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Abstract. Aerosol interactions with clouds represent a significant uncertainty in our understanding of the Earth system. Deep convective clouds may respond to aerosol perturbations in several ways that have proven difficult to elucidate with observations. Here, we leverage the two busiest maritime shipping lanes in the world, which emit aerosol particles and their precursors into an otherwise relatively clean tropical marine boundary layer, to make headway on the influence of aerosol on deep convective clouds. The recent 7-fold change in allowable fuel sulfur by the International Maritime Organization allows us to test the sensitivity of the lightning to changes in ship plume aerosol number-size distributions. We find that, across a range of atmospheric thermodynamic conditions, the previously documented enhancement of lightning over the shipping lanes has fallen by over 40 %. The enhancement is therefore at least partially aerosol-mediated, a conclusion that is supported by observations of droplet number at cloud base, which show a similar decline over the shipping lane. These results have fundamental implications for our understanding of aerosol–cloud interactions, suggesting that deep convective clouds are impacted by the aerosol number distribution in the remote marine environment. 

This dataset is a compressed archive that includes 2 data files in binary format, 4 files in csv format, and 2 metadata files (pdf documents) that provide information on how to interpret the data. This data was collected from instruments deployed on two stratospheric balloons, launched a day apart in late June 2021 from central Oregon. They flew on upper level winds to the west, out over the northeastern Pacific Ocean. The measurement objective was a multi-day set of vertical electric field and polar conductivity measurements at roughly a 10 minute cadence, and from widely separated locations in the stratosphere. The binary format data is comprehensive, including everything that was measured. The csv files have been processed from the raw data files into calibrated, timed, and time-ordered ASCII files containing the primary science measurements and some essential auxiliary measurements such as measurement location and time. This data was collected in an effort to (1) compare the fair-weather return current density at different geographic locations and (2) to compare the fair-weather current density with global thunderstorm activity. 

Abstract Exceptionally high‐energy lightning strokes >10⁶ J (X1000 stronger than average) in the very low‐frequency band between 5 and 18 kHz, also known as superbolts (SB), occur mostly during winter over the North‐East Atlantic, the Mediterranean Sea, and over the Altiplano in South America. Here we compare the World‐Wide Lightning Location Network database with meteorological and aerosol data to examine the causes of lightning stroke high energies. Our results show that the energy per stroke increases sharply as the distance between the cloud'scharging zone(where the cloud electrification occurs) and the surface decreases. Since thecharging zoneoccurs above the 0°C isotherm, this distance is shorter when the 0°C isotherm is closer to the surface. This occurs either due to cold air mass over the ocean during winter or high surface altitude in the Altiplano during summer thunderstorms. Stroke energy decreases with the warm phase of the cloud, as proxied by the cloud base temperature, and increases with a more developed cloud, as proxied by the cloud top temperature, but to a much lesser extent than the distance between the surface and 0°C isotherm. Aerosols play no significant role. It is hypothesized that a shorter distance between thecharging zoneand the ground represents less electrical resistance that allows stronger discharge currents. 

Abstract The known effects of thermodynamics and aerosols can well explain the thunderstorm activity over land, but fail over oceans. Here, tracking the full lifecycle of tropical deep convective cloud clusters shows that adding fine aerosols significantly increases the lightning density for a given rainfall amount over both ocean and land. In contrast, adding coarse sea salt (dry radius > 1 μm), known as sea spray, weakens the cloud vigor and lightning by producing fewer but larger cloud drops, which accelerate warm rain at the expense of mixed-phase precipitation. Adding coarse sea spray can reduce the lightning by 90% regardless of fine aerosol loading. These findings reconcile long outstanding questions about the differences between continental and marine thunderstorms, and help to understand lightning and underlying aerosol-cloud-precipitation interaction mechanisms and their climatic effects. 

Noetzli, J., Christiansen, H.H, Guglielmin, M., Hrbáček, F., Hu, G., Isaksen, K., Magnin, F., Pogliotti, P., Smith, S. L., Zhao, L. and Streletskiy, D. A. 2024. Permafrost temperature and active layer thickness. In: State of the Climate in 2023. Bulletin of the American Meteorological Society, 105 (8), S43–S44, https://doi.org/10.1175/BAMS-D-24-0116.1