Lightning Location Based On Low-frequency Electric Field Pulse And Relationship Between Lightning Initiation And Thunderstorm Structure

Locating total lightning at the low and very low frequency band has become one of the most important directions in lightning detection technology. Low-Frequency E-filed Detection Array (LFEDA), consisting of nine sensors, is developed by Chinese Academy of Meteorological Sciences at Guangzhou from 2014. Locating algorithm is designed under the consideration of fast low-frequency electric field signal produced by flash. A preliminary study on initial breakdown (IB) process of lightning and its relationship with thunderstorm structure are carried out based on locations. The main results are as following.(1) LFEDA network configuration including number of stations, position and methods of data acquisition and storage is introduced firstly. Location algorithm consists of matching the 1-ms waveform, matching the pulses,solving the nonlinear equations and lightning classification algorithm.(2) Theory simulation and objective assessment for the accuracy and efficiency of LFEDA have been done using Monte Carlo method and artificial triggered lightning experiments respectively. The former results show that the station in the network which has a comparatively long baseline can improve horizontal locating accuracy in the perpendicular direction of baseline and height locating accuracy along the direction of baseline. The latter results show that detection efficiency of triggered flashes and return strokes is correspondingly 100% and 95%. Average location error for return strokes in planar is 102 m. By comparing LFEDA with Guangdong power network lightning locating system, we find that two systems on the positioning results have good agreement of 0.84. By locating lightning discharge events in three thunderstorms, we find that lightning events have good agreement with storms' propagating path and present a reasonable charge distribution in the vertical direction. In addition, LFEDA can reveal the development image of lightning through mapping intra-cloud (IC)and cloud-to-ground (CG) flash.(3) Initial breakdown (IB) process of lightning and its relationship with thunderstorms structure are researched by selecting total 1066 obvious vertical-development IB processes. Frequency of down-development IB is less than that of upward-development IB, which is 237 and 829 respectively. The initial height of upward-development IB is generally higher than that of down-development IB,with the average value of 8.4km and 6.8km respectively. So, the initial height shows obvious stratification which is related to spatial multi-layer charge region. The average vertical speed for upward-development and down-development IB is 2.6×105m/s and 3.3×105m/s. With the higher height of IB, the average vertical speed and pulse rate is smaller, but IB step length is longer. Regarding to the relationship between IB positions and radar echo, the initial points are mainly in the regions corresponding to the radar echo ranging from 30 to 40dBZ.(4) Potential areas of convection core in storms that happened on 7 August can be identified by planar projection regions of top height of 35dBZ that is higher than 8 km. The results show that initial height of upward-development IB in the convection core is higher than that out of the convection core ( 8.8km vs 7.5km ) due to the existence of convection. Initial height of down-development IB in the convection core is lower than that out of the convection core (6.6km vs 7.3km) . Change rule of the IB speed in and out of convection core is opposite to the initial height. IB vertical propagating distance regardless of direction is shorter in the convection(upward-development IB: 2.1km vs. 2.3km; down- development IB: 1.9 km vs. 2.3 km). Meanwhile, IB elevation angle regardless of directions is larger in the convection core (upward-development IB: 61.6° vs 57.8°; down- development IB:59.5° vs 51.4°).