Cloud to ground lightning activity over Portugal and its association with Circulation Weather Types

Ramos A.M., Ramos R., Sousa P., Trigo R.M., Janeira M., Prior V.
Atmospheric Research, 101, 84-101, doi:10.1016/j.atmosres.2011.01.014

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The Cloud to Ground lightning activity is analyzed for the Portugal mainland during the 2003-2009 period. Both inter-annual and intra-annual variability are clearly present. Winter months present a smaller number of Cloud to Ground discharges than the remaining warmer seasons. The highest density of discharges in the colder months is found in the coastal regions. On the contrary, for the remaining seasons, Cloud to Ground discharges tend to occur much more frequently in the interior areas of Portugal. A diurnal cycle of the Cloud to Ground discharges activity is clearly present in spring, summer and autumn, with maximum activity being found in the afternoon hours. The relationship between the Circulation Weather Types and Cloud to Ground discharges allowed us to distinguish which types are most frequently associated to lightning activity and also which types are the most favorable to present severe lightning episodes. Moreover, the analysis of additional meteorological fields allowed, at a seasonal scale, to discuss different mechanisms for lightning activity triggering: frontal activity, cut-off lows, and summer thermal lows are the most relevant in Portugal mainland. A case study is also provided for the most notorious event in terms of the total number of Cloud to Ground discharges (10th and 11th of September of 2007).