Abstract. Lightning in winter (December–January–February, DJF) is rare compared to lightning in summer (June–July–August, JJA) in central Europe north of the Alps. The conventional explanation attributes the scarcity of lightning in winter to seasonally low values of variables that create favorable conditions in summer. Here we systematically examine whether different meteorological processes are at play in winter. We use cluster analysis and principal component analysis and find physically meaningful groups in ERA5 atmospheric reanalysis data and lightning data for northern Germany. Two thunderstorm types emerged: wind-field thunderstorms and CAPE (convective available potential energy) thunderstorms. Wind-field thunderstorms are characterized by increased wind speeds, high cloud shear, large dissipation of kinetic energy in the boundary layer, and moderate temperatures. Clouds are close to the ground, and a relatively large fraction of the clouds are warmer than −10 ∘C. CAPE thunderstorms are characterized by increased convective available potential energy (CAPE), the presence of convective inhibition (CIN), high temperatures, and accompanying large amounts of water vapor. Large amounts of cloud-physics variables related to charge separation such as ice particles or cloud base height further differentiate both wind-field thunderstorms and CAPE thunderstorms. Lightning in winter originates in wind-field thunderstorms, whereas lightning in summer originates mostly in CAPE thunderstorms and only a small fraction in wind-field thunderstorms. Consequently, typical weather situations of wind-field thunderstorms in the study area in northern Germany are strong westerlies with embedded cyclones. For CAPE thunderstorms, the area is typically on the anticyclonic side of a southwesterly jet.

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Abstract. Lightning characteristics in all seasons are investigated across Europe because it is observed that lightning strikes to tall infrastructure have no or only a weak annual cycle whereas lightning in general has a pronounced annual cycle. Using cluster analysis on ERA5 reanalysis data and EUCLID lightning data, two major thunderstorm types are found: Wind-field thunderstorms characterized by increased wind speeds, strong updrafts, and high shear occurring mainly in winter. And mass-field thunderstorms characterized by increased mass-field variables such as large CAPE values, high dewpoint temperatures, and elevated isotherm heights, occurring mostly in summer. Several sub-types of these two main thunderstorm types exist. Using principal component analysis, four topographically distinct regions in Europe are identified that share similar thunderstorm characteristics: The mediterranean, alpine-central, continental, and coastal regions, respectively. Based on these results it is possible to differentiate lightning in different seasons without a static threshold or a seasonal criterion.

Abstract. Meteorological environments favorable for thunderstorms are studied across Europe, including rare thunderstorm conditions from seasons with climatologically few thunderstorms. Using cluster analysis on ERA5 reanalysis data and EUCLID (European Cooperation for Lightning Detection) lightning data, two major thunderstorm environments are found: wind-field thunderstorms, characterized by increased wind speeds, high shear, strong large-scale vertical velocities, and low CAPE values compared to other thunderstorms in the same region, and mass-field thunderstorms, characterized by large CAPE values, high dew point temperatures, and elevated isotherm heights. Wind-field thunderstorms occur mainly in winter and more over the seas, while mass-field thunderstorms occur more frequently in summer and over the European mainland. Several sub-environments of these two major thunderstorm environments exist. Principal component analysis is used to identify four topographically distinct regions in Europe that share similar thunderstorm characteristics: the Mediterranean, Alpine–central, continental, and coastal regions, respectively. Based on these results it is possible to differentiate lightning conditions in different seasons from coarse reanalysis data without a static threshold or a seasonal criterion.

Upward lightning (UL) initiated from the Earth surface extending toward the clouds is much rarer than downward lightning initiated within the clouds extending toward the ground. Nevertheless, UL might pose a much larger damage potential as it is capable of transferring large amounts of charge up to hundreds of coulombs within a comparably long period of time (e.g., Birkl et al., 2017;Diendorfer et al., 2015). Tall structures (on the order of 100 m) are preferred starting locations for UL (e.g., Rakov & Uman, 2003). Wind turbines typically exceed such heights and consequently lightning damages to them have gone up hand in hand with their ever-growing number in the quest for renewable energy sources (e.g.