Negative Cloud-to-ground Research Articles

A comparative study of negative cloud‐to‐ground lightning characteristics in São Paulo (Brazil) and Arizona (United States) based on high‐speed video observations

There are only a few prior reports that detail accurate measurements of the number of strokes in natural negative cloud‐to‐ground (CG) lightning flashes. These are known as “accurate‐stroke‐count” studies, and they have been performed using various instruments and techniques. Here, we will examine the lightning characteristics produced by warm‐season thunderstorms in two different climate regimes (southern Arizona, United States, and São Paulo, Brazil) using the same instrumentation. The lightning parameters were obtained from high‐speed video recordings and time‐correlated data provided by lightning locating systems (LLS). The use of these instruments has allowed us to measure the number of strokes in each flash and their polarity, the interstroke intervals, the number of different ground contacts, and the durations of the continuing currents. Altogether 209 negative flashes were recorded on video in the United States and 223 in Brazil (containing a total of 1681 strokes), and the majority of these flashes had at least one stroke reported by a LLS. Statistical analyses of these data sets as a whole did not show any significant differences in the characteristics of negative CG flashes from warm‐season thunderstorms in both locations. The mean values for all data are as follows: video multiplicity, 3.9; single‐stroke flashes, 19.5%; flash duration, 226.5 ms; interstroke interval, 61.5 ms; long continuing current, 17.5%; multigrounded flashes, 49.5%. Those characteristics were very similar to the well‐accepted values for negative flashes in other regions. However, there were large storm‐to‐storm variations.

Lightning activity and electrical structure in a thunderstorm that continued for more than 24 h

Based on the 2A12 product of the TRMM satellite, lightning data observed by SAFIR3000, and a cloud-to-ground (CG) lightning location network, lightning activity and electrical structure were analyzed in a thunderstorm that occurred in Hubei province of China on 30–31 May 2007. This thunderstorm considered to be unusual because it continued for more than 24 h and produced a heavy rainfall in a wide area had some analogous electric characteristics to normal thunderstorms. In convective areas of the thunderstorm, CG flashes tended to be of negative polarity and were spatially clustered. In stratiform areas of the storm, CG flashes tended to be of positive polarity and had a scattered spatial distribution. Based on the spatial distribution of lightning radiation sources observed by SAFIR3000, a typical tripolar electrical structure was inferred to dominate the convective areas, whereas a dipolar structure with anomalously low charge heights was inferred in the stratiform areas. The polarity of the CG flashes appeared to be same as that of the second charge region, as counted from the lower charge region. The mean ratios of positive cloud-to-ground (PCG) flashes were small with 3.52% during active stage and big with 21.25% during decaying stage. It was found that during the decaying stage, the concentration of ice particles in the convective areas decreased much more rapidly than did the concentration in stratiform areas due to the rapidly weakening updraft in convective areas, being related to that negative cloud-to-ground (NCG) flashes activity mainly occurring in the convective areas weakened more rapidly than the PCG flashes activity mainly occurring in the stratiform areas. The main negative charge involved in lightning discharges was located in the region with the highest concentration of graupel particles, and the main upper positive charge involved in lightning discharges was located in the lower part of the region with the highest concentration of ice crystal particles.

Simulated Electrification of a Small Thunderstorm with Two-Moment Bulk Microphysics

Abstract Electrification and lightning are simulated for a small continental multicell storm. The results are consistent with observations and thus provide additional understanding of the charging processes and evolution of this storm. The first six observed lightning flashes were all negative cloud-to-ground (CG) flashes, after which intracloud (IC) flashes also occurred between middle and upper levels of the storm. The model simulation reproduces the basic evolution of lightning from low and middle levels to upper levels. The observed lightning indicated an initial charge structure of at least an inverted dipole (negative charge above positive). The simulations show that noninductive charge separation higher in the storm can enhance the main negative charge sufficiently to produce negative CG flashes before upper-level IC flashes commence. The result is a “bottom-heavy” tripole charge structure with midlevel negative charge and a lower positive charge region that is more significant than the upper positive region, in contrast to the traditional tripole structure that has a less significant lower positive charge region. Additionally, the occurrence of cloud-to-ground lightning is not necessarily a result of excess net charge carried by the storm, but it is primarily caused by the local potential imbalance between the lowest charge regions. The two-moment microphysics scheme used for this study predicted mass mixing ratio and number concentration of cloud droplets, rain, ice crystals, snow, and graupel. Bulk particle density of graupel was also predicted, which allows a single category to represent a greater range of particle characteristics. (An additional hail category is available but was not needed for the present study.) The prediction of hydrometeor number concentration is particularly critical for charge separation at higher temperatures (−5° < T < −20°C) in the mixed phase region, where ice crystals are produced by rime fracturing (Hallett–Mossop process) and by splintering of freezing drops. Cloud droplet concentration prediction also affected the rates of inductive charge separation between graupel and droplets.

Detecting Multiple Ground Contacts in Cloud-to-Ground Lightning Flashes

Abstract Video recordings of cloud-to-ground (CG) lightning flashes have been analyzed in conjunction with correlated stroke reports from the U.S. National Lightning Detection Network (NLDN) to determine whether the NLDN is capable of identifying the different ground contacts in CG flashes. For 39 negative CG flashes that were recorded on video near Tucson, Arizona, the NLDN-based horizontal distances between the first stroke and the 62 subsequent strokes remaining in a preexisting channel had a mean and standard deviation of 0.9 ± 0.8 km and a median of 0.7 km. The horizontal distances between the first stroke and the 59 new ground contacts (NGCs) had a mean and standard deviation of 2.3 ± 1.7 km and a median of 2.1 km. These results are in good agreement with prior measurements of the random errors in NLDN positions in southern Arizona as well as video- and thunder-based measurements of the distances between all ground contacts in Florida. In cases where the distances between ground contacts are small and obscured by random errors in the NLDN locations, measurements of the stroke rise time, estimated peak current, and stroke order can be utilized to enhance the ability of the NLDN to identify strokes that produce new ground terminations.

Charge source of cloud-to-ground lightning and charge structure of a typical thunderstorm in the Chinese Inland Plateau

GPS-synchronized measurements of electric ( E) field changes induced by lightning flashes were recorded at six stations in the northeastern verge of the Tibetan Plateau. The height and magnitude of charge neutralized by 65 return strokes, including 16 negative cloud-to-ground (CG) flashes and 2 positive CG flashes, have been fitted with the nonlinear least-square method based on the E field changes of CG flashes observed in a typical thunderstorm with larger-than-usual lower positive charge center (LPCC). Results show that the height of the charge region neutralized by negative CG flashes ranges from 3 km to 5 km above the ground, corresponding to an ambient temperature between − 2 °C and − 15 °C. For the two positive CG flashes, the neutralized charge regions are located at a height of about 5.5 km and the ambient temperature is about − 18 °C, indicating the existence of upper positive charge in the thunderstorm.

Characteristics of cloud-to-ground lightning in warm-season thunderstorms in the Central Great Plains

In July 2005, a field campaign was conducted in the Central Great Plains to obtain 60-field/s video imagery of lightning in correlation with reports from the U.S. National Lightning Detection Network (NLDN) and broadband electric field waveforms from the Los Alamos Sferic Array (LASA). A total of 342 GPS time-stamped cloud-to-ground (CG) flashes were recorded in 17 different sessions, and 311 (91%) of these were correlated with reports from the NLDN. Only 6 of the 17 recording sessions were dominated by flashes that lowered negative charge to ground, and 11 were dominated by positive CG flashes. A total of 103 flashes recorded on video were correlated with at least one NLDN report of negative CG strokes, 204 video flashes were correlated with one or two positive stroke reports, and 4 had bipolar reports. In this paper, we will give distributions of the estimated peak current, I p, as reported by the NLDN, of negative and positive first strokes that were recorded on video, the multiplicity of strokes that were recorded on video, and the number of ground contacts per flash that were resolved on video. 41 (40%) of the negative flashes produced just a single-stroke on video, and 62 (60%) showed two or more strokes. The observed multiplicity of negative flashes averaged 2.83, which becomes about 3.14 after correcting for the finite time-resolution of the video camera. 195 (96%) of the positive flashes produced just a single-stroke on video, and 9 (4%) showed two strokes; therefore, the observed multiplicity of positive flashes averaged 1.04. Five out of 9 (56%) of the positive subsequent strokes re-illuminated a previous channel, and 4 out of 9 (44%) created a new ground contact. Simultaneous video, LASA, and NLDN measurements also allowed us to examine the classification of NLDN reports during 3 single-cell storms (one negative and two positive). Based on the LASA waveforms, a total of 204 out of 376 (54%) NLDN reports of CG strokes were determined to be for cloud pulses. The misclassified negative reports had | I p| values ranging from 3.8 kA to 29.7 kA, but only 58 (24%) of these had | I p| > 10 kA, and only one misclassified positive report had I p > 20 kA. Radar analyses showed that most of the negative and positive CG strokes that were recorded on video were produced within or near the convective cores of storms. The radar imagery also showed that single-cell storms tended to produce one polarity of CG flashes at a time, and that such storms could switch rapidly from negative to positive CG flashes when the reflectivity was near maximum. Multiple-cell storms produced both negative and positive flashes over a broad region, but each polarity tended to cluster near regions of high-reflectivity.

The characteristics of cloud-to-ground lightning activity in hailstorms over northern China

The characteristics of cloud-to-ground (CG) lightning for ten hailstorms in Shandong Province of China were analyzed statistically. It is found that the hailstorms in this study present dominant positive CG flashes during periods of falling hail. One specific hailstorm on 16 June 2006 was studied in detail using the data from a CG lightning location network, Doppler radar and cloud images. Comparison between the brightness temperature of cloud-top and CG flash locations indicated that most flashes occurred in the region with temperatures lower than − 40 °C, while dense positive CG flashes occurred in the range between − 40 °C and − 50 °C. Negative CG flashes occurred mostly in the relative weak radar echo region, and positive CG flashes were distributed in the strong echo region especially with a large gradient of echo intensity. CG flashes tended to occur in the cloud region with reflectivity between 25 dBZ and 35 dBZ. Comparison between the wind field retrieved from Doppler radar and the location of CG flashes indicated that the flashes were located in the convergent region at lower to middle levels.

Characteristics of negative lightning flashes presenting multiple-ground terminations on a millisecond-scale

By using a high-speed video camera system (1000 frames s − 1 ) in correlation with fast and slow antenna systems, the negative cloud-to-ground (CG) flashes that struck the ground with more than one termination have been analyzed. This kind of stroke, named as multiple-ground terminations stroke (MGTS), was produced by different branches of the same stepped leader during quite a short time. Based on optical images, the 2D progression speed of leader branches was estimated to be in the range (0.9–2.0) × 10 5 m s − 1 . The distance between adjacent striking points of MGTS was from 0.2 km to 1.9 km. The percentage of flashes with multiple-ground terminations occupied about 15% (9 out of 59) of the total negative CG flashes, with a range of 11%–20% in different areas in China. The time intervals between the two adjacent peaks ranged from 4 μs to 486 μs based on the E-field change caused by the MGTS. The flashes which had multiple striking points on the ground during quite a short time may be a common phenomenon in the lightning discharge process. It might produce more serious damage to facilities on the ground and should not be neglected in the design of lightning protection.

Rare measurements of a sprite with halo event driven by a negative lightning discharge over Argentina

As part of a collaborative campaign to investigate Transient Luminous Events (TLEs) over South America, coordinated optical, ELF/VLF, and lightning measurements were made of a mesoscale thunderstorm observed on February 22–23, 2006 over northern Argentina that produced 445 TLEs within a ∼6 hour period. Here, we report comprehensive measurements of one of these events, a sprite with halo that was unambiguously associated with a large negative cloud‐to‐ground (CG) lightning discharge with an impulsive vertical charge moment change (ΔMQv) of −503 C.km. This event was similar in its location, morphology and duration to other positive TLEs observed from this storm. However, the downward extent of the negative streamers was limited to 25 km, and their apparent brightness was lower than that of a comparable positive event. Observations of negative CG events are rare, and these measurements provide further evidence that sprites can be driven by upward as well as downward electric fields, as predicted by the conventional breakdown mechanism.

Observation and study on the whole process of cloud-to-ground lightning using narrowband radio interferometer

A narrowband radio interferometer has been developed and used to locate the entire sources of VHF radiations from a negative cloud-to-ground (CG) lightning discharge which contains 19 strokes. This system uses five antennas to form an array consisting of short-and long-baselines along two orthogonal directions. The system error which comes from frequency conversion is reduced by phase detection through direct high frequency amplifying. An interactive graphic analysis procedure is used to remove the fringe ambiguities which exist inherently in interferometry and to determine the direction of lightning radiation sources in two dimensions (azimuth and elevation) as a function of time at a time resolution of microsecond orders. With the developed system, the whole progression process in time and space of a lightning flash can be reconstructed. In this paper, combining the synchronous data of electric filed change and VHF radiation, the whole processes of an example negative CG flash have been studied in detail. It is found that the preliminary breakdown event of the CG flash started from negative charge region and exhibited firstly a downward pregression and then an upward propagation. There were very intense and continuous radiations during stepped leaders which became much stronger when the first return stroke began. In contrast, there were less and only discrete radiations during dart leaders. Stepped leader and dart leader may transform to each other depending on the state of the ionization of the path. The progression speed of initial stepped leaders was about 105 ms−1, while that was about 4.1×106 and 6.0×106 ms−1 for dart leaders and dart-stepped leaders, respectively. M events produced hook-shaped field changes accompanied by active burst of radiations at their beginnings. Followed these active radiation processes, M events appeared to contact finally into conducting main discharge channels. The mean progression speed of M events was about 7×107 ms−1, greater than that of the dart leaders and dart-step leaders. K events and attempted leaders were essentially the same as dart leaders except that they could not reach the ground and initiate return strokes.

Radar and Lightning Observations of Normal and Inverted Polarity Multicellular Storms from STEPS

Abstract This study discusses radar and lightning observations of two multicellular storms observed during the Severe Thunderstorm Electrification and Precipitation Study. The Lightning Mapping Array data indicated that the charge structure of the 19 June 2000 storm was consistent with a normal polarity tripole, while the 22 June 2000 storm exhibited an overall inverted tripolar charge structure. The 19 June storm consisted of weaker convection and produced little to no hail and moderate total flash rates peaking between 80 and 120 min−1. The cells in the 22 June 2000 storm were much more vigorous, exhibited strong, broad updrafts, and produced large quantities of hail, as well as extraordinary total flash rates as high as 500 min−1. The National Lightning Detection Network (NLDN) indicated that the 19 June storm produced mostly negative cloud-to-ground (CG) lightning, while the 22 June storm produced predominantly positive CG lightning, peaking at 10 min−1 just after two cells merged. However, the Los Alamos Sferic Array indicated that many of the positive CG strokes reported by the NLDN in the 22 June storm were intracloud discharges known as narrow bipolar events. Negative CG lightning was also observed in the 22 June storm, but typically came to ground beneath an inverted dipole in the storm anvil.

A study of the total lightning activity in two hailstorms

Two thunderstorms which developed in the northeastern region of Spain on 17 August 2004 are analyzed. According to radar and ground observations, one of these storms produced large hail (larger than 19 mm) and therefore could be severe. Both thunderstorms exhibited strong vertical developments with cloud tops reaching 17.5 and 14 km for the severe and the nonsevere ones, respectively. The total lightning activity was monitored, thanks to the Spanish magnetic‐direction‐finding and time‐of‐arrival (MDF/TOA) network and thanks to a regional very‐high‐frequency (VHF) interferometer network. Both storms presented low cloud‐to‐ground (CG) flash rates (lower than 2 min−1) during their mature phase, while the intracloud (IC) flash rate reached 92 min−1 for the severe one. The IC/CG flash ratio was very high for both storms: 35 and 60 in average value for the severe and the nonsevere ones, respectively. The lightning characteristics exhibited low values in terms of peak current and multiplicity for negative CG (−CG) flashes and in terms of VHF source number per flash for IC flashes. The average multiplicity of the −CG flashes was 1.74 and 1.17 for the severe and the nonsevere storms, respectively, and their average peak current was −11.7 and −10.65 kA, respectively. When the presence of hail is suspected from high radar reflectivity values in both cells, the flash rates tended to substantially decrease. The severe storm produced positive CG (+CG) flashes during 1 hour, and at that moment, the multiplicity and peak currents of −CG flashes were very low. Lightning activity for both storms ended with a substantial increase of the −CG flash rate. The elevated charge hypothesis is consistent with the observations, especially if we consider two aspects of this hypothesis, the one about charge separation, which could be limited by the strong updrafts, and the one about the lightning initiation, which could be favored by low pressures at high altitude.

Monthly distribution of cloud‐to‐ground lightning flashes as observed by lightning location systems

This paper presents a comparison among the mean monthly distributions of the number of cloud‐to‐ground (CG) flashes, the percentage of positive CG flashes and the peak current of negative and positive CG flashes obtained in Brazil for the period from 1999 to 2004, with the same distributions observed by similar networks for long time periods in other countries. From a correlation analysis, it was found that the mean monthly distributions of the number of CG flashes are very similar, even though the period of larger lightning activity along the year in Brazil, a tropical country, is longer than in the other temperate countries. The mean monthly distributions of the percentage and the peak current of positive CG flashes are also very similar, while the mean monthly distribution of the peak current of negative CG flashes in Brazil differs from the other countries. This difference is related to a significant decrease in the mean negative peak current in Brazil in the months of August and September. Apparently, the decrease is related to the injection in the atmosphere of large amounts of smoke from fires in these months, since the results also show a significant correlation between the monthly distribution of the number of fires and the negative peak current.

Spatiotemporal characteristics of positive cloud-to-ground lightning discharges and bidirectional leader of the lightning

The three-dimension spatiotemporal development characteristics of positive cloud-to- ground (CG) lightning discharges have been analyzed by using the data measured by the lightning mapping array system with high time and space resolution. The results indicate that a positive CG lightning discharge can be divided into three stages based on the characteristics of its development. The first stage is discharge process in cloud with a long duration preceding the return stroke. This process with an average of 370 ms propagated at velocity of 10 5 m/s and produced intensive radiation with a magnitude equal to that of the negative leader. During this stage, the lightning channels developed horizontally in the positive charge region with few branches as the negative polarity breakdown. During the stage after the return stroke of the positive CG lightning, the lightning channels propagated at velocity of 2 times faster than that before the return stroke. This stage involved lots of positive fast impulses and corresponded to the continuing current process producing less and dispersed radiation points and more intensive radiation powers. During the final stage of the positive CG lightning, the lightning channels developed at velocity equal to that before the return stroke and the radiation points appeared mainly at the ends of channel. The spatiotemporal development characteristics of the positive CG lightning are very different from that of the negative CG lightning. All of the radiation points of the positive CG lightning appeared in the positive charge region of cloud. Little or no radiation was detected during the positive leader just before the return stroke. The duration of the positive CG lightning was an average of 730 ms. The positive CG lightning discharges with lasting time of 500―600 ms were 43%. 90% of the positive CG lightning discharges involved one return stroke, the most return stroke number being four. The current of the return stroke was an average of 36.5 kA with maximum and minimum values of 70 kA and 11.5 kA respectively. 40% of the return stroke currents were more than 40 kA.

Charge structures and cloud-to-ground lightning discharges characteristics in two supercell thunderstorms

The charge structures and temporal and spatial characteristics of cloud-to-ground (CG) light- ning discharges in two supercell thunderstorms have been analyzed based on the data of three-dimen- sional VHF radiation sources with high time and space resolution produced by lightning discharges. The results indicate that the charge structures in main part (convective region) of the thunderstorms were inverted tripole while a number of positive CG lightning discharges were occurring in the two thun- derstorms. The positive CG lightning discharges oc- curred in main part of the thunderstorms and origi- nated from the positive charge region located at the middle part of the thunderstorms. While a number of negative CG lightning discharges were occurring, the negative CG lightning discharges occurred in the anvil of the thunderstorm. The charge structure is inverted dipole in the region due to the slant of charge structure in main region toward anvil region. The negative charge region located at the upper part of anvil produced a lot of negative CG lightning dis- charges. No or less CG lighting was produced di- rectly by the charge region located at the lower part of the thunderstorm. The charge region in lower part of the thunderstorm plays an important role for the occurrence of CG lightning from charge region above it.

A 3-year study of cloud-to-ground lightning flash characteristics of Mesoscale convective systems over the Western Mediterranean Sea

In this paper cloud-to-ground (CG) lightning flashes of 33 Mesoscale Convective Systems (MCSs) over the Western Mediterranean area are analyzed. Mean values of 22% for the positive CG ratio, 1.1 (2.4) for positive (negative) CG multiplicity, 17 kA (22.6 kA) of peak current for the positive (negative) CG flashes and a mean flash rate of around 13 min − 1 are obtained. The percentage of positive CGs and the multiplicity of negative CG are higher, while the mean peak currents are lower than in previous studies on MCSs. A more detailed case analysis reveals that there are great differences among the CG characteristics of MCSs. The life cycle of CG lightning associated with MCSs is also analyzed. The growing stages of MCSs are characterised by high CG lightning activity. The positive CG flash rate generally reaches a maximum before the negative CG flash rate does. In both cases the peak is recorded before or when MCSs show the largest area. Maximum flash rate and densities coincide with the area where the MCS shows the minimum cloud-top temperatures and therefore shows highest vertical development.

The possible charge structure of thunderstorm and lightning discharges in northeastern verge of Qinghai–Tibetan Plateau

In the summer of 2002, a comprehensive observation on thunderstorm and natural lightning discharge was conducted in the northeastern verge of Qinghai–Tibetan Plateau (101°35′E, 37°33′N, 2650 m asl). During the experiment, field mill, and fast and slow antenna systems were employed in 6 sites synchronized by GPS with 0.4 μs time resolution. In addition, a high-speed digital camera with 1 ms resolution was used in the observation. The surface electric field for one thunderstorm and a sequence of 30 flashes in the storm revealed a tripole charge structure in the mature stage. Most of the intracloud (IC) flashes occurred in the lower part and only a few occurred in the upper part of the thunderstorm. This suggests that the charging activity in the lower part of the storm was more vigorous than in the upper part. As most of the graupels fell to the ground in the dissipating stage of the storm, the lower positive charge in the thunderstorm tripole decreased, and negative cloud-to-ground (CG) flashes overwhelmingly dominated. The lower positive charge was estimated to be located at about 1.7 km above the ground, while the main negative charge was located higher than about 2.2 km above the ground. Long-duration IC discharges occurred both before and after the return strokes of two negative CG flashes that are studied. Continuing current during the IC discharge could flow along the upward channel for hundreds of milliseconds. The stepped leader of two negative CG flashes developed downward to ground with multiple branches and more than one striking point on the ground were induced as a result. The 2-D progression velocity of stepped leader was estimated to be about 0.8–1.1×10 5 m/s.

Preliminary Analysis of Characteristics of Lightning in Nagqu Area of Qinghai‐Xizang Plateau

AbstractThe data of electric field and electric field changes produced by lightning on the ground in Nagqu area of Qinghai‐Xizang plateau in the summer of 2002 were analyzed. The results showed that the charge structure in thunderstorms was varied and complex. Few cloud‐to‐ground (CG) lightning flashes occurred in the thunderstorm. A long time discharge process in cloud occurred just before step leader of positive and negative CG lightning. Most of CG lightning discharges only involved one return stroke. The proportion of positive CG lightning discharges was 33%, which was obviously higher than that in lower and middle latitude area, and negative 67% in thunderstorms. A continuing current process with short lasting time occurred just after the return‐stroke.

A seven-year study about the negative cloud-to-ground lightning flash characteristics in Southeastern Brazil

A seven-year study of negative cloud-to-ground (CG) lightning flash characteristics in southeastern Brazil is presented. The study is based on approximately 10 million flashes recorded by a Lightning Position and tracking system lightning detection network from November 1988 to December 1995. The data set is the longest ever obtained in the tropics using an almost constant network configuration. It provides a unique opportunity to study the long-term annual, monthly, and local time distributions of the number, intensity (peak current) and multiplicity of negative CG flashes in the tropics. The annual distribution of the number of flashes has variations as large as 80%. The variations does not show any clear relationship with any meteorological parameter, possibly indicating the complex interactions of different processes responsible for the lightning activity. The monthly and local time distributions seem to follow closely the related distributions of air temperature. The annual distribution of peak current shows an average value of 40.4 kA and has a significant decrease from 1991 to 1994, apparently related to an El Niño seasonal effect. The monthly distribution of peak current shows lower values in the winter, in contrast with the results recently reported for the United States, and seems to be related to the monthly distribution of the number of flashes. The local time distribution of the peak current seems also to be related to the local time distribution of the number of flashes; however, the dependency is less evident. The annual distribution of multiplicity has a systematic decrease during the period, with no apparent relationship with any of the variables studied. The monthly distribution of multiplicity is consistent with the hypothesis that the multiplicity is related to the average height of thunderstorms. The local time distribution of multiplicity, in turn, shows a sunrise/sunset effect. The results are compared to similar ones obtained in other regions of the world.

Relationships between Convective Storm Kinematics, Precipitation, and Lightning

Combined multiparameter radar, dual-Doppler, thermodynamic sounding, and lightning observations of 11 thunderstorms (6 from the midlatitudes, 5 from the Tropics) are examined. The thunderstorms span a wide spectrum of intensities, from weak monsoontype to severe tornadic, and include both unicellular and multicellular convection. In general, the kinematically strongest storms featured lower production of negative cloud-to-ground lightning (typically ,1 min21 flash rates for large portions of the storms’ lifetimes) when compared with more moderate convection, in accord with an elevated charge mechanism. The only significant differences between intense storms that produced predominately positive cloud-to-ground (CG) lightning for a significant portion of their lifetimes (PPCG storms) and intense storms that produced little CG lightning of any polarity (low-CG storms) was that PPCG storms featured much larger volumes of significant updrafts (both.10 and .20 m s21) and produced greater amounts of precipitation (both rain and hail). Otherwise, peak updrafts and vertical airmass fluxes were very similar between the two types of storms, and both types were linked by anomalously low production of negative CG lightning. PPCG effects in storms may result from an elevated region of negative charge (reducing negative CG flash rates) combined with enhanced net positive charge regions created by the larger volume of significant updrafts.