Qing Meng

A comparison of the characteristics of total and cloud-to-ground lightning activities in hailstorms

The region of Beijing-Tianjin-Hebei is covered by two different lightning detection networks: SAFIR (Systeme d’Alerte Fondre par Interferometrie Radioelecctrique) for total lightning, including IntraCloud (IC) flashes and Cloud-to-Ground (CG) flashes, and the ADTD (ADvanced TOA and Direction system; TOA denotes time of arrival) network of China for CG lightning. Fourteen isolated hail-bearing thunderstorms in this region were examined in this study, using the data of SAFIR and ADTD. The peak of lightning frequency, for both total lightning and CG lightning, was often observed in advance of the occurrence of hailstones on the ground, with a trend of a rapid increase of lightning frequency before the hail was reported. The average lead times of the two types of lightning jump before hail events were obtained (total lightning: 32.2 min; CG: 25.4 min) through the 2σ lightning jump algorithm. Additionally, in hailstorms with a high ratio of positive CG flashes, the diameter of hail was larger and the duration of hail was longer; when negative CG flashes dominated, the diameter of hail was relatively small. The comparison of the characteristics of total lightning and CG flashes in hailstorms in this study is expected to serve as a supplementary tool for hail forecasting.

Climatological Comparison of Small- and Large-Current Cloud-to-Ground Lightning Flashes over Southern China

AbstractThe first climatological comparison of small-current cloud-to-ground (SCCG; peak current ≤50 kA) and large-current cloud-to-ground (LCCG; peak current >50 kA, >75 kA, and >100 kA) lightning flashes is presented for southern China. The LCCG lightning exhibits an apparent preference to occur over the sea. The percentage of positive LCCG lightning during the nonrainy season was more than twice that during the rainy season, while the percentage of positive SCCG lightning showed small seasonal differences. Positive cloud-to-ground (PCG) lightning was more likely to feature a large peak current than was negative cloud-to-ground (NCG) lightning, especially during the nonrainy season and over land. Distinct geographical differences are found between SCCG and LCCG lightning densities and between their own positive and negative discharges. Furthermore, the percentages of positive lightning from LCCG and SCCG lightning exhibit distinctly different geographical and seasonal (rain and nonrainy season) distribu...

Lightning casualties and damages in China from 1997 to 2010

Lightning-related fatalities, injuries and property damages reported in China from 1997 to 2010 are summarized by using the National Lightning Hazards Database. Therefore, characteristics of the incidents including 5352 deaths, 4931 injuries and 69129 damage reports are analyzed. For the spatial distribution of lightning disasters in China, the eastern costal and southern areas have more frequent lightning disasters than the western areas. Lightning disasters mainly occur in summer months from July to September while fewer damages occur in winter months from October to March, which correlate significantly with the temporal variability of lightning frequency in China. Lightning-related casualties and damages in China have increased for the period of 1997 to 2007, and then began to decrease since 2008. Rural people account for 50.8% and 33.1% of all lightning fatalities and injuries, which makes residents in agricultural and rural area the major lightning victims. Characteristics of lightning disasters and correlative factors are also studied, including hazard affected locations. The results show that farmland is the largest category in lightning-caused casualty locations.

Semi-Idealized Modeling of Lightning Initiation Related to Vertical Air Motion and Cloud Microphysics

A three-dimensional charge–discharge numerical model is used, in a semi-idealized mode, to simulate a thunder-storm cell. Characteristics of the graupel microphysics and vertical air motion associated with the lightning initiation are revealed, which could be useful in retrieving charge strength during lightning when no charge–discharge model is available. The results show that the vertical air motion at the lightning initiation sites (Wini) has a cubic polynomial correlation with the maximum updraft of the storm cell (Wcell-max), with the adjusted regression coefficient R2 of approximately 0.97. Meanwhile, the graupel mixing ratio at the lightning initiation sites (qg-ini) has a linear correlation with the maximum graupel mixing ratio of the storm cell (qg-cell-max) and the initiation height (zini), with the coefficients being 0.86 and 0.85, respectively. These linear correlations are more significant during the middle and late stages of lightning activity. A zero-charge zone, namely, the area with very low net charge density between the main positive and negative charge layers, appears above the area of qg-cell-max and below the upper edge of the graupel region, and is found to be an important area for lightning initiation. Inside the zero-charge zone, large electric intensity forms, and the ratio of qice (ice crystal mixing ratio) to qg (graupel mixing ratio) illustrates an exponential relationship to qg-ini. These relationships provide valuable clues to more accurately locating the high-risk area of lightning initiation in thunderstorms when only dual-polarization radar data or outputs from numerical models without charging/discharging schemes are available. The results can also help understand the environmental conditions at lightning initiation sites.

Climatology of lightning activity in South China and its relationships to precipitation and convective available potential energy

This study examined lightning activity and its relationship to precipitation and convective available potential energy (CAPE) in South China during 2001–12, based on data from the Guangdong Lightning Location System, the Tropical Rainfall Measuring Mission satellite, and the ERA-Interim dataset. Two areas of high lightning density are identified: one over the Pearl River Delta, and the other to the north of Leizhou Peninsula. Large peak-current cloud-to-ground (LPCCG) lightning (>75 kA) shows weaker land–offshore contrasts than total CG lightning, in which negative cloud-to-ground (NCG) lightning occurs more prominently than positive cloud-to-ground (PCG) lightning on land. While the frequency of total CG lightning shows a main peak in June and a second peak in August, the LPCCG lightning over land shows only a single peak in June. The ratio of positive LPCCG to total lightning is significantly greater during February–April than during other times of the year. Diurnally, CG lightning over land shows only one peak in the afternoon, whereas CG lightning offshore shows morning and afternoon peaks. The rain yield per flash is on the order of 107–108 kg per flash across the analysis region, and its spatial distribution is opposite to that of lightning density. Our data show that lightning activity over land is more sensitive than that over offshore waters to CAPE. The relationships between lightning activity and both precipitation and CAPE are associated with convection activity in the analysis region.

An analysis of the initial breakdown pulse for positive cloud-to-ground flashes

In order to further understand the initiating mechanism of positive cloud-to-ground (PCG) flashes, the nature and temporal characteristics of the positive breakdown pulse trains are investigated by electric field data in Conghua of Guangdong province. Considering the difference between the initial polarity of initial breakdown pulses and the first return stoke (RS), three types of bipolar pulse trains, including the same polarity, the opposite polarity and the both polarity, are identified. The percentages are 83.5%, 10% and 5.5%, respectively. The statistic results show that PCG flash with breakdown pulse trains, which occur when the amount of PCG flash is little, is about 11.6% of the total PCG flashes. The average time interval between the peak of adjacent pulses and pulse duration are 270.99 μs and 25.01 μs, respectively. The mean value of pulse train duration and the interval between PBP train and RS is 8.88 ms and 98.48ms, respectively. The average ratio of all samples between the maximum amplitude of pulse train and the amplitude of the first stroke pulse is 0.16. The ratio is smaller in of Guangzhou province than in Hokuriku coast in Japan.

Two new methods of artifically triggering lightning discharges

Two new methods for artificially triggering lightning discharges have been proposed. In the methods, a certain length of thin wire is extended by using relative motion of a parachute and a flying object at a timing controlled wirelessly (or remotely). With these methods, since the wire can be extended at a desired spatial location and timing, different types of lightning discharges such as intracloud and cloud-to-ground discharges can be preferentially triggered in the presence of sufficient thunderstorm electric fields. In order to experimentally verify the proposed methods, a prototype of equipment has been designed and manufactured. Furthermore, possibilities of active lightning protection by using the proposed methods have been presented and discussed.