Understanding the land—ocean contrast in lightning strikes across the Australian tropics

Lightning is commonly associated with both severe and non-severe convective storms. Numerous studies have documented that lightning occurs more frequently over land than over ocean, a contrast that is clear in the Australian lightning record. Many hypotheses have been proposed to explain the differences. For instance, deeper convection over land increasing the opportunity for microphysical interactions responsible for lightning, the presence of greater number of fine aerosols over land enhancing the number of cloud condensation nuclei; or coarse sea salt over the ocean promoting drop coalescence.

To investigate this contrast in Australia’s tropics, lightning strike data from ground-based lightning observations from the Weatherzone Total Lightning Network were analysed in conjunction with satellite-based overshooting top (OT) data. The results reveal a pronounced land—ocean difference in lightning frequency, particularly in northern Australia. However, the OT data show no corresponding contrast in tropopause penetrating convection, suggesting that the lighting difference may be associated with weaker storms.

Further analysis of convective parameters from the BARRA-R2 reanalysis indicates that lightning-producing storms over land typically occur in environments characterized by lower convective available potential energy (CAPE), higher convective inhibition (CIN), steeper lapse rates, lower cold cloud depth and lower freezing level heights than lightning-producing storms over the ocean. These findings suggest that lightning initiation is more easily achieved over land than over ocean, showing that the causes of the observed land-ocean contrast is more complicated than storms being stronger over land and giving insights into the observed differences in lightning activity.