Comparing the Wave Characteristics of Breakdown Pulses of the Lightning Waveforms in the Himalayan Region

We have analyzed the breakdown pulse train with or without the main event in this paper. Among the selected 81 flashes, 36 flashes are starting positively, and 45 are starting negatively. Also, 58 flashes contain positive pulses, and 67 flashes contain negative pulses, whereas 44 flashes contain both positive and negative pulses. Among these 81 flashes, 22 flashes follow the main events, and the rest are isolated events. In this study, we got the main duration of PB pulses as 1.94 ms and the time interval between the breakdown pulse and return stroke as 61.49 ms. On taking each pulse train, we found the rise time to be 2.6 μs, zero-crossing time 14.95 μs, and the time interval between pulses 199.3 μs. The largest pulse amplitude ratio in the preliminary breakdown pulse to the main event return stroke was 0.43.

The Time Evolution of Optical Lightning Flashes

The composition and time evolution of lightning are examined using the Lighting Imaging Sensor (LIS). Frame-by-frame optical lightning measurements are clustered into features whose radiant energy, horizontal footprint, and timing may be analyzed statistically. A LIS series feature is used to describe distinct periods of near continuous illumination that persists over multiple LIS frames. Series are integrated into the LIS clustering hierarchy between the group and flash level. An average series illuminates 40% of the flash footprint while accounting for 20% of the flash radiance, and just 1% of the flash duration. LIS flashes typically contain optical emissions that are exceptionally radiant and may persist over multiple frames. Series features cluster these bright optical pulses, allowing their number and time separation to be quantified in each flash. This optical multiplicity averages 1.7 for flashes with at least one particularly radiant group. Multigroup series most often occur early in the flash duration with 13% to 18% at first light. Series are typically separated by 100 ms or more in multiseries flashes. Bright series, by contrast, typically occur in rapid succession, with at most a few dozen milliseconds between them. Because series are optical features, they may result from any physical process that produces strong optical emissions. The statistics presented herein support the idea that series may originate from multiple physical processes.

Observations of narrow bipolar events reveal how lightning is initiated in thunderstorms

A long-standing but fundamental question in lightning studies concerns how lightning is initiated inside storms, given the absence of physical conductors. The issue has revolved around the question of whether the discharges are initiated solely by conventional dielectric breakdown or involve relativistic runaway electron processes. Here we report observations of a relatively unknown type of discharge, called fast positive breakdown, that is the cause of high-power discharges known as narrow bipolar events. The breakdown is found to have a wide range of strengths and is the initiating event of numerous lightning discharges. It appears to be purely dielectric in nature and to consist of a system of positive streamers in a locally intense electric field region. It initiates negative breakdown at the starting location of the streamers, which leads to the ensuing flash. The observations show that many or possibly all lightning flashes are initiated by fast positive breakdown.

The start of lightning: Evidence of bidirectional lightning initiation

Lightning flashes are known to initiate in regions of strong electric fields inside thunderstorms, between layers of positively and negatively charged precipitation particles. For that reason, lightning inception is typically hidden from sight of camera systems used in research. Other technology such as lightning mapping systems based on radio waves can typically detect only some aspects of the lightning initiation process and subsequent development of positive and negative leaders. We report here a serendipitous recording of bidirectional lightning initiation in virgin air under the cloud base at ~11,000 images per second, and the differences in characteristics of opposite polarity leader sections during the earliest stages of the discharge. This case reveals natural lightning initiation, propagation and a return stroke as in negative cloud-to-ground flashes, upon connection to another lightning channel – without any masking by cloud.

Electro-optic lightning detector

The design, alignment, calibration, and field deployment of a solid-state lightning detector is described. The primary sensing component of the detector is a potassium dihydrogen phosphate electro-optic crystal that is attached in series to a flat-plate aluminum antenna; the antenna is exposed to the ambient thundercloud electric field. A semiconductor laser diode (lambda = 685 nm), polarizing optics, and the crystal are arranged in a Pockels cell configuration. Lightning-caused electric field changes are related to small changes in the transmission of laser light through the optical cell. Several hundred lightning electric field change excursions were recorded during five thunderstorms that occurred in the summer of 1998 at the NASA Marshall Space Flight Center in northern Alabama.