Abstract:
This paper examines how the North Atlantic Oscillation (NAO) influences winter lighting activity over the European North Sea and Britain (50°N–66°N, 20°W–15°E) using data from the World Wide Lightning Location Network (WWLLN) for 2010–2022 and ERA5 datasets for 1993–2022. The study aims to investigate the impact of NAO on the circulation system, sea surface temperatures, and its relationship with lightning activity. The results reveal that NAO is the primary climate system affecting winter lightning activity over the North Sea, with a significant positive correlation between the NAO index and lightning frequency. The composite analysis indicates that the positive phase of NAO enhances lightning activity. This is attributed to enhanced frontogenesis from the intensified North Atlantic Jet, rising sea surface temperatures along the west coast of Europe, and increased water vapor transportation by the Azores high. During the winter season from December 2014 to January 2015, an abnormal increase in lightning occurrences was observed along the western coast of Northern Europe. Lightning frequency soared several times above the mean, with the distribution differing significantly from the typical winter pattern at a 99% confidence level. The study attributes this to cyclonic circulation anomalies generated by the Icelandic low and the anticyclonic anomalies from the Azores high, which speed up the North Atlantic westerly jet, particularly in central North Atlantic. Located in the central part of the North Atlantic, this teleconnection highlights how the accelerated jet stream promotes the formation of cyclone waves at its entry point, propelling them eastward across the ocean surface. The extreme positive anomaly of NAO facilitates frontogenesis, elevates sea-surface temperatures, and enhances moisture transportation, resulting in intensified winter lightning activity in the winter.