Gyroaverage operator for a polar mesh Christophe Steiner, Michel Mehrenberger, Nicolas Crouseilles, Virginie Grandgirard, Guillaume Latu and Fabien Rozar Eur. Phys. J. D, 69 1 (2015) 18 Published online: 16 January 2015 DOI: 10.1140/epjd/e2014-50211-7