Spectral Study of Rare Upward Developing, Circling, and Branching Cloud‐To‐Ground Lightning.

The development of cloud‐to‐ground (CG) lightning channel is one of the main bases reflecting the discharge characteristics. Time‐resolved spectra of CG lightning with eight return strokes were recorded by a slit‐less high‐speed spectroscope. We found an unusual phenomenon in which a branch developed upward from a node following a circling structure into the cloud after the first return stroke. To investigate the propagation properties of this lightning, characteristic parameters such as the two‐dimensional speed of the leader, node temperature, and electron density are analyzed. The physical mechanism of the branch is discussed. Spectral analysis reveals that the main channel temperature and electron density are approximately 2.72–3.07 × 104 K and 0.23–2.03 × 1018 cm−3, respectively. The temperature and electron density increase as the branch approaches the cloud base, similar to the feature of the main channel approaching the ground. The temperature and electron density of the node are higher than at other locations in the circular channel, indicating that massive charge accumulated around the node. Lightning occurred in the Qilian Mountains in a complex landscape, which easily yielded an uneven distribution in the local electric field of the air, resulting in channel bending, kinking, and even circle development. The phenomenon of the branch developed from the node to the cloud may be due to the fact that the branch is formed during the return stroke process. Plain Language Summary: The lightning channel does not usually continue to develop after the lightning return stroke is grounded. However, we discover an unusual phenomenon where the lightning leader formed a circular structure around a node on the main channel during its development. Immediately after the initiation of the first return stroke, a branch developed upward from the node into the cloud. To understand the reason why the branch developed from the node of the main cloud‐to‐ground lightning channel. Based on the time resolved spectra of the channel captured by a slit‐less high‐speed spectroscope, we analyze its physical characteristics, such as the two‐dimensional speed of the lightning leader, the temperature and electron density of the node, the main channel, and the branch channel. Our study found that this phenomenon may be related to the special geographical environment. Key Points: Rare phenomenon of CG lightning branch developed from a node on main channel upwards into the cloud was examined via spectral analysisTemperature and electron density slightly increased as branch channel approaching the cloud baseTemperature and electron density of leader tip reach the maximum when node formed [ABSTRACT FROM AUTHOR]