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Infrared (IR) luminosity of lightning channel in the 3–5 μm range usually persisted throughout the entire interstroke interval, which is in contrast to the simultaneously recorded visible (0.4–0.8 μm) luminosity that always decayed to an undetectable level prior to a subsequent return stroke pulse. A longer visible luminosity period at the end of flash tended to be associated with a longer IR afterglow period following the decay of visible luminosity (and by inference current) to an undetectable level. At the end of flash, the IR luminosity persisted up to about 1 s, and the median IR afterglow duration was a factor of 10 longer than the median visible luminosity duration. The IR luminosity often exhibited a hump when the visible luminosity was monotonically decaying or undetectable, with the corresponding channel temperature being likely around 3400 K. Plain Language Summary Lightning is usually imaged in the visible (0.4–0.8 μm) range, although it also produces significant infrared (IR) emission. In this study, we compare, for the first time, the medium‐to‐far (3–5 μm) IR luminosity of lightning channels with the simultaneously recorded visible luminosity. The key findings include the persistent nature of IR luminosity throughout interstroke intervals, which is in contrast to visible luminosity that always decayed to an undetectable level before the following return‐stroke onset. After the last stroke, IR luminosity persisted much longer than visible luminosity. The IR luminosity often exhibited a hump when visible luminosity was monotonically decreasing or already undetectable. We inferred that the IR hump, occurring when the channel temperature decreases to a few thousand Kelvin, is associated with enhanced IR emission from nitric oxide molecules whose concentration is expected to be maximum around 3400 K. We also examined a number of factors influencing IR afterglow duration, such as the number of preceding strokes, return‐stroke peak current, and the occurrence of M‐components. This study contributes to the very limited literature on the IR emission from lightning and provides new insights into the dynamics of lightning channel cooling process. Key Points In contrast to the visible, infrared (IR) channel luminosity between strokes usually persisted through the following return‐stroke onset IR luminosity profile often exhibited an increase (hump) when the visible luminosity was monotonically decaying or undetectable At the end of flash, IR luminosity persisted up to ∼1 s and its median duration was a factor of 10 longer than its visible counterpart

Channel cutoff is the process by which an active lightning channel cools down, goes dark, and loses its ability to effectively conduct electricity. Current cutoff precedes several lightning phenomena, notably dart leaders and return strokes, but the process by which a hot, highly‐conducting leader channel can undergo current cutoff is poorly understood. In this work, we present self‐consistent simulations of positive leader propagation, which include coupled treatment of electrodynamics and plasma physics. The unstable positive leader spontaneously undergoes channel cutoff and creates the conditions for the emission of dart leaders, that is, it accumulates a packet of negative charge at the intersection between cutoff and conducting channel segments. A residual conductivity in the cutoff section facilitates the conversion of the electric field enhancement into a traveling wave, which retraces and reionizes the channel. This is critical for allowing the frail positive leader to keep propagating.

Terrestrial gamma ray flash (TGF) observations made by the Atmosphere‐Space Interaction Monitor (ASIM) have demonstrated that these TGFs are accompanied by a prominent optical pulse from a hot leader channel. It is hard to confidently resolve the true sequence of the events in the source region due to temporal proximity of the involved processes. Here we report a bright long duration TGF together with its associated optical recordings showing clear temporal separation between the TGF and the optical pulse. In this observation the optical pulse is clearly distinct and subsequent relative to the TGF. The corresponding lightning discharge occurred at the very end of the TGF. We conclude that the current surge inside the lightning leader channel cannot be responsible for generation of this TGF. The current surge that produced the associated optical pulse can itself be conditioned by the TGF and may be responsible for the TGF termination. Plain Language Summary TGFs observed from space are found to be associated with current surges in lightning leader channels. These current surges emit radio waves and can be detected with lightning detection networks. They also produce optical pulses which can be observed by the optical sensors on board of the space satellites. The fact that TGFs have usually short duration does not allow to define the real sequence of events in the source region due to timing uncertainties. In this paper we report a unique observation of a rare coincidence of a long duration TGF accompanied by an optical pulse and a high peak current lightning detection. Duration of the TGF is one order of magnitude larger than the overall observational uncertainty, which allows us to reliably discern the TGF and the accompanying current pulse in the leader channel. We could confidently conclude that the TGF was generated first, in the very end of the TGF the current surge in the leader channel occurred, and the optical pulse was produced. The appearance of the current surge close to the end of the TGF can indicate that the current surge is conditioned by the TGF, and, reciprocally, it could condition the TGF termination. Key Points Accompanying optical pulse is subsequent to TGF TGF precedes the current surge in the leader channel and cannot be generated by this current surge TGF may be terminated by the current surge in the leader channel

Due to the weak radiation generated by positive leaders, our understanding of how positive leaders are initiated and reach the ground remains limited. This study investigated positive cloud‐to‐ground (CG) lightning induced after the long intracloud lightning based on high‐speed video and fast antenna mapping results. Below the cloud base in the field of view, re‐breakdowns of decayed negative branches occurred consecutively beneath the horizontal negative channel in the form of bidirectional leaders. These bidirectional leaders advanced along the same channel, and eventually, the third reached the ground, generating a positive return stroke (RS) with a peak current of 157 kA. Following the RS, new negative discharges emerge adjacent to the vertical return stroke channel, persisting and propagating to form a continuing current (CC) lasting over 200 milliseconds. Plain Language Summary Positive cloud‐to‐ground flash attracts more attention than its negative counterpart because it is more hazardous. Previous studies have confirmed the close relationship between intracloud (IC) lightning and positive cloud‐to‐ground (+CG) lightning. Downward positive leaders forming +CG can originate from branching of intracloud lightning or even from negative polarity leader channels. However, due to the weak radiation from positive leaders during their development within the cloud, common lightning detection devices, such as LF/VLF fast antennas and VHF antennas, find it very difficult to detect positive leaders. Consequently, our understanding of how positive leaders initiate within the cloud and reach the ground remains limited. In this study, we comprehensively utilized lightning channel mapping results and high‐speed video to investigate a case of +CG. We found that the occurrence of downward positive leaders around the negative leader channel is facilitated through multiple side breakdowns, events that continue even after the return stroke. Therefore, we propose that the multiple positive side breakdowns beneath the reactivated negative leader channel are responsible for generating positive leaders from the negative lightning channel. These side discharges play a crucial role in the generation of +CG lightning. Key Points A positive cloud‐to‐ground lightning flash was analyzed based on synchronous high‐speed video and lightning mapping results Downward positive leader initiated, reached ground via three bidirectional side discharges beneath horizontal negative leader channel Side negative breakdowns from vertical return stroke channel and reactivation of decayed negative branches were found

Employing the multi‐station Thunderstorm Energetic Radiation Observation System, we detected X‐ray bursts during two rocket‐triggered lightning events in 2024. By innovatively integrating optical imaging with three‐dimensional lightning channel reconstruction based on Distributed Acoustic Sensing (DAS), we analyzed the X‐ray emission characteristics from these events. During the Tl_20240812 event, lateral deflection of a descending negative leader resulted in X‐rays being detected exclusively by a distal sensor. This clear spatial correlation provides direct and conclusive geometric evidence that the radiation is emitted in a beam‐like pattern along the leader propagation path. Furthermore, based on the Tl_20240801 event, this study achieved the first quantitative estimation of the X‐ray photon beam half‐angle width, determined to be between 40° and 46°. This angular range aligns with the predicted structure of the leader tip electric field, thereby providing robust support for the hypothesis that X‐rays originate from the leader tip high‐field runaway electron mechanism.

We initiated high‐frequency (HF, 3–30 MHz) lightning observations to remotely study lightning processes using skywave propagation. HF lightning skywaves were detected at distances up to 3,300 km (potentially farther) during both day and night, with over 64% of events having peak currents below 50 kA. HF measurements revealed distinct temporal features of negative cloud‐to‐ground (CG) leaders, narrow bipolar events, and negative breakdown following positive return strokes. Unlike VLF and LF methods, which primarily capture current pulses along lightning channels, HF observations detect both transient and prolonged leader emissions. This provides more equal sensitivity to both in‐cloud (IC) and CG events, potentially benefiting IC/CG classification and studies of IC‐associated phenomena such as terrestrial gamma‐ray flashes. Ionospheric conditions may influence HF signal propagation but can be mitigated by observing the full HF band. These findings demonstrate the potential of HF observations for advancing lightning physics and storm monitoring over long distances.

Development of hot lightning channels is facilitated by essentially cold streamers emanating from their extremities. Thus, streamers play a crucial role in lightning, yet they are poorly understood, because they emit primarily ultraviolet (UV) light, which usually goes undetected. Here, we present unique UV images of lightning, including interaction between positive and negative streamers, leading to new inferences on lightning propagation and attachment. We observed an abrupt change in the lightning propagation path to ground, which resulted in an aborted attachment process and a different ground connection point, 200 m away from the expected one. This change was likely due to the self‐choking effect of large negative space charge that was suddenly introduced by the intense streamer burst ahead of the lower end of the descending negatively‐charged channel. Further, the unique UV images show that positive and negative streamer zones are an order of magnitude longer than previously thought.

Previous studies of lightning detection by radar mostly consisted of observations with reflector‐antenna systems yielding slow volume scan times. Phased array radars offer much faster scan times that are likely to capture echoes from propagating lightning channels. Rapidly updated range‐height indicator scans were used to observe severe storms that occurred in central Oklahoma with the fully digital S‐band Horus PAR to examine echoes from lightning plasma. Numerous lightning echoes were observed during the sampling period in good spatial and temporal agreement with lightning mapping array detections of very high frequency radiation sources. Statistically, they result in increased horizontal reflectivity factor, deviations in radial velocity and spectrum width, highly variable differential reflectivity and differential phase, and decreases in correlation coefficient. Results presented also highlight the capability of phased array radars to better observe lightning compared to current radars, and aid in the study of storm electrification and lightning physics. Plain Language Summary Apart from sampling precipitation in thunderstorms, weather radars also have the ability to detect lightning as its plasma backscatters part of the radiation transmitted by the radar. However, previous radar observations were constrained by the slower scan times from conventional reflector‐antenna radars, limiting the number and the detail of the detected lightning flashes. Phased array radars are composed of multiple radiating elements that can be used to electronically steer the transmitted beam. This yields faster scan times, increasing the number of lightning flashes detected, as well as the detail in the observations. In this study, we use the proof‐of‐concept fully digital Horus PAR to sample severe thunderstorms in central Oklahoma, and make the first‐ever observations of lightning echoes with such system. The radar is more efficient in detecting lightning flashes and in greater detail when compared to previous observations. These flashes were characterized by transient changes in the radar Doppler moments and polarimetric variables when compared to the background hydrometeors, as the beam intercepted the propagating lightning discharge inside the thunderstorm. Results showcase the potential of PARs to aid in the study of lightning physics through improved observation techniques and serve as a complementary tool to monitor thunderstorm electrification. Key Points These are the first‐ever observations of total lightning flashes with a polarimetric phased array radar (PAR) The observed lightning echoes had an excellent spatial overlap with very high‐frequency radio emissions from lightning channels Phased array radars can serve as a supplementary tool in the study of lightning through its radar properties, and for lightning detection

The inverted tripole charge structure in thunderstorm over the central Tibetan Plateau was discovered for the first time, primarily through observations from lightning very high frequency interferometer capable of high‐precision lightning channel mapping. The dominant cell exhibited an inverted tripole charge structure initially, characterized by a negative charge region at temperatures near 0°C, a main positive charge region between −30°C and −5°C, and an upper negative charge region at T < −20°C. The cell's rear portion exhibited a normal tripole before detaching, leaving a pure inverted tripole. Dissipation of the lower negative charge transitioned the structure to an inverted dipole, consisting of an upper negative (T < −20°C) and lower positive (T > −20°C). Throughout this thunderstorm, no positive cloud‐to‐ground (+CG) flashes were detected, while five −CG flashes were recorded. Among 109 intracloud (IC) flashes detected, 90% occurred between the upper inverted dipole. Radar reflectivity showed that this thunderstorm was more intense than conventional plateau thunderstorms.

Lightning channel morphology depends on the thunderstorm cloud charge structure, which in turn is influenced by the thunderstorm dynamics. In this paper, based on three‐dimensional radiation source localization data from the Lightning Mapping Array and radar‐based data, our analysis shows that the overall morphology and detailed morphology of the lightning channel correspond to different eddy dissipation rate (EDR) characteristics. Lightning with complex channel morphology occurs in regions with large EDRs. In single lightning events, channels that extend directly within a certain height range without significant bifurcation and turning tend to propagate in the direction of decreasing EDRs, while channel bifurcations and turns usually occur in regions with large radial velocity gradients and large EDRs. This study shows the relationship between channel morphology and thunderstorm dynamics and provides a new method for the direct application of channel‐level localization data to understand thunderstorm dynamics characteristics. Plain Language Summary Turbulence in thunderstorms affects the charge distribution, which in turn affects the lightning channel morphology. Thus, the lightning channel morphology can reflect the characteristics of turbulence. The current understanding of the correlation between the two is still limited to the relationship between macroscopic thunderstorm dynamic characteristics and lightning activity. In this paper, the relationship between the morphology of the lightning channel and turbulence characteristics is investigated based on the Lightning Mapping Array (LMA) localization data and the cube root of the eddy dissipation rate (EDR) estimated from KABX radar‐based data. The turbulence strength affects the overall morphology of lightning, and lightning with complex morphology tends to occur in regions with large EDRs. In single lightning events, channels extending directly within a certain altitude range tend to propagate in the direction of decreasing EDRs, and lightning channel bifurcation or turning tends to occur in regions with large EDRs. This paper establishes the relationship between thunderstorm electricity and thunderstorm dynamics by using lightning channel morphology as a bridge and provides a new method for the direct application of channel‐level localization data to understand thunderstorm dynamics characteristics. Key Points The morphology of lightning channels can reflect the distribution of turbulence intensity, and a certain correlation between the two exist Directly extended lightning channels tend to propagate in the direction of decreasing eddy dissipation rates The location of the channel bifurcations or turns often corresponds to regions with high eddy dissipation rates