I would like to thank my supervisor, G. Boffetta for his friendship
and for the huge support he has given me during my degree
thesis and my Ph.D.
I would also like to thank A. Celani, M. Vergassola, A. Vulpiani,
A. Mazzino, M. Cencini and F. De Lillo for all the work
they have done with me during these years.
I am gratefull to everybody at the ``Istituto di Scienze
dell'Atmosfera e del Clima e del Clima'', Torino,
for their kind hospitality.