-reported peak currents are assumed to be proportional to peak fields, while for the HD approximation, the peak current is proportional to the peak of the integral of the electric radiation field. An additional factor is the limited (400 kHz) upper frequency response of the NLDN.
Transient currents in the global electric circuit due to cloud-to-ground and intracloud lightning
Atmospheric Research, 2009
Intracloud (IC) and cloud-to-ground (CG) lightning flashes produce transient changes in the electric field (E) above a thundercloud which drive transient currents in the global electric circuit (GEC). Using in-cloud and above-cloud E data from balloons, ground-based E data, and Lightning Mapping Array data, the above-cloud charge transfers due to lightning transients are estimated for five IC and five CG flashes from four thunderstorms that occurred above the mountains in New Mexico, USA, in 1999. For the five CG flashes (which transferred −4 to −13 C to the ground), the transient currents moved +1 to +5 C of charge upward from cloudtop toward the ionosphere, with an average transient charge transfer of about 35% of the charge transferred to ground. For the five IC flashes (which neutralized 6 to 21 C inside the cloud), the transient currents moved −0.7 to −3 C upward, with an average transient charge transfer of about 12% of the lightning charge. Estimates for three thunderstorms indicate that the transient currents made only a small GEC contribution compared to the quasi-stationary Wilson currents because of the offsetting effects of IC and CG flashes in these storms. However, storms with extreme characteristics, such as high flash rates or predominance of one flash type, may make a significant GEC contribution via lightning transients.