Acknowledgments
Laurent Y. Alleman - Ecole des Mines de Douai, Douai, France
Vera Bernardoni - Department of Physics, Milan University, Italy
Chiara Bove - Department of Physics, University of Genoa, Italy
Daniela Cesari - Istituto di Scienze dell'Atmosfera e del Clima, ISAC-CNR Lecce, Italy
Aldo Giove - Enel SpA, Italy
Gianluigi Valli - Department of Physics, Milan University, Italy
Roberta Vecchi - Department of Physics, Milan University, Italy