Dongxia Liu

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.

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.

Lightning activity and its relationship with typhoon intensity and vertical wind shear for Super Typhoon Haiyan (1330)

Super Typhoon Haiyan (1330), which occurred in 2013, is the most powerful typhoon during landfall in the meteorological record. In this study, the temporal and spatial distributions of lightning activity of Haiyan were analyzed by using the lightning data from the World Wide Lightning Location Network, typhoon intensity and position data from the China Meteorological Administration, and horizontal wind data from the ECMWF. Three distinct regions were identified in the spatial distribution of daily average lightning density, with the maxima in the inner core and the minima in the inner rainband. The lightning density in the intensifying stage of Haiyan was greater than that in its weakening stage. During the time when the typhoon intensity measured with maximum sustained wind speed was between 32.7 and 41.4 ms−1, the storm had the largest lightning density in the inner core, compared with other intensity stages. In contrast to earlier typhoon studies, the eyewall lightning burst out three times. The first two eyewall lightning outbreaks occurred during the period of rapid intensification and before the maximum intensity of the storm, suggesting that the eyewall lightning activity could be used to identify the change in tropical cyclone intensity. The flashes frequently occurred in the inner core, and in the outer rainbands with the black body temperature below 220 K. Combined with the ECMWF wind data, the influences of vertical wind shear (VWS) on the azimuthal distribution of flashes were also analyzed, showing that strong VWS produced downshear left asymmetry of lightning activity in the inner core and downshear right asymmetry in the rainbands.

Return stroke current during Shandong artificially triggered lightning from 2005–2009

Shandong artificial triggering lightning experiment (SHATLE) by means of rocket-wire technique, aimed to understand the close electromagnetic environment of lightning channel and its correlation to the discharge current, was started at 2005 in Binzhou, Shandong. Artificially triggered lightning is thought to be similar to the subsequent return strokes in natural lightning. Sixty seven negative return strokes were successfully triggered from 2005 to 2009. The discharge current at the base of the discharge channel and electromagnetic fields at different distances were measured simultaneously for 25 return strokes. Although the data is not enough, the distribution of peak current of the triggered strokes shows a probability of lognormal distribution. The geometric mean value was about 11.8 kA with a minimum of 5.8 kA and a maximum of 45.7 kA. The geometric mean of the 10–90% rise time was 1.9 µs, the geometric mean of the half peak width was 22.5 µs and the geometric mean of the charge transfer within 1ms of return strokes was 0.7 C.