Documenting a 400+ km Long Mesoscale Lightning Flash in an MCS Trailing Stratiform Region Using GLM, NLDN, and OKLMA Data

The existence of mesoscale lightning discharges on the order of 100 km in horizontal extent have been known since the radar-based findings of Ligda in the mid-1950s. However, it took until the discovery of sprites in 1989 to motivate significant attention to these large flashes in mesoscale convective systems (MCS). Sprite-parent lightning discharges often are initiated at high altitudes within the leading line convective cores but then descend into the lower regions of the trailing stratiform and propagate for great distances while producing energetic +CGs characterized by extremely large charge moment changes. This same regime is also conducive to the occurrence of both Lightning Triggered Upward Lightning (LTUL) and Self-Initiated Upward Lightning (SIUL) from tall structures. The development of 3-D Lightning Mapping Arrays (LMAs) has enabled investigation of sprite-initiating lightning that can travel up to several hundred kilometers. One such event, in a 2007 Oklahoma MCS, had an LMA-derived length of 321 km, certified by the World Meteorological Organization (WMO) as the longest known lightning flash. The launch of the Geostationary Lightning Mapper (GLM) sensor on GOES-16 has now provided an additional tool well suited to investigating mesoscale lightning.

On 21-22 October 2017, a major leading-line trailing-stratiform (LLTS) MCS moved through the central US. Clearly evident in GLM flash animations were two distinct electrical regimes, numerous IC and (mostly) –CG flashes in the leading convective cells, and vast networks of intermittent mesoscale lightning discharges in the trailing stratiform, accompanied by sporadic but powerful +CGs. This system produced four optically confirmed sprites, and triggered 39 LTUL/SIUL events at an antenna farm near Oklahoma City. At 0513Z, a mesoscale discharge originated in extreme northern Texas, then propagated north-northeast across Oklahoma, and finally terminated in southeastern Kansas. We present a detailed morphological investigation of this event using the GLM, the OKLMA and the NLDN. According to the NLDN, this discharge produced 18 +CGs (two >300 kA peak current), 26 –CGs and 41 ICs. The discharge was too large to be mapped end to end by the OKLMA. But by combining the LMA with NLDN and GLM reports, we estimate the horizontal extent of the 4.117 second-long flash to be at least 428 km. This clearly exceeds the previously reported record distance. This storm was also a classic, textbook example of an LLTS MCS that generated sprites and upward lightning from towers within the vast trailing stratiform region.