Time variation of lightning activity observed around the Nilgiri plateau with GRAPES-3

The atmospheric electric field (AEF) is a key characteristic of the Earth’s atmosphere and changes as a result of local weather, seasonal patterns, and global electrical circuits. Under fair weather conditions, the AEF typically has an ambient strength of a few hundred volts per meter (V/m) near the ground. However, during turbulent weather conditions, the magnitude varies up to several thousand V/m. Once the electric field is beyond a sustainable limit borne out by the air breakdown voltage, lightning discharge occurs. Cosmic rays (CRs) are speculated to influence this process by creating conductive pathways through the ionized regions of the atmosphere during their interaction and propagation. GRAPES-3 is a ground-based CR observatory located in Ooty, on the Nilgiri plateau in India. In April 2011, four electric field mills (EFMs) were installed around the GRAPES-3 site to investigate the interaction between CR secondaries and AEF. Since their installation, the EFMs have continuously measured the AEF at intervals of every 50 milliseconds. In this work, we report the time variation of lightning activity observed around the Nilgiri plateau with the four EFMs since April 2011 and the associated seasonal variations.