Abstract: Gaoligong Mountain, a crucial ecological barrier in Southwest China, has experienced increasing frequency of lightning-induced fires in recent years, threatening ecosystems and human safety. To investigate the underlying meteorological mechanisms, a diagnostic analysis is conducted on two fire events in Gaoligong Mountain Nature Reserve, occurring on 15-16 March 2023, and 17-18 April 2024. Multi-source datasets are integrated, including VLF/LF (very low frequency/low frequency) 3-dimensional lightning location data, MODIS fire spots, ERA5 data, satellite-based vegetation and topography information.
An improved lightning-induced fire identification algorithm is developed for Gaoligong Mountain, involving 3 steps: Spatio-temporal filtering, where the region is divided into 15 km×15 km grids and fire points are selected based on a maximum time lag of 24 h between lightning detection and fire ignition; population density filtering, which retains only areas with a density below 40 people per km; and low-probability verification, where repeated fires within 1 km grids are excluded based on the low recurrence probability (below 0.5%) of lightning-induced fires, thus effectively filtering out human-caused ignitions. Separately, mesoscale circulation signals are extracted using Barnes band-pass filter, with results validated against Himawari-8 satellite data.
Regional analysis indicates a higher ground flash density in the southern part of the Reserve, while greater lightning current amplitudes are observed in the northern Nujiang River Basin. The land cover is dominated by coniferous, broad-leaved, and mixed forests. The complex terrain is found to modulate airflow, promote charge accumulation, and increase the probability of lightning occurrence.
Meteorologically, large-scale circulation features an upper-level cold trough transporting cold air southward, and a mid-low level warm ridge bringing high temperatures. The atmosphere exhibits an unstable configuration with dry air overlaying moist air, providing energy sources for lightning-induced fire events. Mesoscale analysis indicates that both events are associated with a 700 hPa low vortex, with relative vorticity increasing approximately 3 h prior to the lightning occurrence. Fires are in the rear sector of 700 hPa low vortex, controlled by the easterly airflow. Under the influence of terrain, the airflow converged with the local valley wind circulation after crossing the mountain, triggering convection, which leads to the development of thunderstorm clouds and ground flashes. Small-scale conditions included 7 consecutive days without effective precipitation prior to fires, sustained temperatures above the monthly average, and dry surface fuels. The evaporation of precipitation particles in the lower troposphere enhances charge exchange between supercooled water droplets and ice crystals, resulting in ground flashes. These ground flashes with current amplitudes between 20 kA and 30 kA, are identified as the direct cause of the two lightning-induced fire events.
Through these approaches, a multi-scale coupling mechanism for lightning fires is identified, involving unstable energy from large-scale circulation, convection driven by a mesoscale low vortex, and ignition enabled by small-scale dry fuels, thereby providing critical scientific support for regional prevention and early warning.