This work was funded by the NCAS Centre for Global Atmospheric Modelling (CGAM), the University of Reading. Some of this work was completed while the author was visiting the Department of Hydraulic and Environmental Modelling at the University of Tunis (ENIT). The author would like to thank T. Palmer, J. Berner, and C. Ferro for useful discussions, and three anonymous reviewers for their thorough and constructive comments that helped improve the manuscript.
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