We thank three anonymous reviewers for their valuable comments. SLL was funded by a NERC research studentship (Grant NER/S/J/2005/13614) as part of the AMMA-UK project. On the basis of a French initiative, AMMA was built by an international scientific group and is currently funded by a large number of agencies, especially those from France, the United Kingdom, the United States, and Africa. It has been the beneficiary of a major financial contribution from the European Community’s Sixth Framework Programme. Detailed information on scientific coordination and funding is available on the AMMA international Web site (http://www.amma-international.org).
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