Nordic Lightning Information System: Thunderstorm climate of Northern Europe for the period 2002–2011

• A 10-year statistics of thunderstorms in the Northern Europe are presented.
• The avg. number of thunderstorm days is largest in the Baltic area and SW Sweden.
• The largest observed daily number of ground flashes (CG) is 51,500.
• The largest observed daily ground flash density is about 5 CGs km− 2 yr− 1.
• Cold season thunderstorms occur frequently over the North Sea west of Norway.

A 10-year statistics (2002–2011) of the Nordic Lightning Information System (NORDLIS) are presented. NORDLIS is a joined lightning location network between Norway, Sweden, Finland, and Estonia, comprising in 2011 of 32 lightning location sensors. Our data set contains a total of 4,121,649 cloud-to-ground (CG) flashes. We show the regional and temporal distribution of lightning in Northern Europe during the study period. Our results indicate that the average annual ground flash density values are greatest in Southern Sweden, Baltic countries and Western Finland. The average number of thunderstorm days is largest in the Baltic countries and Southwestern Sweden, and the annual number of ground flashes has varied during the study period from 250,000 to 620,000. The largest observed daily number of ground flashes is 51,500, and the largest daily ground flash density is about 5 CGs km− 2; this has occurred in southern Sweden in July 2003. The average daily number of ground flashes peaks in mid-July–early-August. Cold season (October–April) thunderstorms occur frequently over the North Sea west of Norway and in the west coast of Denmark. Our results also show that an intense thunderstorm may occur practically anywhere in the Northern Europe except for certain maritime and mountain areas.