Abstract:

Objective: The occurrence of lightning fire is comprehensively affected by lightning, meteorological conditions, forest fuel, terrain, etc. Various factors are coupled and act together. After the launch of "forest lightning fire prevention and control emergency technology project", a full waveform three-dimensional lightning detection network covering the Daxing'anling Mountains has been built. Combined with the national basic meteorological station, lightning fire meteorological monitoring station, watchtower and ground patrol, the network can be used to carry out collaborative monitoring and early warning of lightning, weather and lightning fire occurrence. The number of mass lightning fires caused by dense lightning processes accounted for most of lightning fires in the spring fire season of 2022. Based on the data of the lightning fire sensing system, this paper aims to analyze the quantitative characteristics of various factors causing lightning fires, and clarify the mechanism of the influence of various factors in the dense lightning process on the occurrence of lightning fires. Method: Based on the lightning fire sensing system, the monitored lightning indicators, meteorological factors and lightning fire occurrence indicators were systematically analyzed. This study also analyzed the basic situation of lightning fire occurrence in Daxing'anling Mountains during the spring fire season in 2022, the impact of dense lightning on lightning fire occurrence, the quantitative characteristics of lightning that caused lightning fire, as well as the lightning location accuracy and lightning fire smoldering period. Result: In 2022, a total of 22 lightning fires occurred during the spring fire season in Daxing'anling Mountains, of which 18 were caused by dense lightning processes. The ground lightning and cloud lightning had one peak respectively in the positive and negative current area. The negative ground lightning accounted for 82.82% of the total number of ground lightning, and the ground lightning formed a high-frequency interval at -8~-50 kA. The number of lightning fires caused by negative ground lightning was the largest, which accounted for 70% of the total number of ground lightning, and accounted for 84.5% of the negative ground lightning. The positive ground lightning that formed a high-frequency range at 10~30 kA accounted for 12.7% of the total ground lightning, and 74.2% of the positive ground lightning, which was much lower than the number of negative ground flashes. The average current intensity of lightning fire in spring fire season was -22.72 kA, the strongest current was -48.34 kA, and the weakest current was -8.70 kA. The occurrence time of lightning that causes lightning fires was relatively concentrated, and lightning fires were mostly ignited around noon. There was a rapid temperature rise before the dense lightning that caused the lightning fire occurred. With the decline of air humidity and the increase of wind speed, the daily maximum temperature was basically the same as the occurrence time of the lightning that caused the lightning fire. It was also the period of time when the lowest relative humidity and the highest wind speed appeared. The smoldering period of lightning fire in spring fire season was from 0.56 to 17.62 h. The accuracy of lightning detection and location was 165~884 m, with an average accuracy of 394.5 m. There were two lightning fires with lightning wood positioning coordinates, and the positioning accuracy reached 165 m and 170 m. The fuels in the fire site were mainly waste mountain grassland, dry wetland meadow, as well as some coniferous forests, coniferous and broad-leaved mixed forests and burned slashes. Conclusion: The mass lightning fires caused by dense lightning processes account for the majority of lightning fires. The occurrence of mass lightning fires requires the coupling of dense lightning processes with extreme weather conditions of drought, as well as fuel available. When the lightning process is not synchronized with the precipitation process or the precipitation is less, and there is a rapid warming process in the early stage, and the intensive lightning process is accompanied by a drop in temperature, the lightning fires often occur in this period. In the process of lightning fire monitoring and early warning, we should pay special attention to the dense lightning process under drought conditions.

Key words: lightning fire, lightning, full waveform VLF/LF Lightning Location Monitoring System, electric current intensity, meteorology