Xiushu Qie

Simultaneously measured current, luminosity, and electric field pulses in a rocket‐triggered lightning flash

[1] Current, luminosity, and electric field pulses in a rocket‐triggered negative lightning flash have been analyzed based on the channel base current, high‐speed video images, and electric field changes at 30 m from the channel. Among the 31 distinct current pulses, there are 4 return strokes, 18 typical M components, 5 large M components with unusual large peak current in a range of kiloamperes, 3 initial continuing current (ICC) pulses, and 1 stroke–M component (RM) event which exhibits both return stroke and M component features. The geometric mean of peak current is 13.5 kA, half peak width is 28.4 ms, and risetime from 10% to 90% peak is 1.1 ms for the 4 return strokes, while the corresponding values are 243 A, 400 ms, and 319 ms, respectively, for the 18 typical M components and 5.1 kA, 76.3 ms, and 34.6 ms, respectively, for the 5 large M components. The electric field and current waveforms of ICC pulses exhibit features similar to those of the M components, indicating the similarity of their mechanisms. Detectable optical luminosity is found just prior to all the pulse events, even return strokes. The M components are superimposed on a slowly varying continuing current, while the directly measured current prior to the return strokeisnotsignificant.ThesimultaneouselectricfieldandcurrentwaveformofRMimplies a superposition of dart leader and M incident wave in the channel, and the possible reason is that two branches with common lower portions coexist simultaneously in the upper part of the discharge channel.

Comprehensive Pattern of Deep Convective Systems over the Tibetan Plateau-South Asian Monsoon Region Based on TRMM Data

AbstractDiurnal and seasonal variation, intensity, and structure of deep convective systems (DCSs; with 20-dBZ echo tops exceeding 14 km) over the Tibetan Plateau–South Asian monsoon region from the Tibetan Plateau (TP) to the ocean are investigated using 14 yr of Tropical Rainfall Measuring Mission (TRMM) data. Four unique regions characterized by different orography are selected for comparison, including the TP, the southern Himalayan front (SHF), the South Asian subcontinent (SAS), and the ocean. DCSs and intense DCSs (IDCSs; with 40-dBZ echo tops exceeding 10 km) occur more frequently over the continent than over the ocean. About 23% of total DCSs develop into IDCSs in the SHF, followed by the TP (21%) and the SAS (15%), with the least over the ocean (2%). The average 20-dBZ echo-top height of IDCSs exceeds 16 km and 9% of them even exceed 18 km. DCSs and IDCSs are the most frequent over the SHF, especially in the westernmost SHF, where the intensity—in terms of strong radar echo-top (viz., 40 dBZ) he...

Lightning activity on the central Tibetan Plateau and its response to convective available potential energy

Lightning flash activities on the central Tibetan Plateau have been studied by using the satellite-based Lightning Imaging Sensor (LIS) database from January 1998 to July 2002. The lightning activity shows a clear diurnal variation on the central Plateau. The peak lightning activity appears at about 17: 00 which is 3 h earlier than that in Jingzhou, Hubei in the same latitude belt nearby, indicating that the lightning activity is a sensitive indicator of solar heating on the Plateau. The lightning discharge is weaker on the Plateau than Jingzhou, Hubei and other low-altitude continental regions because of the lower convective available potential energy (CAPE) on the Plateau. The CAPE on the Plateau is 12 times lower than that in Jingzhou, Hubei, and 20 times lower than that in the sea-level region, such as Guangzhou and Florida. However, the sensitivity of lightning activity to CAPE changes on the Plateau is up to 30 times more sensitive than other prominent low-altitude regions.

Regional distribution and diurnal variation of deep convective systems over the Asian monsoon region

Using 12 years of data from the Tropical Rainfall Measuring Mission (TRMM)-based Precipitation Radar (PR), spatial and diurnal variations of deep convective systems (DCSs) over the Asian monsoon region are analyzed. The DCSs are defined by a 20 dBZ echo top extending 14 km. The spatial distribution of DCSs genesis is also discussed, with reference to the National Centers for Environmental Prediction (NCEP) reanalysis data. The results show that DCSs occur mainly over land. They concentrate in south of 20°N during the pre-monsoon season, and then move distinctly to mid-latitude regions, with the most active region on the south slope of the Himalayas during monsoon season. DCSs over the Tibetan Plateau are more frequent than those in central-eastern China, but smaller in horizontal scale and weaker in convective intensity. DCSs in central-eastern China have more robust updrafts and generate more lightning flashes than in other Asian monsoon regions. The horizontal scale of DCSs over the ocean is larger than that over the other regions, and the corresponding minimum infrared (IR) brightness temperature is lower, whereas the convective intensity is weaker. Continental DCSs are more common from noon through midnight, and DCSs over the Tibetan Plateau are more frequently from noon through evening. Oceanic DCSs frequency has a weaker diurnal cycle with dawn maximum, and diurnal variation of DCSs over the tropical maritime continent is consistent with that over the continent.

Magnetic field measuring system and current retrieval in artificially triggering lightning experiment

A magnetic field measuring system with two rectangular loops perpendicular toeach other is developed and used to detect the total horizontal magnetic field producedby lightning discharges. Two sets of antenna with low gain and high gain aredesigned separately in order to obtain both small and large signals. The systemwas tested experimentally in a high-voltage laboratory, and the results showthat the system is reliable, and the waveforms detected by the system are very similarto the source current. The corresponding maximum current that can be measuredby the system with low gain antenna and high gain antenna locating at a distanceof 60 m from a lightning channel, is about 84.4 kA and 37.7 kA, respectively.For artificially triggered lightning flashes the magnetic field waveforms detectedat 60 m from the channel reflect quite well the channel base currents. UsingAmpere’s law of magnetostatics, the inferred currents from the magnetic fieldsfor three artificially triggered lightning return strokes were 39.8 kA, 29.1 kA and43 kA, respectively, which are close to the directly measured results of 41.6 kA,29.6 kA and 38 kA at the base of the discharge channel. The system can be a usefultool in the research of close electromagnetic environment of lightning flashes.

Lightning activity and its relation to the intensity of typhoons over the Northwest Pacific Ocean

Data from the World Wide Lightning Location Network (WWLLN) were used to analyze the lightning activity and the relationship between maximum sustained wind and lightning rate in 69 tropical cyclones over the Northwest Pacific Ocean from 2005 to 2009. The minimum lightning density was observed in the category 2 typhoon Kong-Rey (2007), with a value of only 1.15 d−1 (100 km)−2. The maximum lightning density occurred in the category 2 typhoon Mitag (2007), with a value of 510.42 d−1 (100 km)−2. The average lightning density decreased with radius from the typhoon center in both weak (categories 1–3) and super (categories 4–5) typhoons. The average lightning density in the inner core of super typhoons was more than twice as large as that for weak typhoons. Both groups of typhoons showed a near-monotonic decrease in lightning density with radius. Results also showed that lightning activity was more active in typhoons that made landfall than in those that did not. The mean correlation coefficient between the accumulated flashes within a 600-km radius and the maximum wind speed in the weak typhoons and super typhoons was 0.81 and 0.74, respectively. For more than 78% (56%) of the super (weak) typhoons, the lightning activity peaked before the maximum sustained wind speed, with the most common leading time being 30 (60) h. The results suggest that, for the Northwest Pacific Ocean, lightning activity might be used as a measurement of the intensification of typhoons.

Burst of intracloud current pulses during the initial continuous current in a rocket‐triggered lightning flash

For a rocket-triggered lightning flash on 2 August 2013, the measurement with one pair of broadband low-frequency (20–400 kHz) magnetic induction coils registered a long sequence of over 600 intermittent pulses during the initial continuous current. The timescale of these pulses is about 3-8 µs, and the typical interpulse interval is about 30 µs. The source discharges of these pulses, which are not readily detectable in the frequency range (140–300 MHz) of a short-baseline very high frequency (VHF) lightning imaging system, are attributed to the stepping processes when the positive leader propagated into the cloud region. The reversals in the polarity of magnetic pulses are related to the variation in the vertical direction of positive leader propagation as resolved by the VHF imaging system.

Land-Sea Contrast in the Lightning Diurnal Variation as Observed by the WWLLN and LIS/OTD Data

Data from the World Wide Lightning Location Network (WWLLN) for the period 2005–2011 and data composite of the Lightning Imaging Sensor/Optical Transient Detector (LIS/OTD) for 1995–2010 are used to analyze the lightning activity and its diurnal variation over land and ocean of the globe. The Congo basin shows a peak mean annual flash density of 160.7 fl km−2 yr−1 according to the LIS/OTD. The annual mean land to ocean flash ratio is 9.6:1, which confirms the result from Christian et al. in 2003 based on only 5-yr OTD data. The lightning density detected by the WWLLN is in general one order of magnitude lower than that of the LIS/OTD. The diurnal cycle of the lightning activity over land shows a single peak, with the maximum activity occurring around 1400-1900 LT (Local Time) and a minimum in the morning from both datasets. The oceanic diurnal variation has two peaks: the early morning peak between 0100 and 0300 LT and the afternoon peak with a stronger intensity between 1100 and 1400 LT over the Pacific Ocean, as revealed from the WWLLN dataset; whereas the diurnal variation over ocean in the LIS/OTD dataset shows a large fluctuation.

Characteristics of a rocket-triggered lightning flash with large stroke number and the associated leader propagation

A negative lightning flash with 16 leader-return stroke sequences, triggered in the summer of 2013 using the classical rocket-and-wire triggering technique, was examined with simultaneous two-dimensional (2D) imaging of very high-frequency (VHF) radiation sources, channel-base current measurement, broadband electric field waveforms and high-speed video images. A total of 28.0 C negative charge was transferred to ground during the whole flash, and the charge transferred during the initial stage was 4.9 C, which is the weakest among the triggered lightning flashes at the SHandong Artificially Triggering Lightning Experiment (SHATLE). The peak current of 16 return strokes ranged from 5.8 to 32.5 kA with a geometric mean of 14.1 kA. The progression of upward positive leader and downward negative (dart or dart-stepped) leaders was reproduced visually by using an improved short-baseline VHF lightning location system with continuous data recording capability. The upward positive leader was mapped immediately from the tip of the metal wire during the initial stage, developing at a speed of about 104 m/s without branches. The upward positive leader and all the 14 negative leaders captured by the 2D imaging system propagated along the same channel with few branches inside the cloud, which might be the reason for the relatively small charge transfer. The 2D imaging results also show that dart leaders may transform into dart-stepped leaders after a long time interval between successive strokes.

A Review of Atmospheric Electricity Research in China

The importance of atmospheric electricity research has been increasingly recognized in recent decades. Research on atmospheric electricity has been actively conducted since the 1980s in China. Lightning physics and its effects, as important branches of atmospheric electricity, have received more attention because of their significance both in scientific research and lightning protection applications. This paper reviews atmospheric electricity research based primarily on ground-based field experiments at different regions in China in the last decade. The results described in this review include physics and effects of lightning, rocket-triggered lightning and its physical processes of discharge, thunderstorm electricity on the Tibetan Plateau and its surrounding areas, lightning activity associated with severe convective storms, the effect and response of lightning to climate change, numerical simulation of thunderstorm electrification and lightning discharge, lightning detection and location techniques, and transient luminous events above thunderstorms.