Open Access. The Published version of this work has been reproduced here in accordance with the Publisher’s self archiving and copyright policies.
Rights
This work was published in the Annales Geophysicae, 27 (6) 2009 p. 2491-2502 published by Copernicus Publications an Open Access Journal of the European Geosciences Union and has be reproduced here under the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/ which permits you to copy, distribute, transmit and adapt the work.