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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 3
Nat. Hazards Earth Syst. Sci., 12, 639–649, 2012
https://doi.org/10.5194/nhess-12-639-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: 2nd International Conference on Ecohydrology and Climate...

Nat. Hazards Earth Syst. Sci., 12, 639–649, 2012
https://doi.org/10.5194/nhess-12-639-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 16 Mar 2012

Research article | 16 Mar 2012

Cloud-to-ground lightning in Portugal: patterns and dynamical forcing

J. A. Santos1, M. A. Reis1, J. Sousa2, S. M. Leite1, S. Correia3, M. Janeira2, and M. Fragoso3 J. A. Santos et al.
  • 1Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal
  • 2Instituto de Meteorologia, 1749 Lisboa, Portugal
  • 3Centre for Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisboa, Portugal

Abstract. An analysis of the cloud-to-ground discharges (CGD) over Portugal is carried out using data collected by a network of sensors maintained by the Portuguese Meteorological Institute for 2003–2009 (7 yr). Only cloud-to-ground flashes are considered and negative polarity CGD are largely dominant. The total number of discharges reveals a considerable interannual variability and a large irregularity in their distribution throughout the year. However, it is shown that a large number of discharges occur in the May–September period (71%), with a bimodal distribution that peaks in May and September, with most of the lightning activity recorded in the afternoon (from 16:00 to 18:00 UTC). In spring and autumn the lightning activity tends to be scattered throughout the country, whereas in summer it tends to be more concentrated over northeastern Portugal. Winter generally presents low lightning activity. Furthermore, two significant couplings between the monthly number of days with discharges and the large-scale atmospheric circulation are isolated: a regional forcing, predominantly in summer, and a remote forcing. In fact, the identification of daily lightning regimes revealed three important atmospheric conditions for triggering lightning activity: regional cut-off lows, cold troughs induced by remote low pressure systems and summertime regional low pressures at low-tropospheric levels combined with a mid-tropospheric cold trough.

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