The “Weekend Effect” in Lightning Activity during Winter Thunderstorms over the Tel-Aviv, Israel, Metropolitan Area

Abstract

We report the analysis of nine winter seasons (December, January, February (DJF)) aerosol and lightning data over the Tel-Aviv metropolitan area, Israel’s largest and densest urban region. Hourly averaged aerosol concentrations (PM2.5 and PM10) were obtained from 27 automatic air quality stations operated by the Ministry for Environmental Protection. Lightning data obtained from the Israeli Lightning Detection Network (ILDN) and by the Earth Network Total Lightning Network (ENTLN) for four overlapping seasons showed an irregular pattern, with lower activity during Sunday–Tuesday, and maximum activity on Wednesday and Thursday, but also on Saturday, when less pollution was present. The accepted explanation for the weekend effect is that increased amounts of particles tend to prolong the lifetime of storms and their total lightning amounts and change their intracloud/cloud-to-ground flash ratios. However, our results suggest that lightning is not directly related to the level of ambient pollution, but likely depends on the synergistic effects of desert dust and urban pollution particles in the area that affect the electrical structure of winter thunderstorms. Since the source of desert dust is independent of any regularity that can be attributed to anthropogenic activity (e.g., increased levels of pollution due to the traffic-load in Tel-Aviv), it obscures any weekend–weekday patterns that are often detected in other large metropolitan areas.

Keywords

• aerosol
• thunderstorms
• lightning
• urban pollution
• convection