Biomass burning smoke aerosols exhibit complex impacts on the temperature profile of the atmosphere and cloud development. Central Africa is a region where smoke aerosols are constantly being transported westward over the remote southeastern Atlantic Ocean. A dedicated measurement platform located on Ascension Island, maintained by the U. S. Department of Energy, observed several plumes of biomass burning smoke during the 2016 and 2017 austral burn season months. It was found that the smoke aerosols displayed different radiative properties while readily activating as cloud condensation nuclei. An anomalously strong African Easterly Jet was responsible for facilitating extreme fire conditions in 2016. During the 2017 burn season, an anomalously weaker jet led to more mixing of mineral dust and marine aerosols which were more efficient at cooling the atmosphere than in 2016.

Hurricane Nicholas was classified as a Category 1 tropical cyclone (TC) at 0000 UTC on 14 September 2021 and made landfall along the upper Texas Gulf Coast at 0530 UTC with maximum sustained winds of 33 m s-1. Much of the electrical activity during Nicholas was monitored by the Houston Lightning Mapping Array (HLMA) network. Deep convection developed in the rainband at 1700 UTC on 13 September, diminished by 2030 UTC, and re-intensified after 2200 UTC. At 2004 UTC (13 September), a curved megaflash (~220 km) was observed by the HLMA in the stratiform precipitation region of the outer rainband. By 0130 UTC on 14 September 2021, vigorous deep convective cells developed in the eastern eyewall region and propagated cyclonically to the western eyewall region. Several “jet-like” transient luminous events (TLEs) were observed by the HLMA emanating from a deep convective cell in the western eyewall region between 0230-0300 UTC with VHF source points ranging from 30-45 km in altitude. Moreover, the TLEs occurred within a region of strong wind shear, upper-level graupel-ice crystal collisions (~15 km), and strong cloud top divergence. Charge analysis of the deep convection during Nicholas revealed an overall normal dipole structure, while the megaflash and TLE deep convective cases exhibited inverted dipole charge structures. Dissipation of the upper-level screening charge layer resulting from cloud top divergence likely played a role in the observed TLE VHF sources escaping to altitudes exceeding 30 km.

Hurricane Nicholas was classified as a Category 1 tropical cyclone (TC) at 0000 UTC on 14 September 2021 and made landfall along the upper Texas Gulf Coast at 0530 UTC with maximum sustained winds of 33 m s-1. Much of the electrical activity during Nicholas was monitored by the Houston Lightning Mapping Array (HLMA) network. Deep convection developed in the rainband at 1700 UTC on 13 September, diminished by 2030 UTC, and re-intensified after 2200 UTC. At 2004 UTC (13 September), a curved megaflash (~220 km) was observed by the HLMA in the stratiform precipitation region of the outer rainband. By 0130 UTC on 14 September 2021, vigorous deep convective cells developed in the eastern eyewall region and propagated cyclonically to the western eyewall region. Several “jet-like” transient luminous events (TLEs) were observed by the HLMA emanating from a deep convective cell in the western eyewall region between 0230-0300 UTC with VHF source points ranging from 30-45 km in altitude. Moreover, the TLEs occurred within a region of strong wind shear, upper-level graupel-ice crystal collisions (~15 km), and strong cloud top divergence. Charge analysis of the deep convection during Nicholas revealed an overall normal dipole structure, while the megaflash and TLE deep convective cases exhibited inverted dipole charge structures. Dissipation of the upper-level screening charge layer resulting from cloud top divergence likely played a role in the observed TLE VHF sources escaping to altitudes exceeding 30 km.

Hurricane Nicholas was classified as a Category 1 tropical cyclone (TC) at 0000 UTC on 14 September 2021 and made landfall along the upper Texas Gulf Coast at 0530 UTC. The sustained maximum wind speed increased from a low-end estimate of 13 m s-1 (0000 UTC 13 September) to 33 m s-1 (0000 UTC 14 September) indicating rapid intensification. Lightning activity, monitored by the Houston Lightning Mapping Array (HLMA), developed in the rainband at 1700 UTC on 13 September, diminished by 2030 UTC, and re-intensified after 2200 UTC. At 2004 UTC (13 September), a curved megaflash (~220 km) was observed in the outer rainband’s stratiform precipitation region. Convection developed and intensified in the eastern eyewall region by 0130 UTC on 14 September. Several transient luminous events (TLEs) were observed in the western eyewall region between 0230-0300 UTC with VHF source points exceeding 40 km during a decline in lightning activity. The TLEs occurred during a period of strong cloud top divergence resulting from complex interactions between southwesterly low-level and westerly deep layer wind shear. Charge analysis of Nicholas revealed an overall normal dipole structure, while the megaflash and TLE cases exhibited inverted charge structures. The upper-level screening and primary charge layer heights of the TLEs heavily influenced the VHF source altitudes. Interestingly, a surface wind gust of 42 m2 s-2 was observed near the time of the first TLE, suggesting a second period of brief intensification. Future investigations of TC evolution and behavior may benefit from charge analyses.