Regime-dependent Impacts of CCN and Cloud Glaciation on Global Lightning Activity 

Lightning activity is influenced by both aerosols and cloud microphysics, particularly ice formation and charge separation. While aerosols can greatly modify microphysical processes via cloud condensation nuclei (CCN), the global relationship between CCN loading and lightning remains unclear. In this study, we used global lightning stroke density, aerosol, and microphysics data to investigate how CCN can alter lightning through microphysical pathways across different regions. Our preliminary analysis reveals a robust CCN-lightning relationship, with lightning peaks at moderate CCN (400-600 cm-3) and decreases at both lower and higher concentrations. A metric used to quantify the microphysical impact is called ‘glaciation ratio (GR)’, which is defined as the ratio between cloud-ice water path and the total water path. We identify distinct continental (high CCN, high GR) and marine (moderate CCN, moderate GR) regimes. Analysis of glaciation ratio shows synergistic effects: optimal lightning requires both appropriate CCN loading and efficient cloud glaciation. Our findings show that more aerosols do not always mean more lightning. However, the hypothesis proposed is that excess CCN diminishes convection through reduced droplet growth, while low CCN suppresses electrification due to the efficient warm-rain process. Our analysis shows that CCN impacts on the observed lightning activity are regime-dependent, with cloud glaciation playing a central role in determining whether CCN enhances or suppresses electrification.