Narrow bipolar events (NBEs) are signatures in radio signals from thunderstorms observed by ground-based receivers. NBEs may occur at the onset of lightning, but the discharge process is not well understood. Here, we present spectral measurements by the Atmosphere‐Space Interactions Monitor (ASIM) on the International Space Station that are associated with nine negative and three positive NBEs observed by a ground‐based array of receivers. We found that both polarities NBEs are associated with emissions at 337 nm with weak or no detectable emissions at 777.4 nm, suggesting that NBEs are associated with streamer breakdown. The rise times of the emissions for negative NBEs are about 10 μs, consistent with source locations at cloud tops where photons undergo little scattering by cloud particles, and for positive NBEs are ~1 ms, consistent with locations deeper in the clouds. For negative NBEs, the emission strength is almost linearly correlated with the peak current of the associated NBEs. Our findings suggest that ground-based observations of radio signals provide a new means to measure the occurrences and strength of cloud-top discharges near the tropopause.

Narrow Bipolar Events (NBEs) are powerful radio emissions from thunderstorms, which have been recently associated with blue optical flashes on cloud tops and attributed to extensive streamer electrical discharges named fast breakdown. Combining data obtained from a thunderstorm over South China by the space‐based Atmosphere Space Interactions Monitor, the Vaisala GLD360 global lightning network and very low frequency/low frequency radio detectors, here we report and analyze for the first time the optical emissions of blue luminous events associated with negative NBEs and located at the top edge of a thundercloud. These emissions are weakly affected by scattering from cloud droplets, allowing us to estimate the source extension and optical energy involved in the process. The optical energy in the 337‐nm band emitted by fast breakdown is about 10⁴ J, which involves around 10⁹ streamer initiation events.

Using a three‐station wideband electric and magnetic field measuring network in conjunction with VHF receivers, we recorded the so‐called compact intracloud discharges (CIDs) in the Greater Khingan Range (51°N) in Northeast China. This type of lightning discharge had never been observed in such high‐latitude regions before. During the summer seasons of 2009 and 2010, a total of 493 CIDs with positive electric field pulses (negative charge moving up) occurring in 31 thunderstorms was recorded, with 87% (27/31) of CID‐producing storms generating less than 20 CIDs. The CID occurrence observed at 51°N appears to differ significantly from that in most lower latitude regions. Specifically, CIDs accounted only for 0.034% of the total of 1.4 million recorded lightning events, and no CIDs with negative electric field pulses (positive charge moving up) were observed. A total of 202 CIDs was located and they clustered at altitudes ranging from 5 to 12 km above ground level (agl), with a median height of 7.9 km agl. The effective ionosphere heights ranged from 75 to 95 km during the time period of 15:00–06:00 (local time). The median maximum heights of the 30 dBZ radar echo for convective cells with CIDs and without CIDs were 10.8 and 9.4 km, respectively. We infer that a relatively small vertical extent of thunderclouds, limited by the height of the tropopause, and a lack of vigorous convective surges in higher‐latitude regions might be responsible for the paucity or absence of CIDs in general and apparent suppression of those with negative electric field pulses in particular.

Blue discharges are one type of rarely observed upward discharge emerging from the top of thunderstorms. The favorable meteorological conditions and charge structures needed to produce this marvelous phenomenon are still poorly understood. In this study, we report on two midlatitude thunderstorms producing 13 blue discharges observed simultaneously by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) and ground‐based lightning detection array. In these two thunderstorms, blue discharges always occurred in the vicinity of the coldest cloud top (∼195 K) and clustered within a bounded area near the convective surge, leading to the overshooting thundercloud top (reaching about 18 km) into the stratosphere. The parent thunderstorms were normally electrified with a main midlevel negative and an upper positive charge layer centered at about 15 km as inferred from source heights of narrow bipolar events (NBEs). The associated negative NBEs near the tropopause indicated that they are upward positive discharges initiated between the upper positive charge layer and the negative screening layer at the cloud top. In addition, the outbreak of negative NBEs in the altitude range of 16–18 km was observed in conjunction with blue discharges observed from space. This suggests that there exists a strong upper positive layer with an intense convection at this altitude of the thunderstorm. It is inferred that an overshooting thundercloud top with intense convective updraft could lead to a strong and high upper positive charge layer and therefore create favorable charge structures for initiating upward positive blue discharges.

To investigate the possible impact of urban development on lightning activity, an eight-year (2010–2017) cloud-to-ground (CG) lightning dataset provided by the National-Wide Lightning Detection Network in China was analyzed to characterize the CG lightning activity in the metropolitan area of Beijing. There is a high CG flash density area over the downtown of Beijing, but different from previous studies, the downwind area of Beijing is not significantly enhanced. Compared with the upwind area, the CG flash density in the downtown area was enhanced by about 50%. Negative CG flashes mainly occurred in the downtown and industrial area, while positive CG flashes were distributed evenly. The percentage of positive CG flashes with I_peak ≥ 75 kA is more than six times that of the corresponding negative CG flashes in the Beijing area. The enhancement of lightning activity varies with season and time. About 98% of CG flashes occurred from May to September, and the peak of CG diurnal variation is from 1900 to 2100 local time. Based on the analysis of thunderstorm types in Beijing, it is considered that the abnormal lightning activity is mainly responsible for an enhancement of the discharge number in frontal systems rather than the increase of the number of local thunderstorms. In addition, there is a non-linear relationship between pollutant concentrations and CG flash number, which indicates that there are other critical factors affecting the production of lightning.