Cloud-to-ground lightning in Austria: A 10-year study using data from a lightning location system

In this paper we present lightning statistics for more than three million cloud-to-ground (CG) flashes located during the 10-year operation period 1992-2001 of the Austrian lightning location system (LLS) called ALDIS (Austrian Lightning Detection and Information System). Like a majority of other LLS operated worldwide, ALDIS underwent configuration changes and continuous performance improvement. Since these changes can alter the lightning statistics, we also relate the variation of the individual lightning parameters during the period of operation to changes in ALDIS configuration and performance. This analysis should be useful to other network operators and data users. Flash densities in Austria are normally between 0.5 and 4 flashes km(-2) yr(-1) depending on terrain. Flashes are classified as negative, positive, or bipolar. Seventeen percent of the flashes were classified as positive, and 2.3% of the total number of flashes were bipolar. Fifty percent of the positive multiple-stroke flashes were bipolar flashes with positive first stroke; this influences the positive flash multiplicity and interstroke interval statistics. Compared to many other networks, the ALDIS network reports much lower median negative peak currents. For 2001, the median first-stroke peak current for negative flashes was 10 kA. Estimated multiplicity of negative flashes for the 10-year period is affected by the algorithm that groups strokes into flashes, as well as the improved DE of the network as a result of the integration of ALDIS into the European LLS (EUCLID). This performance improvement also resulted in a higher number of single-stroke flashes. Interstroke interval and median first-stroke peak current show a clear correlation with multiplicity for negative flashes, irrespective of detection efficiency. Negative flashes with higher multiplicity show smaller average interstroke intervals and larger first stroke median peak currents. No correlation between interstroke interval and stroke order was found. On average, regions with higher flash density show slightly higher flash multiplicity.