Analysis of the Charge Structure and Lightning Activity During a Severe Beijing Thunderstorm via an Innovative Balloon‐Borne 3D Electric Field Observation System

Abstract We developed an innovative balloon‐borne observation system based on China's BeiDou sounding platform that integrates a three‐axis electric field sensor for in‐cloud measurements of thunderstorm electrification. On 13 May 2025, this system was deployed during a severe convective storm over Beijing. In combination with multisource observations, including S‐band dual‐polarization radar, lightning location networks, and surface electric field meters, we analyzed the charge structure, microphysics, and lightning activity. Multiple electric field peaks, including one with a sustained maximum of 333 kV m −1 at altitudes from 7 to 8 km, were sampled via balloon sounding. The retrieved vertical charge structure comprised a thin negative–positive–negative stack at altitudes from 4 to 5 km (≈0.25–0.30‐km thick) and a main three‐layer system above 4.9 km, comprising a lower positive region (+2.5 nC m −3 , 4.9–6.2 km, −10°C to −20°C), a middle negative region (−7.2 nC m −3 , 6.2–6.9 km, −20°C to −25°C), and an upper positive region (+1.1 nC m −3 , 6.9–9.6 km, near −40°C). Although the sensor was designed to measure three‐dimensional electric fields, the horizontal electric field components ( E x and E y ) were found to be dominated by cross‐talk from E z during this flight and therefore cannot be interpreted as independent horizontal electric fields. Consequently, the physical interpretation in this study is based solely on the vertical electric field and the charge structure inferred from it. Lightning was dominated by short, multipulse IC flashes in the convective cores. The balloon traversed the main updraft and mixed‐phase zone (0°C to −40°C), thus confirming that the profiles captured key features of storm core electrification.